Postpartum excretion of internal teat sealant after selective dry cow treatment of dairy cows

To comply with antibiotic restriction policies in the European Union, internal teat sealants (TS) are increasingly used at drying off (DO) in selective dry cow treatment protocols to maintain udder health. Post-calving TS residue attachment to milking equipment and associated cleaning difficulties is a reason for some farmers to stay away from blanket TS use. Our objective was therefore to improve insight in TS excretion visibility and to compare quantity, pattern, and presence versus absence of TS excretion post-calving between the typical 2 cow categories at DO: High (H) and Low (L) SCC cows, treated with antibiotic (AB) plus TS (H-ABTS) or TS only (L-TS), respectively. In herds in the Netherlands (n = 3), and Germany (n = 4), cows were enrolled at DO, and categorized as H-ABTS (n = 93), or L-TS (n = 99). Post-calving, quarter level TS visibility, quantities, patterns, and percentage of TS infused and excreted post-calving were recorded from 50 mL of pre-milk of every quarter at each of the first 15 or 16 milkings. Udder quarter health status was determined by bacteriological culture and somatic cell counting of quarter milk samples taken at DO and at d 3 post-calving and by clinical mastitis incidence from DO until 30 DIM. Univariable and multivariable models were created to explore associations of TS excretion presence versus absence at the first 3 milkings. Irrespective of SCC category, both laboratory personnel, and farmers saw TS residues at the first milking in an equal 72% of quarters. Compared with laboratory as the gold standard, farmer sensitivity to spot TS in pre-milk was 74.5% at the first milking, decreasing to a maximum of 8.3% at the last 3 milking's. At the first milking, TS excretion quantities showed a bimodal distribution pattern and the mean percentage of TS infused (3.83 g) that was excreted in pre-milk at the first milking, was higher in the L-TS (45.5%) compared with the H-ABTS cow category (32%). At the second and third milking, mean adjusted TS percentage excreted was higher in the H-ABTS (8.5% and 1.8%, respectively) compared with the L-TS category (4.6% and 0.4% respectively). The multivariable model of the first 3 milkings showed parity at both the first and second milking, and study group at both the second and third milking, was significantly associated to TS presence. The univariable model showed no association between TS presence at the first milking and udder health. In conclusion, in pre-milk of the first milking, TS residue excretion was bimodal, higher in L-TS cows, more likely present in multiparous cows, and not associated with udder health. At the second and third milking, excretion was higher in H-ABTS cows and TS presence was only more likely in multiparous cows at the second milking.

The effect of selective dry cow therapies based on two different algorithms on antimicrobial use, udder health, milk production, and culling in the absence of internal teat sealant use at dry-off

The objective of this study was to evaluate the effect of selective dry cow therapy (SDCT) strategies based on 2 different algorithms as compared with blanket dry-cow therapy for measures of udder health, milk yield, and culling in herds not using internal teat sealant. Cows from 2 commercial farms in West Texas were randomized into 3 different groups: SDCT Algorithm 1 (ALG1; n = 455) cows treated with an intramammary antimicrobial at dry-off if somatic cell count (SCC) > 200,000 cells/mL at any Dairy Herd Improvement Association (DHIA) test date or if the cow had 2 or more cases of clinical mastitis during the enrollment lactation; SDCT Algorithm 2 (ALG2; n = 458) cows treated with an intramammary antimicrobial at dry-off if SCC >200,000 cell/mL at last test date or any case of clinical mastitis during the enrollment lactation; Control cows (CON = 447) received blanket dry cow therapy. All cows enrolled in the study did not receive an internal or external teat sealant. Data related to milk and somatic cell count linear score (LSCC) was collected monthly. Milk yield and LSCC during the first 6 mo of lactation were analyzed using repeated measures ANOVA models, while Cox's Proportional Hazards models were fitted to culling and clinical mastitis data. The farm was fitted as a random effect in all models. The percentage of cows receiving antimicrobials at dry cow was 51.3, 24.7, and 100% for ALG1, ALG2, and CON, respectively. Treatment did not influence the IMI dynamics during the dry period. Additionally, no statistical differences related to treatment were observed for LSCC and milk yield. The LSCC for ALG1, ALG2, and CON was 2.44, 2.41, and 2.26, respectively. The average milk yield for ALG1, ALG2, and CON cows was 43.2, 43.2, and 44.0 kg/d, respectively. Treatment did not affect clinical mastitis incidence and culling. The cumulative incidence of clinical mastitis was 19.6%, 19.4%, and 21.4% for ALG1, ALG2, and CON cows respectively. Additionally, the cumulative risk of death or culling was 18.5%, 17.1%, and 19.5% for ALG1, ALG2, and CON cows respectively. In conclusion, SDCT strategies led to a decrease in antimicrobial drug use at dry-off, without significantly impacting the incidence of clinical mastitis, the risk of culling, LSCC and milk yield of dairy cows. However, numerical differences in LSCC and milk yield were observed between treatment groups.

Associations of cow- and herd-level factors during the dry period with indicators of udder health in early-lactation cows milked by automated milking systems

This observational study aimed to determine the association of cow-level factors and herd-level housing and management practices during the dry period with indicators of udder health in early-lactation cows in automated milking system (AMS) herds. Data were collected from 166 commercial AMS dairy farms (mean ± standard deviation = 116 ± 111 milking cows; range = 39 to 1,200) across Canada between October 2018 and September 2020. Information on herd demographics, housing, and management practices was obtained on each farm using 2 surveys. On each farm, we selected all cows that had available Dairy Herd Improvement (DHI) somatic cell count (SCC) data for their last milk test before dry-off (>250 d in milk) and their first milk test after calving (5-45 d in milk). Data from 14,007 cows were included after excluding cows with a dry period of <30 d and >120 d. Using the SCC data, we calculated for each cow the somatic cell score (SCS) for the last milk test before dry-off (PreSCS) and the first milk test after calving (PostSCS), which we then averaged per herd at a test-day level. Intramammary infection (IMI) was estimated using cow SCC data. Each cow was classified as not infected (SCC <200,000 cells/mL) or infected (SCC ≥200,000 cells/mL) at her last milk test before dry-off and her first milk test after calving. Based on this classification, cows were further categorized as never infected, always infected, new IMI, or cured IMI. At the cow level, a higher PostSCS was associated with longer dry periods. The odds of having a new IMI were higher for cows of higher parity and that had lower 305-d milk yield before dry-off. Cows with lower parity were more likely to cure an IMI. At the herd level, a higher 305-d milk yield before dry-off was associated with a lower incidence of new IMI and a higher incidence of cured IMI. Separating cows into a different pen as preparation for dry-off tended to be associated with a lower PostSCS and incidence of new IMI. At dry-off, herds that used teat sealants and blanket antibiotic dry cow therapy also had lower PostSCS. During the dry period, housing cows in different groups was associated with a higher PostSCS and a lower incidence of cured IMI, while housing cows in both pack pens and stalls compared with only pack pens was associated with a lower incidence of new IMI. Finally, placing cows onto the AMS to be milked one or more days after calving tended to be associated with a lower PostSCS compared with placing them in the AMS within the first day postpartum. In summary, indicators of udder health in early-lactation cows in AMS herds were associated with several cow-level factors and herd-level housing and management practices before dry-off, at dry-off, during the dry period, and at the beginning of lactation. Thus, if some of the associations identified are causal, AMS producers may be able to improve udder health through modifications of housing and management practices.

Risk factors of high somatic cell count and differential somatic cells in early lactation associated with selective dry cow therapy

The routine use of intramammary antimicrobial products in all dairy cows at the beginning of the dry period is no longer allowed in European Union (EU) countries due to the new Regulation (EU) 2019/6 to reduce antimicrobial resistance. This study investigated the application of a selective dry cow therapy scheme and the risk factors of high individual milk somatic cell count (SCC) and individual neutrophil count in early lactation, as a response to the application of a selective dry cow therapy (SDCT) protocol. The study was carried out on three commercial farms, and a total of 243 lactating cows were monitored at the end of lactation and at the beginning of the next one, 91 of which were dried off without the use of antimicrobials (NoT) based on milk SCC, differential somatic cell count (DSCC), and the response of Vetscan DC-Q milk analyser, using a secret algorithm. The remaining 152 cows received antimicrobials (T). After calving, similar means were observed between the two treatment groups for SCC (4.8 vs 4.9 log10 cells/ml for T and NoT, respectively, P = 0.5) and total milk leucocyte count (TLC) (5 vs 5.1 log10 cells/ml for T and NoT, respectively, P = 0.7) in milk. However, the use of antimicrobials led to a lower DSCC (58 vs 64% for T and NoT, respectively, P = 0.01) and lower percentage of neutrophils (59 vs 64% for T and NoT, respectively, P = 0.05), although the levels of DSCC and percentage of neutrophils in cows dried off without antimicrobials remained lower than the risk threshold suggested by the international literature. A logistic regression was computed after the application of selective dry cow therapy to identify risk factors of high milk SCC (≥100 000 cells/mL) at the beginning of lactation. Increased milk SCC after calving was related to high SCC at the end of lactation and abandonment of antimicrobial therapy at dry-off. Moreover, the length of the dry period, milk protein content, and flank cleanliness in the last test day before dry-off were other factors in the logistic regression. Neutrophil counts at the beginning of the next lactation were affected by the same factors that influenced SCC, together with milk production, TLC, and macrophages on the last test day. The results obtained in these studied farms showed that selective dry cow therapy may be applied without adversely affecting the next lactation.

