5 February 2011

11 minute read

What is an EBV?

An EBV is a value which expresses the difference (+ or -) between an individual animal and the herd or breed benchmark to which the animal is being compared. EBVs are reported in terms of actual product e.g. days, kg of weight or mm of fat depth, etc.

There are two main performance recording services operating in the UK.

• The Australian Breedplan programme is used by many beef breeds in the UK and operates through Pedigree Cattle Services.
• Signet/BASCO is operated by Edinburgh Genetic Evaluation Services (EGENES).

Both systems produce EBVs for many of the same traits, with their databases being accessed via the respective breed societies. Sale catalogues that have EBVs included for each animal should also have an explanation of the traits and a chart showing percentile bands, depicting where the individual animal ranks within the breed depending on its performance for the traits in question.

Contrary to common belief EBVs are not a massive waste of time and money but an estimation of how the progeny of an individual should perform! The purpose of EBVs are to bring all the cattle within a herd or breed onto a common platform so that those making selection decisions can know they are comparing like with like regardless of the system or location they are produced in. It is important at this point to remember that each parent contributes half the resulting calf’s genetic make-up.

This performance estimation measures the parts of the animal that the eye cannot see (figure 5). An animal’s physical appearance (phenotype) is determined by two components, its genetics (genotype) and non genetic or “Environmental” influences. EBVs measure this genetic component and allow cattle within their respective breeds to be compared, excluding their management and Environment. The key point here is what you see is not necessarily what you get!

The environmental (non-genetic) influences include grass quality, disease burden, parasites, supplementary feeding, management ability etc. The environment component is a part that herd keepers have influence over and the ability to compensate for or enhance. Despite the environmental influences, the genotype remains the same and parents do not pass on to their progeny the environmental effects that have influenced them.

EBVs draw information from a number of sources in addition to the animal’s own performance (Figure 1). The basis is comparing individuals within a contemporary group, one to another, minimising non-genetic influences. The system also compares contemporaries in other herds where genetic linkages exist through siblings and ancestors. This is a very simple description of what is involved to outline the principle. The actual calculations are much more complex and beyond anything that a farmer needs to know or understand.

Figure 1 - Information sources used in producing EBVs

Linked traits are those which share common connections with each other. An example of this is that where 600 day weight increases so will birth weight.

Heritability is the term used to describe how strongly a characteristic is transferred from parents to progeny and is rarely considered. It is the proportion of an animal‘s production that comes from its genetics and varies between traits. The higher the value the faster genetic improvement can be made and positive benefits observed. In general terms, maternal traits are poorly inherited and growth traits are moderate to highly heritable. The detail of such is shown in Figure 2.

Figure 2 - Heritability of measured traits

The old adage of cattle performance being “80 per cent feeding and 20 per cent breeding” is not strictly true, but the breeding component will determine how the non genetic component is used. At low to average levels of performance, feeding and health will have more of a contribution to an animals overall performance but for those trying to maximise returns the right genetics are vital. A typical example could be milking ability, where if the genetics for milk are poor, feeding will not make a significant difference, the cow will just get fatter.

No two animals are the same, so the more information that can be collected, the more one can account for the variation between individuals, and so the overall risk of using them can be reduced.

EBV data must generally reach a certain level of accuracy before it can be reported to ensure the information is as relevant as possible and truly reflects the potential performance of the animal in question. Some traits such as growth will not be reported until they reach an accuracy level of 40 per cent, which is typically at the lower range of reported accuracies (these can be up to 99 per cent). Traits which are more difficult to measure such as carcass and fertility related can be reported at much lower levels due to the limited information available, requiring the user to make a judgement decision.

Producing good quality EBVs

Throughout a performance recorded animal’s life, measurements are taken which are used to produce its EBVs. These start with a birth weight and calving ease score. These measurements are supplemented by weights at 200 days, 400 days and 600 days as well as scrotal circumference (bulls only) and ultrasonic measurement of back-fat, rump fat and muscle depth. At weaning time, dam weights will also be collected to contribute to the mature weight EBV.

In the future, genomic data may also be incorporated for the difficult-to-measure traits such as carcass and reproductive characteristics. Disposition data is collected by some overseas breeds and a docility EBV produced to measure their temperament based on “flight time”. In a study carried out in Australia it was found that “flighty” cattle were gaining 0.4kg/day less than their docile contemporaries, a substantial amount in today’s challenging climate. Signet will be launching a docility EBV in 2011, leading the way in the UK.

In addition to the information collected from an individual, the data from siblings and other family members make a contribution. There are many factors involved in the production of quality EBVs but it is useful to mention a few of the factors that lead to poor quality EBVs as well. The most important principle of performance recording is that of grouping the cattle together for the comparison. This is the biggest challenge for the system to overcome and depends on accurate record keeping and submission of raw data.

Where the same sire is used on the same cows year after year or where there is only a small number in the management group there is evidently a lack of genetic diversity. This limits the amount of variation that can be accounted for.

