Effect of estradiol benzoate used at the start of a progestagen treatment on superovulatory response and embryo yield in lactating and non-lactating llamas

Two experiments were conducted to determine the effect of estradiol benzoate (EB) and intravaginal progestagen treatment on ovarian follicular dynamics and superstimulatory response in eCG-treated llamas. The purpose of Experiment 1 was to evaluate the effect of EB and progestagen treatment starting at different phases of dominant follicle (DF1) development on regression pattern and subsequent follicle wave emergence (WE2) in lactating and non-lactating llamas. Early lactating (n =24, 30±4 days postpartum) and non-lactating (n =24) females were assigned in equal numbers (n =8) to one of three groups according to the phase of DF1 (growing, static or regressing) determined by ultrasonography from day −3 to day 0. At day 0, llamas received an intravaginal sponge (MPA, 150mg) and 5mg of MPA (i.m.). Half of the females (n =4) of each group were injected with 2mg (i.m.) of EB and half were not (control group). A 2×2×3 (lactational status, EB treatment and follicular phases) factorial design was used. Each sponge was removed 8 days later. Ovaries were monitored from day 0 to day 12. Daily blood samples were taken to determine 17β-estradiol (E₂) profiles from day 0 to day 8. The DF1 regression pattern was not affected (P >0.05) by the phase of follicle wave at the start of the treatment or any interactions among main effects. Follicle wave emergence in EB-treated llamas was delayed (P <0.05) by 2.3 days compared with non-treated llamas. Following EB treatment, plasma concentrations of E₂ were greater (P <0.05) from day 1 to day 5 in the treated than in non-treated females, but not from day 6 onward (P >0.05). Experiment 2 was designed to evaluate the effect of this treatment on the ovarian superovulatory response and embryo yield following eCG treatment administered on day of follicular wave emergence as determined in the Experiment 1. The same lactating (n =18, 61±4 days postpartum) and non-lactating (n =18) llamas at random stages of follicle wave were treated as those in Experiment 1 and received 1200IU of eCG at the time of WE2 (EB-treated=day 6.5 and non-treated=day 4.5). Llamas were mated 5 days after sponge withdrawal. A second mating was allowed 24h later. Embryos were collected between 7 and 8 days after the first mating and blood samples were taken to determine progesterone (P₄) concentrations. The mean number of follicles on day of mating and the number of CL on day of embryo collection were not affected by lactational status, EB treatment or their interactions (P >0.05). Ovulation rate and mean (±SEM) number of recovered embryos for EB treatment group (67.5% and 2.4±0.4) were greater (P <0.05) than for no EB treatment (51.1% and 1.1±0.4). Plasma P₄ concentrations and number of CL per llama were correlated (r =0.49; P =0.014). In conclusion, progestagen plus EB treatment facilitates the prediction of the emergence of a new follicular wave approximately 6 days after treatment and resulted in a higher ovulation rate and embryo production in ovarian superstimulated llamas regardless of lactational status.