Effects of prepartum intramammary antibiotic therapy on udder health, milk production, and reproductive performance in dairy heifers

Characteristics of mammary secretions collected from infected and uninfected primigravid dairy heifer mammary glands

Intramammary infections (IMI) in primigravid dairy heifers can affect mammary growth and development, which can reduce first-lactation milk yield. Detection of IMI in heifers most often involves the use of culture-based methods that are not often used in production dairy settings given their labor- and time-consuming nature. The objective of this study was to determine whether mammary secretion somatic cell count (SCC) and viscosity were associated with the infection status of primigravid heifer mammary glands. A total of 270 heifers from a single farm were used, selected based on the farmer's willingness to participate. The study was conducted from June to October 2020. Mammary secretion samples were aseptically collected from a randomly selected quarter of each heifer at 75 d prepartum (75PP), and another quarter of each heifer was sampled at 35 d prepartum (35PP). The remaining 2 quarters of each heifer were not examined. Mammary secretion samples underwent bacteriological examination to determine IMI status and quantitative SCC measurement and were also assessed for secretion viscosity based on visual observation. Prevalence of IMI was 26% (69/270) and 28% (71/255) at 75 and 35 d prepartum, respectively. Uninfected secretion samples had 133.2 [95% confidence interval (CI): 16.8 to >999.9] times greater odds to be thick compared with samples infected with a major pathogen, and 14.4 (95% CI: 8.5 to 24.1) times greater odds to be thick compared with samples infected with non-aureus staphylococci (NAS). The mean secretion SCC of uninfected quarters (6.04 ± 0.03 log₁₀ cells/mL) was significantly lower than that of secretions collected from quarters infected with Staphylococcus chromogenes (6.34 ± 0.04 log₁₀ cells/mL), other NAS species (6.28 ± 0.10 log₁₀ cells/mL), or a major pathogen (6.73 ± 0.08 log₁₀ cells/mL). These results indicate that mammary secretion viscosity and SCC measurement may be useful tools in identifying primigravid heifer quarters with IMI. The ability to evaluate viscosity at time of sampling may be a useful strategy that could be incorporated into interventions designed to diminish the negative effects of prepartum IMI on lactational performance.

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.

Effects of Pre-Parturient Iodine Teat Dip Applications on Modulating Aversive Behaviors and Mastitis in Primiparous Cows

Heifers and their human handlers are at risk for decreased welfare during the early lactation period. This experiment investigated pre-parturient teat dipping and parlor acclimation to reduce mastitis and aversive behaviors in early lactation heifers. Three weeks prior to calving, heifers were randomly assigned to receive either: (1) a weekly 1.0% iodine-based teat dip in the parlor (trained; n = 37) or (2) no treatment (control; n = 30). For the first 3 days of lactation, heifers were milked twice daily, and treatment-blinded handlers assessed behaviors and clinical mastitis. Aseptic quarter milk samples were collected within 36 h of calving and analyzed for pathogens. Control heifers had (OR ± SE) 2.2 ± 0.6 times greater (p < 0.01) odds of kicking during milking. Trained heifers had (OR ± SE) 1.7 ± 0.4 times greater (p = 0.02) odds of being very calm during milking, while control heifers had 2.2 ± 0.8 and 3.8 ± 2.1 times greater (p < 0.04) odds of being restless and very restless or hostile during milking, respectively. Quarters of control heifers had (OR ± SE) 5.4 ± 3.4 greater (p < 0.01) odds of intramammary Staphylococcus aureus infection, yet clinical mastitis was similar among treatments. The results indicate that teat dipping in the parlor weekly for 3 weeks before calving may alleviate some aversive milking behaviors and protect against early lactation S. aureus intramammary infections.

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.

The effect of dry cow therapy using systemic tylosin in combination with common intramammary medications on mastitis rate, cull rate, somatic cell count, and milk production in dairy cows affected with subclinical mastitis

Aims

This study was performed to evaluate the effect of systemic tylosin on mastitis rates, cull rates because of mastitis, and quality and quantity of milk production in dairy cows affected with subclinical mastitis.

