Effects of Dietary Boron Supplementation on Performance, Egg Quality, and Physiological Responses in Late-Laying Hens Subjected to Feed Restriction

This study aimed to evaluate how different levels of boric acid (BA) supplementation affect performance, serum biochemistry, endoplasmic reticulum (ER) stress, and intestinal structure in late-laying hens subjected to feed restriction. We randomly assigned 180 laying hens, 70 weeks old, into six groups: a non-feed-restricted control group (CON1), non-feed-restricted groups supplemented with 60 mg/kg feed (B60-1) and 90 mg/kg feed (B90-1) of BA, a feed-restricted control group (CON2), and feed-restricted groups supplemented with 60 mg/kg feed (B60-2) and 90 mg/kg feed (B90-2) of BA. The experiment lasted 56 days. Feed restriction significantly reduced egg production and body weight (p < 0.05). However, feed efficiency improved in the feed-restricted control group (CON2) (p < 0.05). In serum biochemical analyses, Alanine transaminase (ALT) levels were lower in the B60-1 group, while triglyceride and total cholesterol levels were lowest in the B90-2 group. Uric acid levels were highest in the CON2 group (p < 0.05), and total protein levels decreased in the B90-2 group (p < 0.05). Nrf-2, GCLC, and GCLM levels were higher in the control groups (CON1 and CON2) compared with BA-supplemented groups (p < 0.01). ATF-4, ATF-6, IRE-1, and CHOP levels significantly increased in the feed-restricted control group (CON2) and decreased with BA supplementation (p ≤ 0.005). While we did not observe significant differences in duodenal structure (p > 0.05), feed restriction caused reductions in villus height and epithelial height in the jejunum and ileum. These reductions were partially improved in the B60-2 and B90-2 groups (p < 0.05). In conclusion, BA supplementation during feed restriction may help maintain intestinal integrity, adjust cellular stress responses, and support performance-related metabolic changes in late-laying hens.