Quantitative and qualitative determinations of gametogenesis and radiation effects in the prenatal bovine testis

The objectives of this study were to (1) trace the development of the prenatal bovine testis, (2) evaluate the quantitative and qualitative changes in the germ cell population, (3) evaluate the effects of gamma radiation on the developing testis, and (4) correlate sperm production with testicular morphology. The population of germ cells, number of mitotic figures for germinal and supporting cells, and testicular volume were determined in testes from known-age fetuses. Fifty-six males were irradiated with 400 R (air dose to dam) ⁶⁰Co gamma radiation at ages ranging from 15-280 days postcoitum. Seven control and 11 irradiated males were unilaterally castrated at birth. Five control and 38 irradiated bulls were castrated at approximately 10 months of age. The testes were prepared for histological analyses. Semen was collected from control, intact, and unilateral-castrated irradiated animals when they were approximately 2 years old. The germinal ridge was first observed at 32 days postcoitum and sex differentiation occurred as early as day 36. The sex cords were unorganized until about day 70; at this age the supporting cells were located adjacent to the basement membrane and the gonocytes or primitive germ cells were positioned in the lumen of the sex cord or primitive seminiferous tubule. The gonocyte, prior to day 120, had three small acidophilic nucleoli; at later ages a gonocyte with one large acidophilic nucleolus appeared and this cellular type was prevalent at birth. Following tubular organization the cytoplasmic to nuclear ratio increased with age. The overall germ cell population increased from 44 at days 32-35 to 12,000,000 at days 151-180. Only a slight increase in germ cell numbers was noted from 211-240 days until birth (283 days). The mitotic figure index (number of mitotic figures per 50,000 germ cells) was high while the gonad was in the germinal ridge stage and reached a peak at 36-38 days. The index remained high until day 90 and then dropped abruptly during the 91-120 day period. Some germinal mitoses were noted throughout the remainder of the prenatal period with a minor increase occurring in the last days preceeding parturition. Necrotic gonocytes were noted at days 120-150 and their numbers peaked at 241-280 days; necrosis, however, never affected more than 1 percent of the population at any given stage in gestation. The germ cell population prior to day 70 was apparently unaffected by irradiation (400 R to dam) but following irradiation at days 80-130 germ cell numbers were reduced to about 7 percent of the control value in testes excised at 3-19 days postpartum. In testes removed 10 months postnatally, no damage was observed in testes irradiated prior to day 70, but in testes irradiated during the 70-90 day period 69 percent of the 1200 cross-sections observed were sterile. Sterility among tubular cross-sections increased to 88 percent at 91-120 days postcoitum, remained essentially unchanged to day 210 and decreased to 20 percent at 241-280 days of gestation. Bulls irradiated at 130 days of gestation produced 70 and 78 percent fewer sperm-per-ejaculate than their counterpart intact and unilateral-castrate controls, respectively. Sperm motility in the irradiated intact and unilateral castrates was 37 and 20 percent less than the intact and unilateral-castrate controls. Since 400 R is a near-lethal dose for the dam and since bulls irradiated at a stage of maximum sensitivity produced seven-tenths billion sperm-per-ejaculate, a number well above the 6 million motile sperm required for optimum fertility in artificial insemination, the probability of sterilizing the bull in the prenatal state with a single-acute whole-body dose of gamma irradiation is low.