Twenty-four Bos indicus cows of the Mashona/Nkone breeds, 36 dairy crossbreds (Mashona/ Nkone x Friesian), 48 Holsteins, 42 Friesians and 25 Jerseys were used to study the effect on milk production of sometribove (500 mg), a prolonged release formulation of bovine somatotropin (BST). BST was administered at 14-day intervals by subcutaneous injections into the ischio-rectal fossa which lies lateral to and on either side of the anus (tailhead). With the exception of the Bos indicus cows, which received seven injections of BST, all other treated cows received eight.
The administration of BST to Bos indicus cows, significantly (P < 0·05) increased milk yield from 0·45 to 1·75 kg/cow per day, and extended lactation. These effects combined to increase total milk production during the 14-week trial from 226 kg for the control group to 993 kg for the group treated with BST. With dairy crossbreds the use of BST significantly (P < 0·01) increased milk yield from 8·6 to 11·0 kg/cow per day. Milk composition for Bos indicus and dairy crossbreds wasunaffected by the administration of BST
BST significantly (P < 0·05) increased milk yield in Jersey (+ 2·9 kg/day), Friesian (+ 3·6 kg/day) and Holstein (+ 2·7 kg/day) cows. Bodycondition of treated cows tended to be slightly lower than that of the control cows at the end of treatment.
Cows remained in excellent health throughout all the trials. Farmers commented on how easy the injection was to give in the tailhead site, and on the complete absence of any adverse injection site reaction.