As cattle breeders we are constantly challenged with the responsibility of making improvements to our specific breed. This is, more often than not, a much more complex task than we think. Cattle, unlike the biology lab favourite the fruit fly, have a very long generation interval making genetic progress painfully slow. Errors in selection can take years to be identified and many more to correct.
The selection of "improved" livestock is our goal. But what do we want to improve and how do we measure what improvements we have made?
First, let us look at a simple measuring task ...
If I were to ask you to measure the area of a $10.00 bill in square centimetres I am sure that most of you could do this. If all the results were compiled there would most probably be answers near 106cm². This little experiment could be repeated across the country and even at next years AGM with similar results. The size of the $10.00 bill would remain the same even if its value diminished.
Now lets try a more complicated experiment — that of finding the temperature at which water boils. We do this simple task every day but by accurate measurement it can be shown that the boiling point can be influenced by atmospheric pressure (altitude above sea level) and by soluble contaminants in the water. Unlike the area of the $10.00 bill this measurement is influenced by the environment in which the experiment takes place.
Unfortunately attempts to make measurements of living animals are even more complicated by the effects of the environment.
To improve the quality of our livestock we must first select characteristics that we feel are valuable. Once this has been done we must ensure that changes in these traits can be accurately measured, for if we cannot measure accurately then we will not know if we are making any progress.
If a trait can be accurately measured then we must also know if this trait is highly heritable. Fertility, for instance, has a very low heritability and attempts to increase fertility by selection in a herd is a waste of a breeder's time. Fertility may be controlled by a gene or a combination of genes but it is also effected greatly by the management of the animals. Improvements in management may lead one to believe that there has been genetic progress.
There are two terms one should be familiar with:
|The hereditary constitution of an animal.
|The appearance of the individual as a consequence of the interaction of Genotype and environment.
GENOTYPE + ENVIRONMENT.
What are some important traits?
|Growth to Weaning
|Post weaning growth
|Efficiency of gain
Let us now attempt to select a herd that will have high weaning weights, fast growth rate, excellent carcass quality, docility and calving ease. How will we do this and what may be the consequences of our actions? Many times the selection for one trait may produce a reduced performance in another.
As a general rule (in livestock there are always exceptions) selection for high weaning weights eventually increases calf birth weights. Continued selection for this trait may lead to increased calving difficulty. It is interesting to note that selection for post weaning gain does not have as high a correlation with birth weights. It is also important to remember that the fastest gaining bull (post weaning gain) is not necessarily the bull with the heaviest yearling weight.
Selection for carcass quality in live animals by visual appraisal is one of the most dangerous mistakes that cattle breeders make. Time after time studies have shown that it is next to impossible to visually appraise live animals. There are many misconceptions that abound and I doubt if we will ever rid the industry of these biases until all beef cattle are sold and paid for on a rail grade basis.
Carcass quality is a highly heritable trait but its accurate measurement in live animals is one of the challenges to our industry today. As the technique of ultra sound measurement becomes more refined I am sure that it will be a useful tool. Unfortunately this technique is not within the reach of the average Highland breeder.
I therefore will make, I am sure a shocking statement to many breeders present — don't waste your time trying to identify the carcass qualities of your animals. You can only hope to either increase or decrease total muscle of your animals. Selections based on form may introduce body types that are not functionally efficient for the breed. As many of you know, I also raise Salers cattle and one of the favourite criticisms of the breed concerns the high tail head of some animals. The breed gained a reputation for calving ease when it first came from France. Would this very valuable trait be lost if we selected for lower tail heads because the cattle looked nicer? "If it ain't broked don't fix it."
We are now left with docility, an important characteristic to be sure. No one wants to be injured by their animals or worse, have one of your animals injure a buyer. Docility is a subjective measurement and environment has a great effect on its expression. It is possible to quiet an unruly bull and it is also possible to turn a docile animal into a savage. We must always remember that these animals outweigh us 10 to 1. Many times it is the quiet ones that cause the most injuries. How then would I propose to select for improved Highland animals?
Highlands are supposed to be hardy so to maintain that trait I would winter the cows outside with only hay for feed plus salt and mineral. Hardiness would be measured by the failure of females to calve successfully and rebreed in a short period of time (60 days). Failure to do so would indicate that they required either housing or a higher level of nutrition for their environmental conditions.
All the calves would be handled in as similar an environment as possible up to weaning i.e. not creep feed to one group and not another. All calves should be vaccinated and ivomeced to control parasites. Every one gets an equal chance to express their genetic potential.
All calves weaned at the same time and weighed for weaning weight calculations.
Heifer calves separated from bulls. Heifers fed a maintenance ration for gains of 1lb/day. Top 2/3 of the heifer used for replacements.
Bull calves fed as a group to gain 2 lb/day. This amount of gain is large enough to show the spread between individuals. A more accurate estimate of the heifers' post weaning weight could be made using higher rations but milk yield of females can be influenced by early fattening so we opt for the lower ration. Also females are numerous in a herd and one or two replacements have little effect on the herds total performance. A poorly selected bull can prove to be a grave mistake.
Average daily gain on feed is calculated for each individual bull and the top ranking bulls are selected as her sires. Efficiency of gain is very closely related to rate of gain and by selecting the best gainers I have also selected for the most efficient gainers. At this time I also take into account any structural defects and disposition and if the need arises select a lower ranking calf.
These yearling bulls would be expected to settle at least 10 cows in their first year of breeding.
So what has all this accomplished? Hopefully I have a cow herd that is forced to be hardy, have good maternal traits while improvements in post weaning gain is constantly introduced through the introduction of selected sires thereby increasing the efficiency of the cattle