Graduate Student Literature Review: The challenge of drying-off high-yielding dairy cows

The cessation of lactation (i.e., dry-off) in dairy cattle is an area of research that has received much focus in recent years. The dry period is necessary to optimize tissue remodeling of the mammary gland, but represents a stressful event, incorporating several changes in daily routine, diet, and metabolism. Moreover, the high milk yields achieved by modern cows in late gestation exacerbate the need for relevant manipulations in the days around dry-off, as excessive accumulation of milk might jeopardize the success of the dry period, with potential negative effects on future lactation. Production levels over 15 kg/d are an additional risk factor for udder health, delay mammary involution, and worsen metabolic stress and inflammatory responses. Furthermore, the pressure to reduce antibiotic usage in farm animals has resulted in increased attention on the dry period, given that historically most dairy cattle were provided prophylactic intramammary antibiotic treatment at dry-off as a means to reduce the risk of intramammary infections in the subsequent lactation. Several strategies have been proposed over the years to cope with these challenges, aiming to gradually reduce milk yield before dry-off, promoting at the same time the start of mammary involution. Among them, the most common are based on feed or nutrient restriction, a decrease in milking frequency, or administration of prolactin inhibitors. These practices have different capacities to reduce milk yield through different mechanisms and entail several implications for udder health, animal welfare, behavior, endocrine status, metabolism, and inflammatory conditions. The present review aims to provide a comprehensive overview of the dry-off phase in high-yielding cows and of the impact of high milk production at dry-off, and to describe possible strategies that might be implemented by farmers and veterinarians to optimize this critical phase in an integrated way.

Evaluation of test-day milk somatic cell count to predict intramammary infection in late lactation grazing dairy cows

Use of selective dry cow antimicrobial therapy requires to precisely differentiate cows with an intramammary infection (IMI) from uninfected cows close to drying-off to enable treatment allocation. Milk somatic cell count (SCC) is an indicator of an inflammatory response in the mammary gland and is usually associated with IMI. However, SCC can also be influenced by cow-level variables such as milk yield, lactation number and stage of lactation. In recent years, predictive algorithms have been developed to differentiate cows with IMI from cows without IMI based on SCC data. The objective of this observational study was to explore the association between SCC and subclinical IMI, taking cognizance of cow-level predictors on Irish seasonal spring calving, pasture-based systems. Additionally, the optimal test-day SCC cut-point (maximized sensitivity and specificity) for IMI diagnosis was determined. A total of 2,074 cows, across 21 spring calving dairy herds with an average monthly milk weighted bulk tank SCC of ≤200,000 cells/mL were enrolled in the study. Quarter-level milk sampling was carried out on all cows in late lactation (interquartile range = 240-261 d in milk) for bacteriological culturing. Bacteriological results were used to define cows with IMI, when ≥1 quarter sample resulted in bacterial growth. Cow-level test-day SCC records were provided by the herd owners. The ability of the average, maximum and last test-day SCC to predict infection were compared using receiver operator curves. Predictive logistic regression models tested included parity (primiparous or multiparous), yield at last test-day and a standardized count of high SCC test-days. In total, 18.7% of cows were classified as having an IMI, with first parity cows having a higher proportion of IMI (29.3%) compared with multiparous cows (16.1%). Staphylococcus aureus accounted for the majority of these infections. The last test-day SCC was the best predictor of infection with the highest area under the curve. The inclusions of parity, yield at last test-day, and a standardized count of high SCC test-days as predictors did not significantly improve the ability of last test-day SCC to predict IMI. The cut-point for last test-day SCC which maximized sensitivity and specificity was 64,975 cells/mL. This study indicates that in Irish seasonal pasture-based dairy herds,with low bulk tank SCC control programs, the last test-day SCC (interquartile range days in milk = 221-240) is the best predictor of IMI in late lactation.

Udder health of dairy cows with an extended voluntary waiting period from calving until the first insemination

This study aimed to evaluate the effect of an extended voluntary waiting period (VWP) on SCC, SCC elevations and clinical mastitis incidence during the complete lactation and the first 6 weeks of the next lactation. Holstein-Friesian dairy cows (N = 154) were blocked for parity, expected milk yield, calving season and breeding value for persistency and were randomly distributed across 3 VWP (50, 125, or 200 d: VWP-50, VWP-125, VWP-200). Cows were monitored from calving until 6 weeks into the next lactation, or until culling. An elevation of SCC in milk was defined as SCC in milk ≥200 000 cells/ml after two previous weeks with SCC < 200 000 cells/ml. Over the complete lactation, extending the VWP did not affect SCC elevations and the occurrence of clinical mastitis per lactation or per cow per year. There was no clear effect of VWP length on SCC in the complete lactation, except that multiparous cows in VWP-125 had a higher SCC compared with multiparous cows in VWP-50. Dry-off antibiotic usage per cow per year was lower in VWP-200 compared with VWP-50 for multiparous cows. In the first 6 weeks of the next lactation, cows in VWP-200 had a higher SCC compared with cows in VWP-50, with no effect of VWP on the number of elevations of SCC or the occurrence of clinical mastitis. Extending the VWP may therefore be used to reduce the frequency of transition periods and the associated use of dry-cow antibiotics, with limited impact on udder health, and a similar occurrence of SCC elevations and clinical mastitis per year.

Identification of Changes in Rumination Behavior Registered with an Online Sensor System in Cows with Subclinical Mastitis

The aim of the present study is to determine the relationship between subclinical mastitis and rumination behavior registered with an online sensor system. Based on the findings of the general clinical examination of 650 milking cows, 10 cows with subclinical mastitis (SCM) and 10 clinically healthy cows (HG) were selected (without clinical signs of any diseases). Rumination behavior biomarkers were registered with RumiWatch noseband sensors (RWS; ITIN + HOCH GmbH, Fütterungstechnik, Liestal, Switzerland). Sensors were implanted on the first day after calving. Data from the RWS 13 days before diagnosis of SCM and 13 days after diagnosis of SCM were compared with HG data from the same period. Healthy cows were checked alongside SCM cows on the same days. In our study, we found that healthy cows spent more time engaging in rumination and drinking (p < 0.05) and also had more boluses per rumination. Moreover, among cows with subclinical mastitis, rumination time from day 4 to day 0 decreased by 60.91%, drinking time decreased by 48.47%, and the number of boluses per rumination decreased by 8.67% (p < 0.05). The results indicate that subclinical affects time and rumination chews registered with sensor systems. However, additional studies with larger numbers of animals are required to confirm these results. Furthermore, the impact of heat stress, estrus, and other effects on rumination behavior biomarkers should be evaluated.

Invited review: Selective use of antimicrobials in dairy cattle at drying-off

Administering intramammary antimicrobials to all mammary quarters of dairy cows at drying-off [i.e., blanket dry cow therapy (BDCT)] has been a mainstay of mastitis prevention and control. However, as udder health has considerably improved over recent decades with reductions in intramammary infection prevalence at drying-off and the introduction of teat sealants, BDCT may no longer be necessary on all dairy farms, thereby supporting antimicrobial stewardship efforts. This narrative review summarizes available literature regarding current dry cow therapy practices and associated impacts of selective dry cow therapy (SDCT) on udder health, milk production, economics, antimicrobial use, and antimicrobial resistance. Various methods to identify infections at drying-off that could benefit from antimicrobial treatment are described for selecting cows or mammary quarters for treatment, including utilizing somatic cell count thresholds, pathogen identification, previous clinical mastitis history, or a combination of criteria. Selection methods may be enacted at the herd, cow, or quarter levels. Producers' and veterinarians' motivations for antimicrobial use are discussed. Based on review findings, SDCT can be adopted without negative consequences for udder health and milk production, and concurrent teat sealant use is recommended, especially in udder quarters receiving no intramammary antimicrobials. Furthermore, herd selection should be considered for SDCT implementation in addition to cow or quarter selection, as BDCT may still be temporarily necessary in some herds for optimal mastitis control. Costs and benefits of SDCT vary among herds, whereas impacts on antimicrobial resistance remain unclear. In summary, SDCT is a viable management option for maintaining udder health and milk production while improving antimicrobial stewardship in the dairy industry.

