EFFECTS OF LONG-TERM RECOMBINANT BOVINE SOMATOTROPIN (BST) ADMINISTRATION ON MILK-YIELD, MILK-COMPOSITION AND MAMMARY-GLAND HEALTH OF DAIRYEWES

The present investigation was carried out to test the effects of recom binant bovine somatotropin (bST) on galactopoiesis and mammary gland h ealth of the ewe. Twenty-two polytocous lactating Chios ewes were assi gned 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 prol onged release formulation, from the fifth day after delivery until the end of lactation. All animals were fed the same ration. Supplementati on 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 c ontent (%) 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 wit hout 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 contro l group. This difference was significant (P < 0.05) only after the eig hth fortnight after delivery. Differences between groups concerning th e prevalence of bacteriologically positive milk samples were not signi ficant (P > 0.05). Coagulase-negative staphylococci were the predomina nt 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. (C) 1998 Elsev ier Science B.V. All rights reserved.