Materials and Methods

A total of 130 California mastitis test (CMT)-positive cows were randomly selected and divided into four different treatment groups. All treatments were performed on the day of drying off. Cows in Group 1 (n=34) received 12 g of tylosin intramuscularly (IM) and intramammary (IMM) 400 mg novobiocin sodium and 200,000IU penicillin G procaine. Group 2 (n=33) received 12 g tylosin IM and IMM 280 mg benethamine penicillin, 100 mg penethamate hydriodide, and 100 mg framycetin sulfate. Group 3 (n=33) received IMM alone with 400 mg novobiocin sodium and 200,000 IU penicillin G procaine. Group 4 (n=30) received IMM alone with 280 mg benethamine penicillin, 100 mg penethamate hydriodide, and 100 mg framycetin sulfate. The incidence and severity of clinical mastitis (CM), incidence of chronic mastitis, and cow cull rate because of mastitis were recorded during the first 100 days in milk (DIM). In addition, somatic cell count (SCC) and milk production parameters including the average days to peak milk yield, the average milk yield at peak, the average milk yield during the first 100 DIM, and the average 305-corrected milk yield were reported.

Results

The rate of CM was significantly (p≤0.05) less in Group 2 when compared between the current and previous lactations (30% vs. 64%). In Group 1 and 4, the rate of CM was decreased but not significant between the two lactations (59% vs. 79% and 63% vs. 77%, respectively) while in Group 3, the rate of CM was slightly increased (82% vs. 91%). When compared between the four groups in the current lactation, CM rate was significantly (p≤0.05) less in Group 2 compared to the other groups. A significant (p≤0.05) percentage of CM cases in Group 2 was classified as mild. In Groups 1 and 3, a significant (p≤0.05) percentage of CM cases was classified as moderate while severe clinical signs were recorded more significantly (p≤0.05) in Groups 3 and 4. The rate of chronic mastitis was significantly less in Group 1 and Group 2 in the current lactation compared to that in the previous lactation (6% vs. 12% and 0% vs. 6%, respectively). In Groups 3 and 4, the rate of chronic mastitis was not changed significantly when compared between the current and previous lactations. No cows were culled because of mastitis in Groups 1 and 3 while one cow was culled in each of Groups 2 and 4 during the first 100 DIM in the current lactation. The average milk yield during the first 100 DIM and the 305-corrected milk yield were significantly (p≤0.05) increased in Group 2 when compared between the previous and current lactations. Furthermore, cows in Group 2 produced significantly (p≤0.05) more milk during the first 100 DIM and significantly (p≤0.05) more 305-corrected milk yield compared to the other groups. In Group 2, the average SCC dropped significantly (p≤0.05) from 1,600,000 cells/ml at the start of the study to <200,000 cells/ml at 100 DIM.

Conclusions

In dairy herds with subclinical mastitis, dry cow therapy of CMT-positive cows using a combination of tylosin (12 g, IM) and IMM administration of benethamine penicillin, penethamate hydriodide, and framycetin sulfate (Ubrostar; Boehringer Ingelheim, Germany) may result in a significant reduction of the rate and severity of acute and chronic mastitis and cull rates due to mastitis within the first 100 DIM. Furthermore, treated cows may produce significantly more milk with less SCC during the first 100 DIM and therefore produce significantly more 305-corrected milk in the lactation following treatment.

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.

