Administration of internal teat sealant in primigravid dairy heifers at different times of gestation to prevent intramammary infections at calving

Intramammary infections (IMI) are common in primigravid dairy heifers and can negatively affect future milk production. Bismuth subnitrate-based internal teat sealants (ITS) have been used to prevent prepartum IMI in dairy heifers by creating a physical barrier within the teat, preventing pathogens from entering the gland, though determination of when to administer ITS in heifers has yet to be investigated. The objectives of this study were to determine if administration of ITS in primigravid heifers reduced the odds of IMI at calving and if administration of ITS at different stages of gestation (75 vs. 35 d prepartum) affected the odds of IMI at calving. A total of 270 heifers were used at a single farm. One quarter of each heifer was randomly chosen to be aseptically sampled and administered ITS 75 d prepartum (ITS75), another quarter of each heifer was sampled and received ITS 35 d prepartum (ITS35), whereas the remaining 2 quarters of each heifer served as control quarters (CON) and were not sampled before calving. Within 12 h of calving, aseptic colostrum samples were collected from all quarters to determine quarter infection status. When an IMI was caused by mastitis pathogens other than non-aureus staphylococci (NAS), CON quarters were 3 times [95% confidence interval (CI): 1.4–6.3] and 2.5 times (95% CI: 1.2–4.9) more likely to be infected at calving than ITS75 and ITS35 quarters, respectively. For IMI with NAS, CON quarters were 5.8 (95% CI: 3.2–10.5) and 6.4 (95% CI: 3.4–12.0) times more likely to be infected than ITS75 and ITS35 quarters, respectively. Odds of IMI at calving was similar between ITS75 and ITS35 quarters for both NAS (odds ratio = 0.9) and other pathogens (odds ratio = 1.2). Results indicate that ITS administration at either 75 and 35 d prepartum reduced IMI prevalence at calving in primigravid dairy heifers. Farm specific factors may influence prevalence and timing of heifer IMI and earlier administration of ITS provides an extended period of protection for the developing gland.     

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 [I² (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 (I² = 33.6%), whereas the results of studies with negative controls were heterogeneous (I² = 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.     

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.     

Risk factors for intramammary infections and subclinical mastitis in post-partum dairy heifers

The prevalence of intramammary infections (IMI) and subclinical mastitis (SCM) in 436 German Holstein heifers was put in relation with clinical findings of the udder and data regarding individual rearing and housing conditions of the animals. The clinical examination took place on the day of the livestock auction (at approximately 41 d in milk, DIM). On that day, 31% of the heifers had IMI in at least one quarter, and 18% of all quarters were infected. Coagulase-negative staphylococci were the most prevalent bacteria isolated, accounting for 68% of the positive samples. Data were analysed by logistic regression. Criteria such as 'juvenile intersucking', 'teats shorter than 35 mm', 'teats with a diameter <18 mm' and 'udder oedema at the day of the auction' were associated with IMI in heifers during the first 41 DIM. Loose-housing systems during pregnancy (as opposed to tie-stalls), juvenile intersucking, clinical mastitis during the first week after calving, teat diameters <18 mm, and employing organic bedding material in the stables before calving were associated with subclinical mastitis.     

Quarter-level analysis of subclinical and clinical mastitis in primiparous heifers following the use of a teat sealant or an injectable antibiotic, or both, precalving

This study investigated the effect of infusion of a bismuth subnitrate teat canal sealant or an injectable antibiotic, or both, in heifers on the cure of existing intramammary infection (IMI), incidence of new IMI, prevalence of postcalving IMI, and incidence of clinical mastitis in the first 2 wk postcalving at the quarter level. Heifers (n = 1,067) in 30 seasonally calving, pasture-fed dairy herds were randomly assigned at the heifer level to 1 of 4 treatments (no treatment; 3 intramuscular injections of 5 g of tylosin antibiotic at 24-h intervals; infusion of a teat sealant into all 4 quarters; 3 intramuscular injections of 5 g of tylosin antibiotic and infusion of teat sealant into all 4 quarters). Mammary gland secretion samples were collected from each quarter of every heifer before treatment. Heifers within a herd were enrolled on one calendar day, 27 d (on average) before the planned start of the seasonal calving period. Duplicate milk samples were collected from each gland within 5 d after calving for bacterial culture and from glands the herdowners diagnosed as having clinical mastitis. The relative risk of effect of treatment on the incidence of cure, incidence of new IMI, prevalence of postcalving IMI, and incidence of clinical mastitis were calculated at the gland level using multivariate logistic regression analyses. Neither infusion of a teat sealant nor treatment with the injectable antibiotic increased the cure of precalving IMI. Infusion of the teat sealant reduced the risk of new IMI with any pathogen by 74%, reduced the prevalence of postcalving IMI by 65%, reduced the risk of new infection with Streptococcus uberis by 70% in quarters with an IMI precalving, and reduced the incidence of clinical mastitis from which a pathogen was isolated by 70% in quarters with an IMI precalving. Parenteral antibiotic treatment had no effect on any of these outcomes. In conclusion, use of an internal teat-canal sealant in heifers reduced the postcalving IMI prevalence and the incidence of pathogen-associated clinical mastitis postcalving by decreasing the incidence of new infections over this high-risk peripartum period, and may be a useful tool for reducing the risk of mastitis in heifers.     