Potential impacts to antibiotics use around the dry period if selective dry cow therapy is adopted by dairy herds: An example of the western US

Mastitis is a prevalent and expensive disease in dairy herds worldwide. Blanket dry cow therapy (BDCT), in which all quarters of all cows are infused with antimicrobials at the dry-off, is a cornerstone for mastitis control in many countries. An alternative approach is the use of selective dry cow therapy (SDCT), in which only cows with high risk for intramammary infection (IMI) at dry-off receive antimicrobials. Our objectives in this cross-sectional study were to estimate the potential reduction in the use of antimicrobials if SDCT was adopted in the US by using cow-level dairy herd data and to describe the factors associated with cows being classified as high-risk for an IMI at dry-off. Besides, we aimed to describe the seasonality in IMI at dry-off. We used cow-level somatic cell score (SCS) test-day data from herds in the western US (DHIA, Dairy Herd Improvement Association, AgriTech, Visalia, CA) to create five scenarios to classify cows as high risk for IMI at dry-off. Associations between cow-level data and state were also used in logistic regression models. We also calculated the average animal-defined daily dosage of antimicrobials per cow per year around the dry period if a BDCT or SDCT approach is used, adjusting for the risk of cases of clinical mastitis in the next lactation for the SDCT approach. The point prevalence of IMI at the last test-day before dry-off varied between 15.0 % and 54 % for primiparous and 34.0 % and 85 % for multiparous cows, depending on the scenario. By extrapolating our results obtained from using data from dairies enrolled in the DHIA testing program for the western US, we demonstrated that regardless of the criteria used to classify cows as high risk of IMI at dry-off (scenarios 1-5), if selective dry cow therapy is adopted in the US, the dairy industry could reduce the use of antimicrobials around the dry-off between 31 % and 66 %. Multiparous cows had greater odds of being classified as high-risk than primiparous cows. Cows dried off in the spring, summer, and fall had lower odds of being classified as high-risk compared to cows dried off in the winter. Advanced days in milk at dry-off was associated with greater risk of IMI at dry-off. Greater milk yield and higher protein percentage at the last test-day before dry-off were associated with decreased odds of a cow being classified as high-risk at dry-off, cows in small herds had greater odds of being classified as high-risk at dry-off, and a variation among states was observed.

Mastitis Control and Intramammary Antimicrobial Stewardship in Ireland: Challenges and Opportunities

The Veterinary Medicines Regulation (EU 2019/6) came into force in all EU member states on 28 January 2022. This regulation places particular emphasis on prudent and responsible antimicrobial use in food animal production. Key changes include restrictions on the prophylactic use of antimicrobials in animals, and the possibility to reserve certain antimicrobials for humans only. The Regulation presents challenges to the Irish dairy industry, particularly with respect to current approaches to dry cow therapy. In response, the CellCheck technical working group (TWG, a technical group working in support of CellCheck, the national mastitis control programme) have developed pragmatic national and farm-level recommendations in support of improved mastitis control and intramammary antimicrobial stewardship in the Irish dairy industry. This paper outlines these recommendations, and provides an overview of the evidence considered to inform the TWG during its work (including the Regulation, policy perspectives, international best-practice, international scientific reviews and specific Irish challenges). In many key areas of concern, the TWG recognises the challenges in seeking to shape recommendations in the absence of robust and practical scientific evidence. For this reason, some of the recommended actions are pragmatic in nature, informed by national and international experiences. Periodic programme review will be needed, informed by ongoing monitoring of key performance indicators, to identify those actions that are most effective in an Irish context.

Udder health, conceptual construct, and uses of the term: A systematic review from 1962 to 2019

Background and Aim:

Udder health management is essential for the further development of milk production systems and public health. This process depends on the generation of knowledge regarding control, prevention, and promotion of health. In scientific literature, it is impossible to find a synthesis of the categories that would allow comprehension of the complex phenomenon udder health. Different research approaches have allowed this polysemic concept, described by some researchers as multifactorial and by philosophical perspectives as a social phenomenon, to be further studied. Thus, the objective of this systematic review was to systematize the conceptual categories of udder health and the use of the term in the original articles published in the scientific literature from the period 1962 to 2019.

Materials and Methods:

A systematic review with a broad approach was designed by applying the phases of identification, screening, selection, and inclusion criteria described in the Preferred Reporting Items for Systematic Reviews and Meta-Analyzes guide. An exhaustive search of original articles by specificity was carried out in the Science Direct, PubMed, Scielo, LILACS, and Google Scholar databases. The investigation was carried out on November 22, 2019. According to the inclusion criteria established, articles needed to be original studies, to be publications on bovine livestock, written in English, Spanish and Portuguese. Furthermore, the articles considered needed to tackle the term udder health so that its conceptual categorization could be extracted. Google Scholar patents and citations and articles removed from databases or not available were excluded from the study and those that, based on the reading of the complete text, considered the farming of animal species other than bovine. A qualitative synthesis of the year of publication, continent, approach, type of study, and conceptual category of udder health was carried out by calculating frequencies (Statistical Package for the Social Sciences version 24).

Results:

In total, 165 articles were included in the study. Eight conceptual categories, consolidated over time, were systematized, showing that udder health is not a static problem, and that science has been responding through the generation of new knowledge around conceptual categories as different udder health problems emerge.

Conclusion:

Culture and politics were two categories, related to all the others, that stood out in the results. These two categories were of great interest in countries advanced in milk production and in the implementation of udder health policies, which acknowledge the producer and other actors of the production chain as fundamental political actors for policies, decision-making processes, and public health care to be effective. The lack of synonyms for the term udder health (e.g., mastitis) may have led to the exclusion of important articles in each category. However, the constriction to the term udder health was intentional and aimed at constructing the concept. Udder health is hereby understood as a health-disease process, different from the term mastitis, which from its semantic origin, refers only to the disease process. According to this study, the concept can be understood through the categories of traditional epidemiology based on risk factors and disease; microbiology; genetics, resistance, and immunity; animal welfare; nutrition; organic production; culture; and politics.

Effect of selective dry cow treatment on udder health and antimicrobial usage on Dutch dairy farms

Since 2013, selective dry cow treatment (SDCT) has been the standard approach in the Netherlands where farmers select cows for the use of antimicrobials at drying-off. Shortly after its introduction, antimicrobial usage decreased significantly, and no significant association was found between the level of SDCT and clinical mastitis (CM). Obviously, at that time long-term associations could not be evaluated. This study aimed to provide insight into the methods and level of implementation of SDCT on Dutch dairy farms with a conventional milking system (CMS) or an automatic milking system (AMS) in 2016 and 2017, several years after the implementation of SDCT. Udder health and antimicrobial use were also assessed. For this study, 262 farmers recorded dry cow treatments as well as all CM cases in the period from May 1, 2016, until April 30, 2017. Additionally, somatic cell count (SCC) data on cow and herd level, treatment data on herd level and questionnaire results on udder health management were collected. Data were analyzed using descriptive statistics with differences between milking systems being evaluated using nonparametric univariable statistics. In the study period, SDCT was applied on almost all (98.8%) of the participating dairy farms. The main reason for applying antimicrobials at drying-off was either the SCC history during the complete previous lactation or the SCC at the last milk recording before drying-off. The median percentage of cows treated with antimicrobials was 48.5%. The average incidence rate of CM was 27.3 cases per 100 cows per year. From all CM cases that were registered per herd, on average 32.8% were scored as mild, 42.2% as moderate, and 25.0% as severe CM. The mean bulk tank SCC of the herds was 168,989 cells/mL. A cow was considered to have subclinical mastitis (SCM) if individual SCC was ≥150,000 cells/mL for primiparous and ≥250,000 cells/mL for multiparous cows. Passing these threshold values after 2 earlier low SCC values was considered a new case of SCM. The mean incidence rate of SCM in these herds was 62.5 cases per 100 cows per year. Bulk tank SCC and the incidence rate of SCM on farms with a CMS were statistically lower than on farms with an AMS, whereas the incidence rate of CM did not significantly differ between both groups of farms. The AMS farms had more cows per herd treated with antimicrobials at drying-off and a larger proportion of severe CM cases than did CMS farms. It is unknown whether the differences are due to the milking system or to other differences between both types of farms. This study showed the level of adoption of SDCT, udder health, and antimicrobial usage parameters several years after the ban on the preventive use of antimicrobials in animal husbandry. It found that udder health parameters did not differ from those found in Dutch studies before and around the time of implementing SDCT, whereas SDCT was widely applied on Dutch dairy farms during the study period. Therefore, it was concluded that Dutch dairy farmers were able to handle the changed policy of antimicrobial use at drying-off while maintaining indicators of a good udder health.

Bacteriological outcomes following random allocation to quarter-level selection based on California Mastitis Test score or cow-level allocation based on somatic cell count for dry cow therapy

Intramammary infusion of antimicrobials at the end of lactation (dry cow therapy) has been a cornerstone of mastitis management for many years. However, as only a proportion of cows are infected at this time, treating only those cows likely to be infected is an important strategy to reduce antimicrobial usage and minimize risk of emergence of antimicrobial resistance. Such an approach requires the ability to discriminate between cows and quarters likely to be infected and uninfected. This study compared assignment of cows or quarters to antimicrobial treatment at the end of lactation based on cow composite somatic cell count (SCC; i.e., all quarters of cows with a maximum SCC across lactation >200,000 cells/mL received an antimicrobial; n = 891 cows, SCC-group) or assignment to quarter-level treatment based on a quarter level California Mastitis Test (CMT) score ≥ trace (n = 884 cows; CMT-group) performed immediately before drying off. All quarters of all cows also received an infusion of a bismuth-based internal teat sealant. Milk samples were collected for microbiology following the last milking, and again within 4 d of calving. Clinical mastitis records from dry off to 30 d into the subsequent lactation were collected. Multilevel, multivariable models were used to assess the effect of assignment to antimicrobial treatment. At drying off, a total of 575 (8.8%) and 147 (2.3%) of the 6,528 quarters had a minor, and a major intramammary infection (IMI), respectively. At drying off, 2089/3270 (63.9%) and 883/3311 (26.7%) of quarters were treated with dry cow therapy in the CMT and SCC-groups, respectively. Apparent bacteriological cure proportion for any IMI was higher in quarters assigned to the CMT than the SCC-group (349/368 (0.95, 95% CI 0.92-0.97) versus 313/346 (0.90, 95% CI 0.87-0.93)). New IMI proportion was lower among quarters assigned to the CMT than SCC-group [101/3,212 (0.032, 95% CI 0.025-0.038) versus 142/3,232 (0.044, 95% CI 0.036-0.051)]. The prevalence of any IMI postcalving was lower in quarters assigned to the CMT than SCC-group [119/3,243 (0.037, 95% CI: 0.030-0.044) versus 173/3,265 (0.054, 95% CI: 0.045-0.062)]. There was no difference in incidence of clinical mastitis between treatment groups. The total mass of antimicrobials used was 63% higher in the CMT-group than in the SCC-group (3.47 versus 2.12 mg/kg of liveweight). Selection of quarters for antimicrobial treatment at the end of lactation based on CMT resulted in greater proportion undergoing bacteriological cure, reduced risk of any new IMI and reduced post calving prevalence of any IMI compared with selection of cows based on SCC. However, CMT-based selection resulted in higher antimicrobial use compared with SCC-based selection, and further research is required to analyze the cost benefit and impact on risk of antimicrobial resistance of these 2 strategies.

