Effect of oestrus number of nulliparous sows at first service on first litter and lifetime performance

Current industry recommendations are to mate gilts on their second or third oestrous cycle (heat) to ensure that they have reached sufficient maturity and have adequate body reserves in order to sustain reproductive performance over subsequent parities. Delaying breeding has the financial implications of increased non-productive days and extra feed costs. However, these could be offset by increased fertility and/or increased lifetime productivity. The aim of this study was to investigate the effect of heat number (oestrous cycle number) on which gilts where mated on first litter and lifetime performance. In total, 157 gilts born between 2002 and 2006 were mated on either their 1st, 2nd, 3rd, 4th or 5th observed standing oestrus. Litter and reproductive data were collected on a continual basis until all animals had completed their commercial reproductive life. Sows were culled as of normal commercial practice and reason for culling was classified into groups. There was no effect (P>0.05) of oestrus number at first service on first litter performance (numbers of piglets born alive, dead, total born, average birth weight or pre weaning mortality). There was also no effect (P>0.05) on sow performance in the first lactation (feed intake during lactation, weight change during lactation or weaning to service interval). However, over their lifetime, gilts served on their fourth and fifth oestrus had significantly fewer numbers of piglets born alive (P<0.001) and weaned (P<0.001) and gilts served on their fifth oestrus also completed fewer parities compared with gilts served on their first, second or third oestrus. Gilts served on their third oestrus had the greatest (P<0.001) number of piglets born alive and weaned over their lifetime but completed a similar number of parities to those gilts mated on their first, second and fourth oestrus. However, there was no significant effect (P>0.05) of oestrus number at first service on the total weight of piglets born alive, dead or weaned over the sow's lifetime. There was no significant effect (P>0.05) of oestrus number at first service on reason for culling but there was on the culling rates of the sows between parities (P<0.05). This research found that the oestrus number that gilts are first mated on affects their lifetime performance and would suggest that the third oestrus is the optimal oestrus to mate gilts, as this resulted in these gilts producing significantly more (P<0.05) piglets over their lifetime.