SUBCLINICAL MASTITIS AND MILK-PRODUCTION IN PRIMIPAROUS SIMMENTAL COWS

The prevalence of subclinical mastitis in beef cows was investigated a nd its relationship with milk production and 205-d adjusted calf weani ng weights (ADJWW) determined. Primiparous Simmental cows (n = 25) wer e milked six times at approximately 30-d intervals. Before each milkin g, milk samples were aseptically collected from each quarter for bacte riological analyses. After recording milk weights, samples were obtain ed for determination of somatic cell counts (SCC), butterfat (BF), and protein (PRO). Somatic cell counts were transformed to Dairy Herd Imp rovement Association linear scores for statistical analyses. Cows were retrospectively assigned to one of two groups based on their SCC line ar score being either less than (LOSCC) or more than (HISCC) 4.5, whic h 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-posi tive for bacteria (Staphylococcus aureus, Streptococcus dysgalactiae, Streptococcus species, Actinomyces pyogenes, and[or] coagulase-negativ e 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 mi lk production over the entire study (r = -.36; P = .08). Adjusted wean ing weights were similar between calves suckling LOSCC and HISCC cows (243 +/- 5 vs 236 +/- 10 kg; P = .57). In summary, milk SCC concentrat ions in primiparous Simmental cows were highly variable. Higher SCC co ncentrations were associated with lower milk production in cows.