LACTATION CURVES AMONG CROSSES OF GALLA AND EAST-AFRICAN WITH TOGGENBURG AND ANGLO-NUBIAN GOATS

Morning milk yields of nursing does recorded at Ol'Magogo in Kenya fro m 1989 to 1992 were used to characterize goat lactation curves. Kids s uckled residual milk in the morning after milking and suckled unrestri cted in the evenings before being separated from their dams overnight. Consequently, these data represent milk yield surplus to kid nursing requirements that would be expected to be available to smallholder far m families for consumption or for sale. The goat breeds data were from straightbred East African (E), Galla (G) and their crosses with Togge nburg (T) and Angle Nubian (N): TXE, TXG, NXE, NXG, and TXEXNXG. Wood' s equation: Y-t=at(b)e(-ct) was fitted within each breed to estimate b reed type lactation curves. The Y-t represents the average morning mil k yield (kg) in week t of lactation; a, b, and c are parameters which determine the shape of the lactation curve, and e is exponential. Wood 's equation provided a good fit to the breed lactation curves with R(2 ) values from 85% to 92%. Lactation curve parameters differed among th e breed groups. The a values for combined indigenous E and G breeds, T XE, TXG, NXE, NXG, and TXEXNXG were: 0.345, 0.721, 0.813, 0.813, 0.733 , and 0.717 kg; b values were: 0.149, 0.292, 0.248, 0.216, 0.057, and 0.465; c values were: 0.082, 0.049, 0.042, 0.028, 0.014 and 0.066, and persistency values defined as - (b + 1) ln c were 2.87, 3.90, 3.96, 4 .35, 4.51 and 3.98, respectively. The estimated week of peak milk yiel d post kidding was: 2, 6, 6, 8, 4, and 7 weeks; and milk yield at peak was 0.347, 0.907, 0.908, 1.018, 0.750, and 1,116 kg/d, for combined E and G, TXE, TXG, NXE, NXG, and TXEXNXG, respectively. Season of kiddi ng effects were significant for all lactation curve parameters except for a. Does kidding in the hot dry season had a higher rate of increas e to peak yield and a greater lactation milk yield than does kidding i n the dry cold and wet seasons. The synchronization of breeding with s eason has a practical implication for the maximization of lactation yi eld when considered in combination with other biological and economic constraints. The superior production of the four-way cross, TXEXNXG, a nd the potential to increase productivity in later generations through selection, point to the significance of developing composite breed ty pes in developing countries to capitalize on the fitness of indigenous breeds and the high production potential of imported temperate breeds .