Subclinical mastitis and milk production in primiparous Simmental cows.

The prevalence of subclinical mastitis in beef cows was investigated and its relationship with milk production and 205-d adjusted calf weaning weights (ADJWW) determined. Primiparous Simmental cows (n = 25) were milked six times at approximately 30-d intervals. Before each milking, milk samples were aseptically collected from each quarter for bacteriological analyses. After recording milk weights, samples were obtained for determination of somatic cell counts (SCC), butterfat (BF), and protein (PRO). Somatic cell counts were transformed to Dairy Herd Improvement Association linear scores for statistical analyses. Cows were retrospectively assigned to one of two groups based on their SCC linear score being either less than (LOSCC) or more than (HISCC) 4.5, which corresponded to a SCC of 292 x 10(3) cells/mL. Milk samples from 32% (8/25) of the cows and 18% (18/100) of the quarters were culture-positive for bacteria (Staphylococcus aureus, Streptococcus dysgalactiae, Streptococcus species, Actinomyces pyogenes, and[or] coagulase-negative Staphylococcus) at one or more times. Milk production was higher in LOSCC than in HISCC cows (6.3 +/- .2 vs 5.4 +/- .3 kg/24 h; P = .004). Mean SCC linear score tended to be negatively correlated with mean milk production over the entire study (r = -.36; P = .08). Adjusted weaning weights were similar between calves suckling LOSCC and HISCC cows (243 +/- 5 vs 236 +/- 10 kg; P = .57). In summary, milk SCC concentrations in primiparous Simmental cows were highly variable. Higher SCC concentrations were associated with lower milk production in cows.