THE SURI SELECTION TOOL
By Mike Safley
The Suri Network should be applauded for writing and passing a breed standard. The document and the process they used to achieve it is a model for other livestock industries that choose to create a breed standard. The standard itself is balanced and thoughtful. It will be of great help to alpaca judges in the suri show ring and breeders attempting to breed more ideal suris. The breed standard document does have one curious sentence in the first paragraph of the document: “The suri alpaca phenotype is the product of a breeding between a Suri alpaca female and a Suri alpaca male. That sentence is not scientifically certain.
The term “pure suri” is misunderstood. There are a number of ways to define a pure suri. The Suri Network breed standards as adopted, define a pure suri as the phenotypic product of mating a suri male with a suri female. The zoological definition of a pure breed is: A population of a species that have distinct characteristics that differentiate them from other populations in that species. Individuals within that population that reproduce with another individual of the population will produce offspring that are recognizable as members of that population.Animal breeding books allow that a breed can be defined by a breed association and does not necessarily need be “pure”. There is no doubt that a suri can be born of a huacaya parent and that a huacaya can be born of two suri parents. Suri breeders may be better served to use science, not subjective definitions, to accomplish their goal of breeding pure suri. I created the Suri Selection Tool because I don’t think a Suri breeder should have to get on their horse and go looking for a homozygous or “pure suri” male.
I recently discussed the sentence found in the first paragraph of the Suri Networks breed standard with a suri breeder friend of mine, Bill Graham of Old Trails Alpacas. Bill has been in the alpaca business since 1986. He founded Castle Hill Farms, a pioneering suri breeding operations with his then wife Nola Graham. More recently Bill has assembled a herd of more than 200 suris at his 600 acre ranch in Spokane, Washington. He pointed out that the Suri Network explains the reason for the inclusion of the sentence by including the following explanation under a frequently asked question entitled:
2) How is crossbreeding addressed in the breed standard?
In the first section of the breed standard, ‘Phenotype of the Suri Alpaca’, the last sentence states the following. ‘The Suri alpaca phenotype is produced by the breeding of a Suri alpaca male with a Suri alpaca female.’ Perhaps some further discussion might help in explaining what is meant by this statement. It is very important that breeders fully understand the intent. In its most basic form this means that the standard is met if one breeds two alpacas that look like Suris and are registered with ARI as Suris. Another way of stating this is that both the sire and dam should have a Suri phenotype.
The Suri Network document goes on to says that “There is nothing here that implied that either alpaca need to be a homozygous Suri as this a based on phenotype not genotype”. Geneticists define phenotype as: An organism's expressed physical traits, and genotype as: The genetic makeup of an organism.The Q & A makes clear that the suri breed standard is concerned about phenotype not genotype. I believe the emphasis should be on genotype.
Bill Graham mentioned that he has discovered that a significant percentage of highly promoted suri studs are heterozygous carriers of the huacaya gene. Bill is an avid researcher of ARI pedigrees. He pays particular attention to the progeny results for suri males. To prove his point, that many big name suri studs are heterozygous, he searched the progeny records of every suri male represented by a full page color ad in a recent edition of Purely Suri. Many of these studs had huacaya offspring which means that they carry a huacaya gene. It is also interesting to note that many of these heterozygous males, some with more than 100 cria, had sired only huacaya females. Many of these huacaya progeny are more than one year old, which means the owners continue to breed these males with the knowledge that they are heterozygous.
After spending an afternoon with Bill Graham I began to question why an industry that is passionately opposed to cross breeding would use males that produced huacaya cria. There seems to be a range of answers but the one I found most credible is that breeders simply do not understand the science behind the creation of cross bred animals. If they did, it would be very easy to purify the suri herd and make them predominately homozygous.
WHAT ARE THE ODDS?
The diagrams below, known as Punnetts Squares, are used by geneticists to predict the percentage of different genotypes produced from matings between animals whose genotype is known. The diagrams demonstrate that if breeders bred females of suri phenotype and they used only homozygous suri males it would only take 3 generations to create a 87.5% pure suri or homozygous herd in the United States; even if they began with suri females that were 100% heterozygous for the huacaya gene. All of the suri males in these examples were to be assumed homozygous, big S big S (SS), and all of the initial females were heterozygous, big S little s (Ss), for the suri gene. The little s represents the huacaya gene.
In the first generation, the heterozygous (Ss) Suri females would be bred to a homozygous (SS) male, producing progeny which were 100% suri phenotype with 50% heterozygous and 50% homozygous suri genotype.
In the second generation the female suris, half of which are homozygous and half of which are heterozygous, would be bred to homozygous suri sires, producing progeny that were 100% suri phenotype; 75% of the cria would be homozygous suri genotype and 25% would be heterozygous.
