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.

Diverse roles of glucocorticoids in the ruminant mammary gland: modulation of mammary growth, milk production, and mastitis

As endocrine hormones, glucocorticoids (GCs) play a pivotal role in numerous physiological processes, including mammary growth and lactation, circulatory metabolism, and responses to external stimuli. In the dairy industry, milk production from cows or goats is important for newborns and economic benefits. However, the milk yields from ruminant animals are always affected by the extent of mammary development, mammary disease, stress, or changes in metabolism. Thus, it is necessary to clarify how GCs changes in ruminants affect ruminant mammary gland function and mammary disease. This review summarizes the findings identifying that GCs modulate mammary gland development before lactation, but the stress-induced excessive release of GCs leads to milk production loss. In addition, the manner of GCs release may change under different concentrations of metabolites or during mastitis or inflammatory challenge. Nevertheless, exogenous GCs administration to animals may alleviate the clinical symptoms of mastitis. This review demonstrates that GCs offer a fascinating contribution to both physiologic and pathogenic conditions of the mammary gland in ruminant animals. Characterizing and understanding these changes or functions of endogenous and exogenous GCs in animals will be crucial for developing more endocrine regulators and therapies for improving milk production in ruminants.

Residue Concentrations of Cloxacillin in Milk after Intramammary Dry Cow Treatment Considering Dry Period Length

Dry cow treatment with an intramammary antibiotic is recommended to reduce the risk of mastitis at the beginning of the next lactation. The dry period may be shortened unintentionally, affecting antibiotic residue depletion and the time when residues reach concentrations below the maximum residue limit (MRL). The objective of this study was to evaluate residue depletion in milk after dry cow treatment with cloxacillin, considering dry periods of 14 (G14d), 21 (G21d), and 28 d (G28d). Overall, fifteen cows with 60 udder quarters were included in the study. For each cow, three of the udder quarters were treated with 1000 mg cloxacillin benzathine (2:1) on d 252, d 259, and d 266 of gestation; one quarter was left untreated. Milk samples were drawn until 20 DIM and milk composition, somatic cell count and cloxacillin residues were analyzed. The HPLC-MS/MS revealed different excretion kinetics for the compounds cloxacillin and cloxacillin benzathine (1:1). All cows showed a cloxacillin and cloxacillin benzathine (1:1) concentration below the MRL of 30 µg/kg after 5 d. In the udder quarters of G21d and G28d, the cloxacillin concentration was already below the MRL at first milking after calving. The cloxacillin benzathine (1:1) concentration in the milk of G28d, G21d, and G14d fell below 30 µg/kg on the 5th, 3rd, and 5th DIM, respectively. Shortening the dry period affects residue depletion after dry cow treatment with cloxacillin. The risk of exceeding the MRL, however, seems low, even with dry periods shorter than 14 d.

The effect of pre-calving injection of trace mineral supplements on periparturient disease incidence in pasture based dairy cows

Trace minerals, have a role in immune function and a trace mineral supplement (TMS) can improve animal health in dairy herds. This prospective randomised clinical study assessed whether subcutaneous injection of 5.5 mL of TMS (40 mg zinc, 10 mg manganese, 5 mg selenium, 15 mg copper per mL), 14-28 days before planned start of calving (PSC) reduced clinical mastitis (CM), subclinical mastitis (SCM) and purulent vaginal discharge (PVD). From four farms, half of 1700 cows stratified on somatic cell count, age and breed were randomly allocated to treatment or no treatment. Occurrence of CM from - 7 to PSC + 100 days, SCM at PSC + 60 days and PVD at PSC + 24 days was analysed using survival analysis and Bayesian generalised mixed multivariable models. From -7 to PSC +30 days, TMS reduced the adjusted hazard ratio (HR) for CM at quarter and cow level (P < 0.001), with no evidence for an effect beyond 30 days. The adjusted OR (and 95% highest density interval, HDI) for the effect of TMS on CM from -7 to PSC +30 days was 0.40 (95% HDI, 0.26-0.63) at quarter level, 0.51 (95% HDI, 0.38-0.69) at cow level and for SCM, 0.72 (95% HDI, 0.54-0.95). The difference in CM incidence from TMS at the cow level was -2.0% (95% HDI, -3.4 to -1.1%) and -1.2% (95% HDI, -3.2 to - 0.6%) at quarter level. No clear effect was identified of TMS on cumulative incidence of PVD.

