Authors: I.J. JAMES, O.A OSINOWO, O.F. SMITH , M.N. BEMJI, P.I. REKWOT
Journal of Agricultural Science and Environment 2277 – 2755, 2010
Abstract
Optimal dose of bovine somatotropin (bST) in a sustained-delivery vehicle required for maximum milk yield response was estimated in twenty-four lactating West African Dwarf (WAD) goats in three 14-day periods using quadratic equation. The goats were divided equally into four treatment groups, each comprising six does. The first group (control, T ) received no bST while the other groups received bST (T , 20 mg; T 40 mg; T , 60 mg) injected at 2-week intervals commencing from the 7th week postpartum for 6 weeks. Does were milked twice daily (7:30 am and 7:30 pm) and milk yield recorded daily. Daily milk yield response (DMY) to bST was significantly (p<0.001) influenced by bST dose, day from bST treatment and parity during the 2nd period of bST treatment but only bST dose and parity significantly influenced (p<0.001) DMY during the 1st and 3rd periods of bST treatment. The mean relative response of DMY of bST-treated goats exceeded the control by 48 – 78 % in the entire periods of bST administration. Highest predicted response of 80.5 % in the 3rd period and lowest response of 66.2 % in the 1st period of bST treatment (when compared to the control) were observed, thus indicating that bST positively affected the shape of the lactation curve for possible higher yield in extended lactation. Although, the trend of observed and predicted optimal doses of bST needed for maximum DMY were well-fitted by the Quadratic equation during the three periods of bST treatment, it varied inconsistently with periods of bST treatment (stages of lactation). Therefore, the uniform optimal dose of 50.71 mg per 2 weeks estimated by quadratic equations; Y = 141.318 + 4.097X – 0.041X , R = 99.90), Y =100.912 + 2.926X – 0.030X , R = 99.49 and Y = 5935.420 172.071X – 1.735X , R = 99.49 and needed for maximum DMY of 242.86 ml, relative DMY of 74 % and cumulative milk yield response of 10214.29 ml respectively over the entire periods could be adopted in West African Dwarf goats in order to reduce the complexity of differential injections administered with respect to stages of lactation.