Endocrine responses in the llama to copulation

Nine adult female llamas were used to determine the time course for secretion of luteinizing hormone (LH) and estradiol-17beta (E(2)) following a single copulation (average 18 min), and progesterone (P(4)) during the development of the subsequent luteal phase. Heparinized blood samples were obtained through an indwelling jugular cannula at 15-min intervals for up to 24 h following copulation and then once daily for up to 10 d. Luteinizing hormone, assayed by radioimmunoassay (RIA) using a monoclonal antibody 518B7 against the beta subunit of bovine LH, was determined at 15 min intervals for 24 h following copulation. Estradiol-17beta was determined by RIA at 4-h intervals following copulation, then daily, while P(4) values were determined daily by enzyme immunoassay. A significant increase in LH concentration was observed by 15 min after the onset of copulation, with the peak of the preovulatory surge of LH occurring at 2 h; values were basal by 7 h after copulation. Estradiol-17beta values, unchanged through 18 h after copulation, tended to decline at 22 h (24 h, P<0.10) and were significantly lower than 18 h values by 48 h (P<0.05) after copulation. The first significant P(4) increase occurred at 3 d after copulation, with values increasing through 10 d. The LH surge observed subsequent to copulation is consonant with the llama being an induced ovulator.