The tammar wallaby: A marsupial model to examine the timed delivery and role of bioactives in milk

It is now clear that milk has multiple functions; it provides the most appropriate nutrition for growth of the newborn, it delivers a range of bioactives with the potential to stimulate development of the young, it has the capacity to remodel the mammary gland (stimulate growth or signal cell death) and finally milk can provide protection from infection and inflammation when the mammary gland is susceptible to these challenges. There is increasing evidence to support studies using an Australian marsupial, the tammar wallaby (Macropus eugenii), as an interesting and unique model to study milk bioactives. Reproduction in the tammar wallaby is characterized by a short gestation, birth of immature young and a long lactation. All the major milk constituents change substantially and progressively during lactation and these changes have been shown to regulate growth and development of the tammar pouch young and to have roles in mammary gland biology. This review will focus on recent reports examining the control of lactation in the tammar wallaby and the timed delivery of milk bioactivity.

Effect of administration of vitamin E, selenium and antimicrobial therapy on incidence of mastitis, productive and reproductive performances in dairy cows

Administration of vitamin, mineral and antimicrobials at the end of lactation plays potential role in preventing mastitis in dairy cows. A total of 255 cows dividing into five groups (A = 50, B = 50, C = 50, D = 50 and E = 55) at their late gestation period were selected to explore the effect of vitamin E, selenium and antimicrobial therapy on mastitis incidence, their productive and reproductive performances. Each cow of group A received α-tocopherol + sodium selenite orally daily for last 30 days before calving, while each cow of group B, C and D was treated with α-tocopherol + sodium selenite intramuscular injection, procaine penicillin + neomycin sulfate, and dicloxacillin sodium intramammary infusions at Day 30-20 before calving, respectively. Group E cows served as untreated control. California mastitis test (CMT) revealed that 70.0%, 76.0%, 84.0% and 100.0% cows in group A, B, C and D, respectively were free from new intramammary infections (IMIs) during early lactation period. The bacteriological results showed highest IMIs rates (76.3%) in group E and lowest IMIs (2.0%) in group D (P < 0.05). Staphylococcus aureus and Escherichia coli were the most predominant udder pathogens in all groups except group D (only CNS). The mean IMIs incidence (20.5%) was significantly lower in treated cows (P < 0.001). The treated cows had higher cure rates (81.9%) than control cows (23.1%) and overall efficacy of treatments on cure rates was 71.8% for all mastitis pathogens (P < 0.0001). The productive and reproductive performances of the treated cows at postpartum and early lactation period remained always higher than their non-treated counterparts (P < 0.001). A number of cow and herd related factors were identified to be significantly associated with mastitis (P < 0.001). The results concluded that antimicrobial therapy had more beneficial effect in preventing mastitis over vitamin-mineral administration and intramammary infusion with dicloxacillin sodium remained as the best effective preventive strategies for mastitis in dairy cows.

Effects of pathogen-specific clinical mastitis on probability of conception in Holstein dairy cows

The objective of this study was to estimate the effects of pathogen-specific clinical mastitis (CM), occurring in different weekly intervals before or after artificial insemination (AI), on the probability of conception in Holstein cows. Clinical mastitis occurring in weekly intervals from 6 wk before until 6 wk after AI was modeled. The first 4 AI in a cow's lactation were included. The following categories of pathogens were studied: Streptococcus spp. (comprising Streptococcus dysgalactiae, Streptococcus uberis, and other Streptococcus spp.); Staphylococcus aureus; coagulase-negative staphylococci (CNS); Escherichia coli; Klebsiella spp.; cases with CM signs but no bacterial growth (above the level that can be detected from our microbiological procedures) observed in the culture sample and cases with contamination (≥ 3 pathogens in the sample); and other pathogens [including Citrobacter, yeasts, Trueperella pyogenes, gram-negative bacilli (i.e., gram-negative organisms other than E. coli, Klebsiella spp., Enterobacter, and Citrobacter), Corynebacterium bovis, Corynebacterium spp., Pasteurella, Enterococcus, Pseudomonas, Mycoplasma, Prototheca, and others]. Other factors included in the model were parity (1, 2, 3, 4 and higher), season of AI (winter, spring, summer, autumn), day in lactation of first AI, farm, and other non-CM diseases (retained placenta, metritis, ketosis, displaced abomasum). Data from 90,271 AI in 39,361 lactations in 20,328 cows collected from 2003/2004 to 2011 from 5 New York State dairy farms were analyzed in a generalized linear mixed model with a Poisson distribution. The largest reductions in probability of conception were associated with CM occurring in the week before AI or in the 2 wk following AI. Escherichia coli and Klebsiella spp. had the greatest adverse effects on probability of conception. The probability of conception for a cow with any combination of characteristics may be calculated based on the parameter estimates. These findings may be helpful to farmers in assessing reproduction in their dairy cows for more effective cow management.

