Background: Many studies in dairy cows are towards calcium homeostasis and there is a lack of knowledge about the effect of vitamin D in preventing insulin resistance and improving energy balance in the transition period of dairy cows.
Methods: The trial was conducted in a commercial dairy farm with about 1500 lactating cows in Tehran province, Iran. Twenty-four Holstein cows had been randomly selected and divided into control and treatment groups. In the treatment group, 12 cows, received a single dose of 8,000,000 IU vitamin D3 intramuscularly and in the control group, 12 cows were injected placebo (distilled water) 2-8 days before the expected calving time. Blood samples were collected between 8 and 10 AM 2 h after feeding on 21 and 7 days before calving and 1,3,7,15 and 30 days after calving. 25(OH)vitamin D, insulin-like growth factor 1 (IGF-1), insulin, nonesterified fatty acid (NEFA), β-hydroxybutyric acid (BHBA), albumin, total protein, glucose, urea, triglyceride, cholesterol and aspartate amino transferase (AST) were measured by commercially available kits. The insulin resistance index was calculated.
Results: Vitamin D3 injection significantly affected the amounts of 25(OH) vitamin D, urea, insulin and insulin resistance index (p ≤ 0.05). On the other hand, the amounts of glucose, NEFA, BHBA concentration and AST activity were higher in control group (p ≤ 0.05). Time had a significant effect on the amounts of most measured variables except IGF-1 and insulin. There were no group and time interactions for measured variables.
Conclusion: It seems that injection of vitamin D3 in close up period influenced lipolysis potentially modifying energy metabolism and resulted in reducing insulin resistance.
Keywords: dairy cow; insulin resistance; transition period; vitamin D.
© 2021 The Authors. Veterinary Medicine and Science published by John Wiley & Sons Ltd.