HD analysis for the Maine Coon (part 1)
 
 
Introduction - What is Hip Dysplasia?
Cats with Hip Dysplasia (HD) have a deformity of the hipjoint. The hip socket can be too shallow to support the ball of the hip. The ball will not fit well into the socket joint, causing the cartilage to degenerate. When the cartilage has degenerated completely, there will be bone-on-bone contact, which is very painful for a cat and can lead to limping. Arthritis can make the situation worse when the cat ages. With severe Hip Dysplasia a hip surgery is sometimes inevitable to improve the quality of life.
Hip Dysplasia is commonly known in dogs. It can appear in other mammals too, like horses, cows, goats and cats. It can also occur in humans.
 
Hip Dysplasia in cats
Among catbreeders testing the parents on HD is not something that is done by many breeders yet. Maine Coon breeders are the most active HD testers (5329 HD results). Not because HD is mostly in the Maine Coon, because that is not the case, it can occur in any breed. Maine Coon breeders has noticed this problem occur within the breed and decided to act on it by setting up a healthprogram to monitor and control the problem within their breed.
The British Shorthair/Longhair has 279 X-rays evaluated by Pawpeds. X-rays from other feline breeds have been send in as well, but not many. In this article I focus on the analysis of the Maine Coon, since that is the only breed that has enough data to be further analysed. Before I do that, I would like to show one chart that has the Maine Coon and other breeds compared. As the British Shorthair/Longhair does have enough data to be compared at the highest level of total results. I do show other breeds as an indication, but they have too few test results send in to make proper conclusions.
For a better understanding of this chart and the rest of this article, let's first explain the HD statuses. This information is from the Pawpeds website:
  • Normal: good hips, no anomalies
  • Borderline: not quite perfect structure, but not pronounced dysplastic (it was agreed in 2013 to no longer use Borderline, but effectively it wasn't used anymore since Per Eksell took over in 2014 from Lars Audell)
  • Grade 1: the mildest form of dysplasia
  • Grade 2: moderately affected hips
  • Grade 3: badly affected hips
Before you interpret the charts, you need to know two things:
  1. In the HD healthprogram of Pawpeds both hips are evaluated separately and get their own result. For this analysis I only show 1 result of both hips, I have chosen the worst result. For example if a cat has a normal left hip and grade 2 on the right hip, I count this result as grade 2. Take this into consideration within all the charts displayed in this article, that only the worst hip counts.
  2. This data is extracted from the Pawpeds healthdatabase at July 12, 2020. The results that were registered but not published yet at that date are excluded from this analysis.
Chart 1: HD per breed
Chart 1: HD per breed 
 
Looking at chart 1 you can see that 59,3% of the Maine Coons that were tested within the healthprogram over the total period, have normal hips. For a British shorthair or longhair this is much lower at 39,4%, showing that this breed has a high risk of HD. The total bar at the right is mostly based on the large number of Maine Coons, since 93% of these results are Maine Coons. The British short/longhair brings the percentages slightly down and then there are just a few results from other breeds. Don't make the mistake to use the "Other breeds" bar to conclude that HD is not a problem in all other breeds. As for most breeds we simply don't have any data. The 25 test results that are in this bar are scattered into 14 different breeds, which doesn't tell you anything. Also note that the data for Persians & Exotics, Devon Rex, Siberian and Norwegian Forest cat is too little to get a good overall picture of the breed. Yet when you look at the OFA statistics for the Persian & Exotic and Devon Rex they show the same concerning figures. This could be a warning sign and it would be a good idea to test these breeds more often to see where it stands exactly.
Pawpeds recommends to exclude cats from breedingprograms that have moderate or severe HD (grade 2 or 3) for at least one hip. For the total tested population this means that 16,9% is recommended not to breed with. It is not recommended to breed with 16,1% of the HD tested Maine Coons and 31,9% of the British short/longhair (almost twice as much).
The rest of this analysis is only about the Maine Coon test results, because the amount of data is big enough to zoom in further to see trends and look for potential correlations.
 
HD development per year (Maine Coon)
 
In chart 1 you saw the total HD results of the Maine Coon breed (fourth bar). Now let's spread this out further and break it up into each year. The white dotted line shows the amount of HD results for that year. The years before 2000 were left out because they had too little results. The year 2008 has the most HD evaluations done throughout the whole HD healthprogram.
 