A retrospective on claims regarding clinical mastitis in the subsequent lactation, after use of an internal teat sealant in the dry period

Infusion of an internal teat sealant into the mammary gland of the dairy cow at drying off has been claimed to reduce the incidence of clinical mastitis over many months in the subsequent lactation, despite the absence of any ingredient of the sealant remaining for that long. However, these claims have been poorly substantiated, often by lack of identification on when the infection occurred in the period from calving to disease, if the infection was present at post calving sampling and if the pathogen causing the disease was that causing an earlier infection. Moreover, no hypothesis on how any effect on clinical mastitis might occur has been advanced in any of the publications claiming the effect. That the effect might occur is only reported in a minority of publications, and the possibility that this is relatively specific to Gram-negative pathogens is reviewed.

A survey of mastitis pathogens including antimicrobial susceptibility in southeastern Australian dairy herds

The objectives for this study were to (1) describe the pathogen profile in quarters from cows with clinical mastitis and in cows with subclinical mastitis in southeastern Australia; and (2) describe antimicrobial susceptibility among isolated pathogens. As a secondary objective, we aimed to compare antimicrobial resistance prevalence in pathogens isolated from clinical and subclinical mastitis samples. A convenience sample of dairy herds (n = 65) from 4 regions in southeastern Australia (Gippsland, Northern Victoria, Tasmania, Western Victoria) were invited to submit milk samples from cows with clinical and subclinical mastitis over a 14-mo period (January 2011 to March 2012). Farmers were instructed to collect aseptic quarter milk samples from the first 10 cases of clinical mastitis for each month of the study. In addition, farmers submitted composite milk samples from cows with subclinical mastitis at 1 or 2 sampling occasions during the study period. Aerobic culture and biochemical tests were used to identify isolates. Isolates were classified as susceptible, intermediate, or resistant to a panel of antimicrobial agents based on the zone of growth inhibition around antimicrobial-impregnated disks, with antimicrobial resistance (AMR) classified as nonsusceptibility by combining intermediate and resistant groups into a single category. Generalized linear mixed models were used to compare the prevalence of AMR between clinical and subclinical mastitis isolates. For clinical mastitis samples (n = 3,044), 472 samples (15.5%) were excluded for contamination. Of the remaining samples (n = 2,572), the most common results were Streptococcus uberis (39.2%), no growth (27.5%), Staphylococcus aureus (10.6%), Escherichia coli (8.4%), and Streptococcus dysgalactiae (6.4%). For subclinical mastitis samples (n = 1,072), 425 (39.6%) were excluded due to contamination. Of the remaining samples (n = 647), the most common results were no growth (29.1%), Staph. aureus (29.1%), and Strep. uberis (21.6%). The prevalence of AMR among common isolates was low for the majority of antimicrobial agents. Exploratory analysis found that the probability of Staph. aureus demonstrating resistance to penicillin was 5.16 times higher (95% confidence interval: 1.68, 15.88) in subclinical isolates relative to clinical Staph. aureus isolates. A similar association was observed for amoxicillin with subclinical Staph. aureus isolates being 4.70 times (95% confidence interval: 1.49, 14.75) more likely to be resistant than clinical Staph. aureus isolates. We concluded that the most common bacteria causing clinical mastitis in dairy herds in Australia is likely to be Strep. uberis, whereas Staph. aureus is likely to be the most common cause of subclinical mastitis. Despite decades of antimicrobial use to control these organisms, AMR appears to be uncommon.

