Reproductive performance of ewe lambs in non-breeding season exposed to hCG at day 12 post mating

Abstract

The objective of this experiment was to determine the effect of hCG treatment at day 12 post mating on ovarian characteristics, reproductive performance and conceptus growth in ewe lambs induced estrus during the non-breeding season. Corriedale ewe lambs 8 months old were pretreated with progestagen sponges for 10 days and 300IU of eCG. At day 12 post mating, females were treated with either physiological saline (hCG-0; n: 53) or 300IU of hCG (hCG-300; n: 50). Plasma progesterone concentrations were measured at day 17 post mating by radioimmunoassay. Pregnancy was monitored by transrectal ultrasonography on day 40 post mating. At day 41 post mating, 10 ewe lambs of the hCG-0 group and 9 of the hCG-300 group with single pregnancy (randomly chosen) were euthanized and subjected to a morphometric analysis of ovary, uterine and fetal structures. Plasma progesterone levels in the hCG-300 group were significantly higher than those in the control ewe lambs (P<0.05). Pregnancy (49.18% and 46.15%), fertility (60.0% and 56.6%) and prolificacy (1.43 and 1.23) did not differ between the hCG treated and non treated ewe lambs. However, a tendency for a high number of ewe lambs with multiple pregnancies was observed in the hCG-300 group (P=0.08). The percentage of ewe lambs with multiple ovulation was higher in the hCG-300 group compared to the controls (77.8% and 20.0%; P<0.05), while ovary weight and diameters and corpora lutea area did not differ between groups (P>0.05). The length of pregnant horn in ewe lambs of the hCG-300 group showed a tendency to be greater compared with that of the hCG-0 group (P=0.08). Differences were not detected between groups for the uterine weight, number of caruncles and chorionic sac length (P>0.05). Administration of hCG at day 12 post mating increased cranium-caudal length. However, no difference was observed in biparietal diameter and fetal weight between control and hCG treated ewe lambs. Results indicate that hCG treatment did not improve pregnancy rate, prolificacy or fetal weight, however the increase in the plasma progesterone concentration and the percentage of multiple ovulations observed in ewe lambs during the non-breeding season suggest a positive action of this hormone on reproductive performance.