# Weaning Weight

Weight on the date the calf is weaned. This is typically at about 200 days of age. The recommended maximum age at which a calf should be weaned in order to be used in a performance recording program (e.g. genetic evaluation) is 250 days, and the recommended minimum age is 160 days of age.

### Phenotype

Weaning weight should be collected on a high quality digital or mechanical individual animal scale, and it should be recorded in pounds.

The weight should never be estimated and should be recorded to the nearest whole pound if possible. If recording the weight to the nearest whole pound is not feasible, then it can be acceptable to record the weight to the nearest 2-pound increment. Weaning weight should never be recorded to the nearest five pound or other larger increment. Weaning weight should never be estimated by averaging a group weight.

When publishing weaning weights or performing a genetic evaluation on weaning weight, several non-genetic factors should be considered that influence weaning weight, in addition to the contemporary group. The effects of these factors should be adjusted out prior to publishing weaning weights or computing weaning weight ratios.

Obviously weaning weights are affected by the age of the animal, so an adjustment is made for animals all weighed on the same day but differing in age. The standard age for adjustment is 205 days, so the standard then for age-adjusted weaning weight is 205-day weight. To calculate this adjusted weight, the ADG from birth to weaning is multiplied by 205, and then birth weight is added. This is shown in the following:

${\displaystyle 205-Day\,Weaning\,Wt\,=\,{\frac {Weaning\,Wt\,-\,Birth\,Wt}{Age\,at\,Weaning\,in\,Days}}\,\times \,205\,+\,Birth\,Wt}$

Additionally, the age of the dam of the calf as well as the sex of the calf will influence calf weaning weights. These adjustments are typically different for each breed and may change over time as genetic progress is made in growth to weaning.

### Contempory Group

Weaning contemporary group is a group of calves that are of the same sex, are similar in age, and have been raised in the same management group (same location on the same feed and pasture, at the same time) and weaned and weighed on the same day. Contemporary groups should include as many cattle as can be accurately compared. However, if, for example, first-calf heifers are given preferential treatment (better feed) prior to weaning their calves, then these calves should be designated into a separate contemporary group than the calves from mature cows.

Weights should be taken on the same day for an entire contemporary group. Especially for large contemporary groups, water should be provided to calves penned-up prior to weighing so that there is no effect due to differences in dehydration between the first and last calves weighed.

While the recommended age range for collecting weaning weight on calves is 160 to 250 days of age, some organizations may choose to allow weights outside of the age range by grouping the calves into a separate contemporary group (younger calves together and a separate group for the older calves).

### Genetic Evaluation

The additive direct genetic effect on weaning weight is predicted by the Weaning Weight EPD. It is a prediction of the average of the relative pounds of weaning an animal would pass on to its offspring through direct additive genetic effects.

In addition to direct additive genetic effects, the Milk EPD component predicts daughters' additive genetic merit for maternal ability. It is the maternal additive genetic effect in relative pounds of weaning weight a sire's daughters will provide their calves independent of the direct genetic effect.

Total maternal weaning EPDs are provided by many beef breed organizations and are the total additive genetic contribution to daughters' calves weaning weights. It is calculated as.

${\displaystyle Total\,Maternal\,Weaning\,EPD\,=\,{\frac {1}{2}}Weaning\,Direct\,EPD\,+\,Milk\,EPD}$

Because dams wean multiple calves, an additional component due to the dam that is not genetic must be accounted for in genetic evaluation programs; this additional component is called the permanent environment due to the dam.

Because the variance of weight traits can scale due to size (e.g., sex or breed differences), a procedure to account for heterogeneous variance should be considered.

### Usage

Many commercial cattlemen sell their calves immediately after weaning. In these marketing programs weaning weight and its component EPDs (weaning and milk) are considered economically relevant traits because they are directly associated with the income and costs of production.

For commercial producers who market calves at older ages, weaning weight and its component traits it is sensible to include weaning weight in selection decisions (i.e., a selection index) to account for costs to weaning and not revenue. This is because there are not ERT) EPDs for pre-weaning feed consumption.

Weaning weight's component traits often appear in so-called "All Purpose" indices and are most appropriate in maternal indices. The Milk EPD component of weaning weight can affect the income and costs for the commercial cattle producer. Milk EPD can be an indicator trait for the costs of producing milk and maintenance energy requirements of cows, as well as being associated with revenue from calf sale weight.