Lipid metabolism in adipose tissue of cows fed high fat diets during lactation.

The adaptations of fat synthesis in adipose tissue to lactational state, rate of milk production, and dietary fat intake were determined for dairy cows. Lipogenesis and esterification were determined in cows of average or high genetic merit for milk production and fed either a control TMR of corn silage, alfalfa, and concentrate (2.5% fat; 1.47 Mcal of NEL/kg); a TMR with whole cottonseeds replacing 12% of the concentrate (4.4% fat; 1.49 Mcal NEL/kg); or a TMR with 12% cottonseeds and 2.7% of Ca salts of fatty acids (6.0% fat; 1.53 Mcal of NEL/kg). Dietary treatments began on d 17 of lactation and continued for 288 d. Lipogenesis and esterification decreased equally from 15 d prepartum to 15 d postpartum in all groups. Cows of high merit had lower rates of lipogenesis and esterification at d 60 than did low merit cows but had higher rates of lipogenesis at d 120. Rates of lipogenesis were decreased by dietary fat treatments. Esterification rates were lowest on the intermediate fat TMR and highest on the highest fat TMR. Lipogenesis was decreased logarithmically by dietary fat intake; this effect was greater as lactation progressed. Adipocyte size and body fat mass decreased during early lactation and then increased for all treatment groups. Supplemental dietary fat reduces de novo synthesis of fatty acid, and this effect increases as lactation progresses.