EFFECTS OF BOVINE SOMATOTROPIN ON THE PATTERN OF MILK YIELD WITHIN AND BETWEEN INJECTION INTERVALS IN WEST AFRICAN DWARF GOATS

Abstract

Twenty-four West African Dwarf (WAD) goats were used to study the pattern of milk yield response torecombinant bovine somatotropin (rbST) administered in a sustained-delivery vehicle. The goats weredivided equally into four treatment groups, each comprising of six does. The first group (control, T0)received no rbST while the other groups received rbST (T1, 20 mg; T2, 40 mg; T3, 60 mg) injected at 2-week intervals commencing from the 7th week postpartum for 6 weeks. Pattern of milk yield responseto rbST was significantly (p<0.05) influenced by rbST dose, day from rbST treatment, order of rbSTtreatment and parity. Milk yield of treated goats increased from day 1 of treatment, peaked betweenday 5 and day 8 after treatment and progressively decreased until day 14 of treatment but that of thecontrol decreased progressively from day 1 till day 14 of treatment. The mean relative response ofDMY to rbST treatment for T1, T2 and T3 exceeded T0 by 50.36, 68.00 and 71.16 % respectively andsignificantly affected the shape of the lactation curve, thus, improving persistency of lactation. Thepatterns of DMY for T1, T2 and T3 were well-fitted by the Wood’s equations: Y = 16.628n1.728e-0.439n (R2= 63.1), Y = 25.198n0.836e-0.239n (R2 = 75.6) and Y = 0.008n9.081e-1.352n (R2 = 42.3) respectively. Theadministration of 40 mg dose of rbST appears to elicit DMY response that favoured milk yield persistency.But since highest DMY was observed with 60 mg dose of rbST, estimation of optimal dose thatwould elicit maximum DMY response may be required in order to validate the statement. Our findingssuggest that rbST administration to WAD goats after peak of lactation can enhance milk yield, galactopoiesisand persistency of lactation indicating higher milk yield in extended lactation.