Intestinal health of squab pigeons responded to parental dietary protein levels during breeding period

The objective of this study was to determine the effects of dietary crude protein (CP) levels on intestinal antioxidant status, tight junction proteins expression, and amino acids transporters levels in squabs. A total of 180 pairs of White King parent pigeons approximately 10 months old were randomly assigned to 5 groups with 6 replications of 6 pairs of parental pigeons and 18 squabs each, and were fed with 14%, 15%, 16%, 17% and 18% CP diets for 46 days, respectively. Dietary increasing CP levels increased final body weight (linear and quadratic, P<0.05), serum urea nitrogen (linear, P<0.05) and triglyceride levels (quadratic, P<0.05), and reduced kidney relative weight (quadratic, P<0.05) in squabs. Final body weight of squabs in the 18% CP diet group was higher than that of the 14%, 15% and 16% CP diet groups (P<0.05) but was similar to that of the 17% CP diet group (P>0.05). Increasing dietary CP levels reduced intestinal malondialdehyde contents (linear and quadratic, P<0.05) and jejunal total superoxide dismutase (T-SOD) activity (linear, P<0.05), and enhanced (linear and quadratic, P<0.05) ileal catalase and T-SOD activities in squabs, and these effects were more prominent in the 17% CP diet group. Graded CP levels up-regulated the mRNA expression of intestinal zonula occludens 1 and solute carrier family 7 member 9 (linear, P<0.05), ileal claudin 1 (CLDN1, linear and quadratic, P<0.05), CLDN3 and solute carrier family 6 member 14 (linear, P<0.05) but lowered jejunal solute carrier family 6 member 14 (quadratic, P<0.05) and CLDN1 (linear and quadratic, P<0.05) mRNA expression in squabs. The effects of dietary CP levels on intestinal tight junction proteins expression were more apparent when its supplemental levels was 18%. These results suggested that increasing parental dietary CP levels ranged from 14% to 18% during breeding period improved growth and intestinal function of squabs, with its recommended level being 17%.