The importance of recording the performance of your cattle: part two

Meat & Livestock Australia | 12 October 2017

Identifying ‘curve benders’

‘Curve benders’ do not follow the normal trend (e.g. high growth associated with high birth weight), but ‘bend the curve’ (e.g. high growth but low/moderate birth weight). Due to the strong genetic relationships between these trait pairings, we would typically expect that selection for growth would lead to an increase in both birth and mature weights, even if no selection emphasis is placed on birth and/or mature weight. This would have in turn have undesirable consequences for calving ease and mature cow feed requirements.

Fortunately, the correlations that govern these relationships are not absolute and are calculated from the average of the population. Therefore if a breeder records both traits, they should be able to identify individuals that deviate from the average correlation, and thus find animals that bend the growth curve.

However, in situations where the breeder does not record both traits, the BREEDPLAN analysis has to rely on pedigree information and the correlations between traits to estimate the missing breeding value(s). In these circumstances, identifying curve benders is not possible. For example, if birth weight isn’t recorded then the birth weight EBV will be estimated based on the correlations with the 200, 400 and 600 day weight observations. Given that the correlations between the growth traits and birth weight are positive, an animal with high growth EBVs will receive a high birth weight EBV. Therefore, identifying ‘curve benders’ cannot occur.

Relevance of trait recording when using genomics

In breeds where genomic information is currently incorporated into the BREEDPLAN analysis, a genomic test will give an estimate of your animal’s genetic merit (in the form of BREEDPLAN EBVs). However, the accuracy of the genomic EBVs for your herd will depend on a number of factors, including how closely related your animals are to the ‘reference population’. The reference population is a group of animals which have both trait records and genotypes, and is critical for the success of genomic selection.

Recording traits for your animals in addition to having genomic tests done will mean your animals will become part of the reference population. In turn, the genomic tests are likely to be more accurate for animals in your herd, thus increasing the accuracy of your breeding values and allowing you to make more genetic progress. For further information, see the SBTS and TBTS Technical Note ‘An Introduction to Genomic Selection’.

Recording isn’t just for genetic purposes

The traits that you record can also serve a purpose outside of identifying the genetic merit of your herd. For example, the loss of weight in an individual can be an indicator of ill health, while weight loss in a whole mob can indicate that more feed is required. Recording your herd also allows you to benchmark where your herd is so that you can compare it against where you want to be and make appropriate management and strategic genetic decisions in order to reach your production system targets.