Pathogen group-specific risk factors for intramammary infection in treated and untreated dairy heifers participating in a prepartum antimicrobial treatment trial

Heifer mastitis is a well-known problem, with several pathogens being involved. Several generic risk factors associated with the likelihood of intramammary infections (IMI) in fresh dairy heifers have been identified before. Yet, a need exists to identify pathogen group-specific factors, as the effect of (groups of) pathogens on udder health and milk yield is different. The aim of the present study was to identify pathogen group-specific risk factors for IMI in heifers participating in a prepartum antimicrobial treatment trial, allowing us to test the hypothesis that different factors are of importance between treated and untreated control heifers as well. Data from a clinical trial in which end-term heifers were treated systemically (over 3 consecutive days) 2 wk before calving with penethamate hydriodide (n=76) or remained untreated (n=73), were available. Several potential risk factors at the herd, heifer, and quarter level were recorded in the first 3 d in milk. Quarters from untreated heifers supplemented with ≥4 mg of selenium/d prepartum were significantly less likely to be infected with coagulase-negative staphylococci (CNS), whereas quarters were more likely to be infected with CNS when assistance during calving was needed. Udder edema before calving significantly decreased the odds of IMI with major pathogens. In treated heifers, no factors were detected that were associated with the likelihood of CNS IMI, whereas quarters from heifers were significantly more likely to be infected with major pathogens when they were housed in the calving pen more than 1 d and when they had been in contact with the lactating cows before calving. The risk factors for IMI that were identified in treated heifers were different than those in untreated heifers, independent of the pathogen group that was considered. It looks as if prepartum treatment not only changed the likelihood of infection, but also the factors that were associated with infection. However, except for treated heifers with an IMI with major pathogens, only a small proportion of the variation could be explained in the final models. Therefore, factors other than those that were studied could explain the likelihood of infection.

Identification and functional characterization of a novel monotreme- specific antibacterial protein expressed during lactation

Monotremes are the only oviparous mammals and exhibit a fascinating combination of reptilian and mammalian characters. They represent a component of synapsidal reproduction by laying shelled eggs which are incubated outside the mother’s body. This is accompanied by a prototherian lactation process, marking them as representatives of early mammals. The only extant monotremes are the platypus, and the short- and long- beaked echidnas, and their distributions are limited to Australia and New Guinea. Apart for a short weaning period, milk is the sole source of nutrition and protection for the hatchlings which are altricial and immunologically naive. The duration of lactation in these mammals is prolonged relative to the gestational length and period of incubation of eggs. Much of the development of monotreme young occurs in the non-sterile ex-utero environment. Therefore the role of milk in the growth, development and disease protection of the young is of significant interest. By sequencing the cDNA of cells harvested from monotreme milk, we have identified a novel monotreme- specific transcript, and the corresponding gene was designated as the EchAMP. The expression profile of this gene in various tissues revealed that it is highly expressed in milk cells. The peptides corresponding to the EchAMP protein have been identified in a sample of echidna milk In silico analysis indicated putative antimicrobial potential for the cognate protein of EchAMP. This was further confirmed by in vitro assays using a host of bacteria. Interestingly, EchAMP did not display any activity against a commensal gut floral species. These results support the hypothesis of enhancement of survival of the young by antimicrobial bioactives of mammary gland origin and thus emphasize the protective, non- nutritional role of milk in mammals.

