Effects of intramammary infection and parity on calf weaning weight and milk quality in beef cows

The objectives of this study were to determine 1) the effect of intramammar y infection on calf weaning weight, milk somatic cell count, and milk compo sition, and 2) the effect of parity on percentages of infected cows, infect ed quarters, and blind quarters. The number of infected quarters, milk soma tic cell counts, milk components, and intramammary infection were studied a t weaning in 164 beef cows. The percentage of infected cows ranged from 61. 9% at first parity to 66.7% at fifth to ninth parities. Cows with three or four infected quarters had higher (P < .01) milk somatic cell counts than c ows with zero, one, or two infected quarters. Among bacterial isolates, Sta phylococcus aureus-infected quarters had the highest (P < .01) milk somatic cell count. Percentages of butterfat and lactose were lower (P < .01) in m ilk from infected quarters than from uninfected quarters. Infections by S. aureus and coagulase-negative staphylococci were the most common and accoun ted for 67 to 78% of the infections. Percentages of infected quarters and i nfections caused by S. aureus increased with parity (P < .01). Intramammary infections did not affect (P > .10) calf weaning weight. In conclusion, in tramammary infection had no effect on calf weaning weight but increased mil k somatic cell count and decreased the percentage of protein, lactose, soli ds-not-fat, and butterfat. The number of infected and blind mammary quarter s increased with parity.