Effect of betaine supplementation on growth performance, nutrient intake and expression of IGF-1 in Karan Fries heifers during thermal stress.

Heat stress hampers nutrient utilisation and production of animals, and dietary betaine supplementation can mitigate the adverse effects of heat stress on animals and improve their productivity. The present study was conducted to explore the effects of betaine supplementation on the growth performance of eighteen growing Karan Fries (KF) heifers having similar age and body conditions. The experiment was carried out on three groups (n = 6) of KF heifers viz. control, treatment I (betaine supplemented at 25  g/d/animal), and treatment II (betaine supplemented at 50  g/d/animal). The experiment lasted for eight months covering the three major seasons of Indian tropical conditions viz. hot-dry (temperature humidity index, THI = 83), hot-humid (THI = 85) and thermoneutral season (THI = 73). Blood samples were collected at fortnightly intervals and analysed for plasma growth hormone (GH; competitive ELISA) and total insulin-like growth factor 1 (IGF-1; Sandwich ELISA), as well as expression of IGF-I in peripheral blood mononuclear cells (PBMC) using real-time polymerase chain reaction. Betaine supplementation resulted in significant (p < 0.05) increase in dry matter intake, feed conversion efficiency, body weight gain, plasma GH and IGF-1 levels during all seasons. The concentrations of plasma IGF-1 and the mRNA expression of IGF-1 were higher (p < 0.01) in treatment I as compared to other groups during all seasons. Betaine supplementation at 25  g/d/animal was more cost-effective in improving growth performance of heat-stressed heifers as compared to 50  g/d/animal. The study suggests that the betaine protects intestinal integrity, enhances nutrient utilisation during heat stress and improves growth performance of growing heifers.