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.     

The use of a cephalonium containing dry cow therapy and an internal teat sealant, both alone and in combination

The dry period is a critical time in the lactation cycle, being the optimum time to cure existing intramammary infection (IMI) as well as encompassing the periods of highest susceptibility to new infection. Currently, IMI in the dry period is controlled with antibiotic dry cow therapy. The aim of this randomized control trial was to investigate different dry cow therapy regimens by stratifying cows by likely infection status at drying off in herds with low somatic cell count (SCC; bulk milk SCC <250,000 cells/mL) in southwest England. All quarters in 890 cows were recruited. The recruited cows were categorized as either infected or uninfected on the basis of SCC and clinical mastitis history. Ipsilateral quarters within each cow were randomly allocated to receive 1 of 4 different treatment regimens according to their infection category. Quarters in high-SCC infected cows were allocated to receive antibiotic dry cow therapy either alone or in combination with an internal teat sealant; quarters in low-SCC uninfected cows were allocated to receive teat sealant either alone or in combination with antibiotic dry cow therapy. All quarters were sampled for bacteriology at drying off and again within 10 d post-calving. Quarters were subsequently monitored for clinical mastitis for the first 100 d of lactation. The mass of residual sealant was assessed immediately post-calving to allow assessment of the association of sealant retention with treatment efficacy. Models were constructed to assess the efficacy of the different regimens in preventing IMI. Apparent cure rates of existing IMI with major pathogens were consistently >90% in quarters receiving antibiotic. Combination treatment of high-SCC infected cows resulted in an increased likelihood of being pathogen free post-calving (odds ratio = 1.40; 95% credibility interval = 1.03-1.90). The benefits of combination treatment of low-SCC uninfected cows were less clear. With respect to clinical mastitis, combination treatment of high-SCC infected cows resulted in a decreased likelihood of developing clinical mastitis in the first 100 d of the subsequent lactation (odds ratio = 0.68; 95% credibility interval = 0.48-0.98). The retention of the internal sealant was adversely affected by its use in combination with antibiotic dry cow therapy.     

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.     

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.     

Evaluation of selective dry cow treatment following on-farm culture: Risk of postcalving intramammary infection and clinical mastitis in the subsequent lactation

The objective of the study was to evaluate the utility of a Petrifilm-based on-farm culture system when used to make selective antimicrobial treatment decisions on low somatic cell count cows (<200,000 cells/mL) at drying off. A total of 729 cows from 16 commercial dairy herds with a low bulk tank somatic cell count (<250,000 cells/mL) were randomly assigned to receive either blanket dry cow therapy (DCT) or Petrifilm-based selective DCT. Cows belonging to the blanket DCT group were infused with a commercial dry cow antimicrobial product and an internal teat sealant (ITS) at drying off. Using composite milk samples collected on the day before drying off, cows in the selective DCT group were treated at drying off based on the results obtained by the Petrifilm on-farm culture system with DCT + ITS (Petrifilm culture positive), or ITS alone (Petrifilm culture negative). Quarters of all cows were sampled for standard laboratory bacteriology on the day before drying off, at 3 to 4 d in milk (DIM), at 5 to 18 DIM, and from the first case of clinical mastitis occurring within 120 DIM. Multilevel logistic regression was used to assess the effect of study group (blanket or selective DCT) and resulting dry cow treatment (DCT + ITS, or ITS alone) on the risk of intramammary infection (IMI) at calving and the risk of a first case of clinical mastitis between calving and 120 DIM. According to univariable analysis, no difference was observed between study groups with respect to quarter-level cure risk and new IMI risk over the dry period. Likewise, the risk of IMI at calving and the risk of clinical mastitis in the first 120 DIM was not different between quarters belonging to cows in the blanket DCT group and quarters belonging to cows in the selective DCT group. The results of this study indicate that selective DCT based on results obtained by the Petrifilm on-farm culture system achieved the same level of success with respect to treatment and prevention of IMI over the dry period as blanket DCT and did not affect the risk of clinical mastitis in the first 120 d of the subsequent lactation.     

