Research articleThe effects of late gestation maternal nutrient restriction with or without protein supplementation on endocrine regulation of newborn and postnatal beef calves

A study was conducted to evaluate late gestation maternal nutrient restriction (NR) with or without protein supplementation on endocrine regulation in newborn beef calves. This study used multiparous cows (4 and 5 years of age, n = 57) randomly assigned to one of three treatments for the last 100 days of gestation. The control (Con; n = 19) cows were fed to increase body condition score, whereas the NR (n = 19) and NR with protein supplement (NRS, n = 19) cows were fed to lose 1.2 ± 0.2 body condition score units during the last 100 days of gestation. Control cows were allowed ad libitum access to tall fescue/crabgrass paddock and, when grazing became insufficient, ad libitum hay was provided along with 1.3 kg of corn gluten feed 5 days/wk. Tall fescue paddocks were strip grazed to limit forage availability for NR and NRS. The NRS-treated dams were individually penned and fed 0.45 kg of soybean meal 3 days/wk. As forage became limited, the nutrient-restricted paddocks received limited fescue hay. After parturition cow/calf pairs were moved to a common pasture and received ad libitum silage and high-concentrate feed. Maternal NR regardless of supplementation reduced cow plasma glucose and insulin concentrations during late gestation (P < 0.0001 and P = 0.0051, respectively). Calves from NR dams weighed less at birth than Con calves (P = 0.04), whereas NRS calves were intermediate (33.4 ± 1.2, 35.0 ± 1.3, and 37.2 ± 1.3 kg NR, NRS, and Con, respectively). Plasma glucose concentrations of unsuckled calves at birth were reduced (P = 0.037) in NR and NRS calves compared with Con (67.7 ± 6.5 and 60.1 ± 6.9 vs. 83.7 ± 6.1 mg/dL, respectively). At birth, Con and NRS calves had increased (P = 0.0037) plasma leptin concentrations compared with NR calves, whereas calf plasma cortisol concentrations were greater for the nutrient-restricted groups than the Con group (treatment × day P = 0.0135). Plasma IgG concentrations from calves at 5 days of age were similar (P = 0.701) between maternal late gestation treatments. This research reports that late gestation NR reduces postnatal calf birth weight, plasma glucose and leads to reduced plasma leptin. Maternal protein supplementation appears to partially alleviate the effects of late gestation NR on reducing plasma leptin, birth weight, and growth rate from Day 30 of age to weaning.