Effect of early-life plane of nutrition on the transcriptional profile of the hypothalamic arcuate nucleus region in heifer calves

The aim of this study was to examine alterations in the transcriptional profile of the arcuate nucleus region of the hypothalamus between heifer calves offered varying planes of nutrition during early life. Angus X Holstein-Friesian heifer calves (19 ± 5 days of age, BW: 51.2 ± 7.8 kg, mean ± SD) were offered a high (HP, n=14) or moderate plane of nutrition (MP, n=15) from 3 to 21 weeks of age to achieve a target growth rate of 1.2 kg/d and 0.5 kg/d, respectively. At 21 weeks of age, all calves were euthanized and the arcuate nucleus region of the hypothalamus of each calf recovered. RNA was extracted transcriptional profiles examined using RNAseq. Compared with calves on the moderate plane of nutrition, a High plane of nutrition altered the expression of 80 genes within the arucate nucleus. Functional analysis of differentially expressed genes revealed functions including organismal development, behaviour, endocrine system development and function, lipid metabolism, molecular transport, small molecule biochemistry, cellular development, cellular growth and proliferation, and nervous system development and function to be affected by early life plane of nutrition in the arucate nucleus of heifer calves. 29 arcuate nuclues RNA samples were analysed in total. 14 samples were derived from calves fed the High plane of nutrition (HP, n=14) and 15 samples were derived from the claves fed the Moderate plane of nutrition (MP, n=15). Calves on the High-plane of nutrition received 1.5 kg of milk replacer (10 liters) per day and ad libitum concentrates during the calf phase. During the subsequent post-weaning phase this group were then offered concentrates ad libitum and hay to appetite. During the calf phase, the Moderate plane of nutrition group received 0.5 kg of milk replacer (4 litres) per day and 1 kg of concentrates, subsequently receiving 1kg of concentrates and hay to appetite during the post-weaning phase. The calf phase lasted for 8 weeks and was followed by the post-weaning phase which lasted for 11 weeks. All samples were collected at the same time-point (21 weeks of age) all differentially expressed genes reported were up- or down-regulated in HP calves compared to MP calves.