Physiology of the Meishan boar.

Onset of puberty (sperm production) occurs at a much younger age (56-84 days) in Meishans than in conventional boars (120-180 days). Throughout postnatal development, Meishans exhibit markedly higher (two- to ten-fold) concentrations of serum FSH, LH and androgens compared with conventional boars, and these high hormone concentrations are maintained at maturity. Increased gonadotrophin concentrations occur only in Meishan males, since concentrations in female Meishans and conventional females do not differ. In the Meishan boar, FSH increases steadily during establishment of sperm production and LH increases markedly after tubule diameter stabilizes, while FSH and LH concentrations are low and change little during this period of rapid testicular growth in conventional boars. The proportion of the testis occupied by Leydig cells is two-fold greater and average Leydig cell size is two- to four-fold larger in Meishans than in conventional boars during the onset of spermatogenesis and into maturity. Testis size in Meishans is only half that of conventional boars at maturity, and the number of Sertoli cells is markedly reduced in Meishans. However, Meishan testes exhibit reduced degeneration of germ cells and spermatids during spermatogenesis, and spermatogenic efficiency per Sertoli cell in Meishans is double that in conventional boars. At maturity, Meishan pituitaries have greater mass, larger gonadotrophs, higher content of FSH, and greater expression of genes for FSH and LH subunits than found in conventional boars. The high concentrations of serum gonadotrophins in the mature Meishan exhibit a typical postcastration rise, respond to GnRH stimulation and are suppressed by gonadal steroids, indicating that the hypothalamo-pituitary-gonadal axis functions normally but with much higher set points in Meishan boars. These unusual endocrine and physiological attributes in boars of the highly prolific Meishan breed offer a unique model for further investigation of factors influencing early onset of puberty and efficiency of male reproductive function.