Genetics Record-Keeping - Level 2

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This module has been designed to build upon the information covered in Genetics Record-Keeping Level 1. If you have completed the previous module, you may have already identified the areas of your operation where you would like to improve and have set some production goals.

Once you know where you are, you can then start to plan where you would like to go. Maybe you want your calves to be heavier at weaning? Or you’re interested in more uniform coat colour, so that your calves fit into a certain market? While some of your goals will be influenced by your production practices, other goals such as higher weaning weights will be influenced by both genetic and environmental factors (nutrition, stress, health problems, weather, etc.).

Genetic change in cow-calf operations can occur both through sire selection and through replacement female selection in conjunction with cow culling.

EPDS

Expected Progeny Differences (EPDs) are estimates of an animal’s genetic merit as a parent. EPDs are the difference between the predicted average performance of an animal’s future progeny and the average progeny performance of another animal, assuming that the bulls are mated to similar cows, or vice versa. There are EPD’s across breeds but most breeds have independent EPD’s and use different measurements or units as other breeds for certain categories.

To compensate for differences in environment and management, contemporary groupings are used. Contemporary groups are animals of the same age and sex raised under the same management conditions. Once these factors are accounted for, the genetic component is the part that remains, and that is what EPDs predict.

A bull with impressive EPDs does not guarantee a superior calf crop. A common producer complaint about EPDs is that they do not seem to reflect actual data. Because EPDs rely on information provided by the producer, it is critical that the accurate information is submitted. This means reporting all performance data measured on all animals in the herd, and correctly identifying contemporary groups under different management (for example, if one group received creep feed and one group did not). In addition, billions of genetically different progeny are possible from just a single mating! There are plenty of genetic differences between full siblings. Because EPDs predict AVERAGE progeny performance, it is quite common to have a calf or two that doesn’t fit in with the rest. This is where accuracy comes in.

Accuracy is a value between 0 and 1 that reflects how close the prediction (EPD) is to the true genetic merit (breeding value) of the animal. Accuracy values increase as the amount of information known on an animal increases. Adding data on an animal’s own performance, the performance of its relatives, and performance of its progeny will increase accuracy. As accuracy gets higher, an EPD is less likely to change substantially. Some breed associations are incorporating genomic data into their EPD evaluations. By merging DNA test results with the traditional EPDs, more information can be added at a younger age, increasing the accuracy (and confidence) in that animal’s EPDs.

Although all these numbers can get confusing, selection based upon a single trait can often lead to undesired consequences. For example, selecting only for weaning weight in a production system where heifers are retained, will lead to larger mature cows, potential calving difficulties, and perhaps increased feed intake. A balanced selection approach focusing on optimizing traits for your environment and production system works much better than trying to maximize a single trait.

Heritability

Heritability is a measure of how much genetic influence there is on a particular trait. Heritability is a value between 0 and 1 and the higher the number, the more genetic influence there is on that trait. Reproductive traits tend to have low heritability rates, while weight and carcass traits are more heritable.

For example, weaning weight has a heritability of 0.24 to 0.30, which means that 24 to 30% of the differences we see in yearling weights between cattle in a herd are caused by genetics. The range of heritabilitiy shown in Table 3 has been shown as a percentage of heritability. If a trait has a low heritability, this indicates that the environment or management has a much larger influence on that trait. High heritability indicates that genetics play a relatively large role in the trait. The level of heritability in a trait will have an impact on selection decisions. Progress tends to be much slower in lowly heritable traits when attempting change through selection alone. With higher heritability, we usually can achieve more rapid progress through selection².  

Table 3: The impact of genetics or management changes on culling decisions

Sources: The Beef Cow Calf Manual. Alberta Agriculture and Food (2008) and Guidelines For Uniform Beef Improvement Programs. Beef Improvement Federation (2010).

* These traits are known to be heritable, but a formal heritability study has not been conducted since the incidence is low and it would take thousands of animals to derive accurate heritabilities.

Identifying Breeding Goals

No two beef operations in Canada are exactly the same. Factors such as climate, terrain, forage production, management style and marketing schemes will dictate the type of cattle that will perform best in your system.

Determining breeding goals should start by identifying what your production system looks like currently. By outlining the current production parameters, it will become more clear which traits need improvement in order to meet your goals. Once these traits are identified it also becomes easier to select replacement bulls and females and make culling decisions to help you achieve your goals.

Example: In Level 1 we identified improving weaning weights by 5 lbs as a goal. For this example, we will assume that our new group of calves will be raised in the same environment.

In the previous modules we have identified the females that will calve and re-breed within a certain period of time (e.g. 75 days) and have also weaned live calves in the past five years. We have also identified females that maintain their body condition without additional feeding. By doing this, you have identified the females that will most likely calve within a shorter calving period, thus giving the group of calves more time to grow before weaning (see section on calving distribution).