Subclinical and clinical mastitis in heifers following the use of a teat sealant precalving

This study investigated the effect in heifers of infusion of a bismuth subnitrate teat-canal sealant and bacterial intramammary infection (IMI) precalving on prevalence of postcalving IMI and incidence of clinical mastitis in the first 2 wk postcalving. Glands (n = 1,020) from heifers (n = 255) in 5 seasonally calving, pasture-fed dairy herds were randomly assigned within heifer to 1 of 4 treatment groups (no treatment; mammary gland secretion collection; infusion of a teat sealant; or sample collection with infusion of teat sealant). Heifers within a herd were enrolled on one calendar day, 31 d on average before the planned start of the seasonal calving period. Duplicate milk samples were collected from each gland within 4 d after calving for bacterial culture. Herd owners collected duplicate milk samples, before treatment, for bacterial culture from glands they defined as having clinical mastitis. The gland prevalence of IMI precalving was 15.5% and did not differ between herds. Bacteria isolated precalving included coagulase-negative staphylococci (76.9% of all bacteriologically positive samples), Streptococcus uberis (14.1%), Staphylococcus aureus (5.1%), Corynebacterium spp. (3.8%), and others (0.1%). The presence of an IMI precalving increased the risk of an IMI postcalving 3.6-fold and the risk of clinical mastitis 4-fold, relative to no IMI precalving. Infusion of the teat sealant reduced the risk of postcalving IMI due to Strep. uberis by 84%, and of clinical mastitis by 68%. Sampling the glands precalving had no effect on postcalving IMI or on clinical mastitis incidence. Use of an internal teat canal sealant in heifers precalving may be a useful tool for reducing the risk of subclinical and clinical mastitis in heifers.     

Systemic prepartum treatment of end-term dairy heifers with penethamate hydriodide: Effect on udder health,milk yield,and culling until 120 days in milk

Prepartum intramammary treatment with antimicrobials of end-term dairy heifers has frequently been proposed as a practice to reduce the prevalence of intramammary infections (IMI) at calving. From a safety standpoint for both animal and administrator, systemic treatment is preferred. A clinical trial was conducted on heifers from 10 well-managed, commercial dairy farms with a low prevalence of heifer mastitis. The aim was to assess both the short- and long-term effects of a systemic prepartum therapy with penethamate hydriodide on udder health and milk production. Because it was hypothesized that some herds would benefit more from this treatment than others, specific herd-level information was collected before the start of the actual trial to screen for and explain potential herd-specific treatment effects. Further, the effect of treatment on antimicrobial susceptibility of staphylococcal isolates was monitored. End-term heifers were either treated systemically (over 3 consecutive days) 2 wk before expected calving date with penethamate hydriodide (n = 76) or remained untreated (n = 73). Systemic prepartum treatment of end-term heifers with penethamate hydriodide resulted in fewer IMI in early lactation. However, all 6 cases of clinical mastitis in early lactation occurred in the treatment group [Streptococcus uberis (n = 1), Corynebacterium bovis (n = 1), Staphylococcus aureus (n = 1); 1 sample was contaminated; 2 samples remained culture negative]. No long-term treatment effects (from 4 to 120 d in milk) on milk production, udder health, or culling hazard during later lactation were detected, although treated heifers belonging to herds classified as having low-yielding heifers out-produced the control heifers. Moreover, penicillin susceptibility of staphylococci isolated from milk samples of treated or control heifers did not differ. Herds with a low prevalence of heifer mastitis are not likely to benefit from prepartum systemic antimicrobial treatment of the end-term heifers.     

Efficacy of a new premilking teat disinfectant containing a phenolic combination for the prevention of mastitis.

