The New Zealand Charolais Cattle Society (Inc) since 1968
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What Are Economically Relevant Traits?

Learn How ERTs Can Increase Your Profits!

In selecting for improved performance, breeders have concentrated on those traits that have been easy to measure. These include individual weights at varying ages from birthweight to finishing. They have been used as indirect measures of the economically relevant traits that commercial producers benefit from or are directly paid for.

In New Zealand such traits have been birthweight (Indicator trait for calving ease or calf survival) and growth traits (Indicator traits for weaning weights or slaughter weights).   From these data, Estimated Breeding Values (EBV) have been calculated.   Such EBV are a means to select for animals within the limited framework that EBV provides.

Although selection using such EBV is normally more useful than selecting by eye or actual liveweights, the number of EBV now being produced can confuse the selection process and lead to inefficiencies in achieving a breeding objective.

Because of this the NZCCS in co-operation with Colorado State University has used new techniques that combine a number of related “Indicator traits” to make an ERT.

Calving Ease ERT

This is made up of a combination of the calving ease score of heifers and the birthweight information from all dams.

Calving Ease Score
  • Calving ease score is a measure of the difficulty of parturition. Factors affecting calving ease score include birth weight, shape, and sex of the calf in addition to the physiology, pelvic area, and pelvic shape of the dam.

Birth Weight
  • Birth weight EBV alone have traditionally been used to select for calving ease, but birth weight has no economic value.    Birth weight is merely an indicator of calving ease, the trait that directly affects profitability and risk.
  • Birth weight is useful as an indicator trait. When birth weight information is used to calculate the calving ease ERT, that additional information adds accuracy to the calving ease ERT.
  • Birthweights from all calves are used in the ERT production, regardless of age of dam.

Statistical Model
  • Calving ease ERT were calculated using a multi-trait animal model with birthweight being fit in a linear model and calving ease in a threshold model. This is a sophisticated technique and allows for the fact that calving ease, like fertility, will be successful until a certain threshold is reached, then difficulties occur.
  • This model allows a better explanation of calving ease than attempting to combine EBV in a stepwise manner.

For a bull with a direct calving ease ERT of +4.0, we expect his progeny, on   average, to have a 2% (half of his breeding value) greater likelihood of calving ease than the progeny of a bull with an ERT of 0.
  • It is important to realise that calving ease is the economically relevant trait.    Commercial bull buyers should realise that making selection decisions from the calving ease ERT is both more accurate and more sensible than using birth weight EBV or birth weight EBV and calving ease ERT combined.   All the possible information that can be provided by birth weight has already been accounted for in the calving ease ERT.   Using both birth weight EBV and calving ease ERT increases the risk of making an undesirable decision.

Do NOT use both EBV and ERT when selecting. Use only one or the other but ERT will provide the better selection system.

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2025 AGM
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