Effects of long-term recombinant bovine somatotropin (bST) administration on milk yield, milk composition and mammary gland health of dairy ewes

Abstract

The present investigation was carried out to test the effects of recombinant bovine somatotropin (bST) on galactopoiesis and mammary gland health of the ewe. Twenty-two polytocous lactating Chios ewes were assigned into two groups (11 in control group and 11 in treatment group). Treated ewes were injected every second week with 160 mg bST in a prolonged release formulation, from the fifth day after delivery until the end of lactation. All animals were fed the same ration. Supplementation with bST significantly ( P<0.05) increased the 6% FCM (22.21% over the controls) without changing the duration of the lactating period. Fat and protein content of milk (%) increased ( P<0.05) and lactose content (%) decreased ( P<0.05) as lactation progressed in both groups. Differences in the above mentioned contents between groups were not significant ( P>0.05). Mean Somatic Cell Count (SCC) from animals without subclinical mastitis were progressively increased ( P<0.05) from weaning to the end of lactation in both groups, but the mean SCC from the bST group were found to be higher compared with that of the control group. This difference was significant ( P<0.05) only after the eighth fortnight after delivery. Differences between groups concerning the prevalence of bacteriologically positive milk samples were not significant ( P>0.05). Coagulase-negative staphylococci were the predominant organisms isolated from milk samples in both groups. Prevalence of subclinical mastitis was unaffected after bST administration ( P>0.05) although treated animals tended to show higher rates.