Genetic and environmental aspects of reproductive perforhance and pre-weaning growth of three pig breeds in large-scale herds in Kenya
Data on reproductive performance and pre-weaning growth of pigs from three large scale herds in Kenya were studied to evaluate means and the effects of genetic and environmental factors on sow and piglet performance. The data comprised 1646 Landrace, Large White and Hampshire litter records from Zea, Ngata and Lanet herds and 2861 Landrace and Large White weaner records from Lanet. The records spanned a period of 15 years (1975-89). Sow traits studied were litter size at farrowing (LSF) and at weaning (LSW), litter weight at 3 weeks (LW3), litter weight at weaning (LWW) , average piglet weight at birth (ABW) and at weaning (AWW) and farrowing interval (FI). Piglet traits studied were weaning weight (Ww) and pre-weaning average daily gain (ADG). Litter size at farrowing averaged 9.78±2. 42 in Large White sows from Lanet, 8.79±2.41 ln Landrace sows and 7.08±2.64 in Hampshire sows. Litter size at weaning averaged 8.09±1.61 and 7.47±1.40 in Large White sows from Lanet and Landrace sows respectively. Piglet weight at birth averaged 1.45±.19 kg in Large White sows from Lanet, 1.46±.22 kg in Landrace sows and 1.53±.29 kg ln Hampshire sows. The farrowing interval, average litter weight at weaning and average piglet weight at weaning in Landrace sows were 194.46±33.08 days, 95.40±23.50 kg and 12.94±2.4S kg respectively. Landrace piglets grew faster and were heavier (P<O.Ol) at weaning than Large White piglets. Entire males excelled both females and castrates in growth rate and average weaning weight. Parity effects were significant for LSF, FI and litter weights. LSF peaked in the third and fourth parities in the Large White and Landrace sows respectively. Year and season of farrowing influenced growth traits and LSW. Growth performance and litter size at weaning declined in the latter half of the periods studied in the herds at Lanet and 2ea. Inbreeding depression was considered a likely rea~on for t~e decline. At Lanet piglets born between September a~d March grew faster and were heavier (P<O.Ol) at weaning than those born during the rest of the year but the interaction between year and season of birth was significant. Heritability estimates from paternal half-sibs were O.21±.08, O.19±.08, O.13±.07, O.15±.08, O.17±.08, O.23±.09 and O.43±.12 for AEH, L\>,13, LF",yand FT- , respectively, in the Landrace breed. Heritability and repeatability estimatEs for reproductive traits we r s generally low. Genetic correlations between litter size and litter weights ranged from O.94±.10 to O.96±.04, while the corresponding phenotypic correlations ranged from 0.50 to O. 7~, . were positive and high. It was concluded that selection for hi9h L1--Dwou Ld be expected to improve Lr".,lI~.