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 cows (150 +/- 3.1 d in milk) during mid to late lactation to determine effects on performance characteristics, metabolic parameters, or both during mid to late lactation, the dry period, and the first 100 d of the next lactation. All cows received identical diets during the dry period and during early lactation. Increasing the energy density of the diets during mid to late lactation increased DM intake (DMI), plasma nonesterified fatty acid concentration, milk production, and milk protein yield. Compared with the high grain diets, fat supplementation decreased DMI and the percentage of milk protein but increased plasma nonesterified fatty acid concentration without causing elevation of liver triglyceride at the end of mid to late lactation. Increased energy density of the diets did not affect body condition score during mid to late lactation. There were no residual effects for any of the treatments on DMI, lactation performance, or body weight in the subsequent lactation. However, energy supplementation during mid to late lactation increased liver triglyceride content after calving. Compared with high fat diets, high grain diets fed during mid to late lactation increased plasma beta-hydroxy-butyrate concentration in the subsequent lactation. High energy diets fed during mid to late lactation may influence lipid metabolism during the following lactation.