Effects of energy and protein intake on ovulation rate associated with the feeding of lupin grain to Merino ewes

Abstract

Five rations formulated from varying amounts of pasture hay and oat, lupin and pea grains were fed to South Australian Merino ewes at different controlled levels of digestible energy and crude protein intakes. Ovulation was recorded by laparoscopy or laparotomy 17 days and 34 days after the commencement of the experiment, An increase in protein intake supplied by lupin grain increased the ovulation rate through an increased incidence of multiple ovulation only when the initial level of feeding supplied low protein and energy intakes, and not when the initial level of feeding provided moderate intakes of protein and energy. The response in ovulation rate was evident within the first 17 days after protein intake was increased, and did not change further during the second 17-day period. Particularly in November/ December, when a proportion of ewes failed to ovulate, the mean ovulation rate of ewes fed at low protein and energy intakes was increased more by additional protein and energy together than by additional protein alone. It is suggested that increased protein intake per se stimulates the ovulation rate only when the initial intake is close to the maintenance requirement, and that energy, either by itself or together with protein, subsequently becomes the limiting factor.