Nitrogen Retention, Ovulation Rate, and Hormonal Profiles in Gilts Fed a High-Protein Diet

Prepubertal crossbred gilts (avg. initial BW of 109 kg; age 169 d) were used in two experiments to determine N retention, ovulation rate, and hormonal profiles. In Exp. 1, 43 gilts were used to determine apparent N and energy digestibility and ovulation rate. In Exp. 2, 14 gilts were used to measure hormonal profiles and plasma urea N. In both experiments, gilts received 1.8 kg/d of a corn-soybean meal based diet containing either 606.6g (high) or 228.6g (adequate) CP. Diets were formulated to be isocaloric, providing an average of 5,306 kcal/d DE. Gilts were fed their respective diets from d 3 of second estrus until d 10 after third estrus. Energy and N balance and plasma urea N were determined during the second estrous cycle. Hormonal profiles were determined during the second estrous cycle and at third estrus. Ovulation rate and ovarian characteristics were determined on d 10 after third estrus. Mean estrous cycle lengths were 2 d less for gilts fed high-protein than for those fed adequate-protein diets ( P <0.05). High-protein intake did not affect ( P >0.85) energy balance but increased N retention ( P <0.05) and plasma urea N ( P <0.01) during the second estrous cycle. Plasma concentrations of luteinizing hormone and follicle-stimulating hormone were higher ( P <0.01) in gilts fed high CP than in those fed adequate CP. At d 10 after third estrus, high protein intake increased ovulation rate and ovarian and follicular fluid weight ( P <0.01). Results indicate that feeding a high protein diet to gilts increased plasma urea N and N retention during the second estrous cycle, increased ovulation rate at third estrus, enhanced reproductive hormones, and may influence follicular development for subsequent ovulation.