Effect of early-life plane of nutrition on the transcriptional profile of the hypothalamus in heifer calves
The objective of this study was to examine changes in hypothalamic gene expression of 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 hypothalamus of each calf recovered. RNA was extracted and hypothalamic gene expression examined using RNAseq. Compared with calves on the moderate plane of nutrition, a HP of nutrition altered the expression of 39 transcripts in the hypothalamus. Biological pathway analysis revealed these differentially expressed genes to be involved in pathways including acute phase response signalling, STAT3 pathway, and tight junction signalling. Additionally, biological functions affected by early life plane of nutrition included  cell-to-cell signalling and interaction, molecular transport, small molecule biochemistry, behaviour, nervous system development and function, nucleic acid metabolism, and cellular function and maintenance. Overall design: 29 hypothalamus 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.