Energy balance, metabolic hormones, and early postpartum follicular development in dairy cows fed prilled lipid. 
The objectives of this study were to relate energy balance and metabolic hormones during the early postpartum period in dairy cows with dominant follicle development before first ovulation and to evaluate the effects of prilled lipid on follicular development during the first follicular wave after parturition and the postpartum anovulatory interval.  At parturition, 42 cows received a control diet (4.8% fat) or a diet supplemented with prilled fatty acids (7.0% fat).  Energy balance was determined daily.  Ovarian follicular development was monitored by ultrasonography, and blood plasma or serum was analyzed for estradiol, progesterone, and metabolic hormones.  Dry matter intake was lower in cows supplemented with dietary lipids during the first 4 wk of lactation, but energy intake, energy balance, and the postpartum anovulatory interval were similar between diets.  A wave of follicular development occurred in all cows during the 2nd wk postpartum, and 50% of all cows ovulated their first dominant follicle.  Numbers of follicles that were 3 to 5 mm, 6 to 9 mm, and 10 to 15 mm on d 8 postpartum were similar between diets and unrelated to energy balance or metabolic hormones.  Diameter of the dominant follicle during d 8 to 14 postpartum and maximum diameter of the first-wave ovulatory follicle did not differ between diets.  Cows with nonovulatory first-wave dominant follicles had lower mean plasma concentrations of estradiol during d 8 to 14 postpartum, a longer interval to the day of the energy balance nadir, lower serum concentrations of IGF-I, and higher 4% FCM yield than did cows with ovulatory first-wave dominant follicles.  Serum IGF-I during d 1 to 13 was positively correlated with plasma estradiol during d 8 to 14 postpartum.  Possibly because of reductions in dry matter intake, the consumption of prilled lipid by dairy cows during early lactation may be ineffective in altering energy balance, follicular development, and the postpartum anovulatory interval.  Ovulation failure of dominant follicles early in the postpartum period is associated with greater production of 4% fat-corrected milk, a delayed energy balance nadir, and reduced concentrations of peripheral IGF-I.