Invited review: Mastitis in dairy heifers: nature of the disease, potential impact, prevention, and control

Heifer mastitis is a disease that potentially threatens production and udder health in the first and subsequent lactations. In general, coagulase-negative staphylococci (CNS) are the predominant cause of intramammary infection and subclinical mastitis in heifers around parturition, whereas Staphylococcus aureus and environmental pathogens cause a minority of the cases. Clinical heifer mastitis is typically caused by the major pathogens. The variation in proportions of causative pathogens between studies, herds, and countries is considerable. The magnitude of the effect of heifer mastitis on an individual animal is influenced by the form of mastitis (clinical versus subclinical), the virulence of the causative pathogen(s) (major versus minor pathogens), the time of onset of infection relative to calving, cure or persistence of the infection when milk production has started, and the host's immunity. Intramammary infection in early lactation caused by CNS does not generally have a negative effect on subsequent productivity. At the herd level, the impact will depend on the prevalence and incidence of the disease, the nature of the problem (clinical, subclinical, nonfunctional quarters), the causative pathogens involved (major versus minor pathogens), the ability of the animals to cope with the disease, and the response of the dairy manager to control the disease through management changes. Specific recommendations to prevent and control mastitis in late gestation in periparturient heifers are not part of the current National Mastitis Council mastitis and prevention program. Control and prevention is currently based on avoidance of inter-sucking among young stock, fly control, optimal nutrition, and implementation of hygiene control and comfort measures, especially around calving. More risk factors for subclinical and clinical heifer mastitis have been identified (e.g., season, location of herd, stage of pregnancy) although they do not lend themselves to the development of specific intervention strategies designed to prevent the disease. Pathogen-specific risk factors and associated control measures need to be identified due to the pathogen-related variation in epidemiology and effect on future performance. Prepartum intramammary treatment with antibiotics has been proposed as a simple and effective way of controlling heifer mastitis but positive long-lasting effects on somatic cell count and milk yield do not always occur, ruling out universal recommendation of this practice. Moreover, use of antibiotics in this manner is off-label and results in an increased risk of antibiotic residues in milk. Prepartum treatment can be implemented only as a short-term measure to assist in the control of a significant heifer mastitis problem under supervision of the herd veterinarian. When CNS are the major cause of intramammary infection in heifers, productivity is not affected, making prepartum treatment redundant and even unwanted. In conclusion, heifer mastitis can affect the profitability of dairy farming because of a potential long-term negative effect on udder health and milk production and an associated culling risk, specifically when major pathogens are involved. Prevention and control is not easy but is possible through changes in young stock and heifer management. However, the pathogenesis and epidemiology of the disease remain largely unknown and more pathogen-specific risk factors should be identified to optimize current prevention programs.

Vaccination strategies for mastitis

Presently, the most successful use of vaccination strategies as part of a dairy herd mastitis control program involves GNCABs, of which the J-5 bacterins are best understood. Immunization protocols employing this technology should be adapted to individual herd needs. Ironically, the success of these bacterins may rely, in part, on the systemic pathogensis of severe coliform mastitis. Because immune function is impaired in the mammary gland of a lactating dairy cow, and the difficulty in maintaining effective concentrations of antibodies in milk following vaccination, vaccines developed against pathogens that cause more chronic IMI, while promising, have significant obstacles to overcome.

WFDC2 is differentially expressed in the mammary gland of the tammar wallaby and provides immune protection to the mammary gland and the developing pouch young

WAP four disulfide core domain 2 (WFDC2) is a four disulfide core (4-DSC) protein secreted in the milk of the tammar wallaby. It is comprised of two 4-DSC domains assigned domain III at the NH2-terminal end and domain II at the COOH-terminal end. The WFDC2 gene was expressed only during pregnancy, early lactation, towards the end of lactation and involution. The WFDC2 protein showed antibacterial activity against Staphylococcus aureus, Salmonella enterica and Pseudomonas aeruginosa and this activity resided with domain II. There was no antibacterial activity detected against Enterococcus faecalis. The observed expression pattern of tammar WFDC2 and its antibacterial activity suggests a role to either reduce mastitis in the mammary gland caused by S. aureus or to protect the gut of the young at a time when it is not immune-competent. The latter effect could be achieved without disturbing the balance of commensal gut flora such as E. faecalis.

