Protein-restricted diet balanced for lysine, methionine, threonine, and tryptophan for nursery pigs elicits subsequent compensatory growth and has long term effects on protein metabolism and organ development

Abstract

Compensatory growth that can enhance the growth rate of animals and has been used commonly in production. However, the underlying mechanism is largely unknown, and the long-term effects of early protein restriction (PR) on pigs mostly remain unclear. This study aimed to investigate the long-term effects of early dietary protein restriction maintaining levels of lysine, methionine, threonine, and tryptophan on protein absorption and metabolism in pigs during the grower phase. Sixty-four weaning piglets (10.0 ± 0.73 kg) were divided into two groups: a control (NP, 200 g/kg crude protein, CP) and a protein-restricted group (RP, 140 g/kg CP). After a 30-day PR, both groups were offered the same diets ad libitum for another 74 days. PR to day 30 inhibited the growth of pigs but tended to enhance growth rate (P = 0.076) and significantly improved feed: gain in the period 70−104 days. PR significantly decreased (P < 0.01) the diarrhea rate and index. The RP group showed lower nitrogen (N) retention (P < 0.05) and higher N retention rate (P < 0.10) when the dietary protein was restricted, whereas the N digestibility and N retention rate were higher (P < 0.05) in the RP group compared with the NP group at day 104. PR reduced (P < 0.05) the liver and kidney protein content and the villus height in the jejunum during the restricted period but elevated (P < 0.05) the liver protein content and the villus height in jejunum in the compensatory period. Early PR reduced the albumin and serum urea nitrogen (SUN) in the serum, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the serum and liver (P < 0.05) during the restricted period. However, the differences in the AST and SUN in serum and the ALT in the serum and liver were reversed at day 104. Before day 30, the mRNA expression levels of the 4F2 heavy chain (4F2hc) and cationic amino acid transporter 1(CAT-1) was downregulated (P < 0.05), peptide transporter family 1 was upregulated (PepT1) (P < 0.05). In the compensatory period, the level of 4F2hc in the RP group was enhanced, and the levels of CAT-1 and PepT1 were lower compared with the NP group (P < 0.05). The results suggest that early PR improved the development of the liver and small intestine, protein absorption and metabolism subsequent to day 30 and thus enhanced growth performance. There were no treatment effects on overall growth performance.