Hepatic Acetyl CoA Concentration Decreases following Feeding in Early-postpartum but not in Late-lactation Dairy Cows
The relationship between hepatic acetyl CoA concentration (Ac-CoA) and dry matter intake (DMI) was determined using 28 multiparous Holstein cows; 14 were early-postpartum (PP; 12.6 ± 3.8 DIM) and 14 were late-lactation cows (LL; 271 ± 29.6 DIM). Cows were fed once daily and DMI was determined for the first 4 h after feeding. Liver and blood samples were collected before feeding and 4 h after feeding. Feed intake over the 4-h period ranged from 3.2 to 9.6 kg DM and did not differ by stage of lactation. Before feeding, Ac-CoA was greater (P < 0.0001) for PP (mean: 36.0; range: 12.7 to 56.1 nmol/g) compared with LL (mean: 14.1; range: 7.7 to 19.4 nmol/g), and tended to decrease over the 4 h after feeding for PP only (P < 0.10). The range of change in Ac-CoA over the 4-h period was wide for both PP (-24.3 to 10.4 nmol/g) and LL (-5.7 to 16.1 nmol/g), and was negatively related to DMI at 4 h for PP (P < 0.01), but not for LL. The reduction in plasma NEFA concentration over the 4-h period was greater for PP than LL (-684 vs. -52 µEq/L; P < 0.0001), and was greater for PP (P < 0.05) and tended to be greater for LL (P < 0.10) as DMI at 4 h increased. Greater reductions in Ac-CoA were related to higher DMI during the first 4 h after feeding in PP (P < 0.01), which is contrary to our expectation if oxidation of Ac-CoA increased hepatic energy charge. However, hepatic energy charge is dependent upon the relative rates of production and utilization of high-energy phosphate bonds and the rate of utilization might have been greater for cows with higher DMI. Alternatively, increased DMI over the first 4 h after feeding might have been from decreased oxidation of Ac-CoA during meals if the greater reduction in plasma NEFA concentration reduced Ac-CoA production by beta-oxidation. Consistent with this is that the change in Ac-CoA was positively related to the reduction in plasma NEFA concentration for PP (P < 0.05). Besides oxidation, the pool of Ac-CoA is decreased by ketogenesis and hydrolysis and export as acetate. Further research is required to determine the fate of Ac-CoA within the timeframe of meals and the effects of feeding on energy charge in hepatic tissue.
Keywords: acetyl CoA, metabolic control of intake, postpartum