Cholesterol and lipid metabolism at the start of lactation in dairy cows with different body condition scores.

Over-conditioned dairy cows at calving and those experiencing an energy deficit in early lactation are predisposed to postpartum (p.p.) metabolic disorders such as ketosis and fatty liver disease. While alterations in energy and fatty acid metabolism during early lactation are well documented, short-term dynamics of cholesterol and lipoprotein metabolism at the onset of lactation are poorly characterized. In this study, we investigated the short-term dynamics of cholesterol and lipoprotein metabolism during the first wk p.p. in cows with differing BCS at calving and contrasting feed energy supply p.p. On d 42 antepartum, we randomly assigned 24 multiparous Holstein cows to either a high energy feeding regimen (HC; n = 14, 6.5 MJ NEL/kg of DM; parity: 3.6 ± 0.4) or a low energy feeding regimen (LC; n = 10, 5.0 MJ NEL/kg of DM; parity: 3.0 ± 0.4), resulting in 2 groups with higher and lower BCS (HC: 3.69 ± 0.12; LC: 2.68 ± 0.11) at calving. The lower feed energy supply in HC p.p. further intensified the catabolic metabolism, particularly regarding adipose tissue mobilization and hepatic fatty acid influx. We collected daily blood at 2.24 h after calving and from d 2 p.p. until d 7 p.p. between 0530 and 0800 h together with milk samples and recorded performance data continuously. We analyzed metabolite concentrations related to lipid and cholesterol metabolism [nonesterified fatty acids (NEFA), BHB, triglycerides (TG), total cholesterol, and lipoproteins], as well as enzyme activities [gamma-glutamyl transferase (GGT), glutamate dehydrogenase (GLDH)] using enzymatic assays. The HC cows showed similar DMI but increased ECM resulting in a more severe negative energy balance during the first wk p.p. and a more pronounced BW loss (-90 ±  7 kg vs. -70 ±  7 kg) from shortly before until 7 d after calving compared with LC cows. Plasma NEFA, BHB, and TG concentrations were greater in HC compared with LC cows. While total cholesterol and low-density lipoprotein cholesterol (LDL-C) concentrations did not differ between groups, very low-density lipoprotein cholesterol (VLDL-C) concentration was greater and high-density lipoprotein cholesterol (HDL-C) concentration tended to be greater in HC cows compared with LC cows. Our findings indicate that elevated BCS at calving together with lower feed energy supply p.p. intensifies the catabolic state during early lactation, resulting in greater adipose tissue mobilization and hepatic lipid influx. This metabolic state was associated with altered lipoprotein distribution during the first wk p.p., characterized by changes in lipoprotein-associated cholesterol concentrations and enhanced VLDL-associated lipid. Thus, elevated body condition at calving together with lower feed energy supply p.p. not only exacerbated adipose tissue mobilization p.p. but also induced adjustments in cholesterol metabolism, identifying BCS at calving and the extent of feed energy supply p.p. as a key determinant of hepatic lipid handling and metabolic adaptation at the onset of lactation.