Cattle Today

Cattle Today

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Eric Grant and Wes Ishmael

While it's true that a bull contributes 50 percent of the genetics to his offspring, keep in mind that he is also responsible for 25 percent of the genetics in his granddaughters and 12.5 percent of the genetics in his great granddaughters.

The importance of sire-selection decisions comes into sharp focus when you consider the staggering potential genetic contribution of a single sire to the long-term performance of your breeding program.

Traditionally, you selected a bull you thought would work based on visual evaluation of the individual animal, his pedigree, and the reputation of the breeder offering him for sale. You used him, and then waited for his calves to mature (or at least to be weaned) to prove the worth of your selection decision. That took a long time, but you had no choice.

Now, thanks to the extremely sophisticated computers available, collection of performance information over the years, and development of calculations that condense that information into usable figures, we have breed-wide genetic evaluation programs and sire summaries to help take the guesswork out of beef cattle breeding. Incidentally, while you can still obtain hardcopy sire summaries, many breed associations also allow you to access the information via the Internet.

Of course, information access and understanding are different things. People unfamiliar with genetic evaluation are sometimes intimidated by sire summaries because they do involve extremely complex calculations. The good news is that cattle producers don't need to understand those calculations. What you need to understand is the concept behind the calculations and how to interpret the information in the sire summary.

A Single, Comparable Value

The concept is simple enough. A sire summary condenses volumes of information (including a bull's own performance and the performance of his relatives tracked over time, accounting for competition across herds, dam influence, and within-breed genetic trends) into a single figure that indicates genetic potential. It is a usable figure that allows you to compare all bulls in the summary for the traits listed with all other bulls in the summary. This information gives you a pretty good idea of what a bull's calves will do before you ever use him -- or see him.

Sire summaries are published semi-annually or annually by most beef breed associations. Information contained in the different summaries may vary somewhat, but basically each will tell you what you can expect a bull to pass on to his progeny for traits like birth weight, weaning weight, yearling weight and milking ability compared with other bulls. A growing number of breeds also offer genetic evaluations for carcass traits, such as backfat thickness and ribeye size.

If you want more detailed information about performance figures and concepts in general, the Beef Improvement Federation or BIF, (an organization made up of state beef improvement associations, breed associations and AI organizations) publishes "Guidelines for Uniform Beef Improvement Programs," which is exactly what the name implies. For more information about the BIF and the "Guidelines" publication, contact NAAB.


Before discussing sire summaries further, a word of caution is necessary. A sire summary is a fantastic selection tool, but it cannot plan your breeding program. Only you can do that. Before looking at a summary, sit down and evaluate where your program is now and then decide where you want it to be. Realistically appraise your cattle and your resources, your potential market, and your environment and then set your goals.

Consider your herd's strengths and its weaknesses. Consider the direction you want to take. More milk? Increased weaning weights? Heavier yearling weights? More muscle or marbling? And what about crossbreeding? Is it the way to go? If so, do you want a terminal crossbreeding program from which you plan to market all of the calves? Or do you want a maternal crossbreeding program aimed at building replacement females? Because you could use a different bull for each cow if you wanted, AI makes either a terminal or maternal crossbreeding option, or both, more easily possible than does natural service. But you must have a plan.

Once you've made your breed decisions, contact the appropriate breed association or your AI organization and request a sire summary. As mentioned earlier, you can also access this information for a growing number of breeds via the Internet. However you access the information, don't be shy about asking for help in understanding the particular summary.

Remember that breed associations can't recommend individual bulls, but AI organizations can. Plus, it is in their best interests to offer you the best bulls and to help you select the right ones for your program.

When you open up a sire summary, you'll find a list of bulls' names, each with a series of numbers under a series of traits. You'll most likely find numbers listed for birth weight, weaning weight direct (growth), weaning weight maternal (milk and growth), and yearling weight. There also may be a maternal combined figure that indicates the number of pounds by which a sire's daughters' calves are expected to differ from the breed average at weaning. Some summaries will include information for other traits such as carcass, calving ease, scrotal circumference and gestation length.


The positive or negative numbers you find for each trait are expected progeny differences (EPDs). They predict how future progeny of a sire are expected to perform for each of the traits listed compared with the progeny of the average bull for that breed. The EPDs are expressed in the units associated with the trait (weights are in pounds, for example), and they indicate how far above or below breed average a bull is for a particular trait. The EPD is derived from thousands of records, and it is the value you use for comparisons.

Obviously, because most sire summaries are updated semiannually, breed average for a trait can vary. That does not alter a bull's standing as compared with other bulls within the same breed. As an example, you can expect calves sired by a bull with a +50.0 pound yearling weight EPD to weigh an average of 40 pounds more than calves sired by a bull with a +10.0 EPD, no matter what the breed average may be. The thing you do have to remember is that a bull's EPDs can change from one year to the next until his accuracy value is very high. You find the current genetic accuracy for a bull's EPDs under the "ACC" headings in a sire summary.


Accuracy figures accompany each EPD. These figures indicate the likelihood of a change in the EPD as additional progeny information becomes available. This figure indicates how reliable an EPD is because of the amount of data available - .30 ACC means 30 percent reliability; .90 ACC means 90 percent reliability. At .90 ACC, the EPD is much less likely to change than it is at .30 ACC.

Generally, younger bulls will have lower accuracy figures. It makes sense that the EPDs of bulls with only a few progeny are more likely to change as those bulls are used more extensively; and that they will change more than the EPDs of more heavily used older bulls.