Selective dry cow therapy effect on milk yield and somatic cell count: A retrospective cohort study

Antibiotic dry cow therapy (aDCT) at the end of lactation is an effective mastitis control measure. Selective dry cow therapy means that only infected or presumed-infected cows are treated, instead of aDCT being used as a treatment for all cows. Because antibiotic resistance poses a global threat, livestock production is under increasing pressure to reduce antibiotic use. Changes in management should not, however, impair animal welfare or cause significant economic losses. Our objective was to compare milk yield and somatic cell count (SCC) between aDCT-treated and untreated cows in herds that used selective aDCT, taking into account risk factors for reduced yield and high SCC. The information source was 2015 to 2017 Dairy Herd Improvement data, with 4,720 multiparous cows from 172 Finnish dairy farms. The response variables were test-day milk yield (kg/d) and naturally log-transformed composite SCC (×1,000 cells/mL) during the first 154 d in milk (DIM). The statistical tool was a linear mixed-effects model with 2-level random intercepts, cows nested within herds, and a first-order autoregressive [AR(1)] correlation structure. The overall proportion of aDCT-treated cows was 25% (1,176/4,720). Due to the interaction effect, SCC on the last test day prior to dry-off affected postcalving milk yield differently in aDCT-treated cows than in untreated cows. A higher SCC prior to dry-off correlated with a greater daily yield difference after calving between cows treated and untreated. The majority of cows had SCC < 200,000 cells/mL before dry-off, and as SCC before dry-off decreased, difference in yield between aDCT-treated and untreated cows decreased. Postcalving SCC was lower for aDCT-treated cows compared with untreated cows. To illustrate, for cows with an SCC of 200,000 cells/mL before dry-off, compared with untreated cows, aDCT-treated cows produced 0.97 kg/d more milk and, at 45 DIM, had an SCC that was 20,000 cells/mL lower. Higher late-lactation SCC and lactational mastitis treatments were associated with higher postcalving SCC. A dry period lasting more than 30 d was associated with higher yields but not with SCC. Our findings indicate that a missed aDCT treatment for a high-SCC cow has a negative effect on subsequent lactation milk yield and SCC, which emphasizes the importance of accurate selection of cows to be treated.

Engaging with selective dry cow therapy: understanding the barriers and facilitators perceived by Irish farmers

BACKGROUND

Selective dry cow therapy (SDCT) is widely promoted in dairy farming as a method to reduce antimicrobial usage. New legislation introduced by the European Union will restrict and regulate the prophylactic and metaphylactic use of antibiotics from January 2022. Blanket dry cow therapy continues to be a practice engaged in by many farmers in Ireland and for many of these farmers, moving towards SDCT would require a significant infrastructural, behavioural and/or cultural change on their farm. Existing research has reported the important need to understand farmers' motivations to initiate any substantial behaviour change. However, it is currently unknown what farmers know, think and believe about SDCT in Ireland. The aim of this study was to use qualitative methods to explore what barriers and facilitators farmers perceived to exist with SDCT and explore if they had chosen to implement SDCT after voluntarily participating in a funded dry cow consult with a trained veterinarian, with the objective of maximising the dry period udder health performance and moving safely to SDCT.

RESULTS

In this study, 19 farmers were contacted, and telephone interviews were conducted regarding farmers' beliefs about the consequences of SDCT. Audio recordings were professionally transcribed verbatim and analysed qualitatively using an inductive thematic analysis. The analysis identified 6 barriers and 6 facilitators to implementing SDCT. A significant fear of increasing mastitis incidence was evident that caused reluctance towards SDCT and reliance on antibiotics. Mixed perceptions on SDCT, infrastructure limitations, a perceived lack of preventive advice as well as peer influence were presented as barriers to SDCT. Farmers can build confidence when a graded approach to SDCT is implemented, which could help overcome the fear of SDCT and reliance on antibiotics. Regulatory pressure, high standards of farm hygiene and use of targeted veterinary consults were found to facilitate SDCT. Education was suggested to motivate farmers in the future uptake of SDCT. Despite cited negative influences, peer influence can be utilised to encourage the farming community.

CONCLUSIONS

This study prioritises areas to facilitate the major behaviour change required as a dairy industry in order to move from blanket dry cow therapy to SDCT.

Evaluation of 4 predictive algorithms for intramammary infection status in late-lactation cows

The objective of this observational study was to compare 4 cow-level algorithms to predict cow-level intramammary infection (IMI) status (culture and MALDI-TOF) in late-lactation US dairy cows using standard measures of test performance. Secondary objectives were to estimate the likely effect of each algorithm, if used to guide selective dry cow therapy (SDCT), on dry cow antibiotic use in US dairy herds, and to investigate the importance of including clinical mastitis criteria in algorithm-guided SDCT. Cows (n = 1,594) from 56 US dairy herds were recruited as part of a previously published cross-sectional study of bedding management and IMI in late-lactation cows. Each herd was visited twice for sampling. At each farm visit, aseptic quarter-milk samples were collected from 20 cows approaching dry-off (>180 d pregnant), which were cultured using standard bacteriological methods and MALDI-TOF for identification of isolates. Quarter-level culture results were used to establish cow-level IMI status, which was considered the reference test in this study. Clinical mastitis records and Dairy Herd Improvement Association test-day somatic cell count data were extracted from herd records and used to perform cow-level risk assessments (low vs. high risk) using 4 algorithms that have been proposed for SDCT in New Zealand, the Netherlands, United Kingdom, and the United States. Agreement between aerobic culture (reference test; IMI vs. no-IMI) and algorithm status (high vs. low risk) was described using Cohen's kappa, test sensitivity, specificity, negative predictive value, and positive predictive value. The proportion of cows classified as high risk among the 4 algorithms ranged from 0.31 to 0.63, indicating that these approaches to SDCT could reduce antibiotic use at dry-off by 37 to 69% in the average US herd. All algorithms had poor agreement with IMI status, with kappa values ranging from 0.05 to 0.13. Sensitivity varied by pathogen, with higher values observed when detecting IMI caused by Streptococcus uberis, Streptococcus dysgalactiae, Staphylococcus aureus, and Lactococcus lactis. Negative predictive values were high for major pathogens among all algorithms (≥0.87), which may explain why algorithm-guided SDCT programs have been successfully implemented in field trials, despite poor agreement with overall IMI status. Removal of clinical mastitis criteria for each algorithm had little effect on the algorithm classification of cows, indicating that algorithms based on SCC alone may have similar performance to those based on SCC and clinical mastitis criteria. We recommend that producers implementing algorithm-guided SDCT use algorithm criteria that matches their relative aspirations for reducing antibiotic use (high specificity, positive predictive value) or minimizing untreated IMI at dry-off (high sensitivity, negative predictive value).

Comparing Blanket vs. Selective Dry Cow Treatment Approaches for Elimination and Prevention of Intramammary Infections During the Dry Period: A Systematic Review and Meta-Analysis

A systematic review and a series of meta-analyses were conducted to investigate the efficacy of selective dry cow antimicrobial treatment (SDCT) (in which only infected quarters/cows were treated with an antimicrobial) compared with blanket dry cow treatment (BDCT) (all quarters/all cows received an antimicrobial, regardless of their infection status). A full detailed protocol was published before initiating this review. Studies reporting on the (1) proportion of untreated quarters or cows when using SDCT, (2) intramammary infection (IMI) incidence risk over the dry period, (3) IMI elimination risk, (4) post-calving IMI prevalence, (5) early lactation clinical mastitis incidence, or (6) subsequent lactation milk yield and somatic cell counts were considered eligible. Thirteen articles representing 12 controlled trials, whether randomized or not, were available for analyses. SDCT reduced the use of antimicrobials at dry off by 66% (95% CI: 49-80). There was no difference in the elimination of existing IMI at dry off, between SDCT and BDCT. Meta-regression showed that the risk of IMI incidence during the dry period, IMI risk at calving, early lactation clinical mastitis risk, and early lactation milk yield and somatic cell counts did not differ between SDCT and BDCT as long as an internal teat sealant (65% bismuth subnitrate) was administered to untreated healthy quarters/cows at dry off. For trials not using internal teat sealants, SDCT resulted in higher risk than BDCT of acquiring a new IMI during the dry period and of harboring an IMI at calving. Lines of evidence strongly support that SDCT would reduce the use of antimicrobials at dry off, without any detrimental effect on udder health or milk production during the 1st months of the subsequent lactation, if, and only if, internal teat sealants are used for healthy, untreated quarters/cows.

