Effect of prepartum protein restriction on brown adipose tissue thermogenic activity in newborn calves

Abstract

Brown adipose tissue (BAT) thermogenesis was evaluated in Wagyu-sired calves from Angus heifers fed isocaloric diets with adequate (PA, 10%) or restricted (PR, 5.8%) dietary protein levels during the last 150 d of gestation. At 6 h of age, calves were placed in a warm-water indirect-calorimetry system to measure norepinephrine (NE) induced BAT thermogenisis. Calves were infused with NE (20 []g NE/kg BW/min for 10 min), and blood samples collected at birth, and at-5, 0, 20, 40, 60, 80, and 120 min after NE infusion for analysis of NEFA, glucose, urea nitrogen (BUN), cortisol, triiodothyronine (T3), and thyroxine (T4). Brown adipose tissue samples were collected at 12 h of age and analyzed for DNA, protein and lipid content. Protein-adequate heifers were 33% heavier (P < .001) and had higher (P < .001) body condition scores (5.9 vs 2.9) than PR heifers at calving. Protein-adequate heifers had higher (P < .05) BUN concentrations 1, 2, and 3 wks prepartum than PR heifers. Heifer cortisol concentrations were not affected by prepartum protein restriction; however, PR heifers had lower T3 concentrations three weeks prepartum and lower T4 concentrations at parturition than PA heifers. Prepartum protein restriction did not reduce calf birth weights (26.4 kg) or thermoneutral metabolic rates (TMR) which averaged 33.3 cal/kg/min. In support of these findings, visceral organ mass was similar for PA and PR calves. Peak metabolic rates (PMR), which averaged 66.2 cal/kg/min, as well as BAT weight and composition were not affected by prepartum protein restriction. Birth BUN levels were 1-fold higher (P <.01) in PA calves than PR calves. Plasma NEFA concentrations were 19% higher (P <.05) in PR calves 20 min after NE infusion. Average T3 concentrations at 6 h of age were 5 1 % higher (P < . 0 1) in PR compared to PA calves although T4 concentrations were similar. These results indicate that prepartum protein restriction did not affect thermoneutral or BAT thermogenesis in newborn calves. The relatively small birth weights of the calves used in this study may have accounted for the lack of a treatment affect on thermoneutral metabolism.