There is also a favorable genetic relationship between SC and age at puberty in females. Research has also shown a favorable relationship between SC and age at first breeding and subsequent rebreeding in females. This does not mean that negative scrotal circumference EPD bulls should be discriminated against as fertility in beef cattle is influenced by many additional factors. It is suggested that breeders should be more concerned about not using bulls with extremely negative SC EPDs as opposed to using only bulls with positive SC EPDs. That is, use the SC EPD more as a culling tool than as a selection tool for most lines of Angus cattle.

The genetic prediction evaluation is a multiple trait evaluation model including 365-day adjusted yearling weight as a genetically correlated trait to SC. EPDs were adjusted so that the average EPDs of all animals born in 1979 is 0.

Scrotal measurements were pre-adjusted for age to 365 days (.032 cm/day) and for age of dam using the adjustment factors given in Table 1.

Genetic trends for the scrotal trait is given in Figure 1

Table 1: Age of dam scrotal circumference adjustment factors

Age of dam, years, at calf birth Age of dam class Adjustment, cm1 >=1.5 and <= 2.22 2 1.026 >2.2 and <= 3.2 3 0.523 >3.2 and <= 4.2 4 0.187 >4.2 and <= 5.2 5 0.030 >5.2 and <= 6.2 6 0.000 >6.2 and <= 7.2 7 0.000 >7.2 and <= 8.2 8 0.000 >8.2 and <= 9.2 9 0.017 >9.2 and <= 10.2 10 0.100 >10.2 and <= 11.2 11 0.220 >11.2 12 0.420 1Add the adjustment to the age-adjusted yearling scrotal measure. 2the decimal fraction is the age of dam in days beyond a whole year at calf birth date, divided by 365 and rounded to the nearest tenth.