Effects of prenatal transportation stress on endogenous and exogenously-induced LH secretion in sexually mature Brahman bulls

Abstract Text: The effect of prenatal transportation stress (PNS) on secretion of LH before and after GnRH stimulation in sexually mature Brahman bulls was studied in 12 control and 11 PNS bulls. Control bulls were derived from non-transported pregnant cows, and PNS bulls were derived from cows transported for a 2-h period at 60, 80, 100, 120, and 140 ± 5 d of gestation. Temperament of each bull was assessed at weaning by pen score (PS; 1 = calm and 5 = excitable), exit velocity (EV; m/sec) and temperament score [TS = (PS + EV)/2]. Bulls were electroejaculated every 2 wk beginning at a scrotal circumference of 24 cm through sexual maturity (i.e., 500,000,000 sperm/ejaculate). Within 7-21 d after reaching sexual maturity, bulls were fitted with jugular vein cannulas, and blood samples were collected at 15-min intervals for 6 h to determine the pattern of LH release. 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 in serum were determined by RIA. Amplitude of a detectable LH pulse, baseline concentration of LH, and area under the LH curve (AUC) were calculated for the 4-h period immediately preceding GnRH administration. Luteinizing hormone pulse incidence was evaluated using Pulse XP algorithm. The amplitude and height of the GnRH-induced LH release, AUC post-GnRH administration, and the duration of the GnRH-induced LH release were determined. Data were analyzed using a fixed effect model, with treatment and temperament classification included in the model. The occurrence of LH pulses during the pre-GnRH period was compared between treatment groups by chi-square analysis. More PNS bulls exhibited an LH pulse before GnRH injection (10 of 11; P < 0.01) than control bulls (3 of 12). No other characteristic associated with the release of LH during the pre-GnRH treatment evaluated in this study differed between groups (P > 0.1). All bulls responded similarly to exogenous GnRH, with the exception of the duration of the LH response which was greater (P = 0.02) in PNS bulls (268 ± 18 min) relative to control bulls (207 ± 16 min). Pattern of LH secretion before GnRH and duration of GnRH-induced LH release differed between PNS and control bulls. Stress during prenatal development may affect secretion of LH in sexually mature Brahman bulls.

Keywords: Bulls, Prenatal Stress, LH