Key to healthy Maine Coon hearts

One key to healthy Maine Coon hearts - Pedigree Study

Copyright Dirigo 1995

Comments are often made cautioning against breeding two cats of the same cattery lines together. Frequently, it is commented not to combine a certain modern-day cattery line together with itself. But seldom is a clear explanation given. Unhealthy litters can result, and heart problems are a frequently whispered reason. The answer to the mystery is not in the recent generations, but it can be found in the foundation generations. Pedigree research to foundation is essential and a simple tool in breeding healthy kittens. (see MCI search service ) If a pedigree is not researched all the way back, important ancestors will not be recognized.

It is the purpose of this article to explain a suspected inheritance pattern of heart problems and to propose suggestions to help in the recognition of a good or poor pedigree. This will help to eliminate heart problems, through pedigree study to the foundation level. This is a simple method, based on many pedigrees.

It is rare that a breeder that can identify heart problem carrying cats present in pedigrees. Years of experience unfold the accumulation of many peoples’ experiences, and it then becomes obvious that this is a non-random occurrence pointing to certain cats (within certain lines) as carriers of heart problems. It must be clearly and emphatically stated that these conclusions are derived only from the study of pedigrees of cats owned by others. Fortunately, this author has never owned nor bred a cat with heart problems.

The amazing proliferation of new breeders is a recipe for disaster, breeding winning cat to winning cat....only to discover too late that the cats they have chosen also carry lethal defects.

In a letter to the Editor of the Scratch Sheet, Fall 94, Deborah Frick writes,

“...monorchids, kinked tails, hip dysphasia, cardiomyopathy, pectus, and on and on........the typiest and best show lines carry and perpetuate these defects...” After hearing many people tell of their sad stories of cats and kittens with heart defects, and after studying carefully pedigrees of affected cats, a few simple conclusions have become obvious about heart problems.

It still exists!

Heart problems are now understood to be genetic in most cases. It is believed to be an inherited condition, but there will always be those who insist that it is dietary or viral. This condition occurs far too often for such opinions not to bear scrutiny. It is very difficult to discover and to identify affected cats and carriers early enough to prevent breeding. Trial and error, or planned test breedings are two methods, but enlightened pedigree perusal can be invaluable in eliminating tragic possibilities.

Where could the heart problem originate? Only if one understands an important possibility, will the pedigree research be revealing and useful.

An issue of “ The Scratch Sheet, “ Fall 1989, identifies the cause of death of a world-renowned stud cat as cardiomyopathy. Perhaps 90% of the breed is related to this stud cat, and everyone reading this article is 90% likely to own one of his descendants. His ancestry can be traced to the foundation pair of his bloodline and to NO OTHER LINES. It is possible to assume that he inherited his condition from that original pair. Since this problem still occurs, it is possible to assume that future cats have inherited it through him or through his pair of foundation ancestors.

One cannot be sure that other lineage has not contributed to heart problems. Due to the huge number of cats related to that sire, significant progress can be made in outcrossing his lineage.

There undeniably exist cats with no trace of heart problems and who do not carry this problem either. Many are also related to this key cat. What makes the difference?

Suggestion #1

Outcross in the foundation generation is a key.
Pedigrees from the healthiest cats from the finest catteries have characteristics in common. They were outcrossed on the foundation level and often returned to such lines as, Abnaki, Sundar, Highmeadow, Tati-tan, Dirigo, Whittemore, Illya’s, Our, Quan Yin, Havenwood, (to name only a few). And, one can notice that often it is the dam that is of different foundation lineage. Down through the finest pedigrees outcrosses appear frequently.

Pedigree research has shown that when the most popular foundation line was bred only to itself, more deaths have resulted. But if outcrossed early and often, lethal heart problems were bred out, leaving the other valued physical characteristics of large size, heavy weight and larger ears, intact. When clean descendants were discovered, through trial and error of many repeated successful litters, they have gone on to a rich, loving legacy of healthy Maine Coons. Many new breeders have not discovered the key and breed pretty cat to pretty cat only to learn later that heart problems were one result.

Outcross on the maternal side appears the strongest factor in genetically selecting a pedigree. The importance of maternal inheritance cannot be overstressed. When a non-affected carrying male is bred to a clean female, the offspring have a slightly higher than average possibility of being stronger towards the clean gene and will tend towards passing on the clean gene when bred to the next clean female, etc.