HD per year
Chart 2: HD development per year
 
You can see that the current situation is much worse than the total showed in chart 1. In 2019 only around 40% of the evaluated MCO's have normal hips. This current situation for the MCO is very close to the British Shorthair/Longhair bar at chart 1. The trend seems to be a downward trend, where the chances for normal hips took a fall of almost 30% since 2014. The grade 2 and 3 trend is also downward but less steep than the grade 1 and normal results.
 
HD grade 2 3 per year
Chart 3: results with grade 2 or 3
 
In chart 3 you can see for each year how many of the HD tested cats had either grade 2 or grade 3 and were therefor not recommended for breeding. You can see that this trend started to go upward from 2012. It had some more or less "good years" like 2014 and 2018 where "only" 16% of the cats have a serious form of hip dysplasia. When the HD program started, the impact of the breeding recommendations suggests to exclude 12% of the population from breeding. In 2019 this doubled up to 25% of the population. (2020 seems promising, but we only have results until July 12, effectively until May 12 if you consider the 60 days waiting time before publication.)
 
 
So the big question is: Why does HD seem to be more of a problem over the past 7-8 years?
 
 
Possible explanations:
  1. The bigger the better? Many breeders seem to select for bigger size and heavier cats. Also overfeeding kittens making them put much weight on as fast as possible, could have a negative impact on the hip joints. A study of 2019 showed a direct correlation between weight and HD. Bigger and heavier cats have a higher risk of HD.
  2. The popularity of the Maine Coon has exploded around 2015, which has attracted many new kittenmills and back yard breeders all over the world who care little about the health or protection of the breed but instead try to breed for bigger sales. Breeding for size, using high inbreeding and overused lines with no (or little) HD testing done at the cat or the ancestors. Of course also there are new good breeders as well, but this is the minority and also they produce far less than the big kittenmills.
  3. Many untested lines were introduced into the healthprogram with an unknown hip status of the parents or grandparents. Although it is a good thing that more lines are being tested on HD, these cats will have a higher risk of HD and their results will have a negative effect on the average. Sweden has made the biggest contribution to the HD program. Since 2012 the rules for importing cats into Sweden have become less strict, which had an increasing effect on the number of imported cats. Also importing from East European countries has become booming since 2015. These lines have a poor HD test record and breeders of those countries don't participate at the HD healthprogram at all (or at this point not yet). In chart 10 you can see that the amount of HD tested cats with unknown hip status of the parents has climbed enormously starting 2016.
  4. Most MCO breeders work with 70% of the same genepool. The top 5 most common ancestors consist of 70% of the genetic foundation for the average Maine Coon. If some of the foundation stock has HD, it is hard to get rid of, especially when we only do matings with cats that have the same genetic foundation (except for New Foundation lines).
  5. In 2014 the status Borderline was deleted as a possible result. Also the Pawpeds specialist that did the hip evaluation has changed from Lars Audell to Per Eksell in 2014. It could be that a part of the grade 1 results could have been given Borderline if that was still an option. Also it could be that Per Eksell was slightly more strict in his evaluation than Lars Audell, showing worse results since 2014.
 
Difference in gender
 
Between females and males there is a slight difference in chances for bad hips. Females have 15,4% chance of grade 2 or 3 compared to males who have 17,3% chance of grade 2 or 3.
Chart 4 shows the totals of the whole healthprogram over the whole active period in time.
 
Chart 4: HD per gender
Chart 4: HD per gender
 
Since the genders seems to have the highest difference in the grade 2 and 3 area, I've made another chart that breaks down the grade 2 + 3 development over the years, for males and females separately. See chart 5 below.
 
HD per year per gender
 
Chart 5: Grade 2 + 3 per year divided by gender
 
Difference in age
 
Now the next chart shows the difference in age. Pawpeds gives a preliminary result before the age of 10 months, which you can view at the first bar in chart 6. You can see that bad hips (grade 2 + 3) are already shown at a very early age. Some breeders believe that a cat should be better off tested at age 4, as they think the Maine Coon is still growing until it reaches 4 years of age. In chart 5 it shows that cats that the amount of cats with normal hips are about the same when you compare the cats that were tested at age 1 - 2 with age 3 - 4.
 