Advances in therapeutic and managemental approaches of bovine mastitis: a comprehensive review

Mastitis (intramammary inflammation) caused by infectious pathogens is still considered a devastating condition of dairy animals affecting animal welfare as well as economically incurring huge losses to the dairy industry by means of decreased production performance and increased culling rates. Bovine mastitis is the inflammation of the mammary glands/udder of bovines, caused by bacterial pathogens, in most cases. Routine diagnosis is based on clinical and subclinical forms of the disease. This underlines the significance of early and rapid identification/detection of etiological agents at the farm level, for which several diagnostic techniques have been developed. Therapeutic regimens such as antibiotics, immunotherapy, bacteriocins, bacteriophages, antimicrobial peptides, probiotics, stem cell therapy, native secretory factors, nutritional, dry cow and lactation therapy, genetic selection, herbs, and nanoparticle technology-based therapy have been evaluated for their efficacy in the treatment of mastitis. Even though several strategies have been developed over the years for the purpose of managing both clinical and subclinical forms of mastitis, all of them lacked the efficacy to eliminate the associated etiological agent when used as a monotherapy. Further, research has to be directed towards the development of new therapeutic agents/techniques that can both replace conventional techniques and also solve the problem of emerging antibiotic resistance. The objective of the present review is to describe the etiological agents, pathogenesis, and diagnosis in brief along with an extensive discussion on the advances in the treatment and management of mastitis, which would help safeguard the health of dairy animals.

Internal Teat Sealant Administered at Drying off Reduces Intramammary Infections during the Dry and Early Lactation Periods of Dairy Cows

Simple Summary

Internal teat sealant (ITS) at drying off is a strategy used for the prevention of intramammary infections (IMI) during the dry period (DP), as it simulates the keratin plug’s purpose, which is to prevent the access of pathogens into the mammary gland. The results from randomized clinical trials provide valuable information about the efficacy of commercially available products to be used in dairy cattle, assisting farmers to choose the best protocols for mastitis control. This study evaluated a new ITS infused at drying off as an alternative to prevent IMI during DP in a tropical country. Our results showed no effect of treatments on risk of bacteriological cure, subclinical mastitis (SCM) cure, and new cases of SCM postpartum. On the other hand, the use of ITS combined with an intramammary antibiotic (SDCT) reduced the risk of clinical mastitis up to 60 days postpartum, the overall risk of new intramammary infections (NIMI), and the NIMI caused by major pathogens compared to the use of antimicrobial alone (ADCT). Thus, the use of ITS combined with an antimicrobial at drying off was effective to prevent NIMI and clinical mastitis up to 60 days postpartum.

Abstract

The effect of an internal teat sealant (ITS) on subsequent infection of the mammary gland was evaluated on the following mammary gland health indicators: (a) bacteriological cure of preexisting intramammary infections at drying off, (b) risk of postpartum new intramammary infections (NIMI), (c) cure and risk of new cases of subclinical mastitis (SCM), and (d) risk of postpartum clinical mastitis (CM). A total of 553 cows during late gestation were randomly assigned into two treatment protocols at drying off: (a) Dry cow therapy with 0.25 g of intramammary anhydrous cefalonium (ADCT; Cepravin^®, MSD Animal Health); or (b) ADCT combined with ITS (SDCT; 4 g bismuth subnitrate; Masti-Seal^®, MSD Animal Health, São Paulo, Brazil). Mammary quarter (MQ) milk samples were collected for microbiological culture and somatic cell count (SCC) at drying off and early lactation, and data from 1756 MQ were used in the multivariate logistic regression. There was no effect on the risk of bacteriological cure, SCM cure, and new cases of postpartum SCM. Still, SDCT reduced the risk of CM up to 60 days postpartum (DPP), overall NIMI risk, and the NIMI caused by major pathogens compared to ADCT. Thus, the DCT combined with ITS at drying off is effective for preventing NIMI during the dry period and CM up to 60 DPP.

