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Lactating Holstein cows (n = 1100) from 93 dairy herds in Iowa, Wisconsin, Minnesota, and Illinois were genotyped at the bovine lymphocyte antigen DRB3.2 locus by a genotyping system that used polymerase chain reaction and restriction fragment length polymorphisms. Milk samples were obtained after routine processing at a Dairy Herd Improvement Association facility and returned to the National Animal Disease Center for DNA extraction. Somatic cells were used to classify cows that had acutely elevated SCC (one test of SCC > 500,000; group 1), or chronically elevated SCC (three consecutive tests of SCC > 300,000 or two consecutive tests of > 500,000; group 2), or that were eligible as controls. For each cow in groups 1 and 2, controls were selected that were matched for breed, lactation, herd, and days in lactation (+/-60 d). A conditional model for stepwise logistic regression was used to determine the relative odds for the 10 alleles with a frequency > 3%. No significant associations were observed when the 292 cows in group 2 were compared with their 292 controls. Allele *16 was associated with an increased risk of disease for cows classified with an acute SCC (258 cases and 258 controls). This study has identified DRB3.2*16 as a potential risk factor for acute intramammary infection and established the use of Dairy Herd Improvement Association milk samples as a source of DNA that is useful for genetic epidemiologic studies.

The study objective was to compare the efficacy of 3 commercial dry cow mastitis formulations regarding quarter-level prevalence of intramammary infections (IMI) postcalving, cure of preexisting infections over the dry period, prevention of new infections during the dry period, and risk for a clinical mastitis case between calving and 100d in milk (DIM). A total of 1,091 cows (4,364 quarters) from 6 commercial dairy herds in 4 different states (California, Iowa, Minnesota, and Wisconsin) were enrolled and randomized to 1 of the 3 treatments at dry-off: Quartermaster (QT; 1,000,000 IU of procaine penicillin G and 1 g of dihydrostreptomycin; Pfizer Animal Health, New York, NY), Spectramast DC (SP; 500 mg of ceftiofur hydrochloride; Pfizer Animal Health), or ToMorrow Dry Cow (TM; 300mg of cephapirin benzathine; Boehringer Ingelheim Vetmedica Inc., St. Joseph, MO). Quarter milk samples were collected for routine bacteriological culture before dry cow therapy treatment at dry-off, 0 to 6 DIM, and 7 to 13 DIM and an on-farm record-keeping system was used to retrieve data on clinical mastitis cases. Noninferiority analysis was used to evaluate the effect of treatment on the primary outcome, risk for a bacteriological cure during the dry period. Multivariable logistic regression techniques were used to describe the effect of treatment on risk for presence of IMI postcalving and risk of a new IMI during the dry period. Cox proportional hazards regression was used to describe the effect of treatment on the risk and time for quarters to experience an episode of clinical mastitis between calving and 100 DIM. The overall crude quarter-level prevalence of infection at dry-off was 19.2%. The most common pathogen isolated from milk samples at dry-off was coagulase-negative Staphylococcus, followed by Aerococcus spp. and other Streptococcus spp. Noninferiority analysis showed no effect of treatment on risk for a cure between dry-off and calving [least squares means (LSM): QT=93.3%, SP=92.6%, and TM=94.0%] and secondary analysis showed no effect of treatment on risk for presence of an IMI at 0 to 6 DIM (LSM: QT=16.5%, SP=14.1%, and TM=16.0%), risk for development of a new IMI between dry-off and 0 to 6 DIM (LSM: QT=14.8%, SP=12.3%, and TM=14.2%), or risk of experiencing a clinical mastitis event between calving and 100 DIM (LSM: QT=5.3%, SP=3.8%, and TM=4.1%). In conclusion, no difference was observed in efficacy among the 3 products evaluated when assessing the aforementioned quarter-level outcomes.

Cows (n = 139) were sampled within 17 d postpartum and monthly thereafter to examine dynamics of mammary infections and relationships between infection status, milk yield, SCC, NAGase activity, and chloride concentration. Forty-eight and 67% of cows and 19.5 and 30.5% of quarters were infected at first test and lactation end, respectively, with 51% of all infections present at first test. Coagulase-negative staphylococci accounted for 67 and 65% of first test and total infections with 85% persisting to lactation end. Animals with coagulase-negative staphylococci infections had significantly elevated quarter SCC and NAGase activity and a decrease of 821 kg mature equivalent lactation milk production compared with uninfected animals. Clinical cases with no bacterial isolation or major pathogen infections were associated with significant elevations in bucket and quarter milk SCC, NAGase activity, chloride concentration in quarters, and a decrease of 1153 kg mature equivalent lactation milk production as compared with uninfected animals. Correlations between milk production and in SCC and ln NAGase and between ln SCC and ln NAGase were -.15, -.25, and .55 (-.23, -.28, and .41 for first lactation only).

Background Coagulase negative Staphylococcus (CNS) species are currently the most prevalent intra-mammary pathogens causing subclinical mastitis and occasional clinical mastitis or persistent infection in lactating dairy cattle. More than 10 CNS species have been identified, but they are generally managed as one group on most dairies in the United States. However, improved management decisions and treatment outcomes may be achieved with better understanding of the prevalent species, pathogenicity and strain diversity within and across dairies. Methodology A total of 604 CNS isolates were cultured from milk samples collected during a dry-cow treatment clinical trial conducted on 6 dairy herds in 4 states in the US. All the study cows were randomized to receive 1 of the 3 different intra-mammary antimicrobial infusions (Quatermaster, Spectramast DC or ToMorrow Dry Cow) at dry-off. Milk samples were collected at dry-off, calving (0–6 days in milk, DIM), post-calving (7–13 DIM) and at mastitis events within the first 100 DIM. The CNS isolates were identified to species level by partial sequencing of the rpoβ gene, and genetic relatedness within species was investigated by phylogenetic analysis of the pulse-field gel electrophoresis profiles of the isolates. Results The major CNS species identified were S. chromogenes (48.3%), S. haemolyticus (17.9%), S. simulans and S. epidermidis (each at 6.5%). Other CNS species identified at lower frequencies included S. hominis, S. auricularis, S. sciuri, S. spp KS-SP, S. capitis, S. cohnii, S. warneri, S. pasteuri, S. xylosus, S. hyicus, S. equorum, S. microti, S. rostri, S. gallinarum, S. saprophyticus and S. succinus. Phylogenetic analyses of the major species types demonstrated an association between genetic relatedness and epidemiological distributions of S. chromogenes, S. simulans, S. haemolyticus and S. auricularis. Additionally, identical strains of S. chromogenes and S. simulans were isolated from the same udder quarter of several cows at consecutive sample stages. The rest of the minor species had no deducible genetic-epidemiological link. Discussion The observed association between genetic and epidemiological distributions indicated animal-adapted nature of four CNS species, suggesting possible host-adapted and environmental transmission of these species. Multi-stage isolation of the same udder quarter strain was evidence for chronic intra-mammary infection. Conclusion The different CNS species and strains circulating on US dairy herds were genetically diverse. Four species identified were likely udder-adapted pathogens, 2 of which caused persistent infection. Our findings are important in guiding the design of effective mastitis control strategies.