HD per age
Chart 6: HD per age
 
So what does this chart say? My interpretation is that this chart shows that HD is for the most part a genetic issue, since you can already see serious HD at a kitten younger then 10 months. When you look at the official results (>10 months) a consistent trend is visible with a variation between 1-11% per result for the different ages. But if it was ONLY a genetic issue, the cat with normal hips at a young age, should still have normal hips at a later age. You see the amount of cats with normal hips is around 10% less with the older cats. Their increased weight or fast growth could explain the difference. Environmental issues like slippery floors, accidents, low quality food or heavy pregnancies could also be of influence here.
You can also see that the amount of grade 3 affected cats is around 3-4 times higher at an older age. Arthritis can damage the hip joint further when time passes, which can worsen the hip status into a higher grade when the cat ages.
 
 
Difference per country
 
HD per country
Chart 7: HD per country
 
This charts shows the tested cats per country, where I took the country of residence (not birth). Let us first notice that 48,1% of all HD testresults are from Sweden. Sweden and the Swedish breedingprogram therefor has a major impact on the development of the HD healthprogram and on the result of this analysis. France has the most cats who got a grade 3 result (relatively to their tested cats). New Zealand scores the best at normal hips and Norway the lowest. Denmark has relatively the least cats with grade 2 and 3 results. Overall there are no major differences noticeable. What stands out very clearly is that countries who participate very little at the HD healthprogram, show the worst HD results (see the bar: Other countries, 3,5%).
 
HD grade 23 per country
Chart 8: HD grade 2 & 3 per country
 
Chart 8 is the same chart as number 7, with focus only on the grade 2 and 3 results, to compare them better per country. The percentage next to the country shows, how many of the HD tested cats are living in that country. It would be interesting to know if there are differences between countries that can have an influence on the hips of their cats (raising kittens, environment, food).
 
 
 
Inheritance of HD in two generations
 
Now we get to another interesting part. The part of genetics and inheritance. From looking at the trends above you might start to wonder if we can really prevent HD? Let's look at how breeders mating choices can affect the hips of the offspring. Let's look at two generations, the parents and their offspring, and how the hip status of the parents passed through the next generation.
 
HD per parent combination
Chart 9: HD per parent combination
 
In Chart 9 you see different parent combinations for each bar in the chart. The first bar shows the offspring of parents with an unknown hip status. Around 54% of their offspring has normal hips. The second bar shows offspring of a parent combination where 1 parent has normal hips and the other parent has an unknown hip status. You see that with 1 parent with normal hips, the chances for offspring with normal hips has increased to 68%. When you look at bar 7 that shows the offspring of parents that both have normal hips, you see another big jump to 74% chances of offspring with normal hips. Now you know how to read the rest of the chart. The white dotted line indicates how many offspring was tested for each parent combination. This number is also written below each bar (N=...). Some of the parent combinations that are not recommended by the Pawpeds healthprogram (like grade 1 x grade 3) obviously has very few data. There are not a lot of breeders who do these risky matings. Those bars are therefor less reliable, but still can give some indication why those matings are not recommended.
When you study chart 9 you can conclude that a breeder can lower the risk of HD enormously in the offspring, by choosing the right matings. At the same time you can also see that HD cannot be totally prevented. Even with HD N/N matings, there is still a slight change of 2,5% that the offspring will get HD grade 3.
 
HD per year from unknown HD parents
Chart 10: HD per year - from parents with unknown hip status
 
Now in chart 10 I have zoomed into the first bar of chart 9, the 1902 HD result from parents with an unknown hip status. Here in chart 10 you can view just those 1902 results, divided by year, so you can see the development of HD. I'd like to think of this chart as the closest chart to the reality of the whole Maine Coon breed, since these are a collection of cats that with unknown hip status of the parents. For a closer reality you might have to look at more generations, but still this one can give a good indication. For as the far majority of the breed has an unknown hip status, since only a little percentage of the breeders test on HD.
What stands out is the downward trend. When you look at the total bar on the right, you see a kind of optimistic picture, as this is the average from all these years. Unfortunately the reality nowadays is much worse, as you can see from the downward trend. From 2004 until 2014 there was a 50-70% chance of normal hips when you don't know the HD results of the parents. From 2015 until 2020 we see that same chance has dropped to 32-52%. Chances for normal hips are quite less nowadays when you want to test a new line for HD within the healthprogram. When you test a cat for HD within Pawpeds nowadays, you would have around 30% chance of moderately to severely affected hips. Theoretically this is at least one kitten at each litter where the parents are not tested for HD, which is a very serious problem!
 
