Estimate of difference from breed average of the scrotal size
of progeny at 400 days. Positive is desirable
Days to Calving
Estimates the difference in female fertility in terms of the
average number of days from when the bull goes in with the cows
to calving date. Negative is desirable
Average number of days from conception to birth of an animal’s
progeny. Negative (shorter) is desirable. *Also a calving ease
Scrotal size EBV’s are strongly related to bull fertility. Increased
scrotal size is also correlated to earlier onset of puberty in female
progeny. Usually a compromise is necessary when considering scrotal size
EBV (eg where an animal excels in other areas, but is lower than maximum
for scrotal size), but if all other things are equal, the bigger the
better for this trait.
Days to calving (DC) EBV’s will always be low accuracy in sale
age bulls. In the case of bulls bred by AI, any data will only be derived
from ancestral and/or older sibling performance as it is not possible
to collect data for this trait in artificial breeding situations. As
such it is not a highly useful trait for consideration in young bull
selection, however in herd wide terms, DC is an important measure of
fertility. The quicker a cow goes in calf, the more time she has to re
breed at subsequent joining periods and the more advanced her calf will
be at weaning.
Gestation Length EBV is considered a fertility trait, as short gestation
has similar benefits to short days to calving and is a more reliable
trait in young bulls bred by AI.
Summary of fertility traits
Essentially fertility traits are free, that is, strong performance in
these traits has no deleterious side effect on other areas of breeding.
other things are equal, the higher the scrotal, the shorter the days to calving
and gestation length, the better. All these traits have to be considered
in the context of balanced trait selection however, and invariably some compromise
will be made by selecting less than maximum fertility EBV’s to accomodate
desired values for growth, calving ease and/or carcass.