Popular Sire
Often, genetic experts and breeders argue over the phenomenon referred to as “popular sire syndrome.” Breeders argue their goal is to produce the best of the best – the best temperaments, the best conformation, and the best performance in their breed’s sports or working avenues. They’ll utilize the highest performing sire, eager to obtain some of his valuable qualities to improve their kennel, framing their dogs’ lineages with powerful, gold-starred pedigrees. In contrast, geneticists argue that popular sire syndrome promotes harmful DNA mutations, effectively enforcing long-lasting damage on a gene pool that will take generations to repair.
The biggest concern from geneticists are parental mutations. Dominant mutations are easy to exile from the gene pool; a dog is clearly affected, and thus, unlikely to be bred– at least not by a reputable producer. Those dominant mutations are then prevented from being spread generation-to-generation. In contrast, recessive mutations act “silently”. Oftentimes, a sire can carry an undesired recessive allele, but he’ll never demonstrate that trait’s ill effects, as his paired, dominant allele is normal. It “shadows” the harmful recessive allele, as if it isn’t there at all. However, this type of mutation becomes problematic when offspring obtain a recessive allele from both parents, becoming marked as homozygous recessive. These offspring lack the normal, dominant allele; then, their gene fails to operate properly, and the mutation is expressed. This may not seem startling at first– one affected puppy doesn’t entirely negate the sire’s productive or performance success. However, when that one sire is used repeatedly, particularly when paired with dams from various lines, he can effectively produce hundreds of puppies per year, and his heterozygote status can wreak havoc on the breed’s gene pool.
Popular sire syndrome is difficult to efficiently catch. For example, the first generation of offspring from a sire may appear similar to him; no outward displays of mutative genes or undesirable traits. They may succeed readily in show or performance venues, making them highly desired as well. Then, these offspring are bred to produce an additional generation. This generation will often start to exhibit signs of distress. The undesired trait may appear in larger quantities in this generation. Breeders will begin to question; they’ve never had this issue in their lines before, and why is it just popping up now? The answer is simple: carriers may produce clears or carriers, but they can also produce affected offspring.
A notable victim of popular sire syndrome is the German shepherd dog (GSD). A recessive mutation common in their breed is degenerative myelopathy (DM). Degenerative myelopathy is a progressive and incurable disease, which effectively paralyzes a dog first in its hind end, and often eventually in the forelimbs; this is referred to as tetraparesis. It is seen in offspring that carry two copies of the recessive Sod1 gene. Unfortunately, dogs affected by degenerative myelopathy often don’t exhibit signs of the disease until they are geriatric, with the average age of diagnosis being around eight years old. By this time, these dogs have likely completed their reproductive years, meaning the damage has already been done; the damaging recessive Sod1 allele has been passed on. Due to developments in genetic testing, this disorder affects only “an estimated 2% of the German shepherd population,” per the Universities Federation for Animal Welfare. Without genetic testing, experts anticipate the rate of affected individuals would be much higher. Thus, breeders should order DNA testing on any German shepherd individual they anticipate using in their reproductive program, most particularly males as they are capable of producing far more puppies per year than the average female. These determine if the potential sire or dam carries one, two, or no copies of the dangerous, recessive Sod1 allele.
Another dilemma presented by popular sire syndrome is narrowing of the gene pool. By utilizing one highly-awarded and successful sire, breeders are excluding other quality males from their programs, failing to recognize the contributions those sires could make to their offspring as well. Restriction of the gene pool leads to lack of quality and type, increased inbreeding occurrences, and reduced fertility and success in litter survival. There are certainly dogs, both male and female alike, that suffer from hereditary conditions, lack substance, and are scarce in conformational or temperamental soundness, and these individuals should certainly be excluded from reproductive consideration. However, there are many dogs who are simply overlooked in favor of the highest-winning champion their breed currently has to offer; their genetic contributions are wasted, and the breed’s population becomes increasingly restricted. To curb the startling epidemic of popular sire syndrome, the international federation of canine kennel clubs, the Fédération Cynologique Internationale (FCI), recommends that “no dog should have more offspring than equivalent to 5% of the number of puppies registered in the breed during a five-year period”. However, this is merely a recommendation, and few national kennel clubs have taken suit. A key takeaway when considering popular sire syndrome was summarized wonderfully by Tufts-Cummings School of Veterinary Medicine graduate and adjunct genetics professor, Dr. Jerrod Bell, who stated, “...a male's influence on a breed should be gradual, and based on proven production and health testing. Maintaining surveillance of health and quality issues in breeding individuals and their offspring, and preserving the genetic diversity of the gene pool, should allow a sound future for purebred dogs.”