Effectiveness of dry cow therapy and/or internal teat sealant on existing infections in smallholder dairy farms in Kenya

Background and Aim:

Dry cow therapy (DCT) can be an effective treatment of mastitis that has not responded to conventional treatment during lactation. The aim of this study was to establish the effectiveness of DCT options available in reducing intramammary infections in smallholder dairy farms in Kiambu County, Kenya.

Materials and Methods:

The study targeted smallholder dairy farms which were registered at the local dairy cooperatives and which had cows that were at the point of dry-off. A total of 32 cows with 121 quarters that were California Mastitis Test (CMT) positive were recruited, with the quarters randomly allocated to receive either DCT (DCT – neomycin sulfate, penethamate hydriodide, and procaine benzylpenicillin) and internal teat sealant (ITS) or ITS alone (bismuth nitrate) after aseptically collecting quarter milk samples for bacterial culture. Farm- and animal-level factors were captured through a questionnaire which was administered to the principal farmer or a person who was managing the animals. Post-calving, milk samples were also collected for bacterial culture to establish if the infection was cleared or if there was a new infection.

Results:

DCT with ITS significantly reduced the proportion of quarters infected with Staphylococcus aureus from 64.0% at dry-off to 44.0% post-calving (35% reduction). In the control group, ITS alone, there was a small reduction in proportions of S. aureus from 46.8% to 40.4%. Proportions of quarter infections by coagulase-negative Staphylococcus in the treatment group reduced from 16.0% at dry-off to 2.0% post-calving, with a significant reduction in the control group too from 19.1% to 4.3%, which could be due to self-cure. Actinomyces species, Escherichia coli, Streptococcus species, and Pseudomonas species proportions slightly increased in the treatment group, as did E. coli and Pseudomonas species proportions in the control group.

Conclusion:

In smallholder dairy farms with subclinical mastitis, DCT of CMT-positive cows leads to a significant decrease of S. aureus infections at calving.

Survey of veterinarians in the Netherlands on antimicrobial use for surgical prophylaxis in dairy practice

There is increased concern about the selection pressure of antimicrobial use (AMU) in humans as well in farm animals resulting in antimicrobial (AM) resistance. The introduction of monitoring of AMU in food-producing animals since 2011 has led to a considerable quantitative reduction of AMU in those animal species in the Netherlands. This survey was conducted to explore the possibilities to improve prudent use of AM in the cattle industry. We sent an online questionnaire to 373 veterinarians and asked which antimicrobial prophylaxis they used for their most recently performed cesarean section (CS) and left displaced abomasum (LDA) correction. With a response rate of 30%, we found that older graduates used more AM for CS than recently graduated veterinarians (odds ratio = 2.4 to 2.7 depending on category), whereas antimicrobial prophylaxis in LDA surgeries was significantly different for the available surgical correction methods. The results indicate that the respondents do not adjust the surgical antimicrobial prophylaxis for different conditions of the patient or the environment; 37 (38%) respondents consider that the risks of contamination are similar for CS and LDA. In CS and all LDA correction methods preoperative prophylaxis was significantly less often applied than postoperative antimicrobial treatments (odds ratio = 0.05 and 0.08, respectively). When preoperative prophylaxis was applied, the choice of (combinations of) the AM and the timing of administration were not adequate at the start of the surgical procedure (88% for CS and 90% for LDA). We conclude that considerable qualitative (timing, choice of antimicrobial, route of administration) and quantitative (limit AMU to indicated procedures) improvement on antimicrobial prophylaxis for CS and LDA is possible by appreciation of the risks of the type of surgery (CS, LDA) and its conditions as well as by selecting classes of AM and timing and routes of administration that result in effective drug concentrations at the start of the procedure.

Antibiotic use and potential economic impact of implementing selective dry cow therapy in large US dairies

In this study, our objectives were to evaluate the economic feasibility of implementing selective dry cow therapy (SDCT) in large US herds and to estimate the potential reduction in antibiotic use around the dry period if SDCT management is adopted. Cow-level data were obtained from the Dairy Herd Improvement Association (AgriTech, Visalia, CA) and individual dairy herds in California. Logistic regression models were used to predict the incidence risk of subclinical and clinical mastitis in the subsequent lactation for 96 last test-day somatic cell score categories. Linear programming was used to optimize the costs of dry cow therapy in 3 simulated large US dairy herds with different bulk tank somatic cell counts (BTSCC). The objective function was aimed at minimization of the total cost of mastitis around the dry period (TCMD), under a varying constraint of the maximum percentage of cows dried off with antibiotics. A sensitivity analysis was performed on milk price, dry-off antibiotic price, and risk ratio of mastitis in the subsequent lactation when no antibiotics and only teat sealant was used at dry-off. For all situations, blanket dry cow therapy was more expensive than SDCT. In a herd with medium BTSCC, the TCMD was $54.7 per primiparous dry cow and $58.5 per multiparous dry cow annually. In the optimal economic situation where SDCT was used, only 30% of primiparous cows received antibiotics, leading to a TCMD of $52.4 per primiparous dry cow, whereas 88% of multiparous cows received antibiotics, at a cost of $58.2 per multiparous dry cow. This corresponded with an overall reduction of 29% in the use of antibiotics around the dry period in a conservative scenario. This study showed that it is economically feasible to reduce antibiotic use associated with dry cow therapy in large US dairy herds. This contributes to the efforts of reducing antibiotic use worldwide.

Randomized controlled field trial comparing quarter and cow level selective dry cow treatment using the California Mastitis Test

Selective use of antibiotic dry cow treatment can be implemented at the cow or quarter level, with the latter having the potential to further reduce antibiotic use. Our objective was to compare these 2 approaches in 6 herds in the United Kingdom in which environmental mastitis predominated. Eight hundred seven cows were enrolled and categorized as having a high cell count (n = 401) or low cell count (n = 406) in the last 3 mo of lactation and clinical mastitis history. All quarters of all enrolled cows received an internal teat sealant. Within each category, cows were randomly allocated to 1 of 3 groups; in one group antibiotic treatment was allocated at cow level (i.e., all 4 quarters received antibiotic), whereas in the 2 remaining groups antibiotic treatment was allocated at quarter level, based on California Mastitis Test (CMT) findings. Two different thresholds, score 1 and 2, were used to determine likely infection status. Quarter milk samples were collected at dry off and postcalving for bacteriological culture and somatic cell count (SCC). Cows were monitored for clinical mastitis from dry off until 100 d in milk. Cow level SCC and milk yield data were collated from farm records. Within each category, the 2 quarter level treatment groups were compared with cow level treatment at dry off. Leaving quarters untreated with intramammary antibiotic in cows in the high cell count group, with a CMT <2 or <1, reduced antibiotic use by 55% and 31%, respectively, and resulted in no difference in the odds of being infected with any pathogen postcalving, but was associated with a higher SCC at the first test day. Intramammary antibiotic treatment of quarters with a CMT ≥1 in cows in the low cell count category at dry off was not associated with any reduction in the odds of being infected with a major pathogen postcalving but was associated with a decrease in the odds of being infected with a minor mastitis pathogen postcalving. The use of antibiotics in quarters of cows categorized as low cell count at dry off, increased the proportion of quarters treated with antibiotic from 0% at cow level to 31% (CMT ≥ 1) and 12% (CMT ≥ 2) at quarter level, only resulting in a reduction in SCC of around 20,000 cells/mL at the first test day, if all quarters with CMT score ≥1 were treated with antibiotic. No differences in clinical mastitis incidence and milk yield in the first 100 d in milk were detected between any of the treatment groups. These study findings support selective quarter level dry off treatment only in cows with cow level SCC >200,000 cells/mL at dry off.

Dry period management and new high somatic cell count during the dry period in Dutch dairy herds under selective dry cow therapy

The aim of this study was to describe the current management practices that could influence udder health during the dry period and to investigate the associations between management and new high SCC during the dry period. In 2008 the Netherlands started to improve transparency and decrease the use of antimicrobials in animal husbandry. Prevention of new high SCC during the dry period via antimicrobial dry cow treatment (DCT) was no longer allowed in animals with a low SCC before the dry period. An increase of new high SCC during the dry period was expected in dairy cows without antimicrobial protection, but was not observed. In 2018 an online questionnaire was conducted among 1,942 Dutch dairy farms using 12 different veterinary clinics. The questionnaire asked about the management of dry cows at the start of and during the dry period, and around calving, considerations in the use of DCT, and knowledge of the 2012 guidelines for selective DCT. A total of 690 farmers (36%) responded to the questionnaire. Data on new high SCC during the dry period, use of antimicrobials for intramammary DCT and mastitis treatment, herd size, and milking system were available from other sources. Descriptive statistics were used to evaluate the associations between the different variables. For analysis of new high SCC on herd level, explanatory variables were analyzed using a generalized linear mixed model. Respondents indicated that the most important management factor to reduce the risk of new high SCC was reduction of milk yield before dry-off. The variables associated with a lower proportion of new high SCC on herd level during the dry period were the use of dip or spray after drying off, a higher animal-defined daily dose of intramammary antimicrobials for DCT, the use of DCT in low-SCC cows based on SCC or mastitis history, correct knowledge of the guideline, and awareness of importance of low infection rate and good hygiene during dry-off. The variables associated with a higher proportion of new high SCC on herd level were dry cow housing other than cubicles and a higher animal-defined daily dose for intramammary antimicrobials for mastitis. This research clearly indicates that farmers can balance limited use of antimicrobials at dry-off with management measures to maintain good udder health during the dry period.