A novel subtraction diversity array distinguishes between clinical and non-clinical Streptococcus uberis and identifies potential virulence determinants

Streptococcus uberis is an important bovine mastitis pathogen, but not all isolates have equal capacity to cause disease. The aims of this study were to identify possible virulence-associated genes that could be used to identify isolates with enhanced virulence. DNA from a pool of putative commensals was subtracted from a clinical pool resulting in a set of DNA sequences (probes) that were enriched in the clinical mastitis group. The probes were hybridised with DNA from a collection 29 isolates from cases of clinical mastitis and isolates not associated with disease. Hybridization revealed five major clusters. The first cluster (7 isolates) consisted almost entirely of commensals, while the second (7 isolates) was mixed. The remaining three clusters contained 15 S. uberis isolates from cows with clinical mastitis. Twenty-six probes were selected for sequencing based on principal component analysis (PCA) or their presence mainly in clinical isolates. PCA identified five probes with clear differences in intensity between signals from clinical isolates and commensals; these probes could represent novel virulence determinants. Manual inspection of arrays identified genes prominent among clinical isolates that specify carbohydrate and lipid metabolism (possible role in the growth or survival of S. uberis in milk) and genes specifying hypothetical proteins, possibly novel virulence factors. The common occurrence, among clinical isolates, of probes having homology with transposases and insertion sequences suggests recent acquisition of factors that could be associated with virulence. These results suggest the existence of a subset of S. uberis with enhanced virulence, due possession of virulence-associated gene sequences.

Prepartum application of internal teat sealant or intramammary amoxicillin on dairy heifers: Effect on udder health, survival, and performance

Intramammary infusion of antimicrobials (IA) and application of an internal teat sealant (ITS) at the end of the lactation is a common strategy to prevent and treat intramammary infections during the dry period. In heifers, precalving IA has been reported to improve udder health and milk quality; however, the effect of ITS in heifers housed in freestall barns is still unknown. The objective of this study was to investigate the effect of prepartum application of ITS or IA on udder health of dairy heifers. A total of 886 heifers were randomly allocated into 1 of 4 treatment groups when they were 245 ± 3 d pregnant. Control heifers (CON) did not receive any treatment. Heifers in the ITS group received the application of ITS containing 2.6 g of bismuth subnitrate. Animals in the IA group received intramammary administration of 62.5 mg of amoxicillin. Heifers in IA+ITS group received intramammary administration of amoxicillin followed by ITS application. The follow-up period was 270 d in milk (DIM). Clinical mastitis was diagnosed and treated by trained farm personnel throughout the study period. Composite milk somatic cell counts (SCC) were determined monthly for the first 9 mo of lactation by Dairy Herd Improvement Association. Subclinical mastitis was defined as a cow having a SCC >200,000 cells/mL for at least 1 test day and not diagnosed with clinical mastitis during the study period. At 7 ± 3 DIM, composite milk samples were collected for bacteriological analysis for a subset of the study animals. The presence of pathogens in milk at 7 ± 3 DIM was more frequently detected in the CON heifers compared with animals enrolled in the treatment groups. Heifers in IA+ITS group had a decreased incidence of clinical mastitis compared with CON heifers (12.9 vs. 21.4%). Additionally, the incidence of subclinical mastitis was decreased for IA+ITS heifers compared with CON counterparts (20.1 vs. 43.8%). During the first 9 mo of lactation, IA and IA+ITS heifers had lower SCC linear scores compared with ITS and CON counterparts. Although IA+ITS treatment successfully improved udder health, it did not result in better milk yield, fertility, and survivability. In conclusion, ITS alone was not effective in improving udder health; however, the combination of ITS and IA decreased the incidence of clinical and subclinical mastitis during the first 9 mo of lactation. Additionally, IA+ITS had a long-term effect on the SCC linear score throughout the study period.