HD per year from N parents
Chart 11: HD per year - from parents with normal hips
 
In chart 11 I've zoomed into the 1067 test results that are from offspring from parents who both have normal hips on both sides (bar nr 7 at chart 9). These are from breeders that are testing at least two generations. This is still the very best scenario, compared to all other parent combinations. Here is also a downward trend visible, less steep than in chart 10, but still very visible. However, when you compare chart 11 to chart 10 it shows very clearly what a positive impact HD N/N parents can have on their offspring. Also you can see from the white dotted line that the number of N/N x N/N combinations has reduced in 2018 and 2019 which is concerning.
 
Conclusion
 
We can clearly see from this analysis that inheritance plays a big part in developing HD. It shows that breeders can influence the HD results within the breed. HD can't be totally prevented, but it can be reduced. Nevertheless we don't see any improvement over the years, on the contrary, the trend is downwards. This means a strong call for action, we need to be aware of this problem and try to reverse it, before the problem becomes any bigger. If breeders do not volunteer to test on HD, the problem will become so widespread in the breed, leaving the associations no choice but to make the test mandatory. FIFe has attempted to make HD a mandatory test in 2019, but it has been hold of for now. With certain dog breeds the HD problems are very large for a long time, which has lead them to mandatory HD tests in order to apply for a pedigree. I hope the Maine Coon breeders don't let it come to that point and will use their current freedom to do what is responsible.
 
Discussion for MCO breeders
The last few years showed us that we needed to exclude 20-25% of the tested MCO from our breeding stock, if we follow the recommendations of the Pawpeds HD healthprogram. Can we afford ourselves to exclude so many cats, especially when they have a well tested background, from valuable lines and with a high genetic diversity? On the other hand, if we loosen up the current breeding recommendations, how would we be able to turn the tide for HD if we are adding more HD to it? This sword cuts both ways and this needs to be discussed and carefully dealt with.
 
Can we derive conclusions from this analysis about how healthy a breed is in terms of HD?
This analysis can not be used to derive any statement about breed predisposition. The health database is used mostly by breeders who keep track of HD in their healthy breedingcats. This population only consists of the cats that are tested within the Pawpeds HD healthprogram. From these tested cats we get an honest picture, because the breeders signs for publication before the HD picture is taken and evaluated by Pawpeds. Which makes it harder to cheat or to withhold bad results. The population used for this analysis only consist of pedigreed cats. We don't know if the same figures apply for none-pedigreed cats, or pedigreed cats that are not tested within the healthprogram. My guess would be that the number of HD grade 2 or 3 diagnosed cats are higher in none pedigreed cats or within untested lines, simply because these lines are unknown and therefore their HD status is unknown. There are very few breeders of none-pedigreed cats who test the parents on HD before having a litter (I haven't met one yet). In chart 9 you can see that HD tested cats from parents with an unknown hip status, have more chances on HD then tested parents.
With all of this taken into consideration while looking at the charts, the breed as a whole could show a worse picture then the one I presented to you in this article.
 
To be continued...
 
In part 2 of the HD analysis I will look more into detail at the inheritance of multiple generations. This I will do in cooperation with other breeders, as this is too much work for me to do by myself. Also we will look and see if there is a correlation between inbreeding levels and HD and if the clones can have an impact on HD. We might find some other interesting factors too. When you have a suggestion or a lead where to look for, don't hesitate to contact me. Also if you want to help with the next part, so we can publish it sooner, let me know.
 

HCM development analyzed per breed (part 1)

Introduction

Feline Hypertrophic Cardiomyopathy (HCM) is a condition that causes the muscular walls of a cat’s heart to thicken, decreasing the heart’s efficiency which can lead to heart failure. HCM is the most commonly diagnosed cardiac disease in cats. HCM can also occur in other mammals and in humans, but for this article, we focus on the cats only.

There have been health programs set up for HCM for several feline breeds. Within this health program, the cats have been tested by approved cardiologists or radiologists, and their results are sent to Pawpeds for registration in the health database. This has been done for many years and thanks to the breeders that participated in the HCM health program, I was able to analyze the results that were gathered over the years.

