Altrenogest treatment before weaning improves litter size in sows.

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The study aimed to assess whether altrenogest treatment, fed before weaning (from -8 to -2days), could improve fertility of sows showing reproductive seasonality. Ninety sows (50 in winter-spring [WS] and 40 in summer-autumn [SA]) were randomly selected and assigned to control (C; 27 in WS and 20 in SA) or altrenogest treatment (A; 23 in WS and 20 in SA) groups. The diameter and number of ovarian follicles were transrectally scanned at the onset of oestrus. Oestrus was evaluated twice daily from weaning to day 8 post-weaning. Sows in oestrus were post-cervically inseminated at 0 and 24hr after the onset of oestrus with liquid stored semen (1.5×109 sperm/doses), and farrowing rates (FR) and total piglets born (LS) were recorded. More (p<.01) sows showed no signs of oestrus within 8days after weaning in SA (30%) than in WS (2%), without differences between A and C groups. The diameter (cm) of the follicles at the onset of oestrus was larger in A than in C sows (0.76±0.01 vs 0.73±0.01; p<.01), irrespective of the season. No differences in the number of follicles were found. FR did not differ between seasons and groups, being always above 85%. LS was larger (p<.01) in A (14.00±0.46) than C (12.27±0.44) sows, irrespective of the season. In conclusion, a short-term altrenogest treatment at the end of lactation improves the total number of piglets born from weaned sows, probably by promoting a better and more homogeneous follicular development at the start of oestrus.