Effect of 2 herbal intramammary products on milk quantity and quality compared with conventional and no dry cow therapy

Dry cow therapy, administered at the end of lactation, is aimed at eliminating current and preventing future intramammary (IMM) bacterial infections and typically involves intramammary administration of antibiotics. Certified organic dairies in the United States are restricted from using antibiotics and must consider an alternative therapy or no dry cow therapy. The current study compared 2 herbal products to conventional dry cow therapy and no treatment for a total of 5 treatments over 2 trials. Trial 1 was conducted over 3 yr on 1 research farm and trial 2 included 4 commercial farms plus the research herd over 2 yr. Treatments included (1) a conventional IMM antibiotic and internal teat sealant (penicillin-dihydrostreptomycin and bismuth subnitrate; CON); (2) an herbal IMM product purported to act as a teat sealant (Cinnatube, New AgriTech Enterprises, Locke, NY; CIN); (3) an herbal IMM product (Phyto-Mast, Bovinity Health LLC, Narvon, PA; P-M); (4) Phyto-Mast and Cinnatube (PC); or (5) no dry cow therapy (NT). Each treatment group was balanced by breed, lactation number, due date, herd, and year. However, the CON treatment was used only in the research herd because of the intent to avoid antibiotic usage on the other 4 farms. Comparisons among treatments included the difference between pre- and posttreatment 305-d mature equivalent milk production (trial 1), somatic cell score change from dry-off to freshening at the cow and quarter levels (trials 1 and 2), and milk microbiology change over the dry period (trial 2). We detected no significant differences among treatments for milk yield differences between the lactation following treatment and the lactation preceding treatment. Changes in somatic cell score from one lactation to the next also did not differ significantly among treatments in either trial. Cure rates were not significantly different among treatments; only 19.6% of all quarters were infected at dry off. The proportion of quarters with new infections at 3 to 5 d postcalving did not significantly differ among treatments, except between CIN and NT. Percentages (least squares means ± standard error) of quarters with new infections were 24 ± 21% for CON, 15 ± 7% for CIN, 30 ± 10% for P-M, 32 ± 11% for PC, and 35 ± 11% for NT. The efficacy of the herbal products was similar to that of conventional therapy, and the herbal products had no apparent adverse effects.     

A comparison of broad-spectrum and narrow-spectrum dry cow therapy used alone and in combination with a teat sealant

The dry period is a critical time in the lactation cycle, offering the optimum time for cure of existing intramammary infection (IMI), while also encompassing the periods of highest susceptibility to new intramammary infection. Until recent years, intramammary infection in the dry period has been controlled with the use of antibiotic dry cow therapy. The aim of this study was to investigate 3 different dry cow therapy regimens, in low-somatic cell count (SCC; bulk milk SCC < 250,000 cells/mL) herds in southwest England. A total of 489 cows was recruited to the study and randomly allocated to receive either the broad-spectrum antibiotic cefquinome, a combination treatment comprising the narrow-spectrum antibiotic cloxacillin and an internal teat sealant, or the narrow-spectrum antibiotic cloxacillin alone. All quarters were sampled for bacteriology at drying off and again in the week immediately postcalving; 2 quarters were also sampled 2 wk before the estimated calving date to allow an assessment of infection dynamics during the dry period. Quarters were subsequently monitored for clinical mastitis for the first 100 d of lactation. Conventional multilevel (random effects) models were constructed to assess the efficacy of products in preventing IMI. Survival analysis was used to examine factors that influenced the risk of clinical mastitis using conventional Cox proportional hazards models. No differences were identified between the treatment groups in terms of cure of IMI caused by the major pathogens. Quarters in both the combination and cefquinome-treated groups were more likely to be free of a major pathogen or enterobacterial pathogen postcalving. With respect to clinical mastitis, the cefquinome-treated group was less likely to develop clinical mastitis than was the cloxacillin treated group.     

