Secretion patterns of luteinizing hormone in growing mithuns (Bos frontalis).

To characterize the luteinizing hormone (LH) secretion patterns in growing mithun (Bos frontalis), a semi-wild ruminant, six female mithuns (1 year old; BW: 145.5 kg) were maintained in a semi-intensive system. Plasma progesterone (P(4)) level was measured in twice-a-week samples collected for six weeks to assess ovarian status. This was followed by a frequent sampling period. Blood samples collected at 15 min intervals for 9 h were assayed for plasma LH. Luteinizing hormone patterns consisted of pulses of varying amplitudes. Luteinizing hormone pulses occurred at an average rate of 0.54/h ( approximately 5 pulses/9 h). The rate did not differ among mithuns. The mean plasma LH levels was correlated with body weight (r=0.82; p<0.05) and pulse amplitude (r=0.87; p<0.01). Neither the LH amplitude nor the frequency was affected by time (p>0.05). The mean plasma P(4) concentration was 0.37 ng/ml. In conclusion, we demonstrated a pulsatile nature of LH secretion in growing mithuns. In addition, the mean plasma LH level and LH amplitude were positively correlated with body weight. It appears that in contrast to cattle, five LH pulses per nine hours recorded in mithuns were not an indication of approaching puberty.