BUSINESS | DATA
Using figures with mid-micron sheep BY: JAMES HOBAN
F
igures are a fantastic tool when the data behind them is robust and the limitations and validity of the figures are well understood by the people using them. In the Corriedale world, indexes have been a contentious topic for years. While not the only breed grappling with some of the Sheep Improvement Ltd (SIL) complexities and politics, Corriedales and other mid-micron sheep pose a slightly more complicated picture than some other breeds. The most sensible wisdom is that estimated breeding values (EBVs), indices and structural traits need to be balanced. Terminal breeds are a relatively simple breeding proposition compared with a maternal. The NZ terminal worth (NZTW) and NZ maternal worth (NZMW) indices reflect the main important traits
of each type of sheep. Most maternal breeds are strong woolled and provide an umbrella for breeders largely focused on growth and fertility ahead of wool traits. SIL can handle wool traits, and as a result
Suggesting NZMW is a uniform index, which all maternal breeds can be adequately compared with, is misleading. Corriedales and other breeds are able to use a tailored index that reflects the wool value of the sheep and weights it accordingly to other traits. When compared with strong wool breeds using the NZMW index in isolation,
Corriedales generally struggle to stack up on figures because their wool value, a key trait and focus for Corriedale breeders, is not adequately reflected. As a result, mid-micron breeders can use a mid-micron index. This becomes more relevant to them and their clients than the NZMW. Suggesting NZMW is a uniform index, which all maternal breeds can be adequately compared with, is misleading. Some breeders adopt their own indices using the range of traits they rate as most important – this is different again. There is a conflict between using raw data and EBVs. Many clients still revert to looking at a ram’s weaning weight or fleece weight in kilograms. However, both of these are influenced by feed and environmental conditions. EBVs are more relevant because they put that sheep’s value for a particular trait in perspective relative to the flock, and account for other
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October 2020