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How Breeding The Best To The Best Can Be Worse

How breeding the best to the best can be worse

10/15/2014

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by Carol Beuchat PhD

An interesting study was just published about the genetics of behavior in the Belgian Malinois (Cao et al 2014). This is a working breed used in some of the same service environments as the German Shepherd Dog (e.g., military, security, etc), so behavior is important to the breed's function. Malinois that perform well, with good drive and initiative for work, tend to exhibit a circling behavior when in confined spaces, which is a form of obsessive-compulsive behavior. Dogs that do not display the circling behavior, and those that have very high levels of circling behavior, don't perform as well.

It turns out that a gene (Cadherin 2, CDH2; or genes in the same genomic block), that has been linked to obsessive-compulsive behavior in both Dobermans and humans might also be involved in the manifestation of these degrees of working and circling behavior in Malinois, from non-existant to extreme. Maintaining the most useful, moderate behavior in the Belgian Malinois is an example of something called "balancing selection", in which the heterozygous condition (e.g., Aa) is advantageous over either homozygous condition (AA or aa). (This is also referred to as "overdominance".) This means that breeding two dogs that are great working dogs and heterozygous won't produce better dogs, because some of the offspring will lack the drive and initiative to be good working dogs (AA), while others will have a double-dose of the CDH2 gene and be too high-strung to be useful. Because the best dogs will be heterozygous, selection tends to favor the gene combination that is the best combination of advantageous (good worker) and disadvantageous (moderate circling).

You might be familiar with other examples of overdominance in dogs. For example in the Whippet, dogs with one copy of a mutated allele of the myostatin gene (which is involved in muscle function) are significantly faster than dogs with the normal gene, but dogs with two copies of the gene are over-muscled (Mosher et al 2007). One again, the heteroygous condition is superior to either of the homozygous options.

One more interesting example is the ridge of the Rhodesian Ridgeback, which is caused by a dominant mutation (Hillbertz et al 2007). Dogs without the mutation don't have the ridge, and dogs with one copy of the mutation have the breed-typical dorsal ridge. However, dogs with two copies of the gene are predisposed to a congenital developmental disorder called dermoid sinus. Dogs without ridges are generally excluded from breeding because this is considered to be a fault, as are those with dermoid sinus. So again, the genotype resulting in the preferred phenotype is the heterozygous condition. But breeding two heterozygous dogs will result not in a litter with better ridges, but some offspring with ridges, some without, and probably some that are afflicted with dermoid sinus. (This is a simple Punnett square problem.)

These are three examples where assuming that breeding "best-to-best" will not result in "even better" because of failure to understand the underlying genetics. In fact, it can result in removing a dog from the gene pool for a genetic issue (e.g., a Malinois with extreme circling), when in fact breeding that dog to the appropriate mate (e.g., a homozygous dog with low drive) would result in heterozygous offspring that could have the perfect blend of motivation and self-control. Likewise, using Ridgebacks without ridges will produce some offspring without ridges, but it also will not produce pups with dermoid sinus.

With so many breeds facing a growing list of genetic issues as a result of the continued loss of genetic diversity, it is especially imprudent to remove dogs from the gene pool that could be used to produce offspring with the desired genotype (that is, heterozygous for the gene of interest) without the collateral damage of pups with unacceptable phenotypes.

• Cao X, DM Irwin, Y-H Liu, L-G Cheng, L Wang, G-D Want, & Y-P Zhang. 2014 Balancing selection on CDH2 may be related to the behavioral features of the Belgian Malinois. PLos ONE 9(10): e110075. (pdf)

• Hillbertz NHCS, M Isaksson, EK Karlsson, E Hellmen, et al 2007 Duplication of FGF3, FGF4, FGF19 and ORAOV1 causes hair ridge and predisposition to dermoid sinus in Ridgeback dogs. Nature Genetics 39(11): 1318-1320.