For instance, a weaning weight EPD of 18.6 (ACC .87) for a bull born in Missouri during 1993 is directly compara-ble with the 27.5 EPD (ACC .53) of a bull born in Montana in 1996. Although they are directly comparable, keep in mind the EPD of the bull with the .53 accuracy is more likely to change -- either up or down in years and summaries to come -- than the EPD of the bull with the .87 ACC.

Besides the figures for accuracy, some sire summaries also provide other benchmarks for genetic predictability such as the number of herds contributing to birth weight EPD or the number of sons that make up a bulls EPD for scrotal circumference.

With accuracy in mind, it's wise to sample new bulls first, minimizing risk by breeding younger, lower accuracy bulls to only a few cows, and using several of these kinds of bulls. That way, if the EPDs for a bull drop as more data become available, an entire calf crop won't be affected. This kind of sampling is very easy to do in an AI program. At the same time, AI opens the selection door to a wide array of high-accuracy sires, allowing you to lock in predictable genetic inputs.


In addition to understanding how to read a sire summary, you must understand that traits vary in heritability. Some are highly heritable while others are not. Heritability is the proportion of the difference among cattle that is passed on to the offspring. Heritability is measured in percentages.

The higher a trait's heritability, the greater its response to selection. In other words, you will make progress more quickly selecting for a trait with a high heritability as opposed to one with a low heritability. Likewise, the higher the trait's heritability, the more accurately an individual's performance will predict its breeding value in that trait. Plus, no matter the degree of heritability, to substantially enhance a trait you must use bulls superior for that same trait over time, stacking pedigrees for improvement of that trait. However, you need to proceed with caution. If you are selecting for just one trait, you may be overlooking other traits that need improvement. Moreover, because genetic correlations exist between traits, you must understand how selection pressure for one trait area may affect progress in other areas. As an example, some of the same genes that contribute to yearling growth also contribute to birth weight. Unless you select against birth weight while selecting for improved yearling weight, both will increase.

In simple terms, genetic correlations attempt to describe how many of the genes that affect one trait also affect another. The higher the correlation between characteristics, the more difficult it is to find individuals that are exceptions. For instance, bulls with high yearling weight EPD and low birth weight EPD aren't common, but they do exist.

Here, again, a sire summary is invaluable. Not only does it tell you how bulls rank and how their progeny can be expected to perform, it also will help you find bulls that meet your requirements across all traits measured.

Some breed associations offer producers "Sire Selector" programs as software or as part of their electronic sire summaries. These programs allow you to enter minimum EPD and accuracy criteria for the traits you choose, and then generate a list of all of the bulls in the sire summary that meet those criteria. These days, some organizations also offer other genetic measure tools to help with the selection process, everything from systems that measure convenience traits such as udder quality to DNA tests for genetic defects and guaranteed red or black color.

Methods Evolved

If you have been tuned in to performance programs for a number of years, you have witnessed the evolution of ge-netic evaluation measures from ratios and estimated breeding values (EBVs) to the more the commonly used EPDs, which are so far the best means to determine the value of an animal as a parent.

For perspective, widespread beef cattle performance work -- about three decades in the making -- started with ratios, which translated raw numbers to figures that allowed in-herd comparison. But ratios were only valid within a herd or group of cattle managed alike and born in the same season.

Although ratios are still used in-herd today, remember that 100 is average; for every ratio above that figure, there has to be one below. Plus, the ratio of a bull raised in Texas is not comparable with the ratio of a bull raised in Iowa, or the ratio of a bull raised just down the road or even of a bull raised in the same herd the following year.

Some adjustments were made in the ratio system, under the guidance of BIF, to lessen non-genetic effects (like age of dam, weaning at other than 205 days of age, etc.). Even so, ratios are limited to within-herd comparisons.

The EBVs took ratios the next step down the road of progress. They, too, exist as ratios, but they could be used to compare genetics across herds, accounting for the average within-herd contemporary group ratios of progeny as well as the individual performance of the bull and his relatives.

Today, EPDs (half the value of an animal's EBV) have replaced EBVs as the genetic tool of choice because they also account for the dam's contribution, genetic trends for traits within a breed, and the level of production or competition across herds and years.

Contrary to some beliefs, raw figures were never valuable in bull selection. If someone wants to sell you a bull calf that weaned at 600 pounds, that's not telling you much. That 600-pound calf may have been raised by a first-calf heifer in the middle of a three-year drought, or he may have had the best of everything, including exclusive rights to a big old nurse cow. He may have been raised in a herd in which 600 pounds was an average weaning weight, or he may have been raised in a herd in which the average was 500 pounds or 700 pounds. A bull's weight simply does not tell you what you can expect him to produce as compared with other bulls.

Still a Tough Job

Some folks believe sire summaries revolutionized sire selection. We are sold on them, but we are not going to tell you they make selecting the right bull a simple matter. Selection is difficult.

The individual bull still has to be considered. And so does his pedigree and the reputation of his seller. You must evaluate potential AI sires on the basis of your own needs. Finally, successful breeding is still based on the premise that each new sire should be superior to his predecessors.

Choose him very carefully -- with the help of a sire summary.

Much of the information in this article is based on information found in the Artificial Insemination Handbook, which is produced and distributed by the National Association of Animal Breeders. To order a copy of the handbook, available in English, Spanish and Portuguese language versions, contact NAAB at 573-445-4406.


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