On the sire side, we could consider selecting bulls with better EPDs for weaning weight. For example, if Bull A has a weaning weight EPD of +9.0 lbs and Bull B has a weaning weight EPD of +3.0 lbs, this means that Bull A’s calves will have weaning weights that are 6 lbs heavier than whatever the weaning weight of Bull B’s calves are, on average.

Selecting Replacement Heifers

The decision to raise or purchase replacement heifers will vary based on the management and economic goals of each operation. If you have been collecting and analyzing records to this point, you may already have already set breeding goals which will define which characteristics you need to be looking for in your replacements.

Some criteria to consider for raising and purchasing replacement females:

• Birth date? How old do you need heifers to be to fit into a front-loaded calving system?
• What breed composition will work with the bulls you are running?
• How has her dam performed?
• How has she performed herself?

Data to record or request from seller if you are raising or purchasing commercial replacement heifers: 

• Birth date
• Individual identification
• Dam ID
• Birth weight
• Weaning weight
• Calving ease

When to record it: 

• At birth
• At weaning
• After purchase

Example:  

From your records you have identified achieving higher weaning weights as one of your production goals. From your current calf crop you want to select the heifer calves that will have the best chance of producing calves with higher weaning weights. To do this, select heifer calves born in the earliest calving groups in similar management groups.

Example goals:

• Link heifer performance data to their dams for the next calf crop
• Use dam performance as a selection criterion when selecting the next group of replacements

Selecting Replacement Bulls

Purchasing the best bull for your operation starts with good record-keeping to identify your operation’s strengths and weaknesses. From there you can work to narrow down your search based on your breeding system, genetic goals and budget.

Breeding programs will be determined by operational goals and the management practices that fit those goals. A farm that sells their calves at weaning may choose a crossbreeding program with high performance, while a farm that direct markets their beef may prefer a single breed in order to ensure consistent carcass quality.

There are many different types of bulls available, so aiming for complementarity of the bull’s genetics to your cow herd’s genetic makeup and fit with your operational goals will contribute to increased revenue and reduced costs.

Given the plethora of EPDs available, trying to sort through ten or twenty individual EPDs that may not have relevance to your particular operation can easily lead to information overload, so many breed associations provide selection indexes that combine multiple traits with relevant weightings in order to combine several traits of interest into one number.  By focusing on Economically Relevant Traits (ERTs), you can eliminate those bits of information that will not directly impact your operation’s profitability. Economically relevant traits are those that are directly associated with a source of revenue, or a cost.  Not all EPDs represent ERTs – instead they use a related (or indicator) trait to estimate the ERT.

The BCRC produced a series of blog posts that provide more information about bull purchasing decisions which can be found here.

Data to record: 

• Individual identification
• Calving ease
• Weaning weight
• Yearling weight

When to record it: 

• At birth
• At weaning
• Following purchase
• At turn out

Example:  

From your records you have identified achieving higher weaning weights as one of your production goals. This time your focus is to select bulls to breed to the mature cow herd with strong EPDs for weaning weights since these traits are moderately heritable.

Example goals:

• Select bulls for the next breeding season with optimal EPDs for weaning weight

Using Records for Cow Culling Decisions

As discussed in the animal health section, the number one factor impacting cow profitability is whether she successfully produces a calf every year. Other factors such as conformation, milking ability, health issues and temperament can also impact profitability year to year. Cows with impaired mobility or unsound mouths are unlikely to intake sufficient nutrients to maintain body condition and be productive. Newborn calves may have difficulty nursing from large teats or pendulous udders. In any case, there can be large economic consequences of unsound cows. Therefore, using records to make informed culling choices is highly valuable.

There can be confusion as to whether an issue primarily has a genetic component or requires better management. Some of the common traits used in culling decisions are shown in Table 3. If the goal is to reduce certain issues in your herd, the problem may not be solved using only genetics.

Using records to quickly identify cows to be culled can save a lot of time and effort. On some operations this may be as simple as putting a cull tag in the cow’s ear or adding an asterisk* beside her identification in your records. Identifying some of your non-negotiable traits can also help with making culling decisions. For example, some of the traits listed in Table 3 may be non-negotiable for you.

Data to record: 

• Animal ID
• Calf ID
• Calf performance
• Cow performance
• Health treatments
• Conformation issues
• Temperament
• Calving interval
• Pregnancy status

When to record it:

• At each occurrence

Example: 

You need to decide which heifers to keep from your calf crop as replacements. In your records you have put an asterisk beside two cows that both had equally well-performing heifer calves this year. Your notes indicate that one cow had vaginal prolapse this past year before calving, the other cow you marked as treated for foot rot. Since vaginal prolapse is considered to be a heritable trait you decide not to keep the heifer calf from the first cow. Since the foot rot is more of a management issue, you decide to keep the heifer calf from the second cow.

Example goals:

• Link all 2021 calves to their dams
• Apply a cull tag to all cows with poor udders at calving in 2021

Ce contenu a été révisé pour la dernière fois en Janvier 2024.