Herd management factors that affect duration and variation of adherence of an external teat sealant

During 1998 and 1999, a purposive sample of Ontario dairy herds was enrolled in a study to examine management factors associated with adherence of an external teat sealant. A total of 74 herds were recruited that had previously complied with a provincial Sentinel Herd mastitis study. All herds were sent a management survey and a commercially available external teat sealant product. The sealant was applied to all cows in first lactation or greater that were scheduled to go dry. Adherence of the teat sealant was scored on a scale of 1 to 5 (1 = sealant completely removed) for the first 12 d following dry off. Complete data were analyzed from 806 cows in 48 herds (mean of 17 cows/herd). Mean duration of adherence of the teat sealant was 4 d (range 1 to 7 d). Of the management factors recorded, only changing the feed to reduce milk production prior to drying off was significantly associated with 0.78-d prolonged adherence. No factors related to dry cow housing, bedding material, or floor surface were associated with the duration of adherence. The variance around the duration of adherence was examined. The median variance of adherence was 3.0 d², which was equivalent to a standard deviation of 2.6 d. Herds in which dry cows were housed in tie-stall barns, and the herds that used a penicillin and novobiocin combination dry cow antibiotic had the greatest variation. We concluded that modifying the ration to reduce milk production enhanced adherence of an external teat sealant. Teat-end preparation prior to application of the teat sealant is an important factor to consider when choosing to adopt this dry period mastitis prevention strategy. This study demonstrates that beyond cow- and quarter-level factors, herd management factors can influence the duration and variation of sealant adherence experienced among different herds.     

Effect of an intramammary teat seal and dry cow antibiotic in relation to dry period length on postpartum mastitis

Infusion of either a long-acting antibiotic preparation (cefalonium) or the same antibiotic preparation combined with an internal teat sealant (bismuth subnitrite) were compared for the effect on new intramammary infections at calving and clinical mastitis in the first 100 d of lactation, in relation to dry period length. For all cows, a significant reduction in the incidence of new infections in quarters at calving (3.7 vs. 7.3%) was found for the combination treatment group (150 cows) compared with the antibiotic-alone treatment (133 cows). With a dry period of 10 wk or longer, significantly fewer new quarter infections (3.8 vs. 11.4%) were found in those cows receiving the combination treatment compared with antibiotic treatment alone. When the dry period was less than 10 wk, the incidence of new infections in quarters treated with the combination treatment was lower than for the antibiotic treatment alone (3.7 vs. 6%) but this was not a statistically significant difference. Fewer infections caused by Streptococcus uberis and coagulase-negative staphylococci were found in cows receiving the combination treatment compared with the antibiotic treatment alone (not significant). Coliform isolates were less likely in cows receiving the combination treatment with the longer dry period but the numbers of new intramammary coliform infections were low for both dry period categories. Few infections were caused by coagulase-negative staphylococci. The incidence of clinical mastitis in the first 100 d of lactation in quarters infected at calving was significantly lower (4 vs. 15 cases) for the combination treatment than for the antibiotic treatment alone for both dry period lengths. The clinical incidence in quarters in which a pathogen was not detected in either of the samples taken after calving was comparable between groups. No significant difference was found in the total clinical incidence after calving for both groups irrespective of dry period length.     

Decision tree analysis to evaluate dry cow strategies under UK conditions

Economic decisions on animal health strategies address the cost-benefit aspect along with animal welfare and public health concerns. Decision tree analysis at an individual cow level highlighted that there is little economic difference between the use of either dry cow antibiotic or an internal teat sealant in preventing a new intramammary infection in a cow free of infection in all quarters of the mammary gland at drying off. However, a potential net loss of over ?20 per cow might occur if the uninfected cow was left untreated. The only economically viable option, for a cow with one or more quarters infected at drying off, is antibiotic treatment, although a loss might still be incurred depending on the pathogen concerned and the cure rates achievable. There was a net loss for cows with quarters infected with Corynebacterium spp. at drying off, for both the teat sealant and untreated groups (?22 and ?48, respectively) with only antibiotic-treated cows showing a gain.     

