How to use EBVs for Selection

How to use EBVs for Selection

By Quentin de Bruyn

When selecting animals to buy or retain in your herd its physical appraisal or how it “looks” will always be important. Stockmanship, or the art of being able to judge how an animal will breed on its “looks” is an art that takes years of experience, working with cattle, attending breeders courses and learning from experienced stockmen. Nothing can replace this skill. 

However, good stockmen also know that the best “looking” cow is often the poorest producer – these cows either don’t have enough milk to raise a decent calf or they are not good mothers and lose their calves through neglect. “Looks” are also not a reliable indicator of other important traits such as milk, how easily she calves or her ability to raise a healthy calf. The best mothers give everything to their calves, which can leave them looking in poor condition. Therefore, relying on “looks” alone can be problematic. 

Using Estimated Breeding Values (EBVs) from performance tested herds is a critical tool to identify animals that not only look good, but are also good breeders. However, EBVs are only as good as the numbers behind them. They are only useful if they are accurate and they are only accurate if proper performance testing and data collection is done on an ongoing basis across the whole herd. It is very important to understand that inaccurate EBVs could be more misleading than helpful and should not be relied upon to make decisions. 

The following are some broad principles to use EBVs correctly for selection: 

  • EBVs tend to work against each other i.e. high scores in some areas will lead to low scores in others. For example, a cow with a high calving ease index (small calves) will tend to have a lower growth index. Similarly, a high “milk” index often contributes to a lower “fertility”, because cows that give everything to their calf can lose too much condition and struggle to fall pregnant again. The aim is therefore not to “maximise” EBVs but to be aware of the interplay between them and to understand what they say about the animals production potential. 
  • To use EBVs most successfully you need to have a very clear idea of your own breeding objectives and the needs of your particular farming environment. When you know what you want to achieve, accurate EBVs can help you select animals that fit into your environment and help you achieve your breeding objectives by addressing short-comings in your herd like growth or milk. 
  • Ideally, one should strive for balance across performance indicators rather than chasing outliers. 

Interpreting EBVs

Eve VST 14-59

In an auction catalogue, the Breeding Values for each animal are shown in a table at the bottom of each animals Lot card. (See example of Eve VST 14-59). There are four values in each Breeding Value column. The first value given, labelled “BV” on the left is the actual breeding value of that specific trait, the second line “Acc” indicates the accuracy in %,  while the third line expresses the actual breeding value as an INDEX against the breed average. The fourth line is a compilation of the relevant breeding value indexes into a single broader breeding value, such as fertility being based on both AFC and ICP. 

The EBV accuracy will give you an indication of the reliability of the figures. In general, anything less than 50% tells you that the actual recorded data underlying the figures is weak and unreliable. The more data that is collected through performance testing on an ongoing basis over generations within family lines the more value the EBVs have as a selection tool.

Breeding Values and the Breeding Value Indexes

  1. Calving Ease (CE)– The “Calving Ease” Index is compiled from the “Birth direct” and a “Birth Maternal” breeding value. An index of above 100 indicates that the animal will deliver below average size calves and therefore should reduce the chance of calving difficulties due to big calves. 
  2. Growth – The “Growth” Index is compiled from weaning weights and the 12 to 18 month growth performance as well as other data collected in the phase-C and phase-D tests. An index of above 100 indicates better growth than the breed average. This is particularly important for weaner production and an indication of their performance in a feedlot environment. 
  3. Milk – The “Milk” Index is made up of information from pre-weaning weights and weaning weights. An index of above 100 here indicates above breed average milk production which leads to higher calf survival rates and heavier weaners.
  4. Fertility – The “Fertility” Index is made up of Age at First Calving (AFC) and Inter Calf Period (ICP) and I think longevity also plays a role here. An animal with a fertility index of above 100 will give birth for the first time sooner and more frequently thereafter and for longer than the breed average in these traits.
  5. Maintenance – The “Maintenance” Index is based on the size and weight of an animal. The bigger the animal the higher the Direct Breeding Value (2nd to last line) will be, but the poorer the Maintenance Index will be. This is because bigger animals require more food and more hectares. A index of above 100 in maintenance indicates a smaller than breed average animal and will allow higher stocking rates.
  6. Cow Value – The “Cow Value” index is a tool rather than an EBV in itself. The Boran technical committee tries to determine what the ideal Boran animal should look like and how it should breed. This is expressed by giving a weight/importance to each individual breeding value. In the Boran breed the following weights have been determined – calving ease (9%), growth (25%), milk (18%), maintenance (12%) and fertility (36%). The “Cow Value” is a weighted composite of an animal’s individual EBVs and is meant to indicate how the animal is expected to perform against what the breed deems to be the perfect animal. The higher the Index the better the animal is expected to perform against the ideal breed standard.
  7. n my opinion, the individual EBVs are more useful than the “Cow Value” for selecting animals which help to fix a short-coming in your herd or which would be more suited to your own specific environment. Personally, I tend to discount calving ease because I think we are fortunate to have a breed with low birth weights and little calving issues. I also prefer to choose animals that are slightly above breed average in size because the Boran breed is a smaller breed and most South African farmers are weaner producers and want bigger weaners with good growth to get better per kg prices from the feedlots.
  8. Bull Value – The “Bull Value” index is generated from measurements in Phase-D and Phase-C performance tests of the testicles circumference of peer groups. An index above 100 will indicate that the animal will have above breed average testes in the male offspring. Testicle circumference is directly linked to fertility in cows and the quality and quantity of semen produced by bulls, which affects their ability to get many cows pregnant in the shortest time possible.

2021 Vastrap Auction