GROUP
THINK
A
s we move into summer, cows are on pasture, bulls are breeding, and calves are growing. This is a good time to think about groups. One of the key concepts behind genetic evaluation is that of a contemporary group. I know this is a sometimes poorly understood concept, as many of the questions and offhand remarks I encounter regarding EPD are really about groups. Genetic evaluation basically works by comparing animals that are roughly the same age, the same sex and that are managed together. One of the most common concerns I hear about EPD is that “my calves are being compared to my neighbour’s, who creep feeds or whose scale is wrong”. This is fac-
Page 32 • Summer 2021 • Gelbvieh guide
By Sean McGrath
tually incorrect, as calf performance is NEVER directly compared between herds and in fact is NEVER compared between groups within your own herd. The genetic evaluation also does not directly compare bulls and heifers. The concern expressed by the producer about their neighbours’ management or mismanagement is one of the greatest strengths of the EPD system, as opposed to using actual/adjusted weights, ratios or in herd indexes. Let’s walk through an example of what happens, using a bit of a simplified example with 2 herds and 3 groups up to weaning. The adjusted birth weight (BWT), weaning weight (WWT) and difference from group average (BDev, WDev) in pounds is shown for each calf. (see chart) If we just looked at the calves 1-12, we would think that the neighbour has better cattle with more lighter birthweights and more performance. Is this due to genetics or some secret of the neighbours’ management. Certainly, the Neighbour will have more impressive values to print in their sale catalogue, but does it tell the whole story? By only comparing cattle that have been managed in the same way, a different picture emerges. This is what EPD do. In Management Group 1, we can’t include calf 5 in the comparisons, because she is a heifer and can’t be compared to the bull calves in the group. We also can’t compare group 1 and 2 at Good Cow Herd Ranch because they are in different management groups. In other words, the breeder has identified management differences that they feel impacts the relative performance of those groups. It could be different pastures or differences in calving season or a variety of other factors. If we look at Group 1, we can see that Bull X has calves that are 2.5 pounds heavier at birth than the group average but also 14 pounds heavier at weaning. Bull Y’s calf is 7.5 pounds lighter at birth, but 44 pounds lighter at weaning when compared to the group average. In Group 2, Bull X calves are 2.5 pounds heavier at birth and 12.5 pounds heavier at weaning and bull Z’s calf is 5 pounds lighter at birth and 25 pounds lighter than the group at weaning.
