Birth Weight

Calf birth weight is a good indicator trait for calving difficulty. If calving difficulty is a problem in the herd, and calving ease EPDs are not available, selection of breeding animals for lighter birth weight may be an effective strategy to improve direct calving ease. However, single-trait selection for lighter birth weight or shorter gestation intervals may reduce calf viability and growth rate from birth to maturity.

Phenotype

Obtaining an accurate measure of birth weight (in pounds of calf) using a high-quality digital scale is important for producing meaningful calving difficulty EPDs. However, it is not always feasible to obtain birth weights this way. Digital scales for measuring calf birth weights can cost thousands of dollars. Even with good mechanical scales, trying to catch a calf when the mother is being protective, and lifting that calf is a challenge for many producers and their ranch hands. There are reports of producers estimating the calf weights using visual inspection and this can be seen in many breed association birth weight datasets. Experience has shown these data are low accuracy, at best, and should not be submitted to breed associations, or used in selection decisions.

While not ideal, a pragmatic alternative to actual birth weights appears to be using a calf hoof tape device. This method is superior to visually estimating birth weights or not weighting calves.

Adjusted Value

Both sex of calf and age of dam influence birth weight of the calf. BIF recommends the use of additive rather than multiplicative age of age of dam adjustment factors because research indicates that they are more appropriate.

Birth weight adjustments for the age of dam can differ from one breed to another. Some breed associations have developed adjustments using their own data. All breed associations are encouraged to develop their own age of age of dam adjustment factors for birth weight. In most cases, these age-of-dam adjustment factors differ by sex of calf.

Adj. Birth Wt. = Birth Wt. + Age of dam Adj.

Significant amounts of unfavorable heterosis have been observed in birth weight and should be accounted for if adjusting birth weights.

It has been observed that there are significant amounts of birth weight observations that were not collected using an actual scale. Routinely beef breed associations receive birth weights that are collected using calf hoof tape, visually estimated, or "standard" filled in values. Because of this, it is recommended that birth weights be adjusted for sex by age-of-dam and these factors not be fit in the genetic evaluation.

Contempory Grouping

1. Breeder-Herd Code
2. Year
3. Season (January-June, July-December)
4. Sex (Bull, Heifer)
5. Birth Management Code
6. Service Type (Embryo Transfer Calves)

Genetic Evaluation

Birth weight EPDs are generally produced using a multi-trait animal model that includes weaning weight and yearling weight (usually fit as post-weaning gain).

While a maternal effect has been consistently observed on birth weight, it is always small with low heritability. Many analyses performed for EPD production ignore the maternal effect and produce only additive direct genetic effect EPDs for birth weight.

Usage

In all situations, birth weight should be considered as only an indicator trait. In no situation is it an economically relevant trait. When ERT EPDs are available (i.e. calving ease), actual birth weights or birth weight EPDs should never be considered in a selection decision.