The relationship of plasma leptin concentration and puberty in Holstein bull calves (Bos taurus).

The objective of this experiment was to study the changes of plasma leptin concentration during puberty and its relationship with testosterone level and testis dimensions in Holstein bull calves. Six Iranian Holstein bull calves with approximately 6 months of age were used. Semen evaluation was conducted at 1-month interval to determine the puberty state. To detect the plasma leptin and testosterone changes, blood samples were collected from the jugular vein during pre-puberty (6-7 months of age), puberty (8-9 months of age) and post-puberty (10-11 months of age). In addition, body weight (BW), body condition score (BCS) and testicular width and length were measured at 3-week intervals. The effects of time (age) on total sperm number and percentage of progressive motility of sperm, plasma concentration of leptin and testosterone, amplitude and frequencies of testosterone, BW, BCS, testicular dimensions were significant. Sperm number and progressive motility during post-puberty were higher than those during puberty and pre-puberty. Plasma concentration of leptin during the pre-puberty was higher than those during puberty and post-puberty (p < 0.01). Mean plasma testosterone concentrations during puberty were higher than those during pre-puberty (p < 0.05). BW, BCS and testicular dimensions consistently increased throughout the trial. Results indicated that in growing bull calves, plasma concentrations of leptin decreased during puberty, while circulating testosterone increased.