A teat disinfectant containing a phenolic combination was evaluated in a natural exposure study in two dairy research herds. Premilking teat disinfection was compared with a negative control using a split-udder experimental design. In both herds, premilking and postmilking teat disinfections with the phenolic combination were significantly more effective in preventing new intramammary infection (IMI) than was postmilking teat disinfection only. Clinical mastitis and new IMI by Streptococcus uberis, Streptococcus dysgalactiae, Gram-negative pathogens, and coagulase-negative Staphylococcus species were significantly lower in quarters of cows with teats predipped and postdipped than in quarters with teats postdipped only. No chapping or teat skin irritation was observed. Premilking teat disinfection with the phenolic combination in association with good udder preparation and postmilking teat disinfection can further reduce the occurrence of new IMI by numerous mastitis pathogens during lactation.     

Efficacy of a novel internal dry period teat sealant containing 0.5% chlorhexidine against experimental challenge with Streptococcus uberis in dairy cattle

The incidence of clinical mastitis and infection status at calving was assessed in quarters treated with 1 of 2 internal teat sealants at the time of dry off. Two contralateral quarters per cow (n = 63 cows) were treated with a sealant that contained 0.5% chlorhexidine; the other quarters were treated with a commercial teat sealant. Ten cows were untreated (controls). On d 2, 4, and 16 after dry off, cows were challenged with Streptococcus uberis S210 strain. Cows were examined daily for 34 d after drying off and cases of clinical mastitis were recorded. Milk samples were collected for culture from any quarters that developed clinical mastitis during the first 34 d after drying-off and from all quarters on d −5 and 0 relative to treatment and at the first and twentieth milking after calving. The incidence of clinical mastitis during the examination period was lower in treated quarters (n = 7/252; 1.5%; lower incidence for those treated with chlorhexidine-containing teat sealant n = 3/126; 1.2%) than in untreated quarters (n = 13/40; 26.8%). The protection against intramammary infection after calving, adjusted for the effect of cow, was higher in quarters treated with the novel teat sealant (89/105; 15.2%; 95% CI = 9.6-23.4) than in those treated with the commercial teat sealant (71/104; 31.7%; 95% CI = 23.5-41.3) and untreated controls (6/28; 78.6%; 95% CI = 59.8-90.0), respectively. Quarters treated with teat sealants were less likely to have an intramammary infection after calving and had a lower incidence of clinical mastitis during the early dry period than did untreated controls in this challenge study.     

Case-control study of risk factors for clinical mastitis in postpartum dairy heifers

A case-control study was carried out to evaluate risk factors for clinical mastitis occurring in dairy heifers between 1 and 14 d postpartum. Case and control heifers were matched on herd; the control was the heifer that calved closest in time, before or after, the particular case. Data were analyzed by conditional logistic regression. The final multivariate model included 339 case-control pairs. Blood in the milk, udder edema, teat edema, and milk leakage, all recorded at the time of parturition, were significant risk factors. Purchased heifers and heifers with skin lesions between udder and thigh were not at increased risk of clinical mastitis. Separate analysis of a subgroup of case-control pairs identified teat edema, blood in the milk, and milk leakage at calving as risk factors for clinical mastitis caused by Staphylococcus aureus.     

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.     

Modifiable management practices to improve udder health in dairy cattle during the dry period and early lactation: A scoping review

The objective of this scoping review was to characterize all available literature on modifiable management practices used during the dry period that have been evaluated for their effects on udder health in dairy cattle during the dry period and the subsequent lactation. Five databases and two conference proceedings were searched for relevant literature. Articles published in or after 1990 were eligible for inclusion. Eligible interventions or exposures were restricted to modifiable management practices; however, antimicrobial and teat sealant products were enumerated but not further characterized, as systematic reviews have been published on this topic. Other modifiable management practices were reported in 229 articles. Nutrition (n = 79), which included ration formulation and delivery (n = 44) and vitamin and mineral additives (n = 35), was the most commonly reported practice, followed by vaccines (n = 40) and modification of dry period length (n = 27). Risk of clinical mastitis (CM) was the most commonly reported outcome (n = 151); however, reporting of outcome risk periods varied widely between articles. Cure of existing intramammary infections (IMI) over the dry period (n = 40) and prevention of new IMI over the dry period (n = 54) were most commonly reported with a risk period between calving and 30 d in milk. Future systematic reviews with meta-analyses could target management practices such as nutrition, vaccines, and dry period length to quantify their effects on improving udder health during the dry period and early lactation. However, the variation in reporting of time at risk for CM and other outcomes challenges the ability of future synthesis work to inform management decisions on the basis of efficacy to cure or prevent IMI and CM. Consensus on which core outcomes should be evaluated in mastitis research and the selection of consistent risk periods for specific outcomes in animal trials is imperative.     

