Clear Lake Farm Icelandic Horse Blog

In reports and comments about breeding horses we often read about BLUP. “Stallion XY has a BLUP for tölt”. What does it stand for and how can BLUP help a breeder with his breeding program?

BLUP is the abbreviation for Best Linear Unbiased Prediction. The BLUP method has become a standard method for genetic evaluation of livestock (horses included) worldwide.

‘Best’              is a reference to the method which gives the best estimates for the breeding value.

‘Linear’         means that there is a linear relation between parameters in the statistical model.

‘Unbiased’    means that the breeding value estimates are central, that they are expected to be normally distributed with the true breeding value as mean value.

‘Prediction’ normally refers to the future. But prediction also refers to the estimation of realized values of a random variable drawn from a population with known variance- and co-variance-structure.

With BLUP the breeding values are calculated for all animals simultaneously, and at the same time environmental effects can be corrected for. The theory behind BLUP is comparatively complex, and the BLUP method demands a lot of calculations.

BLUP calculations are used to predict everything from hog birth rates to volcanic activity. By compiling fixed numerical values assigned to the traits of any given individual or group of individuals (hogs, volcanoes, horses), it is possible to track and predict those traits objectively. The resulting numbers allow breeders to make informed predictions when choosing breeding stock.

The BLUP consists of three categories:

1. The General category, which consists of horses with 14 or less offspring,

2. The First Prize category, which consists of horses with 15 to 49 offspring, and

3. The Honorary category, which consists of horses with 50 or more offspring.

To determine a rating, the characteristics and talents of a horse, as well as the quality of that horse’s ancestors are considered. A BLUP rating thereby reflects not only the features of the individual horse being judged, but also the quality of its bloodline.

In the rating system, a score of 100 indicates an average horse; a rating of 115 is a horse of good quality; a rating of 120 or better indicates a horse of extraordinary quality. A horse has a BLUP for each trait that is evaluated, and for an overall score. Above 100 means he can improve this trait, below 100 indicates negative development of this trait.

When the BLUP for a trait is calculated, all available individual evaluation scores that are connected to that horse are used for the calculation: both the scores of the horse itself, its parents, its offspring, its grandparents, as well as any other relatives. Virtually all evaluation scores of all known relatives are used. For example, if a horse has 10 evaluated relatives that have a pretty head; it has a high BLUP for head. If the horse is then evaluated and the score for its head turns out to be low, its BLUP for this trait then becomes lower.

Individual horses can be evaluated many times in their life. If a horse gets a good evaluation, lets say 8.5 for tölt, when it is 4 years old, it receives a higher BLUP for tölt than it would if the same evaluation was reached when it was older. The reason for this is that the breeding goal is to produce horses that mature quickly, and don’t need long periods of training to perform well.

If a stallion with a 120 BLUP for tölt is bred to a mare with an 80 BLUP for tölt, it is likely that the resulting offspring will be neither particularly good nor bad, and will therefore get the BLUP 100 for tölt until further information is collected ( such as when the offspring is evaluated, or its offspring, or other relatives).

BLUP evaluation works both ways. A  BLUP score can be raised or lowered.

Stallion A is bred to a mare with a high BLUP for tölt (let’s say 120). The offspring B will have a high BLUP when it’s unevaluated (something like 132). When the offspring is evaluated, and it reaches a good evaluation for tölt, it will help raise the BLUP for tölt of the stallion A.

On the other hand, if stallion A is bred to a mare with low BLUP (let’s say 90) and bad evaluations for tölt (let’s say 7), the unevaluated offspring C will get a lower BLUP (maybe 110). If C’s evaluation then turns out to be as good as B’s, it will improve the BLUP of the stallion A EVEN MORE.

This is because the stallion A has proven his great breeding potential by improving the qualities of the offspring C (out of the bad mare), bringing it up to the level of a good quality horse. So, if both B and C are evaluated, and both receive a 9.0 for tölt, the effect of offspring C on its father’s BLUP will be more significant.

How can one use this information? If one has an unevaluated mare that has a good tölt but is very reluctant to trot, and wants to breed for both gaits in the offspring, it is best to search for a stallion that has good tölt, and a very good evaluation for trot.  A good BLUP for trot would be an added indication that the sire has proven himself to be an individual with good trot, and that his evaluated ancestors and offspring have also had a tendency toward good trot.

BLUP can also be helpful when one is buying a young horse. Its BLUP factors give an indication of its likely quality. The BLUP is used as a supplement to other evaluations – however BLUP ratings can only be a hint and are not necessarily the final truth!

The BLUP method with animal model for simultaneous genetic evaluation for ten correlated traits of conformation and riding ability of Icelandic horses was used as early as 1982. The method is officially used by The Farmers Association of Iceland since 1986, and they have been responsible for publication of results on the genetic evaluations.

The evaluations of more than 100 000 Icelandics can be found in World Fengur (www.worldfengur.com), a large database of information gathered over the last 40 years. This data is the basis for the breeding value calculations on Icelandic horses.

The following BLUP indexes are listed:

1.       Height at withers (BLUP in cm as a deviation from the population mean)

2.      Head

3.      Neck/withers/shoulders

4.      Back/loin/croup

5.      Proportions (harmony)

6.      Legs

7.      Leg stance (correctness)

8.      Hoofs

9.      Mane and tail

10.  Tölt

11.   Slow tölt

12.   Trot

13.   Pace

14.  Gallop

15.   Spirit

16.   Form under rider (expression)

17.   Walk

Evaluations of the use of the BLUP method for genetic evaluations in the Icelandic horse population have shown that the method has been very effective and has had a positive impact on Icelandic horse breeding. It can give a certain insight into the likely quality of a horse.

Information gathered by Kordula Reinhartz