Feed intake is related to changes in plasma nonesterified fatty acid concentration and hepatic acetyl CoA content following feeding in lactating dairy cows

The relationship between hepatic acetyl CoA (AcCoA) content and dry matter intake (DMI) was evaluated using 28 multiparous Holstein cows; 14 were early postpartum (PP; 12.6 ± 3.8 d in milk) and 14 were late-lactation cows (LL; 269 ± 30 d in milk). Cows were fed once daily, and DMI was determined for the first 4h after feeding. Liver and blood samples were collected before feeding and 4h after feeding. Feed intake over the 4-h period ranged from 3.7 to 9.6 kg of dry matter and was similar for the 2 stages of lactation. Before feeding, hepatic AcCoA content was greater for PP compared with LL cows (34.4 vs. 12.5 nmol/g), and decreased over the 4h after feeding for PP only (28.7 vs. 34.4 nmol/g). The range for change in AcCoA 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 related negatively to DMI at 4h for both PP (R(2) = 0.55) and LL (R(2) = 0.31). The reduction in plasma NEFA concentration over the 4-h period was greater for PP than LL cows (-681 vs. -47 µEq/L), and was related to DMI at 4h for both PP and LL (both R(2) = 0.38). Greater DMI among cows over the first 4h after feeding might have been from a sharper reduction in supply of AcCoA in the liver for oxidation during meals because of the reduction in plasma NEFA concentration. Consistent with this is that the change in AcCoA was positively related to the reduction in plasma NEFA concentration for PP cows (R(2) = 0.31). However, change in plasma NEFA concentration was not related to change in hepatic AcCoA in LL cows, indicating that the pool of AcCoA in LL cows is not as dependent on NEFA flux to the liver as that of PP cows. Further research is required to determine production and fate of AcCoA within the timeframe of meals and the effects of feeding on energy charge in hepatic tissue.