The influence of duration of photoperiod and hemicastration on growth and testicular and endocrine functions of boars

Abstract

Yorkshire boars were used to evaluate the influence of duration of photoperiod and hemicastration on growth and testicular and endocrine functions. At 10 wk of age, 5 hemicastrate (HC) and 5 intact (I) boars were assigned to either 8 or 16 hr of light daily until 6 mo of age. Body weights were recorded biweekly throughout the experiment. Venous cannulae were placed in all boars at 6 mo of age, and serum was collected at 30 min intervals from 0800 to 2000 hr. Gonadotropin releasing hormone (GnRH) was infused at 2000 hr (50 μg) and at 2030 hr (250 μg), and samples of serum were collected until 2400 hr. The following day, all boars were castrated, and the weights and sperm content of the testes and epididymides were determined. At castration, all pigs were given implants containing testosterone. Two weeks later, pigs were again canulated, and serum was obtained at 15 min intervals for 2 hr. Growth of boars was not significantly affected by duration of photoperiod or number of testes. Duration of photoperiod did not affect weight or sperm content of testes or epididymides. Hemicastrated boars had greater testicular (P<.01) and capita-corpora (C-C) epididymal weights (P<.05) and more testicular and C-C sperm (P<.01) per testis. Neither average concentrations of luteinizing hormone (LH) nor number and amplitude of pulses of LH were affected by photoperiod treatment. However, HC boars had greater average concentrations of LH (P<.05) than I boars (.71 ± .05 vs .52 ± .05 ng/ml). Hemicastrated boars in 16 hr light daily had greater concentrations of FSH in serum (P<.05) than 8I, 8HC, and 16I boars. Intact and HC boars had similar concentrations of prolactin (PRL) and testosterone. Similarly, concentrations of PRL and testosterone were not affected by duration of photoperiod. Secretion of LH and testosterone after treatment with GnRH was not significantly affected by duration of photoperiod. In general, HC boars released more LH in response to GnRH treatment than I boars. Concentrations of LH were greater (P<.05) in HC than I boars at .5, 1, 2, and 3 hr after GnRH and tended (P<.10) to be elevated at 1.5, 2.5, 3.5 and 4 hr after GnRH. The FSH response to GnRH was greater (P<.05) for 16HC than 8I, 8HC, or 16I boars. At 2.5 and 4 hr after GnRH, when no photoperiod by number of testes interaction was observed, duration of photoperiod did not affect concentration of FSH in serum, but HC boars had greater (P<.05) concentrations of FSH than I boars. Following castration and implantation with testosterone, concentrations of LH were similar for pigs in both photoperiods and from both previous gonadal statuses. However, concentrations of FSH were greater (P<.05) following removal of the remaining testis from HC boars (17.1 ± 1.1 ng/ml) than following castration of I boars (13.3 ± 1.3 ng/ml). We conclude that the testes and epididymides of HC boars contain more sperm than those of I boars at 6 mo of age, but body growth and concentrations of testosterone and PRL in serum are not significantly altered by duration of photoperiod or HC. Hemicastrate boars secrete more LH and FSH in response to exogenous GnRH than I boars. Regulation of secretion of FSH established during puberal development persists in post puberal boars after removal of the testes.