EFFECTS OF INERT FAT ON ENERGY-BALANCE, PLASMA-CONCENTRATIONS OF HORMONES, AND REPRODUCTION IN DAIRY-COWS

The objective was to determine the effects of dietary inert fat on est imated energy balance, hormones in plasma, and reproduction during ear ly lactation. From wk 0 to 12 postpartum, 14 pluriparous Holstein cows were fed individually a TMR, and blood samples were taken twice weekl y for quantification of IGF-I, progesterone, and cholesterol. During w k 5 to 12, one-half of the cows remained on the TMR, and the other hal f were fed the TMR containing inert fat at 1.8% of dietary DM. Estrous behavior was monitored twice daily, and body condition scores were re corded every 4 wk. Cows fed inert fat between wk 5 and 12 post-partum had similar concentrations of IGF-I in plasma but greater luteal phase progesterone secretions than cows fed the control diet. Total cholest erol in plasma also was greater in cows fed inert fat than in cows fed the control diet. Intervals to first, second, and third ovulation or estrus did not differ among cows fed control or inert fat diets. Body condition scores, daily DMI, and milk production were not affected by dietary inert fat. Inert fat fed to cows between wk 5 and 12 postpartu m did not affect ovulatory activity but may enhance luteal activity.