Photoperiodic effects on pubertal maturation of spermatogenesis, pituitary responsiveness to exogenous GnRH, and expression of boar taint in crossbred boars.

Forty-eight weaned, winter-born crossbred males (average age of 42 days) were exposed to either a natural photoperiod (January-June at 60 degrees N, Control) or one of two artificial photoperiods (1400 lx) in light-sealed rooms. The Spring/Summer group was exposed to an artificial photoperiod simulating conditions from the vernal equinox (mid-March) to August at 60 degrees N and the Autumn/Winter group to a photoperiod, simulating conditions from the autumnal equinox (mid-September) to February at 60 degrees N. Plasma samples were collected biweekly until the pigs were slaughtered, after reaching 115 kg, and analysed for testosterone, estrone sulfate, thyroxine and prolactin. Additionally, three animals per treatment (n = 9) were injected with gonadotropin-releasing hormone (GnRH) and plasma samples were collected every 15 min and analysed for luteinizing hormone and testosterone. Boar taint, carcass composition and reproductive traits were measured at slaughter. Live-weight gain from start to slaughter was lower among the Control animals compared with the Autumn/Winter and Spring/Summer animals. There was a peak in plasma testosterone in both the Spring/Summer and Autumn/Winter groups at 71 days of age, whereas plasma testosterone in the Control group remained at prepubertal levels. At 113 and 127 days of age, the Control group had somewhat higher testosterone levels than the Spring/Summer group, but at 141 days of age and on the day before slaughter, the Autumn/Winter group had a higher mean plasma testosterone concentration. There were no differences between treatments in the endocrine response to the GnRH challenge. Bulbourethral gland weight at slaughter was lower in the Spring/Summer group than in the Autumn/Winter group. The percentage of proximal cytoplasmic droplets was higher in the Spring/Summer group than in both the Control and Autumn/Winter groups. Spermatogenesis at the time of slaughter was clearly more mature in animals in the Autumn/Winter group than in those in the Spring/Summer and Control groups. Fat androstenone was lower in the Spring/Summer group than in the Control group. In the sensory evaluation, the Spring/Summer group had less boar taint than the Autumn/Winter group. Artificial short days with moderate initial changes in photoperiod, stimulated spermatogenesis compared with long days, in accordance with the pattern seen in European Wild Boars (Sus scrofa). Boar taint was also affected with higher scores in the Autumn/Winter group than in the Spring/Summer group, although this was not clearly indicated by the traditional measurements of boar taint-fat contents of androstenone and skatole.