Retrospective cohort study of management procedures associated with dairy herd-level eradication of Streptococcus agalactiae in the Danish surveillance program

The aim of this observational retrospective cohort study was to identify management procedures that are associated with herd-level eradication of Streptococcus agalactiae in dairy herds. The objective was to compare herds that recovered from Strep. agalactiae with herds that remained infected with Strep. agalactiae on the basis of specific management procedures. Data from the Danish surveillance program for Strep. agalactiae, where all milk delivering dairy herds are tested yearly, were used to identify study herds. One hundred ninety-six herds that were classified in the program as infected with Strep. agalactiae, in both January 2013 and January 2014, were identified as study herds. These were followed until January 2017. One hundred forty-four herds remained infected every year until January 2017. Forty-six herds recovered from Strep. agalactiae after January 2014 (were tested negative continuously after January 2015, January 2016, or January 2017 and remained noninfected in the program from recovery until January 2017). Herd characteristics and management procedures were obtained through the Danish Cattle Database. Herd characteristics included herd size, yield, milking system, and bulk milk somatic cell count (SCC). Management procedures included the proportion of cows culled within 100 d after calving due to mastitis, the extent of diagnoses relative to the extent of mastitis treatments, the proportion of cows treated for mastitis during lactation, the proportion of cows treated for mastitis early in lactation, the proportion of cows treated at dry-off, and the median length of the dry period for cows receiving dry cow treatment. All variables were calculated on herd level. Multivariable logistic regression was used to analyze the association between herd infection status and management procedures. A higher proportion of culling due to mastitis within 100 d from calving was associated with a higher probability of herd-level recovery from Strep. agalactiae in herds with conventional milking system. For example, herds with conventional milking, a bulk milk SCC of 260,000 cells/mL, and 10% early culling due to mastitis had a recovery probability of 0.13, whereas similar herds with 20% early culling due to mastitis had a recovery probability of 0.15. A higher proportion of mastitis treatments within 250 d postcalving was associated with a higher probability of herd-level recovery for herds with a relatively high bulk milk SCC. For example, herds with conventional milking, a bulk milk SCC of 260,000 cells/mL, and 10% lactational mastitis treatments had a recovery probability of 0.12, whereas similar herds with 20% lactational mastitis treatments had a recovery probability of 0.15. Herds with a low bulk milk SCC (<220,000 cells/mL) combined with a low proportion of lactational treatments (<0.2) had a relatively high probability of herd-level recovery (>0.2). Additional variables, including the proportion of dry cow treatments, were not associated with herd-level recovery from Strep. agalactiae.

Dry cow therapy and early lactation udder health problems-Associations and risk factors

Mastitis remains the most expensive disease of dairy cows, and antibiotic dry cow therapy (DCT) at dry-off is an important part of mastitis control. Regardless of the infection status, blanket DCT is administered to all quarters of all cows, which is controversial due to the worldwide problem of antimicrobial resistance. Even though selective DCT of only infected cows is a more sustainable approach, choosing animals for treatment is not always straightforward. Our aim was to evaluate whether the herd-level DCT approach is associated with early lactation udder health problems, taking into account the cow characteristics. The information source was 2015-2017 Dairy Herd Improvement data with 7461 multiparous cows from 241 Finnish dairy herds. Information on the herd-level DCT approach was obtained from farmers' questionnaire responses in 2017, and the three different approaches were selective DCT, blanket DCT, and no DCT. The statistical tool for the data analysis was a generalized linear mixed model with a random herd effect for binary outcomes and a linear mixed model with a random herd effect for a continuous outcome. The two binary outcomes were the odds of having high milk somatic cell count (SCC ≥ 200 000 cells/mL) on the first test-day within 5-45 days in milk (DIM) and the odds of mastitis treatment in early lactation up to 45 DIM. The third outcome was the mean milk lnSCC (× 1000 cells/mL) within 120 DIM. Selective DCT was the prevailing treatment practice in our data. Blanket DCT was associated with lower SCC after calving. Cows more likely to have high SCC after calving were older cows, cows with high average SCC during the previous lactation, and cows with high milk yield near dry-off. A mastitis treatment in the early lactation was more likely if, during the previous lactation, the cow had high average SCC, high peak milk production, or high milk yield near dry-off. Our findings indicate that DCT is still effective in mastitis control. Cows with high milk yield, especially near dry-off, and cows with persistently high SCC require attention when considering next lactation udder health.

Monitoring udder health on routinely collected census data: Evaluating the short- to mid-term consequences of implementing selective dry cow treatment

In 2013, the preventive use of antimicrobials in Dutch livestock was prohibited, including a ban on the blanket application of antimicrobial dry cow treatment (BDCT). Since then, selective dry cow treatment (SDCT) has become the standard approach. In this study, we aimed to determine the effect of the ban on BDCT and the extent of the subsequent adoption of SDCT on antimicrobial usage (AMU) and udder health on Dutch dairy farms. In the Dutch cattle health surveillance system, AMU for dry cow treatment (AMU_DCT), AMU for intramammary treatment at any point in time (AMU_IMM), and udder health indicators are routinely and continuously monitored. This provided the opportunity to study associations among SDCT, udder health, and AMU on census data of approximately 17,000 dairy herds, with about 1.67 million cows in total (>2 yr old) at one moment in time in the period from 2013 until 2017. Six udder health parameters were evaluated using multivariable population-averaged generalized estimating equation models. The year in which the ban on BDCT was introduced (2013) was compared with the period thereafter (2014-2017). Additionally, AMU_IMM and AMU_DCT were included as independent variables to evaluate whether the extent to which SDCT was implemented on the herd level was associated with udder health. Demographic parameters were included as potential confounders. Since the ban on BDCT, overall declines of 63% in AMU_DCT and 15% in AMU_IMM were observed. The raw data show an improvement in 5 out of 6 evaluated udder health parameters between 2013 and 2017. Nevertheless, the multivariable model results showed that the period since the ban on BDCT was associated with a small but significant increase in the percentage of cows with high somatic cell count (HSCC) and new HSCC (+0.41% and +0.06%, respectively). Additionally, the probability of belonging to the group of herds with more than 25% of primiparous cows having HSCC during the start of lactation increased slightly, associated with the period after which BDCT was banned (odds ratio = 1.08). The probability of belonging to the group of herds with more than 25% cows having a persistent HSCC during the dry period was not affected and bulk milk somatic cell count showed a slight but significant reduction. The only udder health parameter that notably worsened during the study period was the probability of belonging to the group of herds with more than 25% of multiparous cows with a new HSCC after the dry period, during the start of lactation (odds ratio = 1.23). In herds where the farmer decided not to apply any dry cow therapy (≈20% of all herds), all udder health parameters were poorer compared with herds in which dry cow therapy was applied to some extent. The ban on BDCT and implementation of SDCT in the Netherlands was associated with a considerable reduction in AMU without a major impairment in udder health at the national level. Although negative effects of changed dry cow management were observed in some herds, we conclude that SDCT can be introduced without substantial negative effects on udder health.

Evaluation of customized dry-period strategies in dairy cows

Shortening or omitting the dry period to improve the energy balance in early lactation have the trade-offs of reduction in milk production and loss of opportunity for dry-cow therapy (DCT; i.e., intramammary antibiotic use at dry-off). Customized dry-period strategies (i.e., deciding upon DCT and dry-period length per cow) could mitigate negative effects of short or no dry periods on milk production and udder health and simultaneously retain benefits from improved energy balance and fertility. In this study, we evaluated 3 decision trees to customize dry-period strategies for individual cows. In the control tree (CT), all cows had a 60-d dry period, with DCT if somatic cell count (SCC) was >150,000 cells/mL before dry-off. In decision tree 1 (T1), parity 1 and parity >1 cows were assigned DCT if SCC was ≥150,000 cells/mL and SCC ≥50,000 cells/mL, respectively; whereas in decision tree 2 (T2), the threshold for DCT was SCC ≥200,000 cells/mL for all animals. In T1 and T2, cows with DCT were assigned a 60-d dry period, whereas cows without DCT were assigned a 30-d or 0-d dry period if their milk production remained >12 kg/d at 67 and 37 d before calving, respectively. Cows were monitored from 8 wk before to 14 wk after calving. Milk production and composition, SCC, body condition score, body weight, and occurrence of treatment for disease (related to calving and start of lactation) were compared between CT (n = 61 cows), T1 (n = 59 cows), and T2 (n = 63 cows). Effects of decision trees (CT, T1, T2) and of dry-period strategies (60-d dry with or without antibiotics, 30-d dry, or 0-d dry) on measured variables were analyzed separately with mixed models, effects on udder-health status with a logistic regression, and occurrence of treatment for diseases with a Pearson chi-squared test. In T1, 36% of cows qualified for 30-d and 2% for 0-d dry periods, whereas in T2 this was 51% and 30% for 30-d and 0-d dry periods, respectively. Compared with CT, cows in T1 and T2 on average produced more milk in the 8 wk before calving (0.2 vs. 3.9 vs. 7.1 kg/d in CT vs. T1 vs. T2), and less in the 14 wk after calving (40.0 vs. 37.0 vs. 35.2 kg/d in CT vs. T1 vs. T2). There was no difference in udder-health status in the transition period among decision trees. In the first 14 wk after calving, recovery of body weight was greater for T2 than CT and T1. Overall, 30-d and 0-d dry periods reduced milk revenues, but this might be financially compensated by improved cow health with customized dry-period strategies.