To produce good quality EBVs it is important that the herd has a compact calving pattern, with the cows run in reasonably large groups and that any data from that group is collected on the same day. Within this group at least two different sires should be used each year to allow the system to compare the performance levels between these sires’ calves. Ideally the bulls should be a mix of a proven sire and a young or unproven sire from the recorded animal itself. This information depicts the type of genetics that an individual actually possess because it helps estimate the genetics that it will pass to its progeny.

Any animal that may have been sick, fed for a show or sale, used as a sire or introduced to a new group should be identified to ensure it is not compared on a “like for like” basis with the rest of its group.

In small herds the use of AI bulls will lead to rapid improvements in their EBVs and accuracy. This applies to all sizes of herds. In small herds the risk may be to use a bull retained from the herd. His use is limited to only a small number of females each year meaning the chance of getting any meaningful information is negligible. Small herd owners need to evaluate the cost of keeping a bull compared to AI, given modern heat synchronisation techniques which make the process much simpler and more accurate.

The main principle must be to record all calves, the good the bad and the ugly. Selectively recording animals will deny a true picture of what is happening in the herd. It will give a distorted base set unreasonably high or it may undervalue better sires whilst overvaluing lesser sires.

Accuracy in measuring weights and correctly recording dates of birth can make a substantial difference. Estimating weights is not accurate enough and whilst not having a significant effect on the overall group (as the estimate will likely be variable), 50kgs of error either way can have a much more serious impact on the individual, adversely affecting related traits especially those with negative relationships. Accurate honest weights are vital to many processes on farm including medical treatments and pre sale checks. A weigh scale is the most important piece of equipment on a livestock farm.

Popular misconceptions

It is often asked why a good animal does not have good EBVs, or vice versa:

• Firstly an EBV is a performance estimate or prediction for the progeny of a bull or cow and not of their own performance.
• Secondly the animal will most likely have had its environment influenced in some way. It may have been taken away from the rest of its group, been suckling another or several other cows, had creep feed, been housed earlier or weaned later or some other such practice which has compensated for its lack of genetic potential.

Below are two of the reasons why some cattle look outstanding but their EBVs do not reflect this. The questions which should be asked at this stage are “What would this animal have looked like without additional management?” and “What will his calves look like without similar expensive management?”

• Where a calf with superior genetics suffers a setback such as disease affecting it or its mother, the opposite effect can occur. This animal still has all the potential and genetics to produce great progeny but may not look as good as it could or as good as its contemporaries. This highlights the danger of selecting by eye alone, as this animal could be inadvertently rejected.
• Animals that have been imported from overseas can suffer from poor, low accuracy EBVs. With limited or no information about its past performance, its EBVs will unfortunately reflect this until sufficient data is collected and processed, in its new home country.

Concern is often expressed about the possibility of a person exaggerating the weight of an animal to increase its EBV. This could happen but it would be unwise.

There are checks and balances within the EBV system which queries animals that are too far ahead of the group and secondly, as progeny are analysed its failure to perform to expectations will be noticeable. Animals that are outside the boundaries are flagged as “outliers” for further investigation.

Anyone under the illusion that he can beat the system and fool the process is wrong. He may get away with it for one or two calf crops but the cattle will fail to live up to their expectations with their EBVs deteriorating rapidly when they go into production. The biggest victim in this fraud is the person recording the data as he is fooling himself and destroying his reputation. Breed societies need to act aggressively in any cases detected to protect their members and the integrity of the breed.

Selection indexes

Selection indexes take the hard work out of knowing how much emphasis should be placed on each of the available EBVs when making breeding decisions. An index gives a single EBV that reflects the value of an animal in financial terms.

Indexes allow balanced selection as they apportion the amount of selection pressure that needs to be applied for growth, maternal, carcass and fertility traits to give the most profitable herd over the long term. Typical production parameters, prices and production costs underlie each index.

The next part involves steps that combine economics with genetics. Financial values for performance measures are calculated for each breed’s production and market. Using genetic theory these financial values are used to calculate appropriate weightings for the EBVs currently available.

Indices exist for different markets such as terminal index and self replacing index and provide a convenient way of speeding up a search. Choosing the highest index animal will not necessarily result in a suite of traits that will suit the herd and compromise will likely be needed so it is still essential to look at the EBV for each trait and determine if they are appropriate to ultimately satisfy the previously identified needs.

How much is genetic improvement worth?

At this point it is worth using an example to show how value can be calculated using EBV data. As already mentioned Indexes are a financial value. Using the example of Dorepoll 1 10H Headliner (appendix 2) who has a Self Replacing Index (SRI) of £36.00 compared to the breed average of £24.00, there is a difference of £12.00. In a herd producing 100 calves over his breeding lifetime this equates to £1200. Compare this bull to a bull with a self replacing index of £10 and the extra value to the business immediately leaps to £2600!

Irish Cattle Breeders Federation

The Irish Cattle Breeders Federation (ICBF) has developed a product named “Herdplus”. This system produces management reports for both the pedigree and commercial herd owners. EBVs and indexes are also produced for both types of herd meaning that even commercial suckler cow herds have performance recording information available for all their cattle. The system draws on information from markets, abattoirs and data collected by the farmer. Hopefully the UK will be able to develop a similar system in the years to come.