Efficacy of an internal teat seal associated with a dry cow intramammary antibiotic for prevention of intramammary infections in dairy cows during the dry and early lactation periods

ABSTRACT: The present study aimed to evaluate the use of an internal dry period teat seal containing bismuth subnitrate (Teatseal®, Zoetis®, Florham Park, Nova Jersey, USA) associated with a long-acting cloxacilin preparation (Orbenin® Extra dry cow, Zoetis®, Florham Park, Nova Jersey, USA), in preventing new infections during the dry-off and early postpartum period. A total of 150 Holstein cows (average production of 9,000 kg of milk per lactation), with four functional udder quarters without clinical mastitis was included in the study. All animals were dried-off 60 days before the expected calving date. Two teats positioned diagonal-contralaterally received only dry cow antibiotic, control group C (n=300) and the other two teats, treatment group T (n=300) received dry cow antibiotic and infusion with an internal teat seal. Data from SCC variable were transformed by log base-10 transformation. Duncan’s test was used accepting 5% as the level of statistical significance. The occurrence of intramammary infection (IMI) and chronicity rate, and frequency of microorganisms isolated at drying and immediately postpartum in teats of group C and group T were evaluated using a non-parametric Chi-square Test, accepting 10% as the statistical significance level. There was a decrease in the occurrence of new infections in the early postpartum in cows which the sealant was used (C=19.6%, T=11.4%). In the postpartum period, Gram-negative bacteria were isolated from 16 teats in C and seven in T. The greatest reduction was observed for Escherichia coli (8 vs 1) in group T. There was no effect using the internal sealant on the frequency of isolation of environmental Streptococus. The use of sealant reduced the prevalence of subclinical mastitis cows between drying-off and the early postpartum period (C=51% versus T=42%) and resulted in a lower somatic cell count (SCC) in the treatment group when compared with the control group (T=1,073x103, C=1,793x103). The use of the internal teat seal combined with dry cow antibiotic is effective in the prevention of IMI during the dry period and early lactation and results in the reduction of SCC in immediate postpartum period. The treatment is effective in reducing infection between dry-off and the immediate postpartum caused by major and minor pathogens. However, no effect on infections caused by contagious pathogens was observed.

Comparison of cephalonium alone and in combination with an internal teat sealant for dry cow therapy in seasonally calving dairy cows

AIM

To assess the effect of combining an internal teat sealant (ITS) and a long-acting cephalonium-based dry cow therapy (DCT) on the prevalence of cows with a somatic cell count (SCC) >150,000 cells/mL 60-80 days after calving, and the incidence of clinical mastitis diagnosed by farm staff in the first 100 days after calving.

METHODS

Cows from a spring-calving, pasture-based, dairy farm in the South Canterbury region of New Zealand were randomly allocated to receive cephalonium DCT (n=289) or cephalonium and internal teat sealant (n=304) at the end of lactation. Cows were inspected twice daily by farm staff during the dry period and following calving for signs of mastitis. Individual SCC were determined from herd tests conducted in the previous lactation and following calving. Logistic regression models were used to determine relationships with the prevalence of cows with a SCC >150,000 cells/mL after calving, and survival analysis was used to model time to the first case of clinical mastitis following calving at the cow and quarter level.

RESULTS

The OR for a cow with a SCC >150,000 cells/mL after calving, including age and individual SCC in the preceding lactation in the model, was 0.53 (95% CI=0.32-0.89) for cows treated with combination therapy compared to cows receiving cephalonium (p=0.017). At the cow level, including age and preceding SCC in the model, the hazard ratio for diagnosis of clinical mastitis by farm staff in the first 100 days of lactation was 0.60 (95% CI=0.39-0.98) for cows treated with combination therapy compared to cows receiving cephalonium (p=0.04). At the quarter level, the hazard ratio for diagnosis of clinical mastitis, with age included in the model, was 0.41 (95% CI=0.23-0.74) for the combination therapy compared to cephalonium alone (p<0.001).

