BY RUSSELL PRIEST
FROM the New Zealand ANGUS Magazine 2018.
Of all the cattle breeds in New Zealand the Angus is the most genetically diverse and for this reason it is arguably the most exciting breed to be involved with, at least for the genetic purist. Not only is there a lot of genetic variation but there are also a number of bulls (outliers or freaks) displaying abnormal genetic relationships between antagonistic traits.
Genetic variation enables genetic change and the larger the variation the more change is possible. Antagonistic traits are the curse of the animal breeder. However by identifying and breeding from outliers that moderate these antagonisms it is possible to achieve more positive genetic change.
The antagonistic relationship between birth weight and growth was the first of several abnormal genetic relationships now familiar to breeders to be considered. Because the birth weight, growth rate (200, 400 and 600-Day weights) and mature weight traits all share a number of common genes, when selection pressure is applied to one of these the others respond. For example, selecting for high growth will normally drive both birth and mature weights up.
However, with the advent of performance recording and genetic evaluation it was discovered that a good number of animals do not conform to the same extent to this normal trend. These animals generally emerge from large recorded populations like American Angus. A population has to be recorded to identify these outliers and the larger is the population the more likely they are to occur.
An animal with an abnormal genetic relationship between birth weight and growth became known as a ìgrowth curve benderî because it displayed a higher-than-expected growth rate based on its birth weight. Such an animal is very valuable because it will produce calves with lower-than-expected birth weights (potentially fewer calving problems) and higher-than-expected growth ñ both financially positive outcomes. The same scenario applies to growth and mature weight. When upward selection pressure is applied to growth, mature weight increases. The latter is not a positive financial outcome for the cow herd owner because the cost of maintaining the cows will rise (cow maintenance cost is the largest single cost in a cow herd).
Once again an outlier (ìgrowth curve benderî) is identified. However on this occasion the growth curve is bent at the mature weight end ñ mature weight is lower than expected based on the animalís growth rate. So by breeding from such an animal the herd owner is achieving the best of both worlds ñ getting good growth while lowering cow size.
The other good news is that one animal may display several abnormal genetic relationships, as seen in the genetic picture of the following genetically outstanding Angus bull.
Genetically an excellent Angus bull (Bull A)
This bull is an excellent example of an outlier who has broken not just one genetic relationship that we know of but several. Note his high percentile rankings for lighter birth weight and 200, 400 and 600-Day growth. Note also his low percentile ranking (lighter cow weight) for Mature Cow Weight. All of these are financially positive trends.
And thereís more. The traits Direct Calving Ease (the ease with which an animalís calves are born) and Daughters Calving Ease (the ease with which a bullís daughters calve) are also antagonistic traits. This means that if sustained selection pressure is applied to improving one it will generally be at the expense of the other.
This scenario often occurs when breeders buy bulls with high Direct Calving Ease EBVs to mate with their 15-month heifers to minimise calving problems and retain some of the female progeny for breeding. This practise works well if the selected bulls have good Daughtersí Calving Ease figures as well. However, if they donít and this practice continues there is a good chance that a calving difficulty problem may occur in the two-year heifers sired by such bulls.
Note both Bull Aís Calving Ease (Direct and Daughtersí) EBVs are ranked well within the top 10% for the breed and since both are likely to be excellent positive EBVs they will have a significant financial influence on the Self Replacing and AngusPure Indexes.
Rib/rump fat and carcase yield are also antagonistic traits.
These two fats are major contributors to low yielding carcases ñ a financial issue for the processor. However
herd owners want their cows to carry a certain amount of fat on their backs to get them through the winter so fat for them acts like a mobile hayshed.
Note this bullís percentile rankings are all above the breed average for rib and rump fat as well as retail yield ñ yet another example of an antagonistic genetic relationship being modified.
Bulls with moderated antagonistic traits often have better indexes than those showing normal degrees of antagonism. This is particularly so if the traits are significant profit drivers resulting in the financial gains made in one trait being offset by the negative financial effects of the other.
Greater profit results if the antagonism is moderated as is seen in the case of Bull A where the antagonistic effect of the two calving ease traits, the birth and growth traits and the growth and mature weight traits are considerably reduced.
As a direct contrast the following genetic picture displays a genetically very poor Angus bull showing only one abnormality in his genetic relationships ñ one that is definitely not financially beneficial.
Genetically an excellent Angus bull (Bull B)
Note most of the coloured bars are to the left of the 50% percentile line meaning most of Bull Bís EBVs are below average. The only ones above are the Rib and Rump EBVs.
Most of the genetic relationships displayed by Bull B are normal except for the two calving ease traits, which are not displaying their normal antagonism. Both yellow bars representing them are heading in the same negative direction with potentially serious financial implications.