THE EFFECT OF DIETARY ENERGY-SOURCE DURING MID TO LATE LACTATION ON LIVER TRIGLYCERIDE AND LACTATION PERFORMANCE OF DAIRY-COWS

Control [1.61 Mcal of net energy for lactation (NEL)/kg of dry matter (DM)], high grain (1.70 Mcal of NEL/kg of DM), or high fat [1.70 Mcal of NEL/ kg of DM with 2.3% tallow (DM basis)] diets were fed to 43 cow s (150 +/- 3.1 d in milk) during mid to late lactation to determine ef fects on performance characteristics, metabolic parameters, or both du ring mid to late lactation, the dry period, and the first 100 d of the next lactation. All cows received identical diets during the dry peri od and during early lactation. Increasing the energy density of the di ets during mid to late lactation increased DM intake (DMI), plasma non esterified fatty acid concentration, milk production, and milk protein yield. Compared with the high grain diets, fat supplementation decrea sed DMI and the percentage of milk protein but increased plasma nonest erified fatty acid concentration without causing elevation of liver tr iglyceride at the end of mid to late lactation. Increased energy densi ty of the diets did not affect body condition score during mid to late lactation. There were no residual effects for any of the treatments o n DMI, lactation performance, or body weight in the subsequent lactati on. However, energy supplementation during mid to late lactation incre ased liver triglyceride content after calving. Compared with high fat diets, high grain diets fed during mid to late lactation increased pla sma beta-hydroxybutyrate concentration in the subsequent lactation. Hi gh energy diets fed during mid to late lactation may influence lipid m etabolism during the following lactation.