CCS e amiloide A do leite de quartos mamários tratados na secagem com plasma rico em plaquetas autólogo, associado ou não a antibiótico

RESUMO Este estudo teve como objetivo avaliar biomarcadores de mastite após terapia da secagem com plasma rico em plaquetas (PRP), associado ou não a antibiótico. Trinta e seis quartos mamários foram utilizados em três tratamentos (T): T1 - antibiótico (ATB), T2 - PRP e T3 - PRP + ATB. Amostras de leite foram coletadas antes da secagem (A1), no parto (D0) e 14, 30 e 60 dias pós-parto (D14, D30 e D60), para determinar contagem de células somáticas (CCS) e amiloide A (AA). O delineamento foi inteiramente ao acaso, com arranjo em parcelas subdivididas (SigmaPlot®). Dados de CCS foram transformados (log 10). As médias foram comparadas utilizando-se testes de Tukey ou Holm-Sidak (P<0,05). A CCS em A1 foi elevada em todos os grupos (P>0,05). No D30, CCS foi maior em T2 (P<0,05), igualando-se no D60. Não houve diferença na AA entre Ts em qualquer dia de coleta (P>0,05). Houve diferença nos momentos de coleta (P<0,05), A1 maior que D14 e D30. Houve uma correlação positiva fraca com CCS (0,280). Os tratamentos foram semelhantes em manter a saúde da glândula mamária na lactação subsequente. O PRP intramamário pode ser usado para terapia de vaca seca em casos de mastite subclínica.

Point-of-care tests for bovine clinical mastitis: what do we have and what do we need?

Mastitis, inflammation of the bovine mammary gland, is generally caused by intramammary infection with bacteria, and antimicrobials have long been a corner stone of mastitis control. As societal concern about antimicrobial use in animal agriculture grows, there is pressure to reduce antimicrobial use in dairy farming. Point-of-care tests for on-farm use are increasingly available as tools to support this. In this Research Reflection, we consider available culture-dependent and culture-independent tests in the context of ASSURED criteria for low-resource settings, including convenience criteria, scientific criteria and societal criteria that can be used to evaluate test performance. As tests become more sophisticated and sensitive, we may be generating more data than we need. Special attention is given to the relationship between test outcomes and treatment decisions, including issues of diagnostic refinement, antimicrobial susceptibility testing, and detection of viable organisms. In addition, we explore the role of technology, big data and people in improved performance and uptake of point-of-care tests, recognising that societal barriers may limit uptake of available or future tests. Finally, we propose that the 3Rs of reduction, refinement and replacement, which have been used in an animal welfare context for many years, could be applied to antimicrobial use for mastitis control on dairy farms.

Effect of bismuth subnitrate on in vitro growth of major mastitis pathogens

The mode of action of bismuth subnitrate in teat sealant formulations as a preventative for intramammary infections during the dry period is unknown. Although previous studies proposed an action mechanism-creating a physical barrier in the teat canal to prevent bacterial invasion-it has not been proven experimentally. We hypothesized that bismuth subnitrate has an inhibitory effect on bacterial growth, in addition to its barrier effect. The objective of this study was to assess the effect of bismuth subnitrate on bacterial growth of major mastitis-causing agents. A strain of Streptococcus uberis (SR115), 2 strains of Staphylococcus aureus (SA3971/59 and SA1), and a strain of Escherichia coli (P17.14291) were tested in vitro for their ability to grow in the presence or absence of bismuth subnitrate. Disk diffusion testing, impedance measurement, and evaluation of bacterial growth in shaking conditions were the methods used to test this hypothesis. A reduction of growth in the presence of bismuth subnitrate occurred for all the strains tested. However, we observed strain and species variations in the extent of growth inhibition. These results suggest that an inhibitory effect on bacterial growth by bismuth subnitrate could partially explain the efficacy of bismuth-based formulations for preventing intramammary infections over the dry period. Further research is required to test the effect of teat sealant formulations on bacterial growth.

Comparative efficacy of blanket versus selective dry-cow therapy: a systematic review and pairwise meta-analysis

A systematic review and meta-analysis were conducted to determine the efficacy of selective dry-cow antimicrobial therapy compared to blanket therapy (all quarters/all cows). Controlled trials were eligible if any of the following were assessed: incidence of clinical mastitis during the first 30 DIM, frequency of intramammary infection (IMI) at calving, or frequency of IMI during the first 30 DIM. From 3480 identified records, nine trials were data extracted for IMI at calving. There was an insufficient number of trials to conduct meta-analysis for the other outcomes. Risk of IMI at calving in selectively treated cows was higher than blanket therapy (RR = 1.34, 95% CI = 1.13, 1.16), but substantial heterogeneity was present (I2 = 58%). Subgroup analysis showed that, for trials using internal teat sealants, there was no difference in IMI risk at calving between groups, and no heterogeneity was present. For trials not using internal teat sealants, there was an increased risk in cows assigned to a selective dry-cow therapy protocol, compared to blanket treatment, with substantial heterogeneity in this subgroup. However, the small number of trials and heterogeneity in the subgroup without internal teat sealants suggests that the relative risk between treatments may differ from the determined point estimates based on other unmeasured factors.

Randomized controlled non-inferiority trial investigating the effect of 2 selective dry-cow therapy protocols on antibiotic use at dry-off and dry period intramammary infection dynamics

Selective dry-cow therapy (SDCT) could be used to reduce antibiotic use on commercial dairy farms in the United States but is not yet widely adopted, possibly due to concerns about the potential for negative effects on cow health. The objective of this study was to compare culture- and algorithm-guided SDCT programs with blanket dry-cow therapy (BDCT) in a multi-site, randomized, natural exposure, non-inferiority trial for the following quarter-level outcomes: antibiotic use at dry-off, dry period intramammary infection (IMI) cure risk, dry period new IMI risk, and IMI risk at 1 to 13 d in milk (DIM). Two days before planned dry-off, cows in each of 7 herds were randomly allocated to BDCT, culture-guided SDCT (cult-SDCT), or algorithm-guided SDCT (alg-SDCT). At dry-off, BDCT cows received an intramammary antibiotic (500 mg of ceftiofur hydrochloride) in all 4 quarters. Antibiotic treatments were selectively allocated to quarters of cult-SDCT cows by treating only quarters from which aseptically collected milk samples tested positive on the Minnesota Easy 4Cast plate (University of Minnesota, St. Paul, MN) after 30 to 40 h of incubation. For alg-SDCT cows, antibiotic treatments were selectively allocated at the cow level, with all quarters receiving antibiotic treatment if the cow had either a Dairy Herd Improvement Association test somatic cell count >200,000 cells/mL during the current lactation or 2 or more clinical mastitis cases during the current lactation. All quarters of all cows were treated with an internal teat sealant. Intramammary infection status at enrollment and at 1 to 13 DIM was determined using standard bacteriological methods. The effect of treatment group on dry period IMI cure, dry period new IMI, and IMI risk at 1 to 13 DIM was determined using generalized linear mixed models (logistic), with marginal standardization to derive risk difference (RD) estimates. Quarter-level antibiotic use at dry-off for each group was BDCT (100%), cult-SDCT (45%), and alg-SDCT (45%). The crude dry period IMI cure risk for all quarters was 87.5% (818/935), the crude dry period new IMI risk was 20.1% (764/3,794), and the prevalence of IMI at 1 to 13 DIM was 23% (961/4,173). Non-inferiority analysis indicated that culture- and algorithm-guided SDCT approaches performed at least as well as BDCT for dry period IMI cure risk. In addition, the final models indicated that the risks for each of the 3 IMI measures were similar between all 3 treatment groups (i.e., RD estimates and 95% confidence intervals all close to 0). These findings indicate that under the conditions of this trial, culture- and algorithm-guided SDCT can substantially reduce antibiotic use at dry-off without negatively affecting IMI dynamics.