Deterministic model to evaluate the impact of lactational treatment of subclinical mastitis due to coagulase-negative staphylococci

Coagulase-negative staphylococci (CNS) are the most frequently isolated bacteria from milk samples in several studies worldwide. Despite their relative frequency, specific measures aiming at their control are not well established. One possible measure to include in a control programme is lactational antimicrobial treatment. The decision to perform such treatment, as well as other actions on farm, should be based on the likelihood of financial return. A deterministic model was used to evaluate whether performing an antimicrobial treatment during the lactation for quarters infected with CNS was financially justifiable. Input variables for the impact of CNS on udder health were based on a previous study by the same authors and on available literature on the subject. Prices included in the model were based on 2009/2010 conditions in Portugal. The average result per antimicrobial treated quarter was a net loss of €38·74. Performing a sensitivity analysis to evaluate how systematic variation of the input variables of the model would lead to outcome changes showed that variation in input variables nearly always led to a negative outcome, with the greatest variation in losses observed for variation in the length of treatment and milk withdrawal period (-€46·26 to -€28·49). The situations in which a net benefit was to be expected included the bulk tank somatic cell count decreasing to a level corresponding to a premium payment or to penalties being avoided, and the prevention of transmission of CNS in the milking parlour when the possibility of transmission was at its highest level. For most situations, lactational treatment of CNS subclinical mastitis was not financially justifiable.

Antimicrobial susceptibility of coagulase-negative staphylococci isolated from bovine milk samples

The aim of this study was to examine whether antimicrobial resistance profiles of coagulase-negative Staphylococcus (CNS) species isolated from milk of dairy cows differed between bacterial species, and to compare results obtained by phenotypic and genotypic profiling of resistance to penicillin, oxacillin and macrolide-lincosamide (ML) antibiotics. Of 170 CNS isolates, 83 (48.8%) were phenotypically susceptible to all antimicrobial agents tested in minimum inhibitory concentration (MIC) assays, 40.6% expressed resistance to a single compound or a single class of compounds, and 10.6% to multiple drug classes. Nine percent, 68%, 19%, 4% and 1% of isolates were negative for all resistance genes tested by PCR or positive for one, two, three or four resistance genes, respectively. Phenotypic resistance and detection of resistance genes other than blaZ were relatively rare in Staphylococcus chromogenes, which was the most common CNS species (36% of 170 genotypically identified isolates). In Staphylococcus epidermidis, which was the second most common CNS species (14% of isolates), phenotypic penicillin resistance was significantly more common than in other CNS species. Almost half of the S. epidermidis isolates carried multiple resistance genes and 30% carried the methicillin resistance gene mecA. Survival analysis using MIC values showed significant associations between phenotypic and genotypic resistance profiles. We conclude that CNS species from bovine milk differ significantly in phenotypic and genotypic antimicrobial resistance profiles, which has implications for treatment and management decisions.

An evaluation of casein hydrolyzate in combination with antibiotic for bacterial cure and subsequent increase in milk yield in dairy cows

Background

A 3-yr study examined whether prepartum treatment with casein hydrolyzate in combination with antibiotic, as routinely used in Israel for dry cow therapy, improved bacterial cure and increased milk yield in subsequent lactations in comparison with treatment with antibiotic alone. The vast majority of bacterial isolates in samples collected prior to drying-off comprised coagulase-negative staphylococci, mostly as Staph. chromogenes.

