Effect of hCG administration on corpus luteum development and plasma progesterone concentration in llamas

This study aimed to evaluate the effect of hCG injection on Day 3, 4 or 5 post-induction of ovulation on corpus luteum (CL) function in llamas and then, to evaluate its effect on pregnant animals. After induction of ovulation with buserelin (Day 0), llamas were randomly assigned to one of four groups: hCG3 (n = 5), hCG4 (n = 5), hCG5 (n = 5) or control (n = 5), receiving an injection of 750 IU of hCG on Day 3, 4 or 5 or 1.5 ml of saline solution, respectively. All females were examined by transrectal doppler ultrasonography, every other day from Day 6 until Day 12. Blood samples for P4 determination were collected daily from Day 2 to Day 8 and every other day until Day 12. Llamas with hCG4 showed higher plasma P4 concentration on Day 10, higher AUC and plasma P4 remained above 1 ng ml-1 for more days than the control group. Based on these results, Study 2 was performed. Llamas were mated and randomly divided in “Treated” (n = 10) and “Control” (n = 10) group, receiving an injection of 750 IU of hCG or saline solution on Day 4 post-induction of ovulation, respectively. Doppler ultrasonography and blood collection for P4 evaluation were also performed daily, from Day 6 until Day 16 post mating. Plasma P4 concentration post-mating tended to be greater in pregnant treated llamas than in non-treated pregnant females. These results suggest that hCG administration on Day 4 has a luteotropic effect.