Prophylactic effects of two selective dry cow strategies accounting for interdependence of quarter

Infusion of a long-acting antibiotic preparation at drying off in dairy cows as a prophylactic therapy is usually recommended for all quarters where it is in use. Studying the effectiveness of such treatment using quarter as the unit of analysis assumes that each quarter within a cow has a risk of being infected independent of the other quarters of the cow. Failure to account for interdependence of quarters within a cow may lead to inaccurate variance estimates and errors in assessing treatment effects. Data from two trials assessing different dry-cow strategies were examined for interdependence of infection between quarters. Logistic regression with a variance inflation factor or a multilevel analysis was used to assess the effect of antibiotic and internal teat-sealant dry cow strategies. Parity and infection status at drying off were covariates in the analysis. Interdependence of the risk of quarter infections within control-group cows was demonstrated in both dry-cow antibiotic and teat-seal trials. However, cows that received either of these treatments did not demonstrate interdependence. Treated quarters in both trials were 3.0 times less likely to acquire a new infection at calving compared with the untreated controls. Quarters in cows of parity 3 or greater were also at an increased risk in the antibiotic treatment trial. In both trials, quarters with either Corynebacterium spp. or coagulase-negative staphylococci infections at drying off had an increased risk of a new intramammary infection at calving. This study has demonstrated the beneficial and comparable effects of antibiotic and teat seal dry cow strategies; both decreased the risk of intramammary infection at calving. The application of dry-cow strategies at the cow level and not the quarter level is also supported.     

The effect of an intramammary teat seal on new intramammary infections

As concern over the possible overuse of antibacterials increases, attention has focused on reduction of antibiotic usage and on nonantibiotic alternatives. A nonantibiotic intramammary teat sealant, Teat Seal (Cross Vetpharm Group Ltd., Tallaght, Dublin, Ireland), has been available in Ireland, in combination with an intramammary tube of cloxacillin. Teat Seal has been reformulated for use in cows with low cell counts as an alternative to antibiotic dry cow therapy at the end of lactation. The product is now marketed as Orbeseal (Pfizer Animal Health). A comparison between this teat sealant and no treatment was made on new intramammary infections and clinical mastitis, on all cows within four herds, and on low cell count cows in three herds. No cases of clinical mastitis in the dry period were observed in cows treated with Teat Seal (n = 197), whereas a significant number (6 cows) were observed in the untreated cows (n = 204). In all herds, significantly more new infections at calving were found in the untreated group (62 cows in the untreated group compared with 21 cows in the Teat Seal group). In those quarters where infections were first detected at calving, the incidence of clinical mastitis was significantly greater in the untreated group. Quarters in both treatment groups that were infected at drying off with Corynebacterium spp. or coagulase-negative staphylococci were not protected against new infections and had an increased risk of new infection by Streptococcus uberis. The results will inform those restricting their use of antibiotic dry cow therapy in alternative management strategies and the additional risk of new intramammary infection.     

Field survey of clinical mastitis in low somatic cell count herds

Nine commercial dairy herds, each with low herd milk somatic cell counts, were monitored for 1 yr to determine prevalence of intramammary infections and rates of clinical mastitis. Staphylococcus species was the bacterial group most frequently isolated from quarters at calving and at drying off. Environmental streptococci and coliform intramammary infections totaled less than 6% of quarters at both calving and at drying off. Staphylococcus aureus were isolated from less than 1% of quarters and Streptococcus agalactiae from 0% of quarters at both calving and drying off. A total of 646 clinical cases of mastitis were diagnosed in 548 quarters of 406 cows. Mean rate of clinical mastitis among herds was .457 clinical cases/305 cow-days. Rates of clinical mastitis ranged among herds from .273 to .748 clinical cases/305 cow-days. Coliforms and bacteriologically negative and environmental streptococci accounted for 82.3% of clinical cases. Rates of clinical mastitis and severity of clinical signs differed among herds, seasons of the year, parity groups, and stages of lactation. Rates of clinical mastitis were highest during summer, in first lactation cows, and during the first 7 d of lactation.     

