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Informational Articles 

Determining the Percentage of Blood in a Pedigree

You've probably seen the advertisements that tout "41% Poco Bueno" or "25% Leo." Have you ever wondered how they came up with those figures? It's not difficult to do. 

Percentage of blood simply adds up the approximate amount a particular ancestor might have contributed to your horse's genetic make-up. This is not an exact amount, however, as there are a lot of variables involved in breeding animals. (Watch for a future article about breeding terms such as homozygous versus heterozygous and in-breeding, line-breeding, and out-crossing.)

The pedigree below is for Alisa Lark, dam of Two-Time Superhorse, Rugged Lark. She is line-bred on three famous horses - Joe Reed, King, and Joe Hancock.

Parent Grandparent Great-grandparent GG-grandparent GGG-grandparent
Leolark Lemac Leo Joe Reed II Joe Reed
Little Fanny Joe Reed
Fanny Ashwell
Sorrel Sue King Zantanon
Tommy King mare --
Tallalah King Bob Brown Bob Snooper
mare by Harmon Baker Jr
Queen Ann King
Holland mare
Daisy K Copper Tom Benear
May Troutman
Scar Face Golden Bear (TB)
Aliso Gill 3 Pelican Joe Hancock Jr Joe Hancock John Wilkens
Brown Hancock mare
Burnett mare --
Covella (TB) Coventry (TB) *Negofol (TB)
Sun Queen (TB)
Sonora (TB) *Light Brigade (TB)
Ilma (TB)
Snicker Girl Snicker John Gaston Nowata Star
Fleet Sappho
Okie Girl Joe Tom Joe Hancock
TB mare
Miss Tommy 99 Tom (Scooter)
Riding type mare

Each parent contributing 50% of the genes that make up his or her offspring. For example, in the pedigree above Alisa Lark received 50% of her genes from her sire, Leolark, and 50% of her genes from her mother Aliso Gill 3. In turn, Leolark received 50% of his genes from his father, Lemac, and 50% of his genes from his mother, Tallalah. Continuing in this vein, Leolark received 25% of his genes from his paternal grandfather, Leo (Leo gave 50% of his genes to Lemac who in turn gave 50% of his genes to Leolark). Therefore Alisa Lark would have received 12.5% of her genes from Leo - 50% from Leolark, of which only 50% was from Lemac (25%), of which only 50% was from Leo (12.5%). However because of the way genes combine, this is only an approximation.

The chart below summarizes the percentages received from each ancestor in a given generation. Therefore, Leo, a great-grandparent, would have contributed 12.5% to Alisa Lark. For animals that show up more than once in a pedigree, you only need to add the percentages together. For example, Joe Reed shows up twice as a GGG-grandparent, therefore he supplied 3.125 plus 3.125%, or 6.25%. It's the same if the ancestor shows up in different generations. For example, King shows up as a GG-grandparent and as a GGG-grandparent, therefore he supplied 6.25 plus 3.125%, or 9.375%.

Parent 1 generation 50%
Grandparent 2 generation 25%
Great-grandparent 3 generation 12.5%
GG-grandparent 4 generation 6.25%
GGG-grandparent 5 generation 3.125%
GGGG-grandparent 6 generation 1.5625%

To help you figure the percentage of blood of a particular ancestor in your horse's pedigree use the chart and the steps below. Just remember that the percentage of blood is only an approximation of the inheritance a particular ancestor gave to your horse.

Step 1 - Determine the relationship between your horse and the targeted ancestor.

Step 2 - Find that relationship on the chart to determine the approximate percentage of blood that ancestor contributed to your horse.

Step 3 - If, as in many pedigrees, the targeted ancestor appears more than once in your horse's pedigree, repeat steps 1 and 2 for each occurrence and add the amounts together.

Another way to show where and how often an ancestor appears in your horse's pedigree is by listing the generation for each appearance. For example, in the pedigree listed above Joe Reed appears twice in the 5th generation. This would be written as 5 x 5. King appears once in the fourth generation and once in the fifth generation. This would be written as 4 x 5. If an ancestor appears more than twice, just list a generation number for each time that he appears. Larry Thornton calls this a "linebreeding pattern."

Percentage of blood can be used to help determine when two horses would be a good cross, but it is only one tool out of many. Beware of the breeder who uses it as the only tool. Just because two horses have a high percentage of a valuable ancestor doesn't mean they should be bred together, particularly if they have common faults.


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