CHARACTERIZATION OF FEED-INTAKE AND ESTRADIOL-17-BETA DURING GESTATION AND LACTATION IN TWIN-BEARING EWES

The role of estradiol-17beta (E2) in the regulation of feed intake was investigated in two trials. Trial 1, ten twin-bearing Rambouillet ewe s (64 kg, breeding weight) were individually fed com silage ad libitum daily during the last 60 d of gestation and the first 30 d of lactati on. Jugular blood samples were collected weekly for E2 analysis. In tr ial 2, ovariectomized Rambouillet ewes (64 kg) were administered impla nts containing E2 (n = 9) or sham implanted (n = 9). Implants were mad e from three 15-cm lengths of silastic tubing (3.35 mm i.d., 4.65 mm o .d.). Individual daily ad libitum com silage intake was determined. Fe ed intake decreased (linear, P < 0.02; quadratic, P < 0.02) during ges tation and increased (quadratic, P < 0.01) during lactation. Feed inta ke decreased as concentrations of E2 in plasma increased (r = -0.46; P < 0.01) during gestation. In trial 2, implantation of E2 decreased fe ed intake (time x treatment, P < 0.01). Concentrations of E2 in plasma were higher (P < 0.01) in E2 than in sham-implanted ewes (16.6 vs. < 2 pg/ml, respectively). Increased concentrations of E2 in plasma durin g late gestation appeared to be an important factor involved in decrea sed feed intake.