Testicular morphology and function in boars differing in concentrations of plasma follicle-stimulating hormone

The objective of this study was to evaluate morphological characteristics and testicular function of boars with different endogenous concentrations of FSH. Boars were selected at 6 mo of age on the basis of mean FSH concentrations in plasma collected at 4, 5, and 6 mo of age. Boars were classified within half-sibling families based on whether they had high concentrations of FSH (HiFSH, > 500 ng/ml, n = 9) or low concentrations (LoFSH, < 500 ng/ml, n = 7). At 14.5 mo, testes were collected, fixed, sectioned at 1 microm, and evaluated for morphological characteristics. Boars with LoFSH had larger (p < 0.01) testicular and epididymal weights than boars with HiFSH, greater (p < 0.01) daily sperm production per gram of testis, and greater total daily sperm production per boar. Testes of boars with LoFSH had a greater (p < 0.03) volume percentage of seminiferous tubules, a lesser percentage (p < 0.03) of Leydig cells, and a somewhat lesser (p = 0.06) percentage of vascular structures than testes of boars with HiFSH. Testes of boars with LoFSH had greater (p < 0.01) total tubule volume and tubule length than testes of boars with HiFSH. There were no differences (p > 0.70) in volume, diameter, or total number of Leydig cells or in total interstitial volume in testes (p > 0.41) of these two groups. Production of testosterone in vitro per paired testis and per million Leydig cells was not different (p > 0.65) between boars with HiFSH or LoFSH. Greater concentrations of FSH in blood plasma were negatively associated with development of seminiferous tubules and spermatogenic efficiency, whereas Leydig cell development was not different in boars of these two groups.