ESTIMATION OF OPTIMAL DOSE OF BOVINE SOMATOTROPIN FOR MAXIMUM MILK YIELD RESPONSE IN WEST AFRICAN DWARF GOATS

Abstract

Optimal dose of bovine somatotropin (bST) in a sustained-delivery vehicle required for maximum milkyield response was estimated in twenty-four lactating West African Dwarf (WAD) goats in three 14-dayperiods using quadratic equation. The goats were divided equally into four treatment groups, eachcomprising six does. The first group (control, T0) received no bST while the other groups received bST(T1, 20 mg; T2, 40 mg; T3, 60 mg) injected at 2-week intervals commencing from the 7th week postpartumfor 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 frombST treatment and parity during the 2nd period of bST treatment but only bST dose and parity significantlyinfluenced (p<0.001) DMY during the 1st and 3rd periods of bST treatment. The mean relativeresponse of DMY of bST-treated goats exceeded the control by 48 – 78 % in the entire periods of bSTadministration. 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 thatbST 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 werewell-fitted by the Quadratic equation during the three periods of bST treatment, it varied inconsistentlywith periods of bST treatment (stages of lactation). Therefore, the uniform optimal dose of 50.71 mgper 2 weeks estimated by quadratic equations; Y = 141.318 + 4.097X – 0.041X2, R2 = 99.90), Y =100.912 + 2.926X – 0.030X2, R2 = 99.49 and Y = 5935.420 + 172.071X – 1.735X2, R2 = 99.49 andneeded for maximum DMY of 242.86 ml, relative DMY of 74 % and cumulative milk yield response of10214.29 ml respectively over the entire periods could be adopted in West African Dwarf goats in orderto reduce the complexity of differential injections administered with respect to stages of lactation.