Abstract
Multiple ovulation and embryo transfer (MOET) is well accepted and applied worldwide as a powerful tool to disseminate high-quality genetics in livestock. The objectives of this study were to i) determine ovarian follicular dynamics, ii) select an appropriate progesterone device in oestrus synchronization superovulation treatment protocol and iii) determine a suitable embryo vitrification protocol in indigenous sheep. Ovarian follicular dynamics was observed by daily transrectal ultrasonography of the ovaries, measuring VER by electrical heat detector and analyzing peripheral blood progesterone level by ELISA. For embryo production by progesterone device (PD) technique, the donor ewes were induced for oestrus using either CIDR® or Ovigest® or CronogestR for 12 days. Superovulation was induced using pFSH (200 mg, decreasing manner, twice daily, 4 days) in all cases. In some donor ewes (n=10), superovulation treatment (pFSH doses) was started on day 4, and cloprostenol (125 μg, single dose) was injected on day 6 of natural oestrous cycle (Day 0 Day of oestrus) without use of progesterone device (WPD). On detection of oestrus, natural service was performed by fertile ram. Superovulation response (No. of CL≥ 3) was observed and embryos were collected from donor by uterine flushing using inguinal mini laparotomy technique. Grade 1 fresh or vitrified (vitrification protocol 1 and protocol 2) embryos were transferred to recipient ewes by using the same technique. In a cycle of 16.4±0.2 days, 2-4 waves (mostly 3 waves, 67%) of follicular growth occurred with an inter wave interval of 5.1±0.1 days. Size of the preovulatory follicle was 6.3±0.1 mm and the ovulation rate was 1.2±0.1 per cycle. The lowest VER value of 372.9±12.8 was observed just before oestrus, while the value was highest (554.0±2.72) during dioestrus. Serum P4 concentration went down to 0.5±0.0 ng/ml in around oestrus and increased to 3.2±0.1ng/ml by 7-9 days of ovulation. VER and serum progesterone level were positively correlated. Oestrus response was the highest (100%) in CIDR group. Superovulation response was excellent (100%) in CIDR and Ovigest group; but it was lower (90.9%) in Cronogest group. Superovulation rate was the highest in CIDR group (12.0±1.4), followed by Cronogest (11.4±1.9) and Ovigest group (8.4±1.0). The observed embryo recovery rate varied from 81.7% 91.2%; the rate was higher in Cronogest and Ovigest group compared to CIDR group. The proportion blastocyst stage and grade 1 embryo was the highest in each group. The number of usable embryo was higher in CIDR and Cronogest group (8.6±1.4 and 8.7±2.1/donor) compared to Ovigest group (6.8±0.1/donor). Pregnancy, lambing, twining and embryo survival (at lambing) rate was 70%, 60%, 66.7% and 50%, respectively with fresh embryo transfer. Grade 1 warmed embryo was higher in vitrification protocol 2 than protocol 1 (84.7% vs. 80%). The pregnancy (58.3% vs. 33%), lambing (83.3% vs. 50%), twining (50% vs. 33.3%) and embryo survival rate at lambing (45.8% vs. 25%) was higher with embryos vitrified by protocol 2 than protocol 1. The ewes treated for superovulation without progesterone device (WPD) responded excellent (100%) for both oestrous and superovulation. Ovulation and embryo recovery rate was 10.5±1.24/ewe and 80.95%, respectively. Produced usable embryo per ewe was 7.3±1.3. Pregnancy rate was lower (60% vs. 70%), but embryo survival rate at lambing was higher (55% vs 50%) with fresh embryo produced by WPD compared to PD technique. On vitrification, Grade 1 warmed embryo was lower in embryos produced by WPD technique than PD technique (80.6% vs. 84.7%). The pregnancy (70% vs. 58.3%) and embryo survival (at lambing) rate (60% vs. 45.8%) was higher with vitrified embryos produced by WPD technique than PD technique. Vitrified embryo transfer following natural oestrus produced lower pregnancy (50% vs. 58.3%) and embryo survival (40% vs. 45.8%) rate as compared with induced oestrus in ewes. The study fulfilled the objectives successfully. Continued controlled studies are necessary for optimization with a pilot programme at the field level to improve sheep production in Bangladesh.