Twenty-four-hour secretion patterns of luteinizing hormone in mithuns (Bos frontalis)

A 24 h secretion pattern of luteinizing hormone (LH) was not available in mithun (Bos frontalis), a semi-wild ruminant. To characterize the 24 h LH profiles, six female mithun calves (age 7.8 +/- 0.5 months and 102.5 +/- 15.6 kg; group 1) and six female mithuns averaging 25.4 months of age and 240 kg (group 11) were selected from the National Research Centre on Mithun farm and were maintained in semi-intensive systems. Blood samples collected from all the animals at 30 min intervals for 24h were assayed for plasma LH. Plasma progesterone was also estimated in twice-a-week samples collected for 6-week period preceding each 24 It sampling to assess whether any animal had begun ovarian cyclicity. The body weights of all animals were also recorded weekly during the 6-week period. LH patterns consisted of frequent pulses of varying amplitude. Luteinizing hormone pulses occurred at an average frequency of 0.28/h (approximate to 7 pulses/24 h) and 0. 15/h (approximate to 3.5 pulses/24 h) for mithuns of groups 11 and 1, respectively, the rate did not differ markedly among mithuns within each group but was significantly different between the groups. Similarly, the magnitude of LH secretory pulses did not vary among mithuns within the group but was significantly higher in group 11 than in group I animals. In group 11, the LH peaks averaged 1.59 and 1.00 ng/ml in mithun having the highest and lowest LH peaks, respectively and the corresponding values for group I mithuns were 0.66 and 0.51 ng/ml. Mithun with higher peak LH levels also had higher mean LH concentrations (P < 0.05). The mithuns of group 11 had significantly higher plasma progesterone concentration (0.89 +/- 0.02 ng/ml) than those recorded in group I mithuns (0.26 +/- 0.01 ng/ml). Plasma progesterone profiles suggested that no animal reached puberty. In conclusion, there was higher LH secretion with higher pulsatility and greater amplitude in group 11 mithuns than exhibited in mithuns of group I and the prepubertal mithuns of group 11 were in approaching puberty, which were also indicated by their plasma progesterone profiles, critical body weight and age required to attain puberty, in addition to higher pulsatility of LH secretion. (c) 2005 Elsevier Inc. All rights reserved.