Production responses to bovine somatotropin in northeast dairy herds

The commercial response to bovine somatotropin was examined in northeast da iry herds from 1990 to 1998 (4-yr preapproval and 4-yr postapproval). With DHI records and Monsanto customer files, a control group (never purchased P osilac) and a bovine somatotropin (bST) group (used on at least 50% of cows ) were identified. A total of 340 herds were involved and, over the 8-yr pe riod, there were over 80,000 cows, 200,000 lactations, and 2 million test d ays. Herd management comparisons demonstrated the response to bST was relat ively constant each year of the postapproval period. Assuming 100% of cows were supplemented, response to bST over a 305-d lactation equaled 894 kg of milk, 27 kg of milk fat, and 31 kg of milk protein. Comparisons of lactati on curves were used to identify where the bST response occurred in the lact ation cycle. Analysis demonstrated the responses in milk, milk fat, and pro tein yield were minimal in the early phase of lactation, and then gradually increased until reaching a plateau over the last half of the lactation cyc le. Persistency of lactation was also improved by bST, indicating the oppor tunity exists to Extend lactation with combined use of bST and altered repr oductive management. Average age and days in milk did not differ between co ntrol and bST herds. Thus, stayability and herd-life of animals were not al tered by bST treatment. Somatic cell count (SCC) linear scores were minimal ly affected in herds utilizing bST and the pattern of SCC over the lactatio n cycle was unaffected. Overall bST improved lactation yield and persistenc y consistently over the 4-yr postapproval period with no effects on cow sta yability and herd-life.