The use of an internal teat sealant in combination with cloxacillin dry cow therapy for the prevention of clinical and subclinical mastitis in seasonal calving dairy cows

Cows (n = 2,053) from 6 seasonally calving dairy herds were enrolled in a trial to compare the efficacy of 2 dry cow treatments. Cows received either a combination dry cow therapy of 600 mg of cloxacillin (CL) followed by an internal teat sealant (ITS) containing 2.6 g of bismuth subnitrate in all 4 quarters immediately following their final milking for the season, or only an intramammary infusion of 600 mg of CL. All cases of clinical mastitis were recorded and cultured during the first 150 d of lactation in each herd, and cow somatic cell count (SCC) was measured between 7 and 50 d postcalving. A large difference was found between treatment groups in the rate at which cows were diagnosed with clinical mastitis over the first 21 d of lactation, after which time the rate at which cows were diagnosed with clinical mastitis was similar between treatment groups. Analysis of the relative proportions of cows with clinical mastitis was performed at both the gland and cow levels. The relative risk (RR) of clinical mastitis diagnosed within 21, 30, and 100 d of calving in a gland treated with the ITS-CL combination was, respectively, 0.30 [95% confidence interval (CI) = 0.21-0.44], 0.39 (0.28-0.53), and 0.58 (0.46-0.75) that of the CL group. An interaction between treatment and previous SCC was found when clinical mastitis was analyzed at the cow level. In a subset of cows that had low SCC in their previous lactation, the RR of mastitis in cows with the ITS-CL combination within 21, 30, and 100 d of calving was, respectively, 0.54 (95% CI = 0.33-0.87), 0.57 (0.37-0.88), and 0.69 (0.50-0.99) that of cows that received only CL at drying off. In the subset of cows that had at least 1 high SCC in the previous lactation, the RR of mastitis in the ITS-CL combination group within 21, 30, and 100 d of calving was, respectively, 0.26 (95% CI = 0.16-0.44), 0.37 (0.24-0.57), and 0.72 (0.55-0.96) that of the CL-only group. The ITS-CL combination of dry cow treatments was associated with a reduction in subclinical mastitis [SCC ≥250,000 cells/mL; RR = 0.80 (95% CI = 0.65-0.98)] when compared with treatment with CL alone. The use of an ITS in combination with CL dry cow treatment was associated with significantly lower clinical and subclinical mastitis in the following lactation, with a greater difference found in cows that had a history of subclinical mastitis in the previous lactation.     

Evaluation of the use of dry cow antibiotics in low somatic cell count cows

The goal of dry cow therapy (DCT) is to reduce the prevalence of intramammary infections (IMI) by eliminating existing IMI at drying off and preventing new IMI from occurring during the dry period. Due to public health concerns, however, preventive use of antibiotics has become questionable. This study evaluated selective DCT in 1,657 cows with low somatic cell count (SCC) at the last milk recording before drying off in 97 Dutch dairy herds. Low SCC was defined as <150,000 cells/mL for primiparous and <250,000 cells/mL for multiparous cows. A split-udder design was used in which 2 quarters of each cow were treated with dry cow antibiotics and the other 2 quarters remained as untreated controls. The effect of DCT on clinical mastitis (CM), bacteriological status, SCC, and antibiotic use were determined at the quarter level using logistic regression and chi-squared tests. The incidence rate of CM was found to be 1.7 times (95% confidence interval = 1.4–2.1) higher in quarters dried off without antibiotics as compared with quarters dried off with antibiotics. Streptococcus uberis was the predominant organism causing CM in both groups. Somatic cell count at calving and 14 d in milk was significantly higher in quarters dried off without antibiotics (772,000 and 46,000 cells/mL, respectively) as compared with the quarters dried off with antibiotics (578,000 and 30,000 cells/mL, respectively). Quarters with an elevated SCC at drying off and quarters with a positive culture for major pathogens at drying off had a higher risk for an SCC above 200,000 cells/mL at 14 d in milk as compared with quarters with a low SCC at drying off and quarters with a negative culture for major pathogens at drying off. For quarters that were culture-positive for major pathogens at drying off, a trend for a higher risk on CM was also found. Selective DCT, not using DCT in cows that had a low SCC at the last milk recording before drying off, significantly increased the incidence rate of CM and SCC. The decrease in antibiotic use by drying off quarters without DCT was not compensated by an increase in antibiotic use for treating CM. Total antibiotic use related to mastitis was reduced by 85% in these quarters.     

