Effects of Dietary Vitamin D3 Over-Supplementation on Broiler Chickens' Health; Clinicopathological and Immunohistochemical Characteristics

Abstract

Introduction: Vitamin D3 is used as a supplement in the feeds of livestock, pets, and human infants. However, the presence of excessive Vitamin D3 has been shown to cause toxicity in humans and animals. This study investigated the clinicopathological aspects of Vitamin D3 toxicity in broiler chickens. Materials and methods: The median lethal dose (LD50) of Vitamin D3 was estimated by the up-and-down method. To determine long term (21 days) toxic effects of oral Vitamin D3 supplementation, 90 (14-day-old) IBL-80 unsexed chicks were randomly divided into three groups as group A (control, received basal diet), B (basal diet + Vitamin D3 at 16.67 mg/kg body weight daily), and C (basal diet + Vitamin D3 at 33.33 mg/kg body weight daily). Results: The findings indicated that broiler chickens tolerated a single oral dose of Vitamin D3 up to 550 mg/kg body weight (22,000,000 IU/kg) without mortality. The results of long-term (21 days) oral supplementation of divided doses of Vitamin D3 in broiler chickens (groups B and C) showed progressive emaciation, elevated hemoglobin, hypercalcemia, hypophosphatemia, and increased alkaline phosphatase activity. At necropsy, pale liver and kidneys, congestion and hardening of lungs, mild congestion in the brain, and soft bones were observed in Vitamin D3 treated chicks (groups B and C). Microscopically, degeneration and metastatic calcification in lung parenchyma and peribronchiolar epithelium, coagulative necrosis and calcification in kidneys, and calcification with fibroplasia in proventriculus was detected. Lungs and kidneys showed a significant difference in calcification score between groups B and C. Broiler chickens from Vitamin D3 treated groups (B and C) showed strong immunohistochemical expression of Calbindin D28K in the intestine and kidneys but weak expression in the lungs. Conclusion: This study demonstrates that broiler chicks can tolerate very high levels of a single oral dose of Vitamin D3. Toxic effects of prolonged exposure to Vitamin D3 are due to over-expression of Calbindin D28k in the intestine and kidneys, disturbing the calcium and phosphorous homeostasis and leading to metastatic calcification of vital organs. This study supports that prolonged over-supplementation of Vitamin D3 causes toxic effects; hence, appropriate dietary Vitamin D3 supplementation limits should be set.