 

HCM Health program

The Maine Coon was the first breed that had an HCM health program set up, starting from 1998. Then other breeds followed. In the table below you can see which year the program started. There are many more breeds that I have left out here, I’ve only picked the health programs that have more than 100 test results. This data shows the total results for the whole period of the Health program.

 
 Table 1: Population used for each breed

 

I have followed the PawPeds databases to get the group of EMS codes that are registered together in one database. For example, the Siberian and Neva Masquerade are registered together in one Pawpedsdatabase sharing the same health program.

The health program advises repeating the test at certain ages. As you can see by the 7th column, you can conclude that many cats have been tested more than once. Sphynx has the highest test frequency at 1,7 times per cat. The cats that had at least one diagnosis with HCM, is counted in the column HCM positive cats. A cat that has multiple results showing HCM, is counted only once. Results that were equivocal were not included in the HCM positive column, as equivocal is not HCM. PawPeds distinguishes different stages of HCM: mild, moderate, and severe. In the table, those were all counted as HCM (column 8).

You can see from the table that the Maine Coon has the most cats tested within the health program, almost 12.000 cats. Obviously the number of HCM diagnosed cats is, therefore, higher, but compared to the whole tested population, "only" 2,3% of the total tested cats got diagnosed with HCM.

 

Total cats with HCM diagnosis (1998-2020)

 

When you visualize the previous table, showing the total HCM cases compared to the total amount of cats tested, you will see the result in the chart below. This is the result of the total period of the health program, which for each breed has a different start date (shown in the table above).

 
 Chart 2: Cats with HCM during whole health program

 

How to read this chart? The number of cats tested you see next to the breed's name (n=). For example, Siamese & Oriental have 131 cats tested with the health program in the period of 2006-2020. Of those 131 cats, 3,8% got diagnosed with HCM, which comes down to 5 cats. The blue line shows how many cats are tested. The bars are ordered by the number of test results. The lower the blue line, the less reliable the numbers will be. I have divided the chart with a red line. All the results for the breeds left from the red line I consider as reliable and the ones on the right are less reliable because there are not that many cats tested. For example, La Perm shows not one cat with HCM, but only 102 La Perm cats were tested within the health program during all those years. We cannot conclude that La Perm is a breed where HCM never occurs. The same can be said for other breeds that have less than 150 cats tested. Hopefully, when more breeders participate with the health program, we can make better conclusions for those breeds in the future.

When you count all the cat breeds together, 3,1% of the cats got diagnosed by HCM. Reading this chart you see that most HCM cases are found in the Sphynxinx and Persian & Exotic breeds, who stick out far above the others. The Ragdoll and Birman breeds seem to be on the safe side of the chart with less than 1% of cats diagnosed with HCM. Notice that this is the overall average result during the whole health program period, from start until March 2020. Nowadays this can look differently since we hope that the health program will improve the HCM occurrence by time.

 

Total cats with HCM diagnosis (2015-2020)

The previous chart 2 showed the total health program data since it started. But have the breeds improved on their HCM cases ever since? I’ve made the exact same chart, but this time I only took the test results from the cats that were tested between 1-1-2015 and 31-3-2020.

 Chart 3: Cats with HCM during the last 5 years of the health program

 

You can see from this recent chart that the total HCM cases have dropped for most breeds. To make the comparison easier to read, the next chart below will show you the progress for three different periods in time.

 

Progress of the Health program per breed

For each breed I have split the test results over three different periods in time:

  • all the test is done before 1-1-2010 (dark green bar)

  • the test that was done between 1-1-2010 and 31-12-2014 (green bar)

  • the test that was done between 1-1-2015 and 31-3-2020 (light green bar)

Within each time period, I have taken the population of cats that were tested in that period. I have counted the number of cats that were tested and the number of cats that got HCM diagnosed within that period. One cat can be counted in different time periods if the cat was retested in a different period.

 Chart 4: HCM cases in three periods in time - Health program progress

 

I have excluded the breeds that had less than 35 cats tested within each time period. For this Ocicat, Mixed breed, Selkirk Rex, and La Perm are excluded. The two breeds with medium reliable data are right from the red dotted line (Europian Shorthair and Siamese & Oriental).

