EFFECT OF PREMATING NUTRITIONAL-STATUS AND POSTMATING PROGESTERONE SUPPLEMENTATION ON EMBRYO SURVIVAL AND CONCEPTUS GROWTH IN GILTS

This experiment was designed to investigate embryo survival and conceptus growth to Day 30 of pregnancy in five groups of gilts which had been subjected to different combinations of pre-mating diets and post-mating progesterone supplementation. In three of the five groups, gilts received 50, 100 or 200% of standard rations prior to mating. In the remaining two groups, gilts were fed ad libitum for 11-14 days prior to mating. One of these groups of ad libitum-fed gilts received progesterone injections from Day 4 after mating, whereas the remaining ad libitum fed gilts received no exogenous steroid. Consumption of 50, 100 or 200% of standard rations for two oestrous cycles prior to mating resulted in ovulation rates of 14.2, 15.0 and 17.0 respectively, but significantly greater numbers of corpora lutea (19.2) were observed in gilts fed ad libitum for 11-14 days prior to mating. In gilts exhibiting such high ovulation rates as a consequence of ad libitum feeding, supplementary post-mating progesterone increased the number of viable foetuses on Day 30 +/- 3 from 12.4 (66.4% of ovulations) in gilts receiving no exogenous steroid to 15.9 (82.8% of ovulations). Consumption of 50, 100 or 200% rations prior to mating did not significantly affect either the number or the percentage of viable foetuses on Day 30 +/- 3. Gilts which consumed 50% rations prior to mating had lighter foetuses on Day 30 +/- 3 of pregnancy. There were no further effects of pre-mating nutritional status on measures of conceptus growth on Day 30 +/- 3 of pregnancy. Exogenous progesterone increased both the volume and the glucose content of allantoic fluids on Day 30 +/- 3 of pregnancy. Within gilts, there was a linear relationship between position in the uterus and foetal weight, allantoic fluid volume and allantoic glucose content and total protein content. There was a quadratic relationship between foetal length and position in the uterine horn, with longer foetuses in the mid-portion of each horn. Although based on relatively small numbers of gilts, these observations provide an indication of one of the mechanisms by which nutrition affects fertility and suggest a potential means of increasing porcine prolificacy by appropriate nutritional and hormonal modifications. The efficacy of such an approach requires confirmation following extensive trials.