OVULATION RATE AND THE CONCENTRATIONS OF GONADOTROPIC AND METABOLIC HORMONES IN EWES FED LUPIN GRAIN

An experiment in which a lupin grain supplement was fed to ewes (n = 1 1) over days 2-13 of the oestrous cycle was carried out. A group of 12 ewes was used as a control and not fed the supplement. Plasma concent rations of LH and GH (20 min intervals) and FSH, insulin and prolactin (hourly intervals) were determined in plasma samples collected every 20 min over 24 h on day 11 of the oestrous cycle. The changes were rel ated to increases in ovulation rate. Ovulation rate was increased (2.5 +/- 0.2 versus 1.9 +/- 0.2 for lupin-supplemented and control groups, respectively; P = 0.073) in the group that received the lupin supplem ent, but this increase was not associated with significant changes in either LH or FSH concentrations on day 11 of the oestrous cycle. Lupin supplementation had significant effects on the plasma concentrations of prolactin, GH and insulin. There was a transient increase (P < 0.05 ) in the concentration of prolactin 4-8 h after feeding, whereas insul in concentrations were increased immediately after feeding (P < 0.02) and were still high 24 h later (P < 0.02). Growth hormone concentratio ns were reduced in ewes fed with lupin grain (P < 0.001). These metabo lic responses initiated by feeding a high energy and protein supplemen t such as lupin grain may be related to changes in ovulation rate. In particular, the sustained increases in insulin concentrations suggest that an increased supply of glucose to the follicle mediates nutrition ally stimulated increases in ovulation rate.