A study of factors influencing reproductive efficiency in the pig with particular emphasis on the role of artificial insemination
Three studies were conducted on commercial farms. Study 1 sought to compare four combinations of natural mating (NM) and AI, namely AI + AI, AI + NM, NM + AI and NM + NM (first mating on day 1 of oestrous and second on day 2), and evaluate what aspects of insemination quality are related to fertility. The respective farrowing rates (FR) of AI + AI, AI + NS, NS + AI and NS + NS were (number of sows in parentheses) 92.9% (141), 89.6% (134), 89.3% (140) and 89.0% (100) and litter size (LS) was 11.31, 10.49, 11.50 and 10.61 (total births). The number of pigs born per 100 sows mated were 1051, 940, 1027 and 944. Both FR (P < 0.05) and LS (P < 0.01) were significantly influenced by parity. Sow behaviour during insemination significantly influenced (P < 0.01) FR and LS, the mean FR of calm and agitated sows being 91.3 and 83.1 percent and the mean LS being 11.32 and 10.22 respectively. Loss of semen due to backflow during insemination significantly reduced (P < 0.05) FR in sows having one AI. Backflow losses were significantly lower (P < 0.01) in calm than in agitated sows. It was concluded that AI, either alone or in combination with NM, yields fertility results comparable to NM alone and that sow behaviour during insemination has an important effect on sow fertility. Study 2 tested the effect of the addition of 5 i.u. of oxytocin to semen immediately before AI on fertility at two farms. Overall oxytoxin significantly improved FR (P < 0.05) from 73.2 percent (429) to 79.5 percent (385) and substantially improved litter size from 10.70 to 11.18. There was a significant (P < 0.05) treatment x farm interaction, FR on farm A improving from 77.2% (control) to 78.0% (oxytocin) whereas FR on farm B improved from 69.7% (control) to 84.0% (oxytocin). It was hypothesised that differences between farms in operator skill during insemination may have mediated the differing response to oxytocin.