Thursday, December 29, 2011

What is BLUP?

WorldFengur is the international registry for the Icelandic horse.  It contains a treasure trove of fascinating information about your Icelandic horse.  One of the nuggets of information is BLUP.  So if you have a registered Icelandic horse, you can look up its BLUP in WorldFengur.  Note:  If you join the US Icelandic Horse Congress (or the Icelandic breed association in your country), you get free access to WorldFengur for your individual membership fee of $45; normally access to WorldFengur runs around $95.

BLUP  stands for Best Linear Unbiased Prediction. Per C. Clarke (2010, para 1), BLUP indices are “statistical values that are designed to help predict likely future developments based on past performance… However, in animal husbandry they are most widely used to improve the genetic quality of the breeding herd and although originally introduced for dairy cattle they are now regarded by many as an essential tool in the sports horse breeder’s armory.” You can refer to T. Árnason’s (2010) article International Genetic Evaluations with the BLUP Method for more information on how WorldFengur calculates BLUP. 
To summarize, BLUP is a statistical method used for predicting the breeding value of animals based on field assessments of that animal’s progenitors.  Sports competition scores do not factor into the BLUP calculation for Icelandic horses.  BLUP has been used to improve the breeding of French riding horses, Dutch trotters, and American quarter horses (Árnason and Van Vleck, p.485).   As a casual user, the important thing to remember about BLUP is that it is a predictor only.  Now let’s find the BLUP for Blessi.

In interpreting BLUP, you consider a score of 100 as average.   As you can see above, Blessi is predicted as passing on (assuming he were a stallion) above average conformation.  His best conformational features to be passed on are predicted to be his back, legs, and proportions.  And his worst features are predicted to be his mane and tail and head. As for gaits, BLUP predicts his potential offspring would have a decent trot and tolt.  It also predicts they will have a flying pace--which Blessi himself at age 15 has never shown.  BLUP predicts, his offspring would be taller than average (Blessi is 14.1 hands).  BLUP accuracy is calculated at 61% which is fairly low. His total BLUB score is currently 104; when I first got him over seven years ago, it was 108.

As  M. Gates (2010, p. 16) cautions, BLUP is a valuable guide in breeding but ”… BLUP scores are not always accurate due to the fact that some breeding horses are missing either pedigree or evaluated parents in their bloodlines, and are therefore automatically scored lower.”  The BLUP score will change over time as assessments are added to horses in the pedigree tree. 

Remember BLUP refers to what could be passed on to offspring.  However, BLUP can give you some hints as to what to look for when you see the actual horse:  If BLUP predicts that the horse pass on a below average tolt, you could legitimately check on the quality of the actual horse's tolt.  Does BLUP predict that offspring will have a better than average confirmation but average gaits (or vice versa)?  Is the tolt score much lower than the trot score?  Does BLUP predict that offspring will be taller or shorter than average?  Have fun playing with these types of questions and see how the real horse measures up. 

Árnason, T. (November, 2010).  International genetic evaluations with the BLUP method 2010. Found at:
Árnason, T., & Van Vleck, L. (2000).  Genetic improvement in the horse.  In The Genetics of the Horse.  Eds. A. Bowling & A. Ruvinsky, CABI Publishing, London, pp. 473-495.
Gates, M.  (2010).  The art of horse breeding.  In The Icelandic StudBook, Icelandic Stallions of North America, ed. T. Kristjánsdóttir, Cranial Solutions, Chatham, NY.