Pedigree study to foundation of known affected cats (identified by autopsy) reveals no cases of carriers on one side only. This would appear to eliminate a dominant gene and point to a recessive or polygenic pattern of inheritance. It appears that the harmful genes combine when two cats are bred with each having recessive (or cumulative) genetic capability to produce affected offspring, in combination with each other.

Suggestion #2:

Affected cats always pass on the 'carrying" gene to their offspring.
When an affected cat is identified, that identifies it and its parents both as carriers. When a cat dies of heart problems, one must assume that both its parents are carriers. If by chance the affected cat had lived to breed, 100% of the offspring would be confirmed carriers.

Suggestion #3:

Two carriers must combine to create an affected cat.
These identified carriers may lurk 3 or more! generations back and their genes combine lethally in predictable percentage of inheritance in future kittens when these otherwise fine cats are bred together.

Two carriers create in predictable percentage of inheritance.

(See Robinson, Genetics For Cat Breeders page 30, fig. 3) Remember that carriers can produce several generations of carriers, and carriers are unaffected.

Suggestion #4:

Recessive or cumulative carriers can create when bred to CLEAN mates.

(only test breeding can identify carriers, see MCI Fall 95) (Polygenic carriers mimic recessive in that carried conditions do not always show)

Suggestion #5:

When early foundation males of that suspect line were bred to unrelated females, the chance of carrying cats were reduced in the offspring, if bred as a pattern always to unrelated lines.
It was a virtual certainty that this harmful condition was bred out through outcross. Many of the healthiest Maine Coons follow this early outcross pattern. Most retain their other valued physical characteristics.

Comment: If pedigree research shows 3 or more generations of one pair bred only to itself, (descending from two cats only) this is the marker: one ought to avoid breeding back into that line except if and when carefully and significantly outcrossed.

Suggestion #6:

If and when the female side of the pedigree descends from a problem bloodline, it should be assumed that she always passed on the carrying gene to her offspring, an oversimplified suggestion for safety.
Pedigrees show that when certain line-bred females were bred back to partially related cats, the incidence of problems increased as the recessives combined more positively to create definite carriers.

Suggestion #7:

When a carrying cat has been identified in a pedigree, the other side of the pedigree needs to be examined carefully.
Often, inbred or line-bred but otherwise clean cats appear on pedigrees of some well known examples that descend from that primary line. These cats cannot clean up a pedigree but they cannot harm it either. Inexplicably, somehow, genetic tendencies are passed on down unchanged to combine at some future date if such a fine bred cat is mistakenly bred to a carrier.

For years, Maine Coon Breeders have “heard” of problem genetics. A few have responsibly and carefully selected outcrossed cats retaining valued characteristics for their breeding programs but some have dangerously played genetic roulette by breeding tightly line-bred cats descending from the postulated carrying pair.

It is not the purpose of this article to discuss nor judge the ethics involved in breeding heart problem carrying cats. The fact is that they still exist, as many are sadly learning. The purpose of the above suggestions is to assist others in their own intelligent and knowledgeable breeding decisions.

How do we value our cats? By the worldly value system of more and more prizes? The true value of a Maine Coon is in its blend of good genetic capability. In the words of a native Maine Guide, Nate Mitchell, "A good Maine Coon is an outcrossed Maine Coon." All bloodlines are equal in their importance. Drawing completely upon only one line as genetic source for the breed reduces genetic health.


Tracing a pedigree to foundation uncovers essential information for today's responsible breeders. Tracing a pedigree to foundation reveals patterns of bloodlines and inheritance. These patterns of past breedings contain the keys to tomorrow's strong and healthy cats!

Many breeders already have this information available about their breeder/show kittens. If pedigree research uncovers a tightly bred pedigree, outcross may solve the question whether to breed one's cat or not. (see Hybrid Vigor, by Janet Marr MCI) Even outcross in the present generation level will result in genetically healthier kittens. Perhaps hard to locate, outcross is always available as a solution.

Saddened owners often become motivated to solve this ongoing occurrence, but have nowhere to turn. Sharing their pedigree is perhaps the most useful thing to do.

Questions and shared pedigrees are welcomed by the Author.


Genetics For Cat Breeders, Roy Robinson; Pergamon Press
Hybrid Vigor, Janet Marr: Maine Coon International #5
The Scratch Sheet, Fall 1994
The Scratch Sheet, Fall 1989

Update: This article will be updated with recommendations resulting from recent DNA test developments.

Copyright Dirigo 1995-forward.
All rights reserved

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Windham, ME 04062 USA

Revised 3/24/2015