Fertility is much more important to farm profitability than the growth rate and meat qualities of animals. The most important economic key numbers regarding fertility are inter-calving time and age at first calving. The latter depends heavily on the circumference of the father's scrotum. In some breeds of cattle, scrotal circumference has been shown to be clearly correlated with the quantity and quality of semen produced. In other words, a bull with an above-average scrotum circumference will produce more and better semen than its peers which can obviously influence pregnancy results. Therefore, given this great importance, internationally acceptable minimum standards that stud bulls must meet have been established.

International standards for scrotal circumference
Age in months	Minimum scrotal circumference (cm)
>12-15	30
>15-18	31
>18-21	32
>21-24	33
>24	34

Scrotum circumference also appears to be a clear heritable trait, meaning that the sons of a bull with an above-average scrotum circumference have a higher scrotum circumference on average than sons of a bull with a lower or average scrotum circumference. In addition, this trait is also important for heifers , since the daughters of a bull with an above-average scrotum circumference are more early maturing and thus will come in heat earlier as a heifer and may get pregnant earlier.  This leads to the birth of a first calf at a younger age, which has a major impact on farm economics. Therefore, it is important to consider scrotum circumference when choosing a bull. The larger the scrotum circumference of a bull, the more fertile the bull will be and its economic value will be more valuable. Belgian Blue bulls older than two years with a scrotum circumference over 40 cm are very rare, but such bulls can improve the fertility of the Belgian Blue breed. Living conditions and nutrition also affect fertility. Adequate exercise space and soft soil with sufficient grip make for a longer and more expressive heat. Provide adequate daylight in the barn during the stabling period. Often about 10% of the area is provided by daylight openings in the walls and roof. Good hygiene around calving also promotes recovery and, as a result, the cow's heat behavior.