EFFECTS OF POST-OVULATION NUTRITIONAL-STATUS IN EWES ON EARLY CONCEPTUS SURVIVAL AND GROWTH IN-VIVO AND LUTEOTROPHIC PROTEIN SECRETION IN-VITRO

Overfeeding during early pregnancy in ewes compromises pregnancy establishment and/or embryo survival. To determine whether high feed intakes after ovulation alter the secretory dialogue between the conceptus and the endometrium, 24 embryos (8-16-cell) from ewes fed maintenance rations were synchronously transferred in singleton on Day 3 of the cycle (oestrus, Day 0) into the uterus of ewes receiving a high or low plane of nutrition from Day 0 (n = 12 ewes per group). Embryo survival and conceptus growth were assessed on Day 16. At this time, pregnancy was maintained in 11 of 12 recipient ewes per group and conceptus mass was not influenced by nutritional plane (637+/-48 v. 583+/-72 mg for high and low groups respectively). Conceptus and endometrial tissues were cultured separately for a further 24 h in vitro in the presence of [H-3]leucine. There was no quantitative difference between nutritional treatments in the incorporation of radiolabel into proteins synthesized and secreted by the conceptus or endometrium. Secretion of ovine trophoblast protein-1 was also similar in both groups. Peripheral progesterone concentrations were significantly (P < 0.05) lower throughout the luteal phase in recipient ewes on high v. low intakes after ovulation. This effect was independent of ovulation rate which was 3.1+/-0.40 and 2.6+/-0.25 corpora lutea for high and low groups respectively.

A high plane of nutrition after ovulation did not influence embryo survival and development in vivo or luteotrophic protein secretion in vitro despite a reduction in peripheral progesterone concentrations. These results imply that, if a high feed intake affects embryo survival, either it has to reduce progesterone concentrations below those measured in the current study or it acts before the embryo enters the uterus or after the embryo has successfully overcome luteolysis on Day 16 of the cycle.