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.     

The effect of selenium supplementation before calving on early-lactation udder health in pastured dairy heifers

Selenium (Se) deficiency has been associated with lowered resistance to mastitis in dairy cattle. However, little published data exists on the effect of Se supplementation before calving on udder health of pastured dairy heifers. Further, the relative efficacy of injectable barium selenate and oral organic Se for improving udder health in cows has not previously been tested. The objectives of this study were to determine the effects of precalving Se supplementation and type of supplementation on the blood activity of glutathione peroxidase and measures of udder health immediately after calving and during the first month of lactation in pastured dairy heifers. One hundred forty pregnant Chilean Holstein-Friesian heifers were fed a basal diet containing, on average, 0.15 mg of Se/kg of dry matter. One month before predicted calving, heifers were allocated to 1 of 3 groups. Group 1 (n = 49) received no supplementary Se, group 2 (n = 46) received a single subcutaneous injection of Se (1 mg/kg of live weight, as barium selenate), and group 3 (n = 45) was fed Se yeast (3 mg/heifer/d until calving). Heifers supplemented with barium selenate had a higher glutathione peroxidase activity from 14 d in milk onwards. Selenium supplementation, irrespective of source, tended to reduce the prevalence of intramammary infection (IMI) and decrease the prevalence of quarters with high somatic cell count (SCC) at calving. Overall, Se supplementation did not result in a reduction of the incidence of new IMI or clinical mastitis or in decreased SCC during the balance of the first month of lactation. However, in pasture-based heifers injected with barium selenate before calving, and fed diets with 1.3 and 2.5 mg of Se/d precalving and during lactation, respectively, no cases of clinical mastitis were observed in the first month of lactation.     

Pathogen-group specific association between CXCR1 polymorphisms and subclinical mastitis in dairy heifers

The chemokine (C-X-C motif) receptor 1 (CXCR1) gene encodes the homonymous receptor for interleukin 8 (IL8) on polymorphonuclear neutrophilic leucocytes (PMNL). Binding causes migration from blood to milk, activation and prolonged survival of PMNL, a crucial process in the innate immune defence of the bovine mammary gland against invading mastitis-causing pathogens. The main objective of this study was to screen the entire coding region of the CXCR1 gene for polymorphisms and to analyse their association with udder health of dairy heifers. One-hundred-and-forty Belgian Holstein heifers originating from 20 commercial dairy farms were genotyped by DNA sequencing. Detailed phenotypic data on udder health was available including quarter bacteriological culture results and somatic cell count (SCC) in early lactation and composite milk SCC during first lactation. In total, 16 polymorphisms (including 8 missense mutations) were detected. Polymorphism c.980A>G was associated with pathogen-group specific IMI: heifers with genotype AG were less likely to have an IMI due to major mastitis pathogens compared with heifers with genotype GG but did not have less IMI by coagulase-negative staphylococci, so-called minor pathogens. CXCR1 genotype was neither associated with quarter SCC in early lactation nor with composite SCC during lactation. Although mastitis susceptibility is influenced by many factors, some genetic polymorphisms potentially have major effects on udder health of heifers, as was shown here. These results trigger us to further study the relationship between CXCR1 polymorphisms and mastitis susceptibility in both observational and experimental trials.     

Epidemiology of mastitis in pasture-grazed peripartum dairy heifers and its effects on productivity

