May 25, 2019

"90% of the breeding goes down their throat"... most of us will have heard this statement, probably hundreds of times. It is often said to justify a belief that one should worry less about the genetics of the animals and more about how they are managed.

This is partially correct. If you are going to spend a dollar on an animal production system you should first spend it on some management or nutritional intervention. It is likely that these interventions can result in quick and significant improvements to the bottom-line. However, the statement can also be interpreted to mean that you don’t need to consider genetics at all because nutritional, seasonal or management changes will swamp any genetic effects.

In reality, to achieve an efficient, productive animal production system, that has high welfare outcomes and a low environmental footprint, both genetics and management are important.

Nutritional management and year to year variation in feed availability does have a big impact on sheep and cattle production.

However, within any given year, on any given farm, in any given flock or herd, there is a large variation in the performance of individuals and it is this variation that provides the genetic opportunity. Not all of this variation is genetic, but some of it is, and we have good estimates of the proportion of the variation that can be explained by genetics for any given trait. This is called the heritability of the trait.

Progeny tests are a great tool to debunk the “genetics goes down their throat” theory. Under progeny test scenarios all animals have an equal opportunity to perform. The single difference between all the animals in a progeny test is their sire. We can use this information to get a feel for the scale of genetic effects for any trait of interest.

We have grabbed the data from the Beef and Lamb Genetics progeny tests and plotted out the sire effects on weight of progeny at 18 months of age. The range in the average of weight of progeny at 18 months of age is over 30kg. To be clear, any environmental differences between these progeny groups has been removed. All that is left is the impact of the sire on calf growth. If you consider that only half of the sire difference is represented here, because only half of the genes come from the sire, the actual difference in the genetics for growth of these sires is over 60kg. These sires are some of the industry leading bulls, the range in the wider industry will be even greater. Another interesting fact within this data is that there is a complete overlap between Angus and Hereford sires for growth to 18 months of age.

There is an important lesson in that. There is much variation within a breed as there is between breeds. So it doesn't matter what colour cattle you prefer, or the type of sheep that you like, there is a big potential to select for genetically superior ones within any breed or type.

Data from the Beef and Lamb Genetics, Beef Central Progeny Test, NZ, 2018. If it was all about the feeding, these differences would simply not exist.

Of course, progeny testing is a good way of demonstrating differences but isn't particularly helpful for commercial ram and bull buyers to work out which animal to buy. This is the realm of the Estimate Breeding Value (or Australian Sheep Breeding Value, for Australian ram buyers). They take all of the known information about an individual sale animal and predict how it's progeny will perform in comparison to other sires used. While they are not as accurate as the results from a progeny test, they are definitely sufficiently accurate to help guide a selection and purchase decision.

The environment can have a huge impact on the total productivity of sheep or cattle. We have grabbed a couple of snippets of data from the Merino Lifetime Productivity website to demonstrate this point. You can find all of the site reports at merino superior sires

Data from two different sites and two different years are compared in the graph below. This data is from the 2015 drop at the Balmoral site and the 2016 drop at the Temora site. Each dot on the graph is the average of the progeny group for a particular sire.

There is clearly massive difference in the environment of these two different sheep groups. On first impressions, it could look like that all of the sires used at Temora are producing a lot more productive progeny. Fortunately there were two sires that were used in both sites. There identity isn't important for the comparison so we've just called them Sire A and Sire B. Importantly, the sires rank the same for fleece weight and body weight even though the actual differences between sites is huge.

It is really important to understand that although changing the environment tends to result in greater production and greater total variation between individuals, the genetic difference between animals is maintained. What is also clearly obvious on both graphs is the opportunity in the sheep and beef sectors of Australia and New Zealand by choosing the right sires. The total difference in production between sire groups is huge. Importantly, the single difference between groups is the sire, everything else is equal.

Dr Mark Ferguson
Article by:
Dr Mark Ferguson

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