Continuing on, if suri females from the second generation were bred again to homozygous suri sires, creating a third generation, they would produce 100% suri phenotype with 87.5% of the offspring homozygous for the suri gene. Selection for the suri allele could continue for another generation when the proportion of pure or dominant suris in the population would be high, 93.75%. At this point they would generally breed true and produce predominantly suri progeny. Because the huacaya allele would still be present in the new suri population, as it is in the current population, breeders of suris should continue to cull sires which produced huacaya offspring from suri x suri matings. Among suri breeders, proven homozygous suri sires should be especially desirable because they do not produce huacaya offspring.
If in the alternative suri breeders continue to use heterozygous suri males, that carry the huacaya gene, the composition of the United States suri herd will likely develop as follows.
The progeny will be 25% huacaya 50% heterozygous suri and 25% homozygous suri in the first generation. If each suri from this generation are then bred to another heterozygous male, the second generation would develop as follows.
There are 12 possible results, with a 33.3% chance (4 out of 12) of producing a homozygous suri cria (SS), a 50% chance (6 out of 12) of producing heterozygous suri cria (Ss), and a 16.7% chance (2 out of 12) of producing huacaya (ss). The above calculations and text are courtesy of Ken Madl who maintains a herd of suri in Australia and has extensive experience with cross bred suri. Also see Ken’s article, Homozygous Suris: What are the Odds?
I asked Dr. Bruce Van Natta of Sur-Real Alpacas in Indianapolis, Indiana what might happen if a suri breeder continued to breed a heterozygous male to the second generation offspring that were diagrammed above. He made the following observations:
“The mating of two heterozygotes in the first generation would yield: 25% SS, 50% Ss and 25% ss. When these phenotypic suris are bred to a heterozygous male the second generation would yield: 33.3% SS, 50% Ss and 16.7% ss (rounded to the nearest tenth percentile). After culling the huacayas, the third generation from a heterozygous herdsire would yield: 35% SS, 50% Ss and 15%ss. Fourth generation would be: 35.3% SS, 50%Ss and 14.7 ss.”
Another question for Suri breeders is how to determine whether the male they are using is homozygous. This is easy to discover if you breed the male to 11 huacaya females. If one cria is huacaya the male is heterozygous, if all 11 are suri the male is more than 98% sure of being homozygous. If however you are breeding suri to suri it is a bit more problematic to determine homozygosity unless of course the mating produced even one huacaya cria. I asked Dr. Wayne Jarvis of Sixth Day Farm, who has written extensively about alpaca genetics, if he could estimate the number of matings it would take to prove a suri male homozygous when he is mated to heterozygous suri females. His answer follows:
“If (a big word) you KNOW the females are heterozygous, then 10 matings, without any huacaya offspring, would get you to the 95% probability that he is homozygous, 15 matings would get you to the 98% confidence level and 20 matings would get you to the 99+% level of confidence. There is of course no 100% proof without gene analysis which we do not have.”
The above examples may seem overly complicated. The research necessary to accomplish the Suri network goal of eliminating cross breeding may seem daunting, it is not.
THE SURI SELECTION TOOL
I have, with the help of Bill Graham, created a Suri Selection Tool that, with a few key strokes, allows suri breeders to identify potentially homozygous suri males. The tool also identifies suri males with huacaya cria. The data that drives this tool was compiled from ARI records as of May 4, 2007. The tool database contains the progeny records of every suri male and female in the United States as of this date and will be periodically updated.
To use the Suri Selection Tool simply enter either the name, ear tag or ARI number of the stud male you are considering breeding to your suri female. The results table will tell you how many total cria the stud has sired and how many were huacaya or suri. A population geneticist would consider a suri heterozygous if it has sired a huacaya from either a suri or a huacaya dam.
I queried this database for a list of suri males who had sired 50 or more cria. There were 61 in the ARI records as of May 4, 2007, of these, 27 had sired more than one huacaya cria. I did not include males with just one huacaya cria on the basis that it might represent a misidentified phenotype. There were 3 who had 1 huacaya cria. These males sired a total of 5,146 cria, 4,895 suri and 251 registered huacaya. I also realize that some Suri breeders do not register their huacaya cria: at least the males. The twenty seven studs who sired more than one huacaya cria represent 44 percent of all suri herdsires that produced more than 50 cria. If I include the three males that produced one huacaya cria, nearly 50% of these males are heterozygous or in other words carry the huacaya gene.
By using heterozygous sires, suri breeders are assuring the creation of heterozygous suri and huacaya cria. On this basis the national suri herd will remain a mixed breed. It is also interesting to note that a Suri breeder using a heterozygous male significantly slows the growth of their suri herd by producing 25% huacaya. This is expensive in genetic terms since it profoundly impacts selection intensity. In financial terms the breeders are faced with selling huacaya from suri parents, often at a discounted price. If Suri breeders stopped using heterozygous males, the suri population will become more than 90% homozygous in less than three generations. This 90% number assumes that a number of the suri females are already homozygous. Science is the path to pure breeding suris: not subjective definitions placed in a breed standards or breeders who turn a blind eye to reality.