Effect of Supplementation of Drinking Water with Different Levels of Boron on Performance and Immune Organ Parameters of Broilers

This study was performed to investigate changes in growth performance, immune organs weight and microstructure of broilers fed different levels of boron (0, 100, 200 and 400 mg/L) in drinking water for 6 weeks. A total of 240 newly-hatched Gushi chickens [body weight (BW)=34±2 kg; male: female=1:1] were equally divided into 4 treatments with 5 pens each (n=12 per pen). The birds were weighed after fasting for 12 h every two weeks until the end of experiment. The thymus, bursa and spleen samples were collected every two weeks and fixed in 4% paraformaldehyde phosphate buffer at room temperature (25°C). Results showed that BW and average daily gain significantly reduced by addition of 200 and 400 mg/L boron to drinking water compared to control group (P<0.05 or <0.01). Compared to controls, the thymus index of broilers fed 100 mg/L boron increased significantly from 4th to 6th week of age (P<0.05), whereas the weight and immune organs index of broilers fed 400 mg/L boron decreased significantly every week (P<0.05 or <0.01). Microscopic observation showed that the structure of immune organs of broilers fed 100 mg/L boron was well developed from 4th to 6th week of age, and that of broilers fed 200 and 400 mg/L boron was damaged every week. The present study suggests that appropriate supplements of boron (<100 mg/L) could improve the growth of immune organs in broilers after 4 weeks. However, high doses of boron (>200 mg/L) could significantly inhibit the growth of immune organs and even exhibit toxic effects.