CONCLUSIONS

The combination of internal teat sealant and cephalonium DCT was more effective than cephalonium alone at reducing clinical mastitis diagnosed by farm staff in the 100 days after calving, and the prevalence of cows with a SCC >150,000 cells/mL 60-80 days after calving.

CLINICAL RELEVANCE

This study adds to the evidence that the prevention of intra mammary infections throughout the dry period and up to calving by using combination therapy is important in reducing the incidence of farmer-diagnosed clinical mastitis and prevalence of cows with a SCC >150,000 cells/mL 60-80 days after calving.

A survey of drying-off practices on commercial dairy farms in northern Germany and a comparison to science-based recommendations

While dry cow management is important for health, milk production and fertility information on drying-off procedures implemented on commercial dairy farms is lacking. Current drying-off management procedures on commercial dairy farms were evaluated using a questionnaire and results compared with recommendations given in the current literature. Ninety-one participants from a farmer education event completed the survey. On average, cows were dried off seven weeks before calving. Only 9.9 per cent of the farms had a dry period length of five weeks or less. A continuous milking regime without dry period was not established on any farm participating in the survey. Most farmers performed an abrupt drying-off (73.0 per cent). Only 11.8 and 15.0 per cent attempted to lower milk yield prior to drying-off by reducing milking frequencies and adjusting feed rations, respectively. While a blanket antibiotic dry cow treatment was carried out on 79.6 per cent of the farms, selective dry cow treatment was not mentioned by any farmer. Although 77.4 per cent preponed the drying-off date in low-yielding cows, an altered drying-off procedure in high-yielding dairy cows was rare (9.7 per cent). This survey provides an insight into drying-off procedures currently applied on commercial dairy farms in northern Germany.

Effect of dry period length on the effect of an intramammary teat sealant on the risk of mastitis in cattle treated with antibiotics at drying off

AIM

The aim of this study was to evaluate, under farm conditions, the use of a teat sealant in addition to whole herd dry cow antibiotic therapy on the risk of clinical mastitis in dairy cattle at pasture, and to evaluate the impact of dry period length on that risk and the impact of the teat sealant on that risk.

METHODS

Dairy cows in three herds which used routine whole herd antibiotic therapy were randomly assigned to receive either treatment with an internal teat sealant (n=322) or no additional treatment (n=313) at drying-off between March and May 2010. All clinical mastitis cases during the dry period and to the end of the subsequent lactation were recorded by farm staff; factors affecting risk of clinical mastitis were then analysed using a Cox proportional hazards model.

RESULTS

Median duration of the dry period was 112 days with >25% of cows having a dry period >130 days. The incidence risk of mastitis during lactation for cows treated with teat sealant was 9.9 (95% CI=6.9-13.7) cases per 100 cows compared with 17.9 (95% CI=13.8-22.6) cases per 100 cows for cows treated with antibiotic alone. The addition of a teat sealant to dry cow antibiotic therapy decreased the risk of clinical mastitis only in the first 33 days after calving (Hazard risk 0.24 (95% CI=0.12-0.48)). Length of dry period did not significantly affect the risk of clinical mastitis, or the effect of adding teat sealant to dry cow antibiotic therapy on the risk of clinical mastitis.

CONCLUSIONS

In these herds where, based on the mastitis history, whole herd antibiotic therapy had been recommended, the use of a teat sealant significantly reduced the risk of clinical mastitis. This effect was limited to the first 33 days after calving; subsequently there was no significant effect of treatment. There was no effect of dry period length on risk of clinical mastitis, nor any significant interaction with treatment.

CLINICAL RELEVANCE

Combination therapy with teat sealant and antibiotic was effective under New Zealand conditions in herds using whole herd antibiotic treatment at drying off. Teat sealant reduced risk of clinical mastitis in cattle with dry periods substantially longer than 100 days, and there was no evidence that this effect changed as dry period length increased.

