Feeding of high-quality hay modulates hepatic lipid and energy metabolism in weaned dairy calves

The present study aimed to investigate the effects of feeding different hay qualities with or without concentrate supplementation on the mRNA expression of genes related to hepatic lipid and glucose metabolism and cellular energy status in weaned calves. Holstein Friesian calves (5 per dietary group) were fed 4 solid diets: (1) 100% medium-quality hay (MQH; 9.4 MJ of ME, 149 g CP, 522 g NDF/kg of DM); (2) 100% high-quality hay (HQH; 11.2 MJ of ME, 210 g CP, 455 g NDF/kg of DM); (3) 30% medium-quality hay + 70% starter concentrate (MQHC); and (4) 30% high-quality hay + 70% starter concentrate (HQHC). Calves were slaughtered at 100 ± 4 d of age and an average BW of 128.8 ± 19.8 kg. Liver tissue was collected, snap-frozen in liquid N₂, and used in the mRNA expression experiment. The trend for lower mRNA expression of AMP-kinase with HQH compared with MQH indicated higher energetic status of hepatocytes with HQH, which probably triggered the increased mRNA expression of enzymes responsible for lipogenesis and cholesterogenesis. The greater hepatic availability of propionate with the hay-concentrate diets may have upregulated the mRNA expression of AMP-kinase by triggering gluconeogenesis. Both HQH and concentrate supplementation downregulated genes related to nutrient catabolism, such as fatty acid oxidation or amino acid breakdown. In conclusion, results demonstrate the importance of the type of solid feed for the energetic state and respective signaling in hepatocytes of weaned calves.