An observational field study was conducted on 708 heifers in 30 spring-calving dairy herds in the Waikato region of New Zealand. The aim of the study was to describe patterns and effects of intramammary infection (IMI) and clinical mastitis (CM) in the peripartum period. Mammary secretion samples for bacteriological testing were taken from all quarters approximately 3 wk before the planned start of the calving period and within 5 d following calving, in addition to quarters diagnosed with CM within 14 d of calving. Precalving IMI was diagnosed in 18.5% of quarters, and of these, coagulase-negative staphylococci were the predominant isolate (13.5% of quarters). Streptococcus uberis prevalence increased 4-fold to 10.0% of quarters on the day of calving compared with the precalving period. Prevalence of all pathogens decreased rapidly following calving. Clinical mastitis cases were predominantly associated with Strep. uberis (64%). The daily hazard of diagnosis was higher in heifers than in cows (0.06 vs. 0.02/d on d 1 postcalving, respectively), but was not different by d 5 (0.005 vs. 0.002, respectively) of lactation. Intramammary infection with a major pathogen was associated with an increased risk of removal from the herd (15 vs. 10% for infected and noninfected heifers, respectively) and somatic cell count >200,000 cells/mL at subsequent herd tests (15 vs. 8%), but neither CM nor IMI were associated with reduced milk yield or milk solids production. Results suggest that bacterial species involved and the pattern of IMI prevalence in pasture-grazed peripartum heifers differ from those in other production systems. Further, mastitis control programs need to target major environmental pathogens causing precalving IMI, because new infections are likely before the onset of lactation, whereas existing detection and control measures are generally implemented after calving. Novel control programs that reduce new infections due to Strep. uberis immediately before calving are required to reduce the incidence of CM in pasture-grazed dairy heifers.     

Incidence of subclinical mastitis in Dutch dairy heifers in the first 100 days in lactation and associated risk factors

Heifer mastitis is a problem and risk factors may differ between heifers and older cows. The aim of this study was to estimate the heifer subclinical mastitis (HSCLM) incidence based on elevated somatic cell count (SCC) in the first 100 d in lactation and the associated risk factors in Dutch dairy herds. In 2008, 173 farmers filled in a questionnaire regarding housing and herd management factors potentially related to udder health. In addition, monthly milk production and SCC data from all cattle were provided by the Dutch Royal Cattle Syndicate (CRV, Arnhem, the Netherlands). Heifer subclinical mastitis incidence was calculated at the herd level as the number of heifer cases divided by the number of heifers at risk in the first 100 d in milk. Linear regression models were used for the analyses. On average, 25.5% [95% confidence interval (CI): 23.9 to 27.0%] of the heifers had subclinical mastitis. Heifers with a high SCC (>150,000 cells/mL) on the first test day after calving that returned to SCC levels below the cut-off continued to have a higher SCC throughout the study period compared with heifers with a low SCC (≤150,000 cells/mL) at the first test day after calving. Housing heifers together with lactating cows close to calving was protective from HSCLM incidence compared with separate housing (-4.5%; 95% CI: -8.7 to -0.2%). In addition, herds in which the farmer removed supernumerary teats of calves had a 7.0% (95% CI: 2.8 to 11.3%) lower HSCLM incidence and day and night grazing was also protective (-5.9%; 95% CI: -10.6 to -1.3%). Herds that were milked with an automatic milking system had, on average, a 6.9% (95% CI: 2.2 to 11.5%) higher HSCLM incidence and submitting milk samples for bacteriological culturing in the previous year was also associated with a higher HSCLM incidence (4.1%; 95% CI: 1.1 to 7.1%). Heifer subclinical mastitis is prevalent in all dairy herds, with a large variation in incidence. A high SCC in heifers at the first test day after calving appears to indicate a prolonged effect on udder health. Several management factors were found to be associated with HSCLM incidence that may help in reducing HSCLM.     

Heifers infected with coagulase-negative staphylococci in early lactation have fewer cases of clinical mastitis and higher milk production in their first lactation than noninfected heifers

Intramammary infections (IMI) in recently calved dairy heifers are more common than was formerly believed but their relevance for future performance has been studied only rarely. In the present study, the association between the IMI status of fresh heifers and their subsequent udder health, milk production, and culling in first lactation was explored. Quarter milk samples were collected between 1 and 4 d in milk (DIM) and between 5 and 8 DIM from 191 dairy heifers in 20 dairy herds for bacteriological culturing and somatic cell count (SCC) analysis. Monthly milk recording data including composite milk SCC and test-day milk yield (MY) were obtained for the first 285 DIM or until culling. Farmer-recorded clinical mastitis cases were available. Data were analyzed using mixed models and survival analysis. Approximately 80% of the fresh heifers (79.8%) had at least one culture-positive quarter. Coagulase-negative staphylococci (CNS) were the most frequently isolated pathogens (72%), followed by esculin-positive streptococci (4.6%) and Staphylococcus aureus (3.5%). Overall geometric mean SCC at quarter level decreased between the first and second samplings from 348,000 to 116,000 cells/mL. Heifers infected with CNS had an intermediate average test-day SCC (84,000 cells/mL) during the first 285 DIM compared with noninfected heifers (53,000 cells/mL) and heifers infected with major pathogens (195,000 cells/mL). Heifers infected with major pathogens had a much lower average daily MY (18.3 kg) during first lactation compared with noninfected animals (21.3 kg). That CNS-infected heifers out-produced their noninfected counterparts could be at least partially explained by their significantly lower incidence of clinical mastitis (incidence risk 3.6 vs. 21.0%) during first lactation compared with noninfected heifers. We conclude that although CNS cause the majority of IMI in heifers around calving, they should not be a reason for serious concern.     

