Lactation curves among crosses of Galla and East African with Toggenburg and Anglo Nubian goats

Abstract

Morning milk yields of nursing does recorded at Ol'Magogo in Kenya from 1989 to 1992 were used to characterize goat lactation curves. Kids suckled residual milk in the morning after milking and suckled unrestricted 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 farm families for consumption or for sale. The goat breeds data were from straightbred East African (E), Galla (G) and their crosses with Toggenburg (T) and Anglo Nubian (N): TxE, TxG, NxE, NXG, and TXEXNXG. Wood's equation: Y t = at b e − ct was fitted within each breed to estimate breed type lactation curves. The Y t , represents the average morning milk 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 the breed groups. The a values for combined indigenous E and G breeds, TXE, 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 yield 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 kidding effects were significant for all lactation curve parameters except for a. Does kidding in the hot dry season had a higher rate of increase to peak yield and a greater lactation milk yield than does kidding in the dry cold and wet seasons. The synchronization of breeding with season has a practical implication for the maximization of lactation yield when considered in combination with other biological and economic constraints. The superior production of the four-way cross, TXEXNXG, and the potential to increase productivity in later generations through selection, point to the significance of developing composite breed types in developing countries to capitalize on the fitness of indigenous breeds and the high production potential of imported temperate breeds.