Once again, the “popular sire” effect is proving to be a disservice to the health of a breed.
A study done in France followed 10 different dog breeds and their genetic diseases and prevalence. The goal of the study was to evaluate the risk of disseminating genetic diseases when using line breeding, close breeding, and the “popular sire” effect. Line breeding, as they defined it, meant the style of frequently choosing males and females with common ancestors, BUT not breeding full siblings or father-daughter crosses. They also studied these highly controversial “close breeding” practices, including breeding half siblings. The final aspect of their study investigated the “popular sire” effect, which is the intensive use of a particular male throughout the breed.
They studied the mating practices of French dog breeders to study the patterns of breeding, and then simulated a lethal genetic disease and its dissemination through a population. (This was an algorithmic simulation, NOT a literal experiment) For their simulation, they started by assuming that 2% of the 4,000 dogs of each breed would have one of these bad genes. From these 4,000, 800 females and 400 males were selected as being breeding stock. (Similar to choosing only some puppies as breedable quality) The breeding stock was randomly chosen without regard for the bad gene. Any puppy created by these dogs that got 2 bad genes would die. They “bred” these dogs in 4 different patterns: randomly (as a control group), with the popular sire effect, along line-breeding habits, or with close breeding practices. Using a very complex formula, they studied the bad gene and its migration throughout the population over 25 generations, and re-ran the simulation thousands of times. Researchers then calculated the number of simulations in which more than 5% of the final generation carried the bad gene. 
Results were surprising. The popular sire effect caused a dramatic rise in the dissemination of disease genes: the rate of the bad gene was over 4 times as high as with a random breeding scenario. This has led many breed clubs around the world to limit the number of litters any one sire can produce. The study also showed that proportion of affected dogs was much lower for line-bred and closely bred animals, suggesting that these practices are a benefit to the breed.
This study only took into account a relatively simple gene scenario, and does not taken into account the “negative value” of other genetic phenomena. Inbreeding depression, the general decline of genetic fitness due to a small gene pool, was not studied in this simulation. This study shows the value of line breeding (and maybe even close breeding) to a genetic population over a series of generations, but inbreeding depression and other factors must also be considered before “closing” a breeding program.
The crucial warning that we need to take from this study is this:
No matter how wonderful a particular male is, if he’s had a lot of litters, do not breed to him. It may be rough to turn down a male that’s produced many gorgeous kids; but for the love of your breed, don’t do it.
Paper published in “Animal Genetics,” February 2011. Title: Mating practices and the dissemination of genetic disorders in domestic animals, based on the example of dog breeding G. Leroy,R. Baumung. http://www.ncbi.nlm.nih.gov/pubmed/20528847
July 26, 2012
Breeding Dogs, Health and Science