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Fertility Traits

GLOSSARY:

Scrotal Size

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

Gestation Length*

Average number of days from conception to birth of an animal’s progeny. Negative (shorter) is desirable. *Also a calving ease contributor.

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. If all 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.

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