Molecular epidemiology of recurrent clinical mastitis due to Streptococcus uberis: evidence of both an environmental source and recurring infection with the same strain

This study was undertaken because clinicians and farmers have observed that a considerable number of cows diagnosed with Streptococcus uberis mastitis have recurrences of mastitis in the same or a different quarter. The study was an attempt to answer whether these recurring cases were due to treatment failure (in which case a search would have begun for a better treatment for Strep. uberis mastitis) or due to reinfection with a different strain of Strep. uberis. Using pulsed-field gel electrophoresis (PFGE), we determined that the majority of recurrences (20 of 27) were caused by a new strain of Strep. uberis, indicating that treatment of the initial infection had been successful. A small number of recurrences (5 of 27) were caused by the initial strain, indicating persistence. The remaining 2 recurrences occurred in a new quarter but with the initial strain of Strep. uberis, indicating either spread between quarters or reactivation of a previous subclinical infection. Analysis of the PFGE profiles failed to reveal any strain-specific propensity to persist, because strains causing recurrences occurred in most of the major clusters.

The effect of internal teat sealant products (Teatseal and Orbeseal) on intramammary infection, clinical mastitis, and somatic cell counts in lactating dairy cows: a meta-analysis

The objective of this study was to assess the efficacy of internal teat sealant products containing bismuth subnitrate (Teatseal and Orbeseal; Pfizer Animal Health, West Ryde, Australia) when used alone, or in the presence of antibiotic dry cow therapy (ADCT), before or at drying off on the incidence of new intramammary infections (IMI), clinical mastitis, and milk somatic cell count (SCC) during lactation. The literature search identified 18 English-language publications on the use of Teatseal in dairy cattle. A total of 12 studies with 17 subtrials or comparisons including 13 positive control subtrials (internal teat sealant and ADCT vs. ADCT) and 4 negative control subtrials (internal teat sealant vs. untreated) examining IMI were included in the analysis. Internal teat sealants, alone or in the presence of ADCT, reduced the risk of acquiring new IMI after calving by 25% [risk ratio (RR)=0.75; 95% confidence interval (CI): 0.67 to 0.83]. Internal teat sealants reduced the risk of IMI by 73% compared with untreated cows (RR=0.27; 95% CI: 0.13 to 0.55). The results of both meta-analyses of IMI, with positive and negative controls, were heterogeneous [I(2) (a statistic that describes the proportion of total variation in study effect estimates that is due to heterogeneity)=65.4 and 92.1%]. No farm or cow factors studied significantly contributed to the heterogeneity of the results. A total of 16 studies (21 subtrials), including 14 positive control subtrials and 7 negative control subtrials, examining clinical mastitis were included in the analysis. Internal teat sealants alone and in the presence of ADCT reduced the risk of clinical mastitis after calving in lactating cows by 29% (RR=0.71; 95% CI: 0.62 to 0.82), and 48% (RR=0.52; 95% CI: 0.37 to 0.75), respectively. The results of the meta-analysis on clinical mastitis with positive controls were homogeneous (I(2)=33.6%), whereas the results of studies with negative controls were heterogeneous (I(2)=60.4%). No farm or cow factors studied that had sufficient data to evaluate significantly contributed to the heterogeneity of the results. The estimated linear score (LS) of milk SCC after calving in published studies (n=3) and for studies that provided raw data (n=2), was significantly lower for cattle treated with internal teat sealants and ADCT in 3 studies than for cattle treated with internal teat sealants only. The estimated LS of pooled raw data of 3 studies from 32 herds showed that the LS of cows treated with internal teat sealant and ADCT was not significantly different than those treated with ADCT only. This study found that the application of internal teat sealants in the presence of ADCT or the use of internal teat sealants alone at dry off significantly reduced the incidence of IMI and clinical mastitis in lactating dairy cows compared with respective control groups. Further studies are needed to investigate the effect of internal teat sealants on postpartum milk SCC in lactating dairy cows.