An observational cohort study on persistency of internal teat sealant residues in milk after calving in dairy cows

Our objectives were to evaluate the prevalence of quarters with an observable internal teat sealant (ITS) plug at first milking following calving and investigate persistency of ITS residues in milk after calving. An observational cohort study was carried out on 557 quarters of 156 cows treated with ITS in 6 farms in Quebec, Canada. The presence of an ITS plug at first milking and ITS residues in milk at each milking were observed by producers. The effects of various factors on the odds of observing an ITS plug and persistency of ITS residues in milk were studied using generalized logistic mixed and generalized negative binomial mixed models, respectively. Milk samples were taken on the day before dry-off and on 2 occasions after calving for bacterial identification to detect intramammary infection (IMI) using bacteriological culture followed by MALDI-TOF identification. The association between the absence of an ITS plug and the presence of new IMI was assessed using a mixed logistic regression model. Internal teat sealant plugs after calving were more often observed in rear quarters and in quarters receiving ITS alone at drying-off versus antimicrobial and ITS. We observed an average (standard deviation) persistency of 4.0 d (2.3 d). When an ITS plug was still present at first milking (83% of quarters), the elimination of ITS residues in milk after calving was significantly longer (4.5 d, on average) compared with 1.2 d when an ITS plug was absent. In cows with an ITS plug at calving, we observed a higher number of days of excretion in older cows. When a plug could not be observed, rear quarters, older cows, and cows with a long dry period duration excreted ITS residues for a significantly longer period. The lack of a significant association between the absence of a plug and the odds of new IMI at calving suggests that despite the loss of the plug, cows were still protected against new IMI. Although we were able to highlight some statistically significant risk factors explaining persistency of ITS residues following calving, observed differences were often relatively small and, perhaps, not clinically relevant. In conclusion, an ITS plug was present until first milking after calving for 83% quarters, quarters without an ITS plug at first milking appeared to have been protected from new IMI, and ITS residues could be observed in milk up to 12 d in milk.     

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.     

Heifer and quarter characteristics associated with periparturient blood and milk neutrophil apoptosis in healthy heifers and in heifers with subclinical mastitis

Polymorphonuclear neutrophilic leukocytes (PMNL) play an important role in the first line cell-mediated immune defense of the body in general and of the mammary gland against mastitis pathogens in particular. Reduced viability of PMNL close to parturition may explain the high incidence of infectious diseases and the high prevalence of intramammary infections (IMI) in periparturient dairy heifers. Apoptosis of blood PMNL 1 wk before the expected calving date and of blood and milk PMNL at 1 to 4 d in milk was determined using flow cytometry. Information on heifer and gland characteristics was collected before calving and in early lactation. Data were analyzed using multivariable, multilevel regression analysis. Supplementation of a commercial mineral/vitamin mix before calving was associated with less blood (14.4 ± 2.9 vs. 22.4 ± 2.1%) and milk PMNL apoptosis (19.0 ± 1.1 vs. 26.4 ± 0.9%) near calving, presumably related to higher blood selenium concentrations. Both blood and milk PMNL apoptosis showed seasonal variation with the highest proportion of apoptotic cells between January and March (32.0 ± 6.1 and 34.6 ± 2.7%, respectively) and April and June (31.3 ± 5.7 and 37.8 ± 2.3%, respectively). Heifers losing 0.25 points or more of their body condition in the periparturient period had higher proportions of apoptotic blood PMNL in early lactation compared with heifers losing less than 0.25 points (24.0 ± 2.8 vs. 16.6 ± 1.7%). Milk PMNL apoptosis was less pronounced in quarters having teat orifices colonized with non-aureus staphylococci before calving (18.9 ± 1.0 vs. 29.4 ± 1.0%). The variation in blood PMNL apoptosis before and after calving mainly resided at the heifer level (71.4 and 98.4% of the total variation, respectively), whereas the variation in milk PMNL apoptosis mainly resided at the heifer (45.7% of the total variation) and quarter levels (45.5% of the total variation). These data imply that the impaired blood and milk PMNL viability in periparturient heifers can be reduced by optimization of certain heifer management practices such as supplementation of minerals/vitamins, and pasture and feeding strategies.     