Prepartum antibiotic treatment of heifers: milk production,milk quality and economic benefit

Prepartum intramammary antibiotic infusion of heifer mammary glands at 7 or 14 d before expected parturition is an effective procedure for eliminating many infections in heifers during late gestation and for reducing the prevalence of mastitis in heifers during early lactation and throughout lactation. Mastitis pathogens were isolated from 76% of samples obtained from untreated control quarters 7 d before expected calving, from 47% of samples obtained 3 d after calving, and from 29% of samples obtained 10 d postpartum. Mastitis pathogens were isolated from about 30% of control quarters through 240 d of lactation. A similar percentage of samples (70%) was positive for mastitis pathogens at C-7 before antibiotic treatment. However, only 8% of samples obtained at 3 d after calving and 4% of samples obtained at 10 d postpartum from quarters of antibiotic-treated heifers contained mastitis pathogens. Throughout the remainder of lactation, mastitis pathogens were isolated from an average of about 11% of quarters. The percentage of samples with mastitis pathogens was higher in untreated controls than in antibiotic-treated quarters at all sampling intervals during lactation. A similar response was observed in heifers that were treated with antibiotics at 14 d before expected parturition. Prepartum antibiotic-treated heifers produced significantly more milk than control heifers and had significantly lower somatic cell count scores than untreated control heifers. These observations are likely associated with or due to the lower prevalence of mastitis pathogen isolation in prepartum antibiotic-treated heifers throughout lactation. Prepartum antibiotic-treated heifers produced 531 kg more milk than heifers in the untreated control group. Multiplying this increase by a milk price of 0.407 dollars/kg yielded a 216.24 dollars per-heifer increase in gross revenue. The cost of treatment, including the cost of testing for antibiotic residues, was estimated at 15.60 dollars for a net revenue of 200.64 dollars per heifer. Prepartum antibiotic treatment to reduce the rate of mastitis in heifers during lactation was highly effective and economically beneficial.     

Invited review: Microbiota of the bovine udder: Contributing factors and potential implications for udder health and mastitis susceptibility

Various body sites of vertebrates provide stable and nutrient-rich ecosystems for a diverse range of commensal, opportunistic, and pathogenic microorganisms to thrive. The collective genomes of these microbial symbionts (the microbiome) provide host animals with several advantages, including metabolism of indigestible carbohydrates, biosynthesis of vitamins, and modulation of innate and adaptive immune systems. In the context of the bovine udder, however, the relationship between cow and microbes has been traditionally viewed strictly from the perspective of host-pathogen interactions, with intramammary infections by mastitis pathogens triggering inflammatory responses (i.e., mastitis) that are often detrimental to mammary tissues and cow physiology. This traditional view has been challenged by recent metagenomic studies indicating that mammary secretions of clinically healthy quarters can harbor genomic markers of diverse bacterial groups, the vast majority of which have not been associated with mastitis. These observations have given rise to the concept of “commensal mammary microbiota,” the ecological properties of which can have important implications for understanding the pathogenesis of mastitis and offer opportunities for development of novel prophylactic or therapeutic products (or both) as alternatives to antimicrobials. Studies conducted to date have suggested that an optimum diversity of mammary microbiota is associated with immune homeostasis, whereas the microbiota of mastitic quarters, or those with a history of mastitis, are considerably less diverse. Whether disruption of the diversity of udder microbiota (dysbiosis) has a role in determining mastitis susceptibility remains unknown. Moreover, little is known about contributions of various biotic and abiotic factors in shaping overall diversity of udder microbiota. This review summarizes current understanding of the microbiota within various niches of the udder and highlights the need to view the microbiota of the teat apex, teat canal, and mammary secretions as interconnected niches of a highly dynamic microbial ecosystem. In addition, host-associated factors, including physiological and anatomical parameters, as well as genetic traits that may affect the udder microbiota are briefly discussed. Finally, current understanding of the effect of antimicrobials on the composition of intramammary microbiota is discussed, highlighting the resilience of udder microbiota to exogenous perturbants.