Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance

- Feeding sows ractopamine during their first lactation reduced body tissue loss.
- Ractopamine increased the number of sows expressing oestrus by day 10 post-weaning.
- Feeding sows ractopamine reduced milk protein and decreased piglet growth.

Excessive mobilization of body reserves during lactation delays the return to reproductive function in weaned primiparous sows. This study tested the hypothesis that supplementing the lactation diets of first-parity sows with ractopamine hydrochloride would reduce maternal weight loss and improve subsequent reproductive performance. Gestating gilts were allocated to one of two treatment groups (n = 30 sows/treatment), with one group fed a standard lactation diet (2.5 g/Mcal LYS: DE) throughout lactation (CTRL), whereas the treatment group received the standard lactation diet supplemented with 10 mg/kg ractopamine hydrochloride (RAC) from d 1 to 13 of lactation and 20 mg/kg RAC from d 14 of lactation until artificial insemination (AI). Weaning occurred on d 21 of lactation, with AI occurring at the first post-weaning estrus. Compared to CTRL, RAC supplementation decreased (P < 0.05) liveweight loss between d 13 and 20 of lactation (4.3 ± 0.90 versus 1.3 ± 0.96 kg), and tended to increase (P = 0.06) the number of second litter piglets born alive (9.5 ± 0.52 versus 8.1 ± 0.74). Treatment (RAC versus CTRL) reduced milk protein levels on d 13 and 20 of lactation (P < 0.05), and piglet weight gain between d 13 and 20 of lactation (260 ± 0.01 versus 310 ± 0.01 g/day, P < 0.01). In conclusion, it is evident that dietary RAC altered milk composition and stimulated conservation of maternal body reserves during the third week of lactation, resulting in a beneficial effect on subsequent reproductive performance.