A preliminary report on the effect of dietary energy on prostaglandin F-2 alpha production in vitro, interferon-tau synthesis by the conceptus, endometrial progesterone concentration on days 9 and 15 of pregnancy and associated rates of embryo wastage in ewes

Two groups of ewes were fed to provide 1.70 x (high energy group; n=15) or 0.56 x (low energy group; n=15) energy requirements for maintenance of live weight from 14 d before a synchronized mating in November until slaughter a t 9 or 15 d after mating. We investigated the effects on interferon-tau (IF N tau) secretion by the conceptuses, prostaglandin F-2 alpha (PG) productio n in vitro by endometrial tissue, and associated rates of embryo mortality, endometrial progesterone content and progesterone production by luteal tis sue. No differences between groups in pregnancy rate were detected on Day 9 between the 2 groups. Proportionately (6/6 vs 2/5), there were more pregna nt ewes in the high energy group on Day 15, although this difference did no t reach significance (P=0.06). The proportion of corpora lutea represented by embryos was significantly lower in undernourished ewes (P<0.05). Secreti on in vitro of PG was lower in the 2 pregnant ewes of the low energy group on Day 15, and it was accompained by higher IFN tau secretion by conceptuse s recovered from these ewes. However, the limited number of pregnant ewes r ecorded on Day 15 prevented any statistical comparison. Neither mean endome trial content of progesterone nor ovarian venous progesterone concentration s and production of progesterone by luteal were affected by nutrition. The provisional results of the present experiment indicate that undernutrition may induce a reduction in the rate of secretion of IFN tau and can therefor e increase production of PG from the endometrium, This could initiate luteo lysis. The lower pregnancy rates observed in underfed ewes could be mediate d through this alteration in the signal of maternal recognition of pregnanc y. However, these findings remain to be shown in further experiments includ ing a larger number of animals, as they only represent data from 2 undernou rished animals. (C) 1999 by Elsevier Science Inc.