Effects of energy balance of hormones, ovarian activity, and recovered oocytes in lactating Holstein cows using transvaginal follicular aspiration.

The effects of energy balance on hormonal secretion patterns and the structure of recovered oocytes were evaluated in 20 lactating Holstein cows during two trial periods. Cows were randomly assigned to one of two dietary treatments formulated so that dry matter consumption was 3.6% of body weight (high energy; 1.78 Mcal/kg) or 3.2% of body weight (low energy; 1.52 Mcal/kg). Ovum recovery procedures were conducted twice weekly between d 30 and 100 of lactation. Follicle size and number were recorded. Follicular fluid aspirated from the largest follicle and serum samples were collected for hormone assay. Milk yield averaged 41.6 +/- 0.3 kg/d (mean +/- SE) for high energy fed cows and 32.8 +/- 0.3 kg/d for low energy fed cows. Oocyte numbers increased linearly from d 30 to 100 postpartum. Cows fed high energy diets produced more good (+) oocytes than did cows fed low energy diets.