Improving the accuracy of EBVs for your animals in Wagyu BREEDPLAN by submitting performance data requires some planning so that you can get the best bang for your buck. Australian Wagyu Association CEO, Dr Matt McDonagh explains how it works.
- A contemporary group is considered to be animals of the same sex, born within the same herd within a 60-day period and managed together as one mob.
- The size of a contemporary group influences the accuracy of EBVs – two in the group improves the results; six increases it significantly. Ideally, 10 in the group gives reasonable results for small herds.
- Heritability in most traits, such as marble score, is less than 50%, which means the majority of observed variation between individuals is not due to genes. The marble score trait is 30% heritable. This means that 70% of the difference between animals can be attributed to environment and management, not genes.
- Comparing animals in a contemporary group allows us to better determine the difference between individuals that is due to genes.
- Through BREEDPLAN, EBVs are calculated to give an indication of the animal’s genetic merit for production.
Wagyu BREEDPLAN is a genetic evaluation system that produces Estimated Breeding Values (EBVs) for a range of important production traits (eg. weight, carcase, fertility). EBVs are an estimate of an animal’s genetic merit for a production trait.
Included in the calculation of EBVs are the animal’s own performance, the performance of known relatives, the heritability of each trait and the relationship between different traits.
A range of factors influence how performance data is used within the Wagyu BREEDPLAN, with things like heritability (the amount of the observed trait that is due to genes) and contemporary group size being two important ones.
Heritability is the proportion of the trait expressed that is due to genes. Heritability of most traits is less than 0.5. This means that for most traits, the majority of the phenotype you see expressed in an animal is due to the environment or management of the animal. As a result, it is important to understand how animals raised within the same management group (contemporary group) perform against each other to determine the genetic variation between individuals.
A contemporary group is a group of individuals that were born together and managed as one group for their whole of life. For example, a drop of steer calves from one paddock that are managed together, are then fed in the same feedlot pen and slaughtered at the same facility on the same day, are considered contemporaries. These ‘contemporaries’ have shared the same production environment whole-of-life. Using their pedigree and DNA information, we are able to determine the amount of difference in their phenotypes that is due to their genes.
The effectiveness, and use of performance data to calculate EBVs is dependent on comparing animals within contemporary groups. The more animals within a contemporary group, the more information can be extracted to determine the genetic contribution to the data. So how many do you need to give some quality results?
The effectiveness of an individual animal’s performance data to contribute to its own EBV within BREEDPLAN increases as a contemporary group size increases. A performance record in a single animal contemporary group is not used by BREEDPLAN. It can be accepted and loaded, but it is not informative. It’s like trying to compare one apple to a box of oranges.
A performance record in a contemporary group size of two is 50% effective and starts to give some usable data to BREEDPLAN. This increases as contemporary group size increases as shown in Figure 1. Once you get past a contemporary group size of six, the benefit of more individuals in the contemporary group starts to level out for individual EBVs within the contemporary group.
The other part of the equation is Heritability and how other traits are correlated with the record of interest. Using marble score as an example – a highly desirable trait for Wagyu – the EBV data for an individual animal is calculated as follows: the marble score trait is 30% heritable. This means that 70% of the difference between animals can be attributed to environment and management, and is not due to genes. In a contemporary group size of six, the influence of the individual performance record on the animal’s EBV is calculated as: the difference to the mean of the group, X 0.85 (Record Effectiveness from Figure 1) X 0.3 (heritability of trait) + the existing mid-parent EBV.
This example is approximate, as the impact from other correlated traits (eg rump fat) and the relative ranking compared to link Sires (common Sires like Itoshigenami or Michifuku) is not considered but would be done in Wagyu BREEDPLAN.
For a steer with marble score record of 1.2 above average in a contemporary group that has a range of marble scores across six individuals, and assuming that the animal starts with a base marble score EBV (mid parent) of +0.2, the EBV would be calculated (roughly) as follows:
1.2 X 0.85 X 0.3 = +0.3 plus the original mid parent EBV (+0.2) = +0.5 for a new animal EBV, which is approximate, without adjustment for things like rump fat and relative effects due to link Sire rankings.
Hence as the EBV is estimating the genetics, not the phenotype, the mid-parent EBV is the starting point and this EBV is adjusted according to the individuals own record, based on their difference to the average of the contemporary group. Again, other factors such as correlated traits and link-Sire rankings are also considered within Wagyu BREEDPLAN.
In general, comparing animals based on EBVs is more reliable than comparing animals based on raw data. It is not sound to compare individual animal data from different production systems to each other and make assumptions about genetic merit. Every production system is different and the majority of any trait observed is not due to genetics. For this reason, it is also not sound to compare individual animal data from one production system and presume it will perform the same in your production system. EBVs are the best estimate of genetic merit.
Minimum contemporary groups for informing sires EBVs
For carcase traits in BREEDPLAN, a contemporary group can be considered to be animals of the same sex which are born within an individual herd in a 60-day period and are managed together as one mob under the same conditions until slaughter. A Sire’s EBV will be influenced by the data from its progeny in a contemporary group.
The number of animals within a contemporary group then affects accuracy, assuming a Sire starts with 0% accuracy for the marble score EBV as shown in Table 1.
Table 1: Effective progeny at 30% trait heritability
With a minimum contemporary group size of 10, with five progeny derived from each of two different sires, the increase in accuracy is 0.4 (40%) if the Sire had 0% accuracy previously.
Using Table 1, if a Sire had 50% accuracy previously, then the above scenario would increase the Sire’s accuracy by half of 0.4 = 0.2 (20%), roughly, to about 70% accuracy.
Using Table 1 again, If a Sire had 50% accuracy previously, and 10 progeny from this Sire, along with 10 progeny from another Sire were provided within the same contemporary group, the Sires accuracy would increase by half of 0.52 = 0.26 (26%), roughly, to about 76% accuracy.
In the above example, it is presumed that the other Sire in the contemporary group is a well proven Link Sire that has a marble score EBV accuracy of greater than 80%.
Please consider the above as indicative only, as these examples and calculations provided would be influenced by other factors considered within Wagyu BREEDPLAN. This explanation is designed to provide a simple understanding only and is not meant to be an accurate reflection of what happens within the full range of traits and management variations that occur across different production systems.
What does this mean for herds looking to contribute data to BREEDPLAN?
In general, based on the example above, a contemporary group of 10 animals from two Sires should be seen as a minimum. These animals need to be the same sex. Hence, in breeding to produce a contemporary group to improve the accuracy of your Sire, consider mating 24 females to two Sires (12 each) as a bare minimum. On average, six from each Sire will be potential male slaughter stock, with five of each needed for an effective contemporary group.
It is worth noting that for Wagyu, in small herds with limited opportunity to form contemporary groups based on mating 24 females to two Sires, improvement in accuracy in the order of 10% can be achieved through genomic profiling (using the 50K SNP chip) and submitted to Wagyu BREEDPLAN.