Endogenous Cortisol, Luteinizing Hormone, and Testosterone Secretion and GnRH-induced Luteinizing Hormone and Testosterone Secretion in Prenatally Stressed Sexually Mature Brahman Bulls

The purpose of this experiment was to determine the effects of prenatal transportation stress (PNS) on LH, testosterone, and cortisol secretion before and after GnRH stimulation in sexually mature Brahman bulls. Forty-eight Brahman cows were exposed to a transportation event at 5 stages of gestation (and 48 cows were non-transported controls). Bulls from these cows were electroejaculated every 2 wk beginning at a scrotal circumference of 24 cm through sexual maturity (i.e., 500 million sperm/ejaculate). The initial 11 control and 12 PNS bulls to reach sexual maturity were selected for endocrine evaluation. Within 7-21 d after reaching sexual maturity, bulls were fitted with jugular cannulas, and blood samples were collected at 15-min intervals for 6 h. Exogenous GnRH was then administered intravenously (10 ng/kg BW) and blood collection continued at 15-min intervals for an additional 8 h. Concentrations of LH, testosterone, and cortisol in serum were determined. Amplitude and maximum concentration of a detectable LH pulse and testosterone response, baseline concentration, average concentration in the h prior to GnRH administration, and area under the curve were calculated for LH and testosterone in the 4-h period immediately preceding and 6-h period immediately following GnRH administration. Cortisol in the h prior to GnRH administration and area under the curve were calculated for the 4-h period immediately preceding GnRH administration. Duration of the GnRH-induced LH release was determined. More PNS (10 of 11) than control (3 of 12) bulls exhibited an LH pulse prior to GnRH administration (P<0.01). More PNS bulls exhibited an endogenous testosterone response to endogenous LH secretion (9 of 11; P=0.02) relative to control bulls (4 of 12). In the h preceding GnRH administration, testosterone was greater (P=0.0064) in PNS compared to control bulls, and cortisol was lower in PNS compared to control bulls. No other characteristic associated with the release of LH, testosterone, or cortisol secretion prior to GnRH administration differed between groups (P>0.1). Bulls responded similarly to exogenous GnRH, except duration of GnRH-induced LH release which was greater (P=0.02) in PNS (268?18 min) relative to control (207?16 min) bulls. Prenatal stress affected postnatal secretion of LH, testosterone, and cortisol in sexually mature Brahman bulls.