Onset of spermatogenesis in meishan and large white male piglets

We have compared the development of somatic and germ cells from foetal life until adulthood in Large White and Meishan male pigs. Before puberty, in b oth breeds, after logarithmic transformations, the testis weight and the to tal numbers of Leydig and Sertoli cells per testis evidenced a close linear relationship with post-conception age. During foetal life, the MS males ha d significantly lower total numbers of gonocytes, of Leydig and of Sertoli cells per testis (gonocytes: -32%, P=0.05; Leydig: -80%, P<0.001; Sertoli: P=0.001) than LW ones; the number of gonocytes per Sertoli cell was signifi cantly higher (+26%, P=0.04) in MS than in LW foetuses. At birth the stocks of Sertoli cells per testis did not differ between breeds. Total numbers o f Sertoli cells per testis increased by a factor 6 between end of gestation and adulthood in LW males and by a factor 2 in MS ones, resulting in a sig nificantly lower total numbers of Sertoli cells per testis (-72%; P<0.01%) in MS than in LW boars which had equal numbers of Leydig cells per testis. Mean individual Leydig cell diameter did not vary after birth with age in M S pigs while it significantly increased before 145 d. pc of age and later d ropped in LW prepubertal pigs. In adult, Leydig cell mean diameter was high er in MS (+24%, P=0.02%) than in LW boars. Primary spermatocytes and round spermatids were observed respectively in 135 and 175 d. pc-old MS testes wh ile they were firstly observed in 205 d. pc-old LW piglets. The yield of sp ermatogonial divisions was significantly higher in MS than in LW testes whi le those of meiotic divisions or of spermiogenesis did not differ. Testoste rone mean plasma levels was low (<2 ng. Ml(-1)) in 175-205 d. pc LW piglets and it reached 12 ng. Ml(-1) at 250 d. pc; in 175 d. pc-old MS it was 15 n g. Ml(-1) and decreased to 8 ng. Ml(-1) at 250 d. pc; testosterone mean pla sma levels were significantly lower in adult MS (3 ng. Ml(-1)) than in LW ( 7 ng. Ml(-1)) adult boars.