Effects of age and growth rate at onset of boar exposure on oestrus manifestation and first farrowing performance of Landrace×large white gilts

The objective of this study was to evaluate the effects of age and growth rate until the onset of boar exposure on oestrus manifestation and reproductive performance in Landrace×large white crossbred gilts (DanBred). Gilts were retrospectively classified into groups according to age at boar exposure - BE (140-155 and 156-170 days) and in three classes of growth rate (GR) at BE (low GR: 500-575 g/d; intermediate GR: 580-625 g/d; and high GR: 630-790 g/d). Overall, gilts had an average weight of 105.4±0.53 kg and age of 170.6±0.41 days at their first oestrus. There was no significant effect of age×GR interaction (P>0.05) on weight and age at first oestrus, interval between boar exposure and oestrus (BEOI), and percentages of gilts showing oestrus. Gilts exposed at 140-155 days of age showed oestrus at a lower age (167.6±0.76 vs. 173.7±0.73 days) but with similar BEOI (15.1±0.75 vs. 14.2±0.73 days) and weight (104.7±1.04 vs. 105.5±1.00 kg) compared with gilts exposed at 156-170 days (P<0.05). Gilts exposed to boar at 140-155 days had lower oestrus manifestation (60.8% vs. 77.0%) within 30 days than those exposed at 156-170 days of age. High GR gilts showed the first oestrus at a lower age (169.3±0.78 vs. 172.1±0.82 days of age) and had a shorter BEOI (13.5±0.77 vs. 16.0±0.81 days) than low GR gilts (P<0.05). Lower percentages of gilts in oestrus within 30 days after BE (P<0.05) were observed in low GR and intermediate GR gilts (65.5 and 64.3%) than in high GR gilts (74.3%). Farrowing rate and number of total born piglets were neither affected by age and GR at onset of boar exposure nor by their interaction (P>0.05). In conclusion, first oestrus manifestation is greater when gilts are exposed to boars after 155 days of age or with a GR>625 g/d. Provided that gilts are bred with a minimum of 130 kg, the reproductive performance is not affected by age or GR at boar exposure.