LIPID-METABOLISM IN ADIPOSE-TISSUE OF COWS FED HIGH-FAT DIETS DURING LACTATION

The adaptations of fat synthesis in adipose tissue to lactational stat e, 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 co ntrol TMR of corn silage, alfalfa, and concentrate (2.5% fat; 1.47 Mca l of NE(L)/kg); a TMR with whole cottonseeds replacing 12% of the conc entrate (4.4% fat; 1.49 Meal NE(L)/kg); or a TMR with 12% cottonseeds and 2.7% of Ca salts of fatty acids (6.0% fat; 1.53 Meal of NE(L)/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 de creased by dietary fat treatments. Esterification rates were lowest on the intermediate fat TMR and highest on the highest fat TMR. Lipogene sis was decreased logarithmically by dietary fat intake; this effect w as greater as lactation progressed. Adipocyte size and body fat mass d ecreased during early lactation and then increased for all treatment g roups. Supplemental dietary fat reduces de novo synthesis of fatty aci d, and this effect increases as lactation progresses.