• Mosher DS, P Quignon, CD Bustamante, NB Sutter, CS Mellersh, et al. 2007 A mutation in the myostatin gene increases muscle mass and enhances racing performance in heterozygote dogs. PLoS Genetics 3: 779-786. (pdf)

How Often TO Breed You Bitch

How often to breed your Bitch

The experts all seem to agree that the least healthy approach for a breeding bitch is to skip heat cycles and keep the bitch unbred. This is not only Dr. Hutchinson's philosophy as Dr. Threlfall at Ohio State Univ. teaches the same thing (my husband just attended a Cont. Ed seminar on Canine Repro earlier this year at OSU). This is NOT new information, either. I was reading Dr. Billinghurst's book GROW YOUR PUP WITH BONES, which addresses the health of puppies as well as their parents and reproductive issues. This is not a new book (maybe 10 years old?). He states the same thing. Canines are meant to be pregnant on every heat cycle.

As Dr. Hutchinson explains it in his seminars, the hormones are the same and the bitch goes through the same changes whether they are bred or not. So when the hormones 'do their thing' to a uterus that does not have pups, it is "hammered" (his term) by the hormones and causes aging and thickening which makes the uterine lining less conducive to implantation and more prone to infection over time. The recommendation it to breed them young, breed on every heat cycle until you are done, then spay them. THAT is the healthiest scenario for your breeding bitch. While Dr. Threlfall and Dr. Hutchinson don't see eye to eye on some issues, this one they completely agree on. I have to wonder if anyone has found a vet knowledgable on repro issues who states otherwise.

Yet there are still people who refuse to believe this advice. I have often wondered about the practice of condemning back-to-back breedings. I wonder if it stems from the way bitches blow their coat post weaning which may lead people to feel the bitch is not recovering well. I know that our girls blow their coat at the same time they would after being in heat (about 4 months) whether bred or not, but the post puppy coat loss is usually more. I suspect that this appearance made people believe that the bitch was completely run down and it "was hard on her" having the pups.

Unfortunately, in our current PC environment, we want to suggest that people who breed more than one litter every several years are simply money hungry puppy mills and some of us are quick to condemn their practices based on this mentality. So if someone follows the EXPERTS advice concerning their dogs, the self appointed Ethics Police talk poorly of them ignoring the fact that what they are doing is biologically in the BEST interest of their dogs.

I think many people want to act like dogs are little people in fur coats. They want to suggest that what we may feel is how a dog feels. While I wouldn’t personally want to have a new child every year, I do believe that my dogs have always adored having puppies. Granted, there are certainly reasons why some bitches should probably not be bred again. Some are poor mothers. Some don't produce much milk. Some can't whelp or conceive w/o veterinary intervention. But the bottom line is that in a healthy normal bitch, breeding every heat cycle for as many litters as you want from that bitch, then spaying her, is the most healthy way to go. And that is from the people who are qualified to say so.

You know, cattle are kept pregnant every year starting when they would "freshen" (have their calf) at 2 years of age. They breed them until they won't breed anymore. If a cow is "open" (not pregnant), the farmer either tries to get her bred or sells her because wintering an open cow is a big money loser. Yes, it is certainly a business having calves (no one denies that), but the cattle certainly seem fine being pregnant all but three months of the year and well into their teen years. Just as an aside, cows/heifers start having calves at 2 years of age (earlier and they aren't fully grown so often can't calve on their own). They are bred back EVERY year.  I know cattle is a money business and many of the Doggy PC Police want to say that breeding more than a few litters a year is only out of greed, but cattle NEVER get a break and apparently have no ill effects as a result. Also, dairy cows won't have milk unless they are bred back each year. But my point is that this does not seem to effect their health in a bad way at all and has been the way cattle have been kept for many many decades. If you tried to tell them that it is too hard on the cow to be pregnant every year, they would think you were a COMPLETE idiot!

The bottom line is that if you are a breeder… well, you breed! Perhaps it is time for some of us to rethink our beliefs that dogs should get a break between heat cycles for their health because under normal circumstances, this is simply not true.

As always, I encourage anyone with ideas on issues I’ve discussed, or issues they would like to see addressed, to please share their thoughts with me. I can be reached at shilogr@yahoo.com  Thanks so much!