Yearling Weight

Yearling weight is a measure of combined pre-weaning and post-weaning growth and is reported in pounds.

Phenotype

Yearling weight measurements should be taken between 320-410 days of age. This range may vary depending on the breed association. Suggested time between weaning and yearling weight measurement is 160 days. It is important to not take the yearling weight measurement too closely to the weaning weight to allow for more post-weaning growth and a more accurate measure of the yearling weight trait[1].

Proper measurement procedures are also important. Yearling 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. Yearling weight should never be recorded to the nearest five pound or other larger increment. Yearling weight should never be estimated by averaging a group weight.

Adjusted 365-day weights are used to adjust for age of dam and actual age of calf at weighing. Age of dam is known to have an impact on calf weights, and each calf is not going to be exactly a year old when the yearling weight measurement is taken, so an adjustment is used. Age of dam is accounted for in the Adj 205-day Wt. The equation used is shown below:

${\displaystyle Adj\,365-day\,Wt\,=\,{\frac {Yearling\,Wt\,-\,Weaning\,Wt}{Number\,of\,days\,between\,weights}}\,\times \,160\,+\,Adj\,205-day\,Wt}$

Contemporary Group

A contemporary group is a group of cattle that are similar in their age, sex, and breed composition and have been managed similarly. Management includes feeding, health treatments, and environment. All cattle in a contemporary group have their yearling weights taken on the same day.

Genetic Evaluation

The adjusted yearling weight is used to calculate the yearling weight EPD. The yearling weight EPD predicts the amount of yearling growth (pounds) that will be transmitted to offspring. It is a reflection of both pre-weaning and post-weaning growth for that animal. Typically, there are not as many yearling weight records as there are weaning weight records because once the animal reaches the feedlot, yearling weights are often not reported. Most organizations account for missing yearling weights by using a multiple-trait model for the yearling weight EPD. These multiple-trait models use genetic correlations between birth, weaning, and post-weaning 160-day gain to calculate yearling weight EPDs. Multiple-trait models help avoid selection bias caused by culling lightweight calves from herds before yearling weights are reported. Yearling weight is also sometimes used as an indicator trait for other EPDs such as Mature Weight.[2]

For genetic evaluation, yearling weight EPDs are usually the result of a multiple-trait genetic evaluation that includes weaning weight and post-weaning 160-day gain. The resulting reported yearling weight EPD is the sum of the weaning weight EPD and the 160-day post-weaning gain EPD. Because weaning weight and yearling weight have a part-whole relationship, fitting post-weaning gain instead of yearling weight improves the condition of the model equations to be solved. This is a result of both a lower genetic correlation between post-weaning gain and the other traits (e.g. weaning and birth weight), and not needing to include a maternal effect for yearling weight. The resulting 160-day post-weaning gain EPD resulting from these multiple-trait analyses is used by some organizations to produce an average daily gain EPD by dividing it by 160 days.

Usage

Yearling weight is an important trait for producers who plan on retaining ownership and feeding out calves. The greater the yearling weight EPD, the more growth potential that animal has to pass to its offspring. Higher growth rates can mean fewer days on feed and lower input costs to reach market weights. Yearling weight measurements may not be as important for those producers who sell their calves directly after weaning. However, producers who purchase weaned calves may be interested in the genetic growth potential the calves have to offer.

References

1. American Angus Association. 2019. Adjusted 365-Day Yearling Weight. https://www.angus.org/Performance/AHIR/PerfLinks.aspx. 16 April 2019
2. Bormann, J.M., 2010. Data Collection and Interpretation. Beef Sire Selection Manual. Pages 21-23. http://www.nbcec.org/producers/sire_selection/chapter7.pdf. 16 April 2019