Results

Bacterial cure associated with the combined treatment was 73.8% in cows, significantly higher than the 51.7% cure recorded when cows were treated only with antibiotic. During the study, the annual milk yield of non-casein hydrolyzate treated and treated control cows increased at ~2% per year, which is consistent with the national annual increase attributed to genetic selection. In cows treated with casein hydrolyzate the increase was 9% (above the 2% expected) in the first lactation after the treatment, and 6.3% (above the 4% expected for 2 years) in the second lactation after treatment. These increases were significantly higher than those in the controls and those expected through genetic improvement.

Conclusions

Treatment with casein hydrolyzate at dry-off was shown to be a viable mean to eliminate existing environmental bacterial infection, and to improve milk yield in the next lactation.

Invited review: The role of contagious disease in udder health

Contagious diseases are a threat to animal health and productivity, both nationally and at the farm level. This makes implementation of biosecurity measures to prevent their introduction and spread within countries and farms a necessity. Mastitis is the most common and costly contagious disease affecting dairy farms in the western world. The major mastitis pathogens are endemic in most countries, and biosecurity measures to prevent introduction and transmission must therefore be implemented at farm level. The 40-yr-old mastitis control plan remains a solid foundation to prevent the spread of contagious intramammary infections. Contagious diseases that do not affect the mammary gland directly may have an indirect effect on mastitis. This is true for list A diseases such as foot and mouth disease, for which biosecurity measures may need to be taken at national level, and for other infections with nonmastitis pathogens such as bovine viral diarrhea virus and Mycobacterium avium ssp. paratuberculosis. Maintaining a closed herd decreases the risk of introduction of pathogens that affect udder health directly or indirectly. If animals are purchased, their udder health history should be evaluated and they should be examined and tested for contagious diseases. Transmission of infections by and to humans and nonbovine animals may occur. Contact with visitors and nonbovine animals should therefore be minimized. Because of globalization and heightened consumer awareness, the importance of biosecurity now supersedes individual farms, and increased pressure to control transmission of contagious diseases can be expected at industry or government levels in western countries and elsewhere.

Oxidation of lanthionines renders the lantibiotic nisin inactive

The peptide antibiotic nisin A belongs to the group of antibiotics called lantibiotics. They are classified as lantibiotics because they contain the structural group lanthionine. Lanthionines are composed of a single sulfur atom that is linked to the beta-carbons of two alanine moieties. These sulfur atoms are vulnerable to environmental oxidation. A mild oxidation reaction was performed on nisin A to determine the relative effects it would have on bioactivity. High-mass-accuracy Fourier transform ion cyclotron resonance mass spectrometry data revealed the addition of seven, eight, and nine oxygens. These additions correspond to the five lanthionines, two methionines, and two histidines that would be susceptible to oxidation. Subsequent bioassays revealed that the oxidized form of nisin A had a complete loss of bactericidal activity. In a competition study, the oxidized nisin did not appear to have an antagonistic affect on the bioactivity of nisin A, since the addition of an equal molar concentration of the oxidized variant did not have an influence on the bactericidal activity of the native antibiotic. Electron microscopy data revealed that the oxidized forms were still capable of assembling into large circular complexes, demonstrating that oxidation does not disrupt the lateral assembly mechanism of the antibiotic. Affinity thin-layer chromatography and fluorescence microscopy experiments suggested that the loss of activity is due to the inability of the oxidized form of nisin to bind to the cell wall precursor lipid II. Given the loss of bioactivity following oxidation, oxidation should be an important factor to consider in future production, purification, pharmacokinetic, and pharmacodynamic studies.

