Effect of a low-protein diet during mid-to-late gestation on reproductive performance and serum amino acid profiles in sows

Low-protein (LP) diets have been proposed as a strategy for animal production to conserve protein resources and reduce environmental nitrogen pollution. The aim of this study was to investigate the effect of a LP diet during gestation on the reproductive performance, serum amino acid concentrations, and nitrogen excretion in sows. A total of 24 healthy Landrace × Yorkshire sows (4 to 5 parities) with similar body weight and back fat were fed with normal gestational diet (control group, crude protein = 13.65%, n = 12) or a LP gestational diet (LP group, crude protein = 11.30%, n = 12) from day 30 of gestation to the day before parturition. All sows received same diet during lactation. Results showed that LP diet during mid-to-late gestation reduced the gain of backfat thickness during days 30 to 60 of gestation (P < 0.05) compared with the control group, without changing the reproductive performance of the sows. The gene expression levels of amino acid transporters in the placenta, and the organ indices of neonatal and weaned piglets, were all unchanged by the LP diet. The digestion and metabolism experiment revealed that the LP diet decreased nitrogen excretion and net nitrogen deposition during late gestation (P < 0.05). Additionally, the LP diet reduced serum concentrations of valine, arginine, lysine, and methionine on day 110 of gestation, and arginine, lysine, and methionine on day 21 of lactation, while it tended to decrease serum concentration of the total essential amino acids and the level of threonine in the milk throughout lactation (P < 0.05). Gestational LP diet al.o significantly reduced concentrations of serine and the total non-essential amino acids in the serum of neonatal piglets (P < 0.05) and serum threonine in weaned piglets, but increased leucine (P < 0.05) in the serum of weaned piglets. In conclusion, an appropriate reduction of dietary protein during mid-to-late gestation in sows (11.30% vs. 13.65%) could reduce their nitrogen excretion while maintaining reproductive performance, and it is recommended to supplement arginine and valine in the LP diets in addition to lysine, methionine, tryptophan, and threonine. This study highlights the significance of low-protein diets in protein feed saving and environmental protection.