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The effects of prenatal stress and postnatal temperament on age and body weight at first sperm, puberty and sexual maturity in Brahman bulls
The objectives of this study were to determine if prenatal stress (PNS) or postnatal temperament affect age and BW at first sperm, puberty and sexual maturity. Based on temperament pregnant Brahman cows were assigned to a control (n=44; C) or transport group (n=45; transportation stress for 2 h on 60, 80, 100, 120 and 140±5d of gestation; PNS). At weaning bulls (n=25 C and n=18 PNS) were selected for this study. Temperament was assessed at weaning using temperament score [TS; (PS+EV)/2], pen score (PS; 1=Calm and 5=Excitable), and exit velocity (EV=m/s). These TS were then converted into temperament classes of calm (TS= < 1.78, n= 26), intermediate (TS=1.7 to 2.90, n= 9) and temperamental (TS= > 2.90, n= 8). Bulls were measured every 2 wk from 10 mo of age for BW, scrotal circumference (SC), and right and left testis length. Electroejaculation was used to collect semen when SC reached 24 cm. Semen was analyzed for sperm motility and concentration using a hemacytometer. Sexual maturation was characterized by first sperm (the first visible sperm in the ejaculate), puberty (50 X 106 sperm in the ejaculate) and sexual maturity (500 X 106 sperm in the ejaculate). Paired testes volume (PTV) was calculated as PTV=[0.0396125 X (average testes length) X (SC) 2]. Dependent variables were analyzed using repeated measures, mixed linear models. Fixed effects included temperament class, treatment, and interaction effects. Random animal effects were across repeated days. Age at first sperm, puberty and sexual maturity were similar between C and PNS bulls (P=0.47, 0.73, 0.99, respectively). Times between first sperm and puberty (P=0.32) and puberty to sexual maturity (P=0.92) were not affected by PNS. Temperamental bulls had a greater (P=0.009) time (69.25±11.45 d) from puberty to sexual maturity than calm (28.47±7.53 d) or intermediate bulls (38.19±9.95 d). BW at first sperm was greater for PNS (382.16±11.29 kg) than C bulls (353.19±10.55 kg). Scrotal circumference at first sperm was greater (P=0.03) in temperamental (26.8±0.7 cm) than calm (25.5±0.5 cm) or intermediate (25.1±0.6 cm) bulls. There was a tendency for temperamental bulls to have a greater PTV at first sperm (P=0.06) and sexual maturity (P=0.07) than calm or intermediate bulls. While PNS influenced BW, SC and PTV at first sperm, ages at puberty or sexual maturity were not affected by PNS. Temperamental bulls had retarded sexual development between puberty and sexual maturity.
Keywords: prenatal stress, temperament, bull sexual maturity