Outcross, Line Breeding and Inbreeding. A genetics walk through, and the importance of Genetic Diversity.

The Importance of Genetic Diversity

It is often falsely stated that all Silver Labs are inbred or line bred. While the first kennels to register and breed dilute Labs were excited to learn about what they had, little was known about how to get predictable, repeatable results from these pairings. Some dogs were bred to close relatives to retain these traits and maintain the lines. This is a generally accepted practice, common in both Field and Show lines; It’s how you reinforce a type and desired traits. In many cases, the dilute Lab line’s Coefficient of Inbreeding, or COI is no better or worse than what you would find in any other Show or Field line. Let’s walk through some of these terms.

Outcross: This is a breeding of two dogs whose pedigrees in the first 5+ generations have NO common ancestry. To achieve a successful outcross, determine if the chosen male offers “locked in” genetic abilities to produce such virtues by observing his offspring. When possible, visit his sire and dam as well as siblings. If the stud of choice does not appear to produce what you need, there is no point in breeding your bitch to him. Using an inbred or closely line bred bitch when introducing new characteristics may assist you, as this particular type of breeding invites a lack of uniformity. Outcross litters will offer different types, often resulting in “What you see is not always what you get.”

Line Breeding: Line breeding is the concentration of valuable characteristics. It allows some control over predictable, repeatable results. This method requires the selected parents having one or more common ancestors in the pedigree in the last several (5-6) generations. These ancestors themselves may be a successful line breeding of outstanding individuals. Use only health tested individuals or the breeding program will meet with disaster. Health, fertility, temperament, and type are imperative because compromises will negatively affect your future breeding program and will require further elimination.

Inbreeding: Also called Close Line breeding. Once reaching the pinnacle of desired virtues, many programs will inbreed. This is pairing closely related dogs to one another, Grandfather to Granddaughter, Mother to Son, littermates or half siblings to each other. This “sets” the type and defines a certain look or set of traits, trainability, drive, etc. You will reap what you sow, as inbreeding results in the best of the best and worst of the worst. This risk is not for the faint of heart.

What is COI? COI stands for Coefficient of Inbreeding. Essentially, it measures the common ancestors of dam and sire, and indicates the probability of how genetically similar they are. There are consequences to being genetically similar, some good, some bad. The fact that dogs within individual breeds are so genetically similar is what makes them that breed. If you breed any Labrador to any other Labrador, the puppies will look recognizably like Labradors. There are some 20,000-odd genes that go into any dog of a particular breed, most of which are ‘fixed’. That means that every Labrador will have two identical copies of them; one inherited from their dam, one from their sire. Others however, are not so fixed, such as the genes in Labrador Retrievers that code for color. Genes always come in pairs. The gene pair is called an “allele”. When the pair is identical, it is called “homozygous”. When the pair is not identical, it is called “heterozygous”. Allele, homozygous, and heterozygous are three good terms to understand if you are a dog breeder. Homozygous and heterozygous are terms often used more generally when talking about diversity. The more gene pairs that are homozygous = less diversity. The more gene pairs that are heterozygous = more diversity. Geneticists generally consider diversity a good thing. Many pedigree breeds are already highly homozygous, ie many of their alleles contain only a single gene type. This means that the characteristics that these genes produce will be the same in all puppies, regardless of which parents from the breed are used(no breed diversity). The COI is really just measuring the probability of any individual allele being homozygous due to an identical gene being passed down to the puppy along both the dam and sires lines from single common ancestors. COI’s are much more than looking at a dog’s parents, though. COI’s also track how related dogs are further back in the pedigree. Look back 10 generations in your own family trees, and you are unlikely to see the same name twice. This is not true for dogs, however. The same names can appear many times. Traditionally breeders have commonly used grandfather/grand-daughter pairings(and often even closer) to ‘fix’ certain traits. To get a true picture of how inbred a certain dog is, you should go back at least five generations and ideally ten. As you go further back, in most instances, the COI is likely to rise.

Why are high COIs considered a problem? Two reasons:

1. Inbreeding will help cement ‘good’ traits but there’s a danger of it also cementing bad ones. In particular, it can cause the rapid buildup of disease genes in a population. CNM in Labrador Retrievers was recently tracked to a mutation in a single famous stud dog that has been copied thousands of times in his descendants, which are now distributed all over the world.

2. Even if a breed of dog is free of serious genetic disorders, inbreeding is likely to affect them in more subtle, but no less serious, ways. These include smaller litter sizes, less vigorous/viable puppies, fertility problems, and weakened immune systems. These effects have been very well documented in other species and are known as inbreeding depression. Farmers, who used to breed livestock in much the same way as we still breed dogs, have now changed the way that they breed their animals. In fact farmers so recognize the benefit of hybridization that much of the meat, milk, and eggs we eat and drink are from crossbreeds. That’s due to the fact that the yield is likely to be healthier and disease resistant than that from purebred stock. A study of Standard Poodles discovered that dogs with a COI of less than 6.25% lived on average four years longer than those with COIs over 25%.

COIs are not the be all and end all of a dog. They are just one measure. So don’t freak out if you discover your dog has a ten generation COI of 30%. Likewise, if your dog has a COI of only 1% it does not guarantee his health and fitness, but his chances of having inherited a double dose of defective genes is far less. This is why as dilute breeders, and any breeder for that matter, it is so important to perform genetic screening and test your breeding stock for common inherited diseases. With modern technology and newly discovered testing methods, health testing is a valuable tool for producing litters that are free of easily avoidable inherited diseases.

It’s a fine line to walk, but something that type breeders need to do to produce consistent results. When you outcross(breed two dogs with completely separate lines, no shared ancestors in 10gen pedigree) you run the risk of getting unpredictable results in both appearance and performance. Breeders who own a Champion and breed that dog, but fail to produce consistent Champions off that dog tend to take this route. When you line breed, or inbreed, you minimize the number of alleles that will not be homozygous. When you line breed there are far less factors that change, and you end up with more consistent results. The down side to this is that if there is a carrier of an undesired trait or disease you will almost certainly see that trait pop up in a line bred litter. It’s a necessary evil, but one that breeders need to take, and be ready to make the tough decisions with. You run the risk of having pups returned, pups that will need to be culled(sterilized). When line breeding it is recommended to keep multiple pups, if not the whole litter until 18-24mos, to really see what the prime examples are and which ones should be bred for the following generation. It’s tough work most breeders are not able or willing to do nowadays. Most breeders today are merely production breeders, while necessary to maintain a breed, but are not improving the breed. Very few breeders can say they’ve truly produced their own lines, tough to do with the breeds already being so established.

Do your research, as both a buyer and/or breeder. Determine what your goals are and what is right for you and your Family. Keep in mind that though Dilute Labs have some differences, in the end they are just like any other Lab at their foundation. They are produced from the same methods and have the same genetic background.