Prevalence of pathogens in milk samples of dairy cows with clinical mastitis and in heifers at first parturition

Prevalence of mastitis pathogens in milk samples from dairy cows and heifers was studied over a period of 1 year (Aug 2005-Aug 2006) in ten dairy herds in Germany. Milk samples (n=8240) were collected from heifers without clinical mastitis at parturition (n=6915), from primiparous cows with clinical mastitis (n=751) and from older cows with clinical mastitis (n=574). Coagulase negative staphylococci (CNS) were the predominant group of bacteria isolated (46.8% of samples) from clinically healthy quarters of primiparous cows around parturition, followed by streptococci (12.6%), coliforms (4.7%) and Staphylococcus aureus (4.0%). Thirty-three percent of samples were negative on culture (range on farm level, 12.0-46.4%). In cases of clinical mastitis in primiparous and older cows, streptococci were the predominant finding (32.1 and 39.2%) followed by CNS (27.4 and 16.4%), coliforms (10.3 and 13.1%) and Staph. aureus (10.0 and 11.7%). Negative results were obtained from 21.3% (range, 0.0-30.6%) and 19.5% (range, 0.0-32.6%) of these samples. Results indicated substantial differences in the prevalence of pathogens among herds. There was a positive within-herd correlation between the monthly prevalences for Streptococcus dysgalactiae between the three groups of samples. This correlation was also found between clinical samples of primiparous and older cows for Staph. aureus. These correlations were not found for the other pathogens. Besides herd, prevalence of pathogens was influenced by parity, type of sample and season.

Risk Factors for Peripartum Mastitis in Pasture-Grazed Dairy Heifers

A longitudinal observational field study was conducted using 708 heifers in 30 spring-calving dairy herds in the Waikato region of New Zealand. The aim of the study was to investigate risk factors for subclinical and clinical mastitis (CM) in the peripartum period using path analysis methods and to find the factors most important at the population level as a basis for potential control programs. Body condition and udder hygiene scores, blood samples, and quarter mammary secretion samples for bacteriology were collected approximately 3 wk before the planned start of the seasonal calving period and again within 5 d following calving. Additionally, milk samples were collected from quarters diagnosed with CM within 14 d of calving. Significant risk factors for subclinical mastitis postcalving were precalving subclinical mastitis (3.32 incidence risk ratio; IRR), low minimum teat height above the ground (1.32 IRR), and unhygienic udder postcalving (1.32 IRR). Significant risk factors for clinical mastitis postcalving were precalving subclinical mastitis (2.14 IRR), Friesian breed (1.94 IRR), low minimum teat height above the ground (2.05 IRR), udder edema (1.81 IRR), and low postcalving nonesterified fatty acid serum concentration (1.55 IRR). Control of precalving subclinical mastitis and udder edema by producers, and enhancement of breed immunity by geneticists were important factors at a population level, and hence, are likely the most rewarding areas to target in any heifer mastitis management program.

Effects of periparturient systemic treatment with penethamate hydriodide on udder health and milk yield of dairy heifers

Sixty dairy heifers from seven Austrian herds, with high prevalence of Staphylococcus aureus mastitis, were used in this pilot study. Heifers were randomly allocated to two groups. The treatment group received at parturition intramuscularly 10 million i.u. of penethamate hydriodide and then 24 h later, 5 million i.u.; the control group received no treatment. Bacteriological examination was conducted on 7, 14, 21, 35 and 49 d post partum (pp) and milk yield data, fat and protein contents and SCC data were collected every 5th week for the first 200 d of lactation. Occurrence of retained placenta and endometritis were recorded, and the days open of both groups were compared. No effect was observed on the postparturient genital tract health and reproduction indicators. On day 7 pp, four intramammary infections (IMI; two severe clinical; one mild clinical; and one subclinical mastitis) were detected in the untreated control group, whereas there were no IMI in the antibiotic-treated group. At subsequent samplings, there were fewer IMI in the antibiotic-treated group, which were later in lactation, less severe and less persistent. Although SCC was numerically lower in the treatment group, significant differences in SCC between groups could not be detected. Antibiotic-treated heifers produced significantly more milk during the first 15 weeks of lactation than untreated heifers. Over the whole observation period (200 d), peripartum antibiotic-treated heifers produced 323 kg more milk than heifers in the untreated control. Periparturient antibiotic treatment of heifers with penethamate hydriodide prevented IMI during the first week after parturition and achieved a significant increase in milk yield, which was found to be economically beneficial.