Variation i fruktsamhet hos semingaltar

Abstract: Artificial insemination (AI) has had a great influence on the development of pig production and is today widely practiced (Gerrit et al., 2005). With AI, genetic progress can at a short period of time be spread worldwide compared with using natural service and the best boars can be intensively used. This is also one of the biggest risks with AI; the impact of semen containing a genetic disease or contamination of pathogens can be enormous. Fortunately, it is a small risk of disease transmission due to many tests of the boars and the semen before use (Maes et al, 2008). It is important that the boars used for insemination have good breeding values along with good reproduction features and have good fertility results (Robinson et al., 2005). Furthermore, it is of economical interest that they produce high quality ejaculates with high number of sperms (Wierzbicki et al., 2010). The impact of the male´s reproductive efficiency, which is very important for the insemination industry, is not easily predicted (Robinson et al., 2005). The aim of this study was, with data on litter size and remating incidence from inseminated sows, analyze the variation in fertility among AI-boars from two different breeds, Landrace and Yorkshire. A second aim was to investigate if there are effects of season or parity number on fertility traits.The sows’ first litter had the lowest total number of total born piglets and live-born piglets. The total number of born piglets increased to the fifth litter. Highest litter size was found during late spring and early summer and the lowest during autumn. The results showed no effect of heterosis on litter size; instead the purebred litters of Landrace had the highest litter size. This is probably due to selection in the nucleus herds of secondary sows for crossbreeding and superior sows for purebreeding. Highest remating incidence was after weaning of the first litter. Among the 500 boars (with >50 litters in the data) which were analyzed for remating incidence, 2.6 % had none. There was a significant negative correlation between remating incidence and litter size for boars of both breeds. In comparison there was no significant correlation between remating incidence and number of stillborn piglets in the litter.