Changes in plasma concentrations of luteinizing hormone, progesterone and oestradiol-17β during the periovulatory period in cyclic swamp buffaloes ( Bubalus bubalis)

Abstract

Changes in plasma concentrations of luteinizing hormone (LH), progesterone and oestradiol-17β were analysed in relation to the chronology of behavioural oestrus and ovulation in six cyclic swamp buffaloes. Blood samples were collected every 3–6 h from Day 17 of the cycle until ovulation, with additional samples for LH determination only taken at 1-h intervals during oestrus. The time of oestrus manifestation and ovulation was checked every 3 h throughout the experiments by using a vasectomized bull or by rectal palpation, respectively. Animals came in oestrus between Days 19 and 22, with a mean duration of oestrus of 20.5 ± 1.2 h (± s.e.m.). Ovulation was detected at 15 to 18 h after the end of oestrus. Plasma concentrations of progesterone began to decrease 2–3 days before oestrus manifestation. The progesterone withdrawal during luteolysis was followed by a threefold rise ( P < 0.05) in the basal LH and a sustained increase ( P < 0.05) in oestradiol concentrations. Oestradiol levels reached maximum values near the onset of oestrus and rapidly decreased to the basal levels by the end of oestrus. LH surge began immediately after the onset of oestrus and lasted 7–12 h. The LH peak (61–126 ng/ml) was observed 4–15 h after the onset of oestrus or 9–14 h before the end of oestrus. Ovulation occurred within a fixed time of 26–29 h after the LH peak. The data obtained here were basically similar to those well documented in cattle, although the cause and effect relationship between each endocrine event still requires further clarification.