Pregnancy and lambing rates in anestrous ewes bred to a new synchronization protocol and laparoscopic timed artificial insemination (TAI)
Reproductive performance in seasonally anestrous ewes is poor even after the application of conventional controlled breeding techniques. Estradiol-17β (E2) has been shown to synchronize follicular wave emergence in anestrous ewes treated for 12 or 14 d with a medroxyprogesterone acetate sponge. The objective of this study was to determine the effects of an E2 treatment administered 6 d after CIDR insertion on E2 concentrations, estrus, pregnancy rates, and lambing rates in ewes bred out of season. Ewes from three farms (Farm A: n=22; Farm B: n=48; Farm C: n=28) received CIDRs (Day -12) followed by an injection of eCG (500 IU; Day 0) at CIDR removal and an injection of sesame oil without (1 ml; Control) or with E2 (350 µg; Day -6) 6 d before CIDR removal. Treatments were balanced for breed, age, parity, and BCS. Blood samples were taken from half of the ewes on Day -6 and 0 to determine E2 concentrations. On Day 1 ewes were exposed to rams to observe estrus. Ewes were subjected to laparoscopic TAI on Day 2. Pregnancy was diagnosed by transabdominal ultrasonography on Day 50. Estrus, pregnancy rates, and lambing rates were analyzed using logistic regression. Day of lambing and E2 concentrations were analyzed using ANOVA. The percent of ewes observed in estrus within 36 h of CIDR removal was similar between treatments (E2: 24.5%; Control: 34.7%; P>0.05). Pregnancy rates were similar between treatments (E2: 40.8%; Control: 40.8%; P>0.05) and were higher on Farm C than Farm B (Farm A: 45.5%; Farm B: 22.9%; Farm C: 67.9%; P<0.05). Lambing rates were also similar between treatments (E2: 34.7%; Control: 34.7%; P>0.05) and were higher on Farm C than Farm B (Farm A: 40.9% Farm B: 16.7%; Farm C: 60.7%; P<0.05). Relative to CIDR removal, ewes lambed earlier on Farm B (Farm A: 141.7±1.3 d; Farm B: 136.6±1.4 d; Farm C: 143.2±0.9 d; P<0.05) and ewes treated with E2 lambed earlier (E2: 138.9±1.0 d; Control: 142.2±1.0 d; P<0.05). Concentrations of E2 were similar between treatments on Day -6 (E2: 1.5±0.1 pg/mL; Control: 1.6±0.1 pg/mL; P>0.05) and Day 0 (E2: 1.6±0.1 pg/mL; Control: 1.3±0.1 pg/mL; P>0.05). Differences were mainly observed among farms potentially due to differences in breed, BCS, semen, or management practices. The addition of an E2 treatment during a CIDR-eCG heat synchronization protocol does not clearly increase pregnancy and lambing rates in seasonally anestrous ewes.
Keywords: Anestrus, ewes, controlled breeding