T.N Mangwiro - Department of Animal Science, Faculty of Agriculture and Environmental Science, Bindura University of Science Education P Bag ۱۰۲۰ Bindura, Zimbabwe
M Dhliwayo - Department of Animal Science, Faculty of Agriculture and Environmental Science, Bindura University of Science Education P Bag ۱۰۲۰ Bindura, Zimbabwe
T.J Mandere - Department of Animal Science, Faculty of Agriculture and Environmental Science, Bindura University of Science Education P Bag ۱۰۲۰ Bindura, Zimbabwe

Effects of genetic and non-genetic factors on traits of economic importance in pigs at an imported multiplier herd in Zimbabwe were studied using data collected from 1166 litters. The traits studied were number of piglets born alive (NBA) and average birth weight (ABWT). The independent variables in the study were breed of boar (BOB), breed of sow (SOWBRD), parity, season of farrowing (SOF) and year of farrowing (YOF). The season was classified into four categories namely, cold dry (May, June, July), hot dry (August, September, October), post rain season (Late February, March, April), and hot wet season (November, December, January and early February). Data were analyzed using the general linear models (GLM) of the statistical analysis software (SAS). NBA and ABWT were significantly higher for the mid-parities (2 to 7) than for the first parity and later parity (8 and above) sows. NBA was significantly lower in the hot wet season than at any other time of the year and the litters came from mating done in the hot dry months of August, September and October. Average birth weights were significantly lower in the hot dry season, the period where NBA was largest. Different breeds reached peak productivity at different parities. The Landrace breed recorded the highest NBA, whereas Duroc sows produced litters with the highest ABWT. The conclusion from this study is, the Large White and the Landrace breeds are ideal dam lines for the traits NBA and ABWT, and a cross between the two would further exploit heterosis effects for the reproductive traits which are known to be lowly heritable.The Duroc breed, excellent in carcass traits such as weight, is mostsuitable as a terminal sire breed crossed to the LargeWhite*Landrace F1 gilts for the production of fattener pigs. In thehot dry season boar fertility is poorest and could be enhanced bysprinkling the animals with cold water. Wet feeding could bepracticed to encourage feed intake in sows. Both interventions wouldmimic conditions prevailing in the post rain season where optimalNBA and ABWT are recorded due to cool temperatures and less dryair. When a farmer practices on-farm rearing and selection ofreplacement gilts it is important to take parity as one of the mostimportant criteria for selection. Gilts below parity 3 should not beconsidered for breeding replacement gilts as their records are notfully dependable. On the other hand, poorly performing gilts in termsof NBA and ABWT can still do better if allowed to grow to maturityrather than being culled; hence culling decision should be less hushfor gilts.

Birth weight, Breed, Parity, Season, Sow