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Control of ovarian follicular dynamics in early postpartum llama (Lama glama)

Abstract:

The effect of treatment with medroxiprogesterone acetate (MPA, intravaginal sponge) combined with or without injection of estradiol benzoate (EB) on the patterns of follicular regression, follicular wave emergence and ovulation rate in early postpartum and non-lactating llamas was evaluated. This work was carried out at the Experimental Station of Altitude INTA Abra Pampa (3484 m above sea level). A total of 48 adult females were categorized as lactating (n= 24; 30±4 d postpartum, mean±SD) or non-lactating (n= 24). Each one was distributed according to the follicular phase (FP= growing, static or regressing) of dominant follicle (DF1) determined by daily ovarian ultrasonography from 3 days before treatment. At day 0, intravaginal sponge (150 mg MPA) was inserted to all llamas for 8 days plus 5 mg MPA (im). Half of the females randomly received 2 mg of EB (im). The ovarian response was monitored daily by ultrasonography from day 0 to day 14. At day 12, females having a new dominant follicle ≥6 mm (DF2) were treated with GnRH (8 μg, im) to induce ovulation. Blood samples were collected to determine plasma estradiol-17β (from day 0 to day 8) and progesterone (day 14) concentrations to confirm ovulation. Factorial design 2 x 2 x 3 (lactational status, treatment with or without EB and follicular phases) was used. There was lactational status by FP interaction on the regression patterns of DF1 attributed to greater duration in non-lactating females (6.0 days) than for lactating females (3.5 days) in the follicular static phase. The day (mean±SEM) of follicular wave emergence was different (p<0.05) between treatments (with EB= day 6.5±0.6 vs. without EB= day 4.5±0.5). At day 12, the DF2 diameter (mean±SEM) was affected (p<0.05) by the treatment (with EB= 6.4±0.3 mm vs. without EB= 8.2±0.3 mm) and the lactational status (nonlactating= 8.0±0.4 mm vs. lactating= 6.6±0.3 mm). The total ovulation rate (females with ovulation/ treated females) in EB-treated females (45.8%) was lower (p<0.05) than non-treated females (82.6%). In conclusion, the MPA treatment (intravaginal plus intramuscular) combined with injection of EB approximately delayed in two days the emergence of a new follicular wave. Therefore, follicular diameter at day 12 and the ovulation rate were lower than no EB treatment. Lactation was associated with depressed follicular development, however, it did not affect the ovulation rate.