Effect of estradiol-17β injections during the luteal phase on the plasma progesterone concentration in llamas

Abstract

The aim of this study was to evaluate the effect of estradiol-17β (E2)injections during the luteal phase on the plasma progesterone (P4)concentration in llamas. Twenty-one females were induced to ovu-late by GnRH injection in presence of a follicle ≥ 8 mm and randomlyassigned into one of three groups: control (n=7) without treatment;G7-8 (n=7) treated with 1.6 mg of E2 IM on Day 7 and 0.8 mg of E2IM on Day 8; and G7-10 (n=7) treated with 1.6 mg of E2 IM on Day7 and 0.8 mg of E2 IM from Day 8 to 10 post-GnRH. Blood sampleswere collected every other day from Day 0 to 7 and daily until Day 15post-GnRH to determine plasma P4 concentration by RIA. The datawere analyzed using an ANOVA test, and the effect of days withingroups was compared by a Tukey Test with Bonferroni adjustment.Mean plasma P4 concentration increased from Day 0 to Day 8 post-GnRH in all females. In the control group, mean plasma P4 con-centration decreased to below 1 ng/ml on Day 10, being statisticallydifferent from treated groups (P<0.01). In the G7-8, mean plasma P4concentration decreased between Day 11 and 12 post-GnRH, beingin those days significantly lower than in llamas from G7-10 (P<0.01).In conclusion, E2 injection from Day 7 post-induction of ovulationresults in a luteotrophic effect in llamas. The E2 administration fromDay 7 to Day 10 post-GnRH prolongs the corpus luteum function forthree more days than in control animals, which gives further supportto the hypothesis that E2 would be involved in the process of mater-nal recognition of pregnancy in this species.