Wednesday, April 24, 2024

DON’T BE FOOLED by well-fed bulls

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What you see in an animal is not always what you get in the progeny. A lot of what you are seeing is not controlled by that animal’s genes and thus not passed on to its offspring.
Reading Time: 4 minutes

Estimated breeding values (EBVs) are predictions of average production differences between animals’ offspring resulting from the activities of those animals’ genes. Often the production effects of these genes are hidden by the generally much stronger effects of such things as feeding and animal health.

This is why EBVs are so powerful – they remove this outer covering laid down by things not controlled by genes (age, feed, health status etc) and reveal the true genetic makeup of an animal, the only part of the animal passed on to its progeny.

This outer covering varies the most where animals for sale come from several different farms. EBVs/indexes place animals from these farms on a level playing field by removing the differences that exist between them, such as feeding levels and trace-element status. So remember, in making a decision on the performance part of the selection process, what you should be interested in is the animal’s genes (EBVs).

If both raw figures such as birthweight and sale-day weight and EBVs/indexes are presented on an animal at a sale, always use the EBVs/indexes, as they are the most accurate prediction of how an animal will breed. Raw figures can be misleading if they are used to predict how an animal will breed. These figures are more of an indication of how well an animal has been looked after than a prediction of how it will perform as a parent.

This is the why bulls bought using raw figures often leave disappointing progeny. Just as a vehicle should not be bought without looking under its bonnet, neither should a bull be bought without considering its EBVs/indexes.

The following are a few facts that may improve your buying decision:

  • EBVs/indexes should not be compared between breeds e.g. Angus EBVs/indexes cannot be compared with Hereford EBVs/indexes.
  • The average EBVs for a breed represent the average change in the EBVs since the breed started recording and evaluating each trait using modern genetic evaluation technology. This “start” year is known as “the base year” and it is not necessarily the same year for each trait. As an example, the NZ Angus 2011 Group Breedplan average EBV for 600-Day Weight is 92kg. This means that since NZ Angus began recording the 600-day weight trait with Breedplan (its base year), the breed’s average 600-day weight has increased 92kg.
  • The milk EBV, or more correctly the 200-day milk EBV, is expressed as kilograms of calf weaned. A bull with an EBV for milk of 10kg will produce daughters that will wean calves on average 5kg (10kg/2) heavier at weaning than calves belonging to daughters of a bull with an EBV of 0kg. Remember that this EBV is not strongly inherited (it is not strongly influenced by genes), meaning things like level of feeding and animal health have a far greater influence. Therefore improvement by selecting for it using EBVs will be slow unless a bull with an extreme milk EBV is used.
  • An EBV is a measure of how productive an animal’s genes are for a particular trait, compared with those of other animals. It is not a measure of the actual performance of an animal. For example, knowing an animal’s birthweight EBV gives you no indication of its actual birthweight.
  • It is believed by some that the EBV for scrotal size (SS) and the actual measurement for SS target the same trait. This is not the case. The EBV for SS is generated from a measurement of SS at around 10-14 months of age (after puberty is reached), combined with information from relatives and related traits. SS at this age is related to some extent to the age that a bull’s daughters start cycling and the future fertility of these daughters. The actual scrotal measurement is related to a different trait, that is, the amount and quality of semen a bull is capable of producing and is influenced by a bull’s age and condition score. In general, the larger the SS of a bull, the more semen he will produce and given that his mating and semen quality are satisfactory, the more cows he should be able to get in calf. A bull that has a SS less than 30cm at 18-20 months of age should be treated with caution, because as SS decreases below this measurement, the percentage of fertile sperm falls dramatically, along with the ability of the bull to get cows in calf.

So remember, when you are on the lookout for a bull this year know what things you want to improve in your herd and use the appropriate EBVs and Indexes to make the right selection. If you don’t get it right it could cost you a lot of money. Conversely if you get it right you will significantly improve your bottom line – but definitely don’t use raw figures.

Key points:
• Raw data is of no use in selecting animals to make genetic progress.
• EBVs are the best available predictors of how an animal will perform as a parent.
• EBVs/Indexes should not be compared between breeds.
• Breed average EBVs represent the change in each EBV since the trait was first genetically evaluated using today’s genetic evaluation technology.
• The milk EBV is an estimate of the ability of a bull’s daughters, via their milk genes, to produce kilograms of weaning weight in their calves. The milk EBV is poorly inherited, which means it is far quicker to improve calf weaning weights by feeding cows better than it is to improve them through the milk EBV.
• EBVs are not a measure of the actual performance of an animal but a measure of the difference in performance between animals.
• The SS EBV and the actual scrotal measurement relate to different traits.

Related story: The fat dilemma

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