Factors affecting the survival of sheep embryos after transfer within a MOET program

University of Wales, Cardiff, Wales, United Kingdom
Theriogenology (Impact Factor: 1.85). 03/2003; 59(5-6):1265-75. DOI: 10.1016/S0093-691X(02)01162-7
Source: PubMed

ABSTRACT Multiple ovulation and embryo transfer (MOET) has the potential to increase the rate of genetic improvement in sheep. However, better realization of this potential requires maximum survival rates of transferred embryos of high genetic merit after transfer into recipient ewes. These studies were therefore conducted to investigate the effect of both embryonic and recipient ewe factors on the survival rate of transferred embryos. Survival rate was similar after transfer of morula or blastocyst stage embryos, and these were higher (P<0.05) than for very early morulae and early morulae. Advanced embryos (Day 5 blastocyst) had an advantage (P<0.05) in survival rate over retarded embryos (Day 6 morula). Grades 1 and 2 embryos survived significantly (P<0.05) better than Grades 3 or 4 embryos. There was no difference in embryo survival rate following transfer to recipients with different numbers of corpora lutea. In general, age or parity of recipient ewes did not affect embryo survival rate, although a higher (P<0.05) embryo survival rate was observed for yearling recipients. Buserelin (GnRH agonist) treatment of recipient ewes 5 or 6 days after transfer of embryos (Day 12 of the cycle) did not improve embryo survival rate. These results confirm that both embryonic and recipient factors can play an important role in the success of a MOET program in sheep.

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    ABSTRACT: The present study was undertaken to investigate the contribution of laparoscopic insemination to the improvement of fertilization and embryo recovery. The experiment was conducted in breeding season. Twelve nonpregnant and cycling Awassi ewes of 3-4 years of age were randomly allocated in equal number (n = 6) to two groups. Each ewe was treated with progesterone impregnated intravaginal sponge for 12 days. All ewes were superovulated with eCG (equine chorionic gonadotropin) 1200 IU once by intramuscular injection 48 h prior to sponge removal. Ewes of group 1 were mated naturally at least two times with Awassi rams of proven fertility. Ewes of group 2 had intrauterine insemination and were conducted 44-46 h after sponge removal, under laparoscopic visualization of uterine horns, depositing 1 ml of semen in the distal portion of each uterine horn. Ovarian response was assessed by determining number of corpora lutea by laparoscopy on day 6 after mating. Embryo recovery was performed by semi-laparoscopic and by flushing of both uterine horns. Results of the present study revealed high number of unfertilized ova (P<0.05) was observed in ewes when naturally inseminated than ewes inseminated intrauterine using laparoscopic technique. Higher rate of embryo recovery (P<0.05) was achieved when ewes inseminated via intrauterine (4.66 ± 0.66) than ewes naturally mated (2.16 ± 0.74). The fertilization rate in ewes inseminated intrauterine using laparoscopic techniques and naturally mated were 79.93% and 40.07%, respectively. Fertilization failure in ewes inseminated intrauterine using laparoscopic techniques and naturally mated were 7.37% and 49.35%, respectively. It could be concluded that the use of eCG to induce superovulation in Awassi ewes combined with laparoscopic intrauterine insemination can increase the fertilization rate.
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    ABSTRACT: The aim of this study was to compare the efficacy of two different short-term progestagen treatments for estrus synchronization in cyclic ewes. A total of 292 ewes of 3 flocks (A-C) on different farms were treated for 6 days with Eazi-breed (TM) CIDR (R) G (n = 145) or Chronogest (R) CR (n = 147) vaginal inserts in combination with 0.125 mg Cloprostenol and 300IU eCG at device removal. Blood samples were taken for progesterone (P4) determination at insert application and removal as well as 14 days later. One day after insert removal rams fitted with marking harnesses were joined to ewes for 35 days and marked ewes recorded daily. Lambing data were recorded and fertility to first service period and overall assessed. Results show that 24-96 h after insert removal 98.8% and 89.4% of the synchronized ewes in the flocks B and C were in estrus. Estrus response was not affected by the type of progestagen treatment and was lower (P < 0.05) in nulli- (82.1%) than in pluriparous (97.5%) ewes. Type of progestagen treatment did not affect fertility, but flock and parity influenced the percentage of ewes that lambed as well as the lambing rate. Overall more ewes (P < 0.001) lambed in flock A compared to flocks B and C (93.0 vs. 72.5 and 59.1%). In nulliparous animals the percentage of ewes that lambed was higher to the first service (P < 0.05) period but lower (P < 0.001) to the overall service period compared to pluriparous animals (51.5% vs. 49.3% and 64.7% vs. 84.2%). Lambing rates were higher in flock A than in flocks B and C to first service period and overall (1.3 +/- 1.4, 0.9 +/- 1.0, and 0.7 +/- 1.0, P < 0.01 and 1.9 +/- 1.1, 1.3 +/- 0.9, and 1.0 +/- 1.0, P < 0.001) and in nulliparous overall lower than in pluriparous ewes (1.1 +/- 1.1 and 1.6 +/- 1.1, P < 0.01). Serum P4 concentrations measured 14 days after insert removal were higher in the Chronogest (R) CR than in the Eazi-breed (TM) CIDR (R) G group (6.8 +/- 4.1 ng/mL vs. 5.7 +/- 3.3 ng/mL). Ewes of flock A had higher P4 values compared to ewes of flocks B and C (8.3 +/- 4.1 ng/mL vs. 4.5 +/- 1.5 ng/mL and 3.8 +/- 1.7 ng/mL) and nulliparous lower P4 concentrations than pluriparous ewes (4.5 +/- 2.2 ng/mL vs. 6.7 +/- 4.0 ng/mL). In conclusion, a 6-day treatment with Chronogest (R) CR and Eazi-breed (TM) CIDR (R) G with prostaglandin and eCG at insert removal resulted in high estrus response and similar fertility in cyclic ewes.
    Small Ruminant Research 10/2012; 107(2-3):141-146. DOI:10.1016/j.smallrumres.2012.05.014 · 1.10 Impact Factor

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