The light green bar is the most recent bar showing the HCM diagnosed cats of the last five years. You can see that in most breeds the light green bar line shows fewer HCM cases than the dark green or green bar. Which shows an improvement. Only the Ragdoll didn't improve compared to the previous period, but it also has improved compared to the first period before 2010. All other breeds show good progress with less HCM diagnosed cats. The biggest improvement is shown at the Maine Coon, the Persian & Exotics, and the European Shorthair. There is a total improvement of 2,4% less HCM diagnosed cats for all shown breeds since the start of the breeding program.

 

In order to see if the health programs have a positive effect, a difference should be made in lines that are tested for multiple generations and new lines that have been tested for the first time. This data doesn’t show this difference, but gives you an overall picture of the total tested cats within the Health program. Still, you can see an overall improvement.

 

Question: how can we know for sure that the other cats (not diagnosed with HCM) didn't catch HCM later in life? How old were they first tested and were they tested again at a later age? At what age does HCM occur? At which age is the cat tested on HCM? Let's find out.

 

Age of test

First, let us take a look at what age a cat is tested. This chart shows the age of all HCM tests within the health programs. If a cat is tested for HCM multiple times, all these results are counted in the relevant age-groups. So this chart is based on the test results and not on the number of cats. The youngest cats (group 1, dark green) are tested before they were one year of age. The second group of test results shows the test results where the age of the cat was a minimum of 1 year old and less than 2 years old. And so on.

 
 Chart 5: Age of the cat when tested on HCM - per breed

 

You can see that 72% of the Ragdolls are tested on HCM before their 2nd birthday, while only 40% of the Persian & Exotics are tested within that age group. Take this chart into consideration when looking at the previous charts again. It seems logical that breeds that have mostly very young cats tested, would have found fewer cases of HCM than if they would have tested their cats at an older age. For example, the Ragdoll showed only 0,6% HCM cases in the period of 2015-2020, but what would this result be if they tested their cats at the age of 5 years? At what age is HCM discovered?

 

The other way around, the Sphynx and the Persian & Exotic breed showed the highest percentage of HCM diagnosed cats. While you can see at this chart that they have tested their cats at an older age than the other breeds. 34% of the Sphynx was tested at 3 years or older and 38% of the Persian & Exotics were tested at 3 years or older, compared to only 15% of the Ragdoll. To analyze this further we need to know first at which age HCM starts to occur.

 

Age of the first diagnosis of HCM

 

This chart shows the first age where a cat is diagnosed with HCM. When a cat is retested at a later age with HCM again, this is not shown in the chart. Of course, we don’t know how long the cat already had HCM when he/she was tested. Some cats had a normal diagnosis before, but not all cats are tested multiple times. Some cats are tested for the first time at a later age and some cats are only tested normal at a young age and we don’t know what happened after. Still, I think this chart can give a good picture of when HCM reveals itself, because of the large amount of data available for some breeds.

I have added more age groups here, to view more specifically at which age most cats got an HCM diagnosis. The population that I have used for this chart is all the cats that got an HCM diagnosis (mild, medium, or severe). The breeds that are on the right side of the red dotted line are less reliable because of less available data.

 
 Chart 6: Age of first diagnosis HCM - per breed

 

Let's look at the Birman breed. The Birman scored very well on the previous charts, with only 0,6% HCM diagnosed cats of all tested cats within the health program. In the previous chart, you could see that 13% of the Birmans were tested at age 5 or older. In this chart, however, you can see that 41% of the HCM diagnosed Birmans were diagnosed at the age of 5 or older. The test data shows only 22 Birmans with HCM, this might be too little to make conclusions. I do wonder how the first chart would look if the Birmans older than 5 years were (re)tested on HCM.

 

Let's look at the Cornish Rex. You see in the previous chart that 52% of the Cornish Rex cats are tested before they reach 2 years of age. In this chart however you see that only 6% of the HCM diagnosed Cornish Rex cats got that diagnosis at that same age. My question is: how useful is it to test a Cornish Rex before the age of 2?

 

PawPeds Health program test age recommendations:

The HCM health program of PawPeds recommends testing for HCM at age of 1, 2, 3, and 5 years. With important breeding cats or cats with elevated risks, another test at the age of 8 is recommended.

