Changes in milk fatty acids and metabolites in dairy cows supplemented with varying levels of rumen-protected glucose during early lactation

Abstract

Due to insufficient energy intake, postpartum dairy cows experience a decrease in plasma glucose, which may result in lipid metabolism disorders. Rumen-protected glucose can improve energy balance and alter lipid metabolism in postpartum dairy cows. However, research on the changes in milk fatty acid composition and metabolites in early-lactating dairy cows fed different levels of rumen-protected glucose is very limited. The purpose of this study was to investigate the effects of dietary rumen-protected glucose supplementation levels on the milk fatty acid composition and metabolome of early-lactating dairy cows. Thirty-two Holstein cows were divided into 4 treatment groups based on body weight, parity, and lactation performance in a randomized block design. Dairy cows in each treatment group (n = 8 per diet) were supplemented with 0, 200, 350, and 500 g/d of rumen-protected glucose from calving to d 35 postpartum. Milk samples from these dairy cows were collected on the last day of the experiment for fatty acid composition analysis using gas chromatography and for milk metabolite analysis using untargeted metabolomics. The results showed that increasing supplementation of rumen-protected glucose significantly linearly decreased milk fat content and tended to decrease milk SCC but had no significant effect on milk yield. The increasing addition of rumen-protected glucose linearly increased the proportions of C6:0, C8:0, C10:0, C14:0, C16:0, and the sum of saturated fatty acids, short-chain fatty acids, and medium-chain fatty acids (MCFA). Conversely, the proportions of C16:1 cis-9, C18:1 cis-9, C18:2 cis-9,12, MUFA, PUFA, and long-chain fatty acids (LCFA) linearly decreased with increasing supplementation of rumen-protected glucose. Dairy cows in the 350 g/d group had higher proportions of C10:0, C11:0, C12:0, C13:0, C14:0, C15:0, C16:0, and MCFA, and lower proportions of C18:1 cis-9 and LCFA in milk, compared with those in the 0 g/d and 200 g/d groups. Meanwhile, compared with the control group, rumen-protected glucose supplementation downregulated metabolites primarily involved in adipose tissue mobilization and inflammatory response. Glycerophospholipid metabolism, which plays an important role in building cellular membranes and signal transduction, was upregulated in the rumen-protected glucose treatment groups. The results of our study revealed that rumen-protected glucose supplementation during early lactation can effectively reduce adipose tissue mobilization in dairy cows. Supplementation with rumen-protected glucose at 350 g/d is the recommended dosage for early-lactating dairy cows.