The role of protein restriction and interaction with antibiotics in the regulation of compensatory growth in pigs: growth performance, serum hormone concentrations, and messenger RNA levels in component tissues of the endocrine growth axis.

The present study investigated the effects of protein restriction and antibiotics on the hypothalamus-pituitary-liver growth axis during the compensatory growth of growing and finishing pigs. Growth performance, serum hormones, and messenger RNA (mRNA) levels of hormones and their receptors in growth axis tissues were recorded for analyses. A total of 64 piglets (large white × Landrace × Duroc cross) with an initial weight of 10.07 ± 0.14 kg were randomly divided into 4 treatment groups of 16 piglets per group. The dietary treatments consisted of 2 protein levels (14% and 20%) and 2 antibiotic levels (no antibiotics and 20 mg/kg colistin sulfate with 50 mg/kg kitasamycin) in a 2 × 2 factorial arrangement. The study was performed over 30 d for the first stage (S1, restriction phase) and 74 d for the second stage (S2, realimentation phase). The 4 treatment diets were maintained throughout the duration in the restriction phase. The 4 groups were fed the same diet in the realimentation phase. The trial period totaled 104 d. Protein restriction decreased BW, average daily food intake, and ADG in weaning pigs (P < 0.01) and induced compensatory growth after feeding a normal diet during the growth of finishing pigs. Average daily gain increased during the last phase of compensatory growth (P < 0.01). Protein restriction increased serum GH and leptin (LEP) and the mRNA levels of liver IGF-1 receptor (IGF-1-R; P < 0.01) but decreased serum IGF-1 (P < 0.01) and the mRNA levels of liver GH receptor (GH-R; P < 0.01) and IGF-1 (P < 0.05) in weaning piglets. Serum GH was increased, but serum IGF-1 was decreased during the realimentation phase (P < 0.05). Antibiotics increased the mRNA levels of GHRH (P < 0.05) and decreased somatostatin (P < 0.01) in the hypothalamus of weaning pigs. Protein restriction and antibiotics had no interactions across the entire trial. In conclusion, the slowing of growth caused by early protein restriction may be compensated for in the later stages of pig raising, and the mechanism of compensation is related to the regulation of GH, IGF-1, GH-R, and IGF-1-R.