Antibiotic dry cow therapy, somatic cell count, and milk production: Retrospective analysis of the associations in dairy herd recording data using multilevel growth models

Antibiotic dry cow therapy (DCT) is an important part of most mastitis control programs. Updating DCT recommendations is an ongoing topic due to the global problem of antimicrobial resistance. Finland, along with other Nordic countries, has implemented selective DCT for decades. Our study analyzed Dairy Herd Improvement (DHI) information from 241 Finnish farmers who participated in a survey about their drying-off practices. The aim was to evaluate herd-level associations between milk somatic cell count (SCC), milk production, and various antimicrobial DCT approaches both cross-sectionally in 2016 and longitudinally in 2012-2016. The three DCT approaches in the study were selective, blanket, and no DCT use. An additional aim was to evaluate whether dynamic changes occurred in herd-average SCC and annual milk production over five years, and whether these potential changes differed between different DCT approaches. The method for the longitudinal analyses was growth modeling with random coefficient models. Differences in SCC and milk production between farms with different DCT approaches were minor. Regardless of the farm's DCT approach, annual milk production increased over the years, while average SCC was reasonably constant. The variability in SCC and milk production across all DCT groups was low between years, and most of the variability was between farms. Compared to other milking systems, farms with automatic milking system (AMS) had higher SCC, and in 2016 higher milk production. The results of this study suggest that it is possible to maintain low herd-average SCC and good milk production when using selective DCT and following the guidelines for prudent antimicrobial use. Average SCC and milk production varied across the herds, suggesting that advice on DCT practices should be herd-specific. The methodology of growth modeling using random coefficient models was applicable in analyzing longitudinal data, in which the time frame was relatively short and the number of herds was limited.

Evaluation of rapid culture, a predictive algorithm, esterase somatic cell count and lactate dehydrogenase to detect intramammary infection in quarters of dairy cows at dry-off

Our objective was to compare four tests to standard milk culture followed by MALDI-ToF in quarters of cows at dry-off. Cows (n = 432) were randomly selected from seven U.S. dairy herds already participating in a multi-site clinical trial in summer 2018. Aseptic foremilk samples were collected from quarters (n = 1728) two days prior to dry-off, and subjected to index and reference tests. The four index tests included rapid culture, a predictive algorithm, an esterase strip test measuring somatic cell count (SCC) and a cow-side lactate dehydrogenase (LDH) test. Rapid culture was performed by inoculating quarter milk samples onto a commercial rapid culture plate. Plates were evaluated by technicians after 30-40 h of incubation at 37 ± 2 °C. Quarters were classified as infected if any bacterial growth was observed. For the algorithm test method, all quarters were classified as infected if the cow met any of the following criteria: 1) any Dairy Herd Improvement Association (DHIA) test with a SCC > 200,000 cells / ml during the current lactation or 2) two or more clinical mastitis cases during the current lactation. Esterase-SCC and cow-side LDH tests involved adding milk to the test strip and reading for color changes. For esterase-SCC and cow-side LDH tests, low (≥250 cells / ml and ≥100 U / L) and high (≥500 cells / ml and ≥200 U / L) thresholds were used to classify quarters as infected or not. Composite samples (4 × 2 mL quarter-milk samples commingled) were also tested for rapid culture, esterase-SCC and cow-side LDH tests, such that if a composite sample was positive, then all quarters contributing to that sample were classified as infected. The reference test was traditional aerobic culture conducted in an accredited laboratory using MALDI-ToF for identification of isolates. Traditional culture was only conducted on quarter-milk samples, and consequently, IMI was always considered at the quarter-level. Unconditional logistic regression was used to estimate sensitivity (SE), specificity (SP), apparent prevalence, positive predictive values (PPV) and negative predictive values (NPV) for each index test. Cohen's Kappa (κ) was used to measure agreement between tests. Algorithm, esterase-SCC and cow-side LDH tests had poor agreement with the reference test (κ ranging from 0.01 to 0.12), while rapid culture had fair agreement (κ = 0.28). No test had concurrently high SE and SP. Negative predictive values were moderate to high for all tests.

Milk microbial composition of Brazilian dairy cows entering the dry period and genomic comparison between Staphylococcus aureus strains susceptible to the bacteriophage vB_SauM-UFV_DC4

Brazil has the second-largest dairy cattle herd in the world, and bovine mastitis still can cause significant losses for dairy farmers. Despite this fact, little information is available about milk microbial composition of Brazilian dairy cows, as well as the potential use of bacteriophages in the control of S. aureus. Here, we investigated milk bacterial composition of 28 Holstein Fresian cows (109 teats), selected in the dry-off period, using 16S rRNA analysis. Furthermore, a representative S. aureus strain (UFV2030RH1) was obtained at drying-off for isolation of a bacteriophage (vB_SauM-UFV_DC4, UFV_DC4) and bacterial genomic comparison purposes. Our outcomes revealed that Staphylococcus was the third most prevalent genus and positively correlated with subclinical mastitis events. As a major finding, genomic analyses showed the presence of adhesive matrix molecules that recognize microbial surface components (MSCRAMM) in UFV2030RH1 and might indicate great biofilm formation capability. A minimum inhibitory concentration (MIC) assay showed that resistance to ampicillin was the highest among the antibiotic tested in S. aureus 3059 and UFV2030RH1, displaying values four and sixteen times greater than MIC resistance breakpoint, respectively. Together, our results suggest that Staphylococcus is highly prevalent in dairy cows at drying-off and the use of the phage UFV_DC4 as a biocontrol agent must be investigated in future studies.

Investigation of differential somatic cell count as a potential new supplementary indicator to somatic cell count for identification of intramammary infection in dairy cows at the end of the lactation period

The objective of this study was to investigate the new differential somatic cell count (DSCC) as a supplementary indicator to SCC for the identification of intramammary infection (IMI) in dairy cows at the end of the lactation period. Different approaches for identification of cows with IMI (i.e. often based on SCC) and targeted antimicrobial treatment of those rather than of all cows have been developed (i.e. selective dry cow treatment). Recently, DSCC representing the proportion of polymorphonuclear neutrophils and lymphocytes, has been introduced as an additional indicator for the presence of IMI. We used the last dairy herd improvement (DHI) samples taken within 42 d prior to dry-off as well as hand-stripped samples collected within 5 days prior to dry-off to measure DSCC and SCC. The bacteriological status was determined using quarter foremilk samples collected close to drying off. In total, 582 cows were dried off during our study but not all of them could be included in the data analysis for different reasons (e.g. incomplete data, samples too old for reliable determination of SCC and DSCC, contamination). Eventually, the final data set comprised of 310 cows of which 64 and 149 were infected with major and minor pathogens, respectively, and 97 were uninfected. The area under receiver-operating characteristics curves (AUC) were calculated to compare the diagnostic abilities of the different parameters. The AUC for identification of IMI by major pathogens when using the combination of DSCC and SCC was 0.64 compared to 0.62 for SCC alone and 0.62 for DSCC alone. The different parameters were further compared based on test characteristics and predictive values. For example, classifying cows as infected based on a cut-off of 200,000 cells/ml for SCC alone and in terms of using DSCC combined with SCC based on either >60% and/or >200,000 cells/ml, the sensitivity changed from 47 to 66% and the specificity from 74 to 54%. At the same time, the negative predictive value changed from 84 to 86% and the positive predictive value from 32 to 27%. Test characteristics and predictive values of the parameters DSCC and SCC were similar using DHI and hand-stripped samples. In conclusion, our study provides first indications on test characteristics and predictive values for the combination of DSCC and SCC. However, more work on this subject and the actual practical application is needed.

Effect of using internal teat sealant with or without antibiotic therapy at dry-off on subsequent somatic cell count and milk production

The objective of this study was to assess the effect of treating cows with teat sealant only compared with antibiotic plus teat sealant at drying off on weekly somatic cell count, potential intramammary infection, and milk production across the entire subsequent lactation. In 3 research herds in the south of Ireland, cows with SCC that did not exceed 200,000 cells/mL in the previous lactation (LowSCC) were randomly assigned to 1 of 2 treatments at drying off: internal teat sealant alone (ITS) or antibiotic plus teat sealant (AB+ITS). Cows with SCC that exceeded 200,000 cells/mL in the previous lactation were treated with AB+ITS and included in the analyses as a separate group (HighSCC). Weekly individual animal composite SCC records were available for 654 cow lactations and were transformed to somatic cell scores (SCS) for the purpose of analysis. Data were divided into 3 data sets to represent records obtained (1) up to 35 DIM, (2) up to 120 DIM, and (3) across the lactation. Foremilk secretions were taken from all quarters at drying off, at calving, 2 wk after calving, and in mid-lactation and were cultured to detect the presence of bacteria. The LowSCC cows treated with ITS alone had higher daily milk yield (0.67 kg/d) across lactation compared with LowSCC cows treated with AB+ITS. The LowSCC cows treated with ITS alone had higher SCS in early, up to mid, and across lactation compared with LowSCC cows treated with AB+ITS. We detected no difference in weekly SCS of LowSCC cows treated with ITS alone and SCS of HighSCC cows. The least squares means back-transformed SCC across lactation of the LowSCC cows treated with ITS alone, LowSCC cows treated with AB+ITS, and HighSCC cows were 41,523, 34,001, and 38,939 cells/mL respectively. The odds of LowSCC cows treated with ITS alone having bacteria present in their foremilk across lactation was 2.7 (95% confidence interval: 1.91 to 3.85) and 1.6 (1.22 to 2.03) times the odds of LowSCC cows treated with AB+ITS and of HighSCC cows treated with AB+ITS, respectively. In this study, Staphylococcus aureus was the most prevalent pathogen isolated from the population. Recategorizing the threshold for LowSCC cows as ≤150,000 cells/mL or ≤100,000 cells/mL in the previous lactation had no effect on the results. The results indicate that herds with good mastitis control programs may use ITS alone at dry-off in cows with SCC <200,000 cells/mL across lactation with only a small effect on herd SCC.