Selective Dry Cow Therapy as a Tool to Decrease the Use of Antimicrobial Drugs in Dairy Farms

The objective of this study was to evaluate the effect of selective dry cow therapy (SDCT) strategies based on two different algorithms compared with blanket dry-cow therapy on udder health, milk yield, and culling in herds not using internal teat sealant. Cows from 2 commercial farms in west Texas were randomized into three different groups: Algorithm 1 (ALG1; N = 455) cows treated with an intramammary antimicrobials infusion at dry-off if SCC > 200,000 cells/mL at any test date or had 2 or more cases of clinical mastitis during the current lactation; Algorithm 2 (ALG2; N= 458) cows treated with an intramammary antimicrobials infusion at dry-off if SCC > 200,000 cell/mL at last test date or any case of clinical mastitis during the enrollment lactation; Control cows (CON = 447) received blanket dry cow therapy. Milk yield and somatic cell count linear score (LSCC) during the first 6 months of lactation were analyzed using repeated measures ANOVA models, while Cox’s Proportional Hazards models were fitted to culling and clinical mastitis data. The farm was fitted as a random effect in all models. The percentage of cows receiving dry cow therapy was 51.3, 24.7, and 100% for ALG1, ALG2, and CON, respectively. The parity by time interaction term was retained in the model evaluating the effect of treatment on LSCC. Among primiparous, LSCC was lower for CON cows in comparison to ALG1 and ALG2 counterparts. Treatment did not affect LSCC among multiparous cows. Milk production was not different between ALG1 and ALG2 cows, and ALG1 and CON cows, but it tended to be lower for ALG2 cows in comparison to CON counterparts. Treatment did not affect clinical mastitis incidence and culling. In conclusion, although the SDCT strategies did not lead to an increased incidence of clinical mastitis and culling, they led to increased LSCC in primiparous cows. Also, numerical decreases in milk production were observed in cows receiving selective dry cow therapy.