The effect of intramammary antibiotic therapy at calving on udder health traits

The effect of intramammary antibiotic therapy at calving on mastitis infection prevalence, linear score milk somatic cell count, and milk NAGase activity, 30 d postpartum, and on milk production, 90 to 120 d postpartum, was tested. Cows (n = 175) were split into treatment and control groups at drying off. All cows received commercial dry cow therapy. At calving, treated cows received commercial lactating cow therapy in all quarters after the first two milkings; control cows were not treated. Composite milk samples were aseptically collected from all cows at drying off, calving, and 30 d postpartum. Udder health traits: linear score milk SCC, NAGase activity, and bacterial content in milk, were determined on all samples. The first three DHI milk weights were recorded for all cows. Treatment and control cows had similar prevalences of intramammary infections during the dry and 30-d postpartum periods. Least squares means of linear score milk SCC and NAGase activities were similar at drying off and calving. Cell count scores were similar between groups; NAGase activities were higher in control cows at 30 d postpartum. Control cows tended to produce more milk postpartum. Results demonstrated no advantage of intramammary therapy at calving in improving milk production or udder health.     

Effectiveness of an internal teat seal in the prevention of new intramammary infections during the dry and early-lactation periods in dairy cows when used with a dry cow intramammary antibiotic

The objectives of this study were to determine the effect of infusion with an internal teat seal at dry off, when used as an adjunct to long-acting antibiotic infusion at dry off, on the risk for acquiring a new intramammary infection (IMI) during the dry period, prevalence of IMI and linear score (LS) after calving, and risk for experiencing a clinical mastitis event between dry off and 60 DIM. A total of 437 cows from 2 dairy herds, with no clinical mastitis and 4 functional quarters, were enrolled at dry off. Prior to the final milking, all quarters were sampled for bacteriological culture and SCC analysis. After milking, all 4 quarters were infused with a commercially available long-acting dry cow antibiotic. Two contralateral quarters were then infused with an internal teat seal (Orbeseal, Pfizer Animal Health, New York). Following calving the teat seal was stripped out at first milking. Duplicate milk samples were collected between 1 to 3 DIM and again between 6 to 8 DIM for culture and SCC analysis. Quarters treated with Orbeseal had significantly lower prevalence of IMI at 1 to 3 DIM (tx = 22.8%, control = 29.1%), had significantly fewer quarters that acquired a new IMI between dry off and 1 to 3 DIM (tx = 20.2%, control = 25.4%), and had significantly fewer quarters affected by a clinical mastitis event between dry off and 60 DIM (tx = 5.9%, control = 8.0%). Multivariable analysis showed a significant effect of treatment, with treated quarters being 30% less likely to develop a new IMI between dry off and 1 to 3 DIM, 31% less likely to have an IMI present at 1 to 3 DIM, 33% less likely to experience a clinical mastitis event between dry off and 60 DIM, and having significantly lower linear score measures at 1 to 3 DIM and 6 to 8 DIM, compared with control quarters.