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In the bull, DSP is correlated with total SC number (R = +0.83) and SC per gram (R = +0.47) but is not correlated with the number of germ cells supported per SC. Testicular parenchyma weight is also correlated with total SC number (R = +0.61). Total SC number is the foremost determinant of the variation in DSP among bulls (R² = 68.2%) [60, 61]. However, total SC number and the number of germ cells per SC are not correlated with the quality of either fresh or frozen bull semen [62]. Moreover, SC number in the horse (R² = 68) and human (R² = 39) is also correlated with DSP. The association between SC and DSP goes back to the association between SC and the number of A₁ spermatogonia (R² = 55 for the horse) [33].

In the bull, the majority of SC proliferation happens during fetal life in utero. SC number increases by five times from birth until puberty and no increase in SC number occurs after puberty. Once mitosis in SC stops, the cells differentiate to mature SC and continue their adult function for the reproductive life of the bull [63]. However, the stallion being a seasonal breeder has no permanent SC number after puberty and SC number and volume of SC nuclei per testes increase during the breeding season for a 4‐ to 20‐year‐old stallion. The size of horse SC does not differentiate with respect to breeding season [33]. A concurrent increase in the number of A spermatogonia accompanies increased SC number during the breeding season [64].