Evaluation of the influence of prenatal transportation stress on GnRH-stimulated luteinizing hormone and testosterone secretion in sexually mature Brahman bulls

Authors: LITTLEJOHN, BRITTNI - Texas A&M University; ROBERTS, MEGHAN - Texas A&M University; BEDENBAUGH, MICHELLE - Texas A&M University; LEWIS, ANDREW - Texas A&M Agrilife; NEUENDORFF, DON - Texas A&M Agrilife; RILEY, DAVID - Texas A&M University; Carroll, Jeffery - Jeff Carroll; VANN, RHONDA - Mississippi State University; AMSTALDEN, MARCEL - Texas A&M University; RANDEL, RONALD - Texas A&M Agrilife; WELSH, THOMAS - Texas A&M University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2016
Publication Date: 1/4/2017
Citation: Littlejohn, B.P., Roberts, M.C., Bedenbaugh, M.N., Lewis, A.W., Neuendorff, D.A., Riley, D.G., Carroll, J.A., Vann, R.C., Amstalden, M., Randel, R.D., Welsh, T.H. 2017. Evaluation of the influence of prenatal transportation stress on GnRH-stimulated luteinizing hormone and testosterone secretion in sexually mature Brahman bulls. Journal of Animal Science. 95(1):129-138.

Interpretive Summary: This research represents a continuing collaborative effort among scientists from Texas A&M University, the ARS’ Livestock Issues Research Unit, and Mississippi State University to determine the influence of repeated transportation of gestating Brahman cows on the subsequent physiological, immunological and endocrine profiles of their offspring. Previous results from this collaborative effort have demonstrated that repeated transportation of gestating cows at 60, 80, 100, 120, and 140 days of gestation alters the postnatal stress and immune responses of their offspring. Results of this present study reveal that sexually mature Brahman bulls that were exposed to prenatal transportation stress may have a stress axis that is less sensitive to stress. This potential adaptation may have allowed PNS bulls to recover more rapidly from the stress compared to bulls that were not exposed to the prenatal transportation events. The more rapid recovery from a stress response may have allowed cortisol concentrations to decline sooner in these prenatally stress bulls which may have allowed the pulsatility of their reproductive hormones such as luteinizing hormone and testosterone to resume normal activity more quickly than control bulls. These reproductive related hormones in the prenatally stress bulls might undergo suppression by cortisol for a shorter duration in times of stress compared to control bulls. These differences observed in prenatally stressed bulls may promote reproductive performance to prepare bulls to be better adapted to transmit their genetics in stressful times. This model of a higher order species can provide insight into the genetic and/or epigenetic effects of prenatal stress on postnatal health and performance of animals and humans. Future studies should examine potential mechanistic epigenetic modifications in these prenatally stressed bulls, the existence of which modifications could impact future generations. These data will be of interest to scientists in the field of stress physiology, as well as cattle producers, and can be used to modify management practices in order to improve the well-being of gestating cows.

Technical Abstract: This study examined the relationships of prenatal transportation stress (PNS) with cortisol, luteinizing hormone (LH), and testosterone secretion before and after gonadotrophin releashing hormone (GnRH) stimulation of sexually mature Brahman bulls derived from the calf crop of 96 Brahman cows (48 cows were stressed at 5 stages of gestation and 48 were controls). All bulls from this calf crop were electroejaculated every 2 weeks beginning at a scrotal circumference of 24 centimeters until sexual maturity (SM; i.e., 500 million sperm/ejaculate). The initial 11 control and 12 PNS bulls to reach SM were selected for the GnRH stimulation test. Within 7-21 days after reaching SM, bulls were fitted with jugular cannulas, from which blood samples were collected at 15-minute intervals for 6 hours prior to GnRH administration and 8 hours after GnRH administration. Exogenous GnRH was administered intravenously (10 ng/kg of body weight) and blood collection continued at 15-minute intervals for 8 hours. Serum concentrations of cortisol, LH, and testosterone were determined by radioimmunoassay. The following were analyzed for the 4-hour period immediately preceding GnRH administration: amplitude and maximum concentration of LH pulses and testosterone response; baseline concentration of LH and testosterone; average LH, testosterone, and cortisol in the hour prior to GnRH; LH, testosterone, and cortisol area under the concentration curve (AUC); and LH, testosterone, and cortisol profiles. In the 6-hour period after GnRH delivery, amplitude and maximum concentration of the GnRH-induced LH and testosterone response, duration of the GnRH-induced LH response, LH and testosterone AUC, as well as LH and testosterone profiles were compared. More (P < 0.01) PNS (9 of 11) than control (3 of 12) bulls exhibited an endogenous LH pulse prior to GnRH delivery. More (P = 0.02) PNS bulls (9 of 11) exhibited an endogenous testosterone response after GnRH delivery than control bulls (4 of 12). In the hour preceding GnRH administration, testosterone tended to be greater (P = 0.07) in PNS (1.46 ± 0.30 ng/mL) than control (0.68 ± 0.28 ng/mL) bulls, and cortisol was lower (P < 0.01) in PNS (4.00 ± 0.91 ng/mL) than control (7.8 ± 0.87 ng/mL) bulls. No other characteristic associated with LH, testosterone, or cortisol secretion prior to GnRH administration differed between groups (P > 0.1). All bulls responded similarly to exogenous GnRH in the 6-hour period after GnRH delivery. Collectively, these data indicate that prenatal transportation stress affected secretion of endogenous LH, testosterone, and cortisol secretion in sexually mature Brahman bulls.