Restricted feed intake in lactating primiparous sows. I. Effects on sow metabolic state and subsequent reproductive performance

The effects of feed restriction (60% of anticipated feed intake; Restrict; n = 60) during the last week of a 21-day lactation in primiparous sows compared with feeding at 90% of anticipated feed intake (Control; n = 60) on sow metabolic state, litter growth and sow reproductive performance after weaning were compared. Metabolisable energy (ME) derived from feed was lower, ME derived from body tissues was higher and litter growth rate was reduced (all P < 0.05) in Restrict sows during the last week of lactation. Treatment did not affect weaning-to-oestrus interval, pregnancy rate, ovulation rate, embryonic survival or the number of live embryos (P > 0.05) at Day 30 of gestation: However, embryo weight was greater (P < 0.05) in Control than in Restrict sows (1.55 ± 0.04 vs 1.44 ± 0.04 g, respectively). These data suggest the biology of the commercial sow has changed and reproductive performance of contemporary primiparous sows is increasingly resistant to the negative effects of lactational catabolism. Overall, catabolism negatively affected litter weaning weight and embryonic development of the next litter, but the extent to which individual sows used tissue mobilisation to support these litter outcomes was highly variable.

Restricted feed intake in lactating primiparous sows. II. Effects on subsequent litter sex ratio and embryonic gene expression

Expression of panels of candidate genes controlling myogenesis, angiogenesis and gender-specific imprinting of development were analysed in embryonic, placental and endometrial tissues recovered at Day 30 of gestation from a subset of primiparous sows that were either feed restricted (Restrict; n = 17) or fed to appetite (Control; n = 15) during the last week of the previous lactation. Embryos were also sex typed to investigate gender bias in response to treatments. Average embryonic weight was lower in the subset of Restrict compared with Control litters (1.38 ± 0.07 vs 1.59 ± 0.08 g, respectively) and the male : female sex ratio was higher (P < 0.05) in embryos (litters) recovered from Restrict sows. Treatment affected (P ≤ 0.05) the expression of embryonic and placental genes involved in insulin-like growth factor (IGF) 2 signalling, including IGF2, INSR and IGF2R. Embryonic expression of ESR1 was also affected by treatment (P < 0.03) and sex × treatment interactions were observed for the expression of embryonic ESR1 (P < 0.05) and placental ANGPT2 (P < 0.03). At the molecular level, these results support the suggestion that changes in placental function are not the primary mechanism mediating detrimental effects of previous sow catabolism on early embryonic development in the feed-restricted lactational sow model. However, perturbations in the IGF2 system are implicated as mediators of these effects.

Nutritional restriction in lactating primiparous sows selectively affects female embryo survival and overall litter development

This study explored the possibility of sex-specific effects on embryonic survival in primiparous sows subjected to restricted feed intake during the last week of lactation and bred after weaning (Restrict; n = 16), compared with control sows fed close to ad libitum feed intakes (Control; n = 17). Restrict sows were in a substantial negative net energy balance at weaning, and lost 13% of estimated protein and 17% of fat mass during lactation, yet the weaning-to-oestrous interval and ovulation rate were not different between treatments. However, embryonic survival at Day 30 of gestation was lower (P < 0.05) in Restrict than Control sows, and selectively reduced the proportion of female embryos surviving (P < 0.01). A decrease in weight and crown–rump length of surviving female (P < 0.05) and male (P < 0.05) embryos was seen in Restrict litters. The mechanisms mediating this sex-specific effect on embryonic loss in feed-restricted sows are unclear. The data presented here indicate that feed-restriction during the last week of lactation in primiparous sows causes a selective decrease in survival of female embryos and limits the growth of all surviving embryos.