EXCESS DIETARY UREA INTAKE IN EWES AND ITS EFFECT ON OVULATION RATE AND EMBRYO DEVELOPMENT.

The effect of excess dietary urea on ovulation and early embryo develop­ ment of sheep was studied. Thirty Border Leicester x Scottish Black face ewes randomly assigned to three treatments were given a basal control diet (C) which met energy requirements for body weight maintenance. Other treatments were basal diet plus 24g of urea/day (low urea, L) or plus 48g (high urea, H)/day. The reproductive cycles of the ewes were synchronized using a single injection of prostaglandin (PGF 2«) and progesterone by an intravaginal controlled internal drug release (CIDR) device for 12 days. Ovulation was induced by the use of pregnant mare serum gonadotrophin (PMSG). Ewes were inseminated approximately 52 hours after CIDR device removal using a laparoscopic techni­ que. Embryos were recovered at Day 4 or Day 11 after insemination from half of the ewes from each treatment group. There were no significant differences in ovulation rates among the three groups. The embryo recovery rates were not affected by day of recovery. At embryo recovery on Day 4, 7/13 in C, 3/6 in Land 017 in H embryos were morulae. After 72 hours of in vitro culture 6/10 in C, 2/3 in Land 0/4 in H embryos developed to the blastocyst stage. Pregnancies sustained were C 6/8, L 517 and H 113 of the autotransfers. Throughout the experiment plasma urea levels were significantly affected by diet (p < O. 01). Plasma ammonia levels in the H group were significantly higher than those in the C and L groups (p < O. 05) for 4 hours after each feed. There was no treatment effect on plasma prog­ esterone concentration. The luteinizing hormone (LH) surge onset time and amplitude were not correlated to ovulation rate and were not affected by treatment. It is concluded that high circulating concentrations of plasma urea