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Age of Dam
Traits affected by a maternal contribution have the potential to have an effect that results from the age of the dam. BIF has identified the following categories as a standard classification for fixed age-of-dam effects in prediction models. The categories are also used in determining adjustment factors for some traits.
It is clear that the age-of-dam effect can be different in different breeds. This is likely to be mostly due to the effect of scaling. If adjusting weights or measures for age of dam, different breed or size/scaling effects should be considered.
It has been observed that some breeders preferentially treat different ages of dams differently resulting in a contemporary group by age-of-dam interaction on some traits where there is a main effect of age of dam. This should be evaluated and considered when performing genetic evaluation analyses where multiple breeds are included.
Also, when evaluating age-of-dam effects it should be remembered that culling and selection will occur as cows age. This can result in culling and selection bias in the estimates of age-of-dam effects.
Age-of-Dam Categories
Age in days for age-of-dam categories (years of age).
| Age-Of-Dam Classification | |||
|---|---|---|---|
| AOD | Low | High | # of Days |
| 2 | 639 | 1003 | 365 |
| 3 | 1004 | 1369 | 366 |
| 4 | 1370 | 1734 | 365 |
| 5 through 9 | 1735 | 3560 | 1826 |
| 10 | 3561 | 3925 | 365 |
| 11 | 3926 | 4291 | 366 |
| 12 | 4292 | 4656 | 365 |
| 13+ | 4657 |