Is this a logical recommendation when we look at the total average of all breeds together (cumulative), showing at which age HCM is diagnosed:

  • 7% of the cats that got HCM was first diagnosed before age 1

  • 30% of the cats that got HCM were first diagnosed before age 2

  • 51% of the cats that got HCM was first diagnosed before age 3

  • 64% of the cats that got HCM was first diagnosed before age 4

  • 76% of the cats that got HCM was first diagnosed before age 5

  • 84% of the cats that got HCM was first diagnosed before age 6

  • 89% of the cats that got HCM was first diagnosed before age 7

It looks that these guidelines are correct as every new age of testing gives enough percentage of risk that HCM still can occur when you retest.

But when you look at the different breeds separately, you do see differences in which age HCM can reveal itself. For some breeds, HCM seems to reveal itself at a much younger age than at other breeds. This could raise questions if the recommended test age applies to all breeds, or that we should look at each breed separately to advise recommended ages for HCM testing.

 

Testing cats on HCM that are 5 years or older

 

As mentioned before, most cats are tested at a young age and never got a retest at an older age. There might be more HCM hidden from the previous charts since we don't know if the cats who got a normal diagnosis would still have a normal heart at age 5. It would be interesting to see what the same chart would look like if we only counted the cats who were tested at age 5 or older, because of all the cats that develop HCM in life, 76% would be discovered before age 5. Those test results taken at that age are much more reliable, but on the other side, there aren't as many results as there are at younger ages. Still, some breeds like the Maine Coon, Norwegian Forest Cat, British short/longhair, Siberian, and Sphynx do have enough older cats tested to draw important conclusions.

 
 Chart 7: Cats 5 years or older with HCM compared over three periods of the health program

 

The number next to the breed indicates the total of cats that are tested at the age of 5 or older. (For example, the Bengal had 225 cats tested total over all three periods in time.) The breeds on the right side of the red dashed line shows less reliable results (less data). The two breeds between the yellow and red lines don't have reliable data for the first period <2010, but still have reliable data for the other two periods.

You can see here that some good progress is made with the Maine Coon (-4,9%), Norwegian Forest cat (-1,9%) and Siberian (-5,7%). The Sphynx and British short/longhair however, show an increase in cats with HCM.

 

 

Cats of all ages compared to cats tested at 5 years or older

 

The previous chart 7 showed that the last period (between 1-1-2015 and 31-3-2020) has the biggest number of cats tested at age 5 or older. The actual period is also the most interesting as it shows how many HCM cases we can expect nowadays for each breed. To make it easier to compare, I have taken the last period from Chart 7 again and compared it to the results of cats of all ages that was shown in Chart 3.

 
 Chart 8: All cats compared to cats 5 years or older, with HCM diagnosis (recent period of the last 5 years)

 

The number of cats that were in this population is shown behind the breed. For example, the Ragdoll had 1.838 Ragdolls tested of all ages, of which 0,6% showed HCM, and it has 93 Ragdolls tested of age 5 years or older, of which 2,2% showed HCM (2 cats).

 

As expected, every breed shows a lot more HCM diagnosed cats when you only count the cats that are tested at the age of 5 years or older. On average of all breeds, the HCM cases are 3 times as high (2,2% and 6,6%). Let's look at the Birman breed again. In the previous charts, this breed scored very well with very few HCM cases but most cats were tested at a young age. We see in this chart that when you look at the 91 Birman cats that were tested at 5 years or older, 4 cats (4,4%) were HCM diagnosed. Although 91 tested cats might not be enough to draw conclusions, it does show that age needs to be taken into consideration when looking at the previous charts. It is definitely clear that 1 HCM screening before the first litter is hardly enough. Retesting at an older age (5+) is very important and quite essential.

 

Considerations

 
Can we derive conclusions from this analysis about how healthy a breed is in terms of HCM?
This analysis can not be used to derive any statement about breed predispositon. The health database is used by breeders who keep track of HCM in their healthy breedingcats. Cats who are not healthy will be excluded from breeding by those breeders and won't be tested.
In table 1 you can view that a lot of cats are just screened once at a young age. The cats who got screened as normal could still die of HCM later in life, and this information never reaches Pawpeds. The screenings that are done in older cats are more reliable (chart 7 and 8), but do not give you the complete picture also. There could be many breeding cats that died of HCM where breeders didn't do a necropsy, or that necropsy is not send into pawpeds. Necropsies were not part of this analysis. Also breeders who screen their cats well and often enough, can exclude their cats from breedingprograms, and therefor prevent more HCM diagnosed cats at their offspring. This way HCM can be reduced. With all of this taken into consideration while looking at the charts, the breed as a whole could show a totally different picture then the one I presented to you in this article.
 

