Effects of genetic and non genetic factors on sow performance – a case of an imported multiplier herd in 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 most suitable as a terminal sire breed crossed to the Large White*Landrace F1 gilts for the production of fattener pigs. In the hot dry season boar fertility is poorest and could be enhanced by sprinkling the animals with cold water. Wet feeding could be practiced to encourage feed intake in sows. Both interventions would mimic conditions prevailing in the post rain season where optimal NBA and ABWT are recorded due to cool temperatures and less dry air. When a farmer practices on-farm rearing and selection of replacement gilts it is important to take parity as one of the most important criteria for selection. Gilts below parity 3 should not be considered for breeding replacement gilts as their records are not fully dependable. On the other hand, poorly performing gilts in terms of NBA and ABWT can still do better if allowed to grow to maturity rather than being culled; hence culling decision should be less hush for gilts.