Do these populations represent different breeds as a whole?

No, the population only consists of the cats that are tested within the Pawpeds HCM health program. The health program has specific requirements to ensure the quality of the test result. The only specialist who meets the requirements can participate with the program and only those testresults are accepted for registration. From these tested cats we get an honest picture, because the breeders signs for publication before the heart screening takes place and the specialist verifies the chip id of the cat. Which makes it very hard or impossible to cheat or to withhold bad results.

The population used for this analysis only consist of pedigreed cats. We don't know if the same figures apply for none-pedigreed cats, or pedigreed cats that are not tested within the healthprogram. My guess would be that the number of HCM diagnosed cats are higher in none pedigreed cats, simply because these lines are unknown and not (well) tested. There are very few breeders of none-pedigreed cats who test the parents on HCM before having a litter and who repeat the screening at an older age.
 

Why didn't we reach more significant progress when we have a health program for 20 years?

Some breeds have reduced the number of cats affected with HCM by half over time. Not all breeds have made significant progress though. The population that is used in this analysis is only a fraction of the total population of cats within that breed. We can see progress in the health program, but we don't know what's happening with the other cats. How fast and successful the health program is, depends highly on the participants. There is more work to do to find more breeders who are willing to participate and to screen their cats multiple times.

Another aspect is that these results might contain a lot of "new lines" with no track record yet that are added to the health database for the first time and could be at higher risk of HCM. This is what I want to look into more in the next part of this analysis.

 

To be continued...

It would be interesting to see if the progress is different in some countries, where more breeders participate in the health program. It would also be interesting to zoom in more into the inheritance of HCM by looking at multiple generations of tested cats. Another part of HCM testing is DNA testing on the MyBPC 3 gene. I am curious if this DNA test has a significant impact on the occurrence of HCM. Another aspect that I didn't cover here is the equivocal status. How many cats will get HCM after being diagnosed with equivocal? To make this article not too long I will try to cover these subjects in the next part.

 

By: Debbie Sprenger

Kinked Tails

Kinked tails are something we do see now and again on cats within all breeds and even domestic cats.
Most often it’s located at the very end of the tail and it can vary a bit in type and also degree.
It’s not known how they are inherited, but it seems like a single recessive gene or polygenes might be responsible for the kinked tails. It seems like it’s different types of kinked tails, which are also inherited in different ways.

A kinked tail might also be caused by trauma (an accident).

In some cases, you will see the kinked tail in the newborn kitten, but sometimes it takes a lot longer until it will be visible. In some cases first around 1 year of age. Before 1 year the skeleton is not fully outgrown and hereditary kinked tails seem to gradually evolve.

I have seen many cases where the kinked tail is no more than stiffness at the very end of the tail.
But I have also seen really visible kinked tails in kittens.

In this kitten, the kinked tail is very visible and even if there is hard to see on this photo where the kitten is no more then a couple of hours old, this kitten actually got two bends on the tail the one we can see very visible and one more you could just imagine in the very end of the tail. This kinked tail is a bit further up than the very end of the tail. This particular kitten went to be a very nice companion, he got a brother who is used in a breeding program but I have never seen any other kinked tail in any of his brothers offsprings, and I have never seen any other kitten with a kinked tail in any of his mothers or fathers litters so this one seems to be the only one. 

I have also seen false kinked tails, those can be visible for a short while at about 7-12 weeks of age and are the result of ligaments not growing evenly. This will cause some ligaments on one side of the tail to drag the tip of the tail to one or another side. If it’s a false kinky tale this will disappear in a couple of weeks to never come back again. But it can be hard to tell whether its a false or a real one until the kitten is full-grown.

I would not recommend that you use a kitten with a kinky tail in breeding IF there is an equally good kitten without a kinky tail in the litter. I would never use a kitten with a severe kinky tail in breeding programs.
Though I have used it, and I know a lot of breeders who had cats with small kinky tails located at the very end of the tail in breeding programs. This is a descition you need to do for yourself and consider if there is an equally good sibling to keep instead.

By: Malin Sundqvist