MITRAL VALVE DISEASE
MITRAL VALVE DISEASE is the most
serious problem facing the Cavaler King Charles Spaniel today. Nearly 100%
of all Cavaliers will develop MVD by age 10. MVD is a developmental fault
involving the mitral valve of the heart. With each beat of the heart the
four different valves open to let blood through at the right time and then close
so that blood cannot flow backward. When a dog develops MVD, the
collagen/connective tissue that makes up the mitral valve starts to break down
and starts causing the mitral valve to not be able to close all the way.
Blood leaks backwards and this *leakage* causes a sound that is called a murmur.
Over time the mitral valve gets sloppier and more and more blood leaks backwards
causing the murmur to get louder. The more blood that leaks backwards the
harder the heart has to work to keep the blood moving so the body can get enough
oxygen. The valve can get so sloppy that eventually the dog will go into
congestive heart failure. At this point in time, medication is necessary
to prolong the dog's life.
Sweden did a study in 1993, showing that MVD is a multi-factoral polygenic trait. This means that genetic factors AND environmental factors (i.e. diet, environmental toxins/vaccinations, fitness of body--underweight or overweight) can contribute to how severely MVD will be expressed. The genetic component is QUITE strong. Puppies WILL, on average, tend to follow in their parent's footsteps as to when they will develop MVD, in fact this incidence is somewhere in the 86-88% range in just the first generation. This means that if both mom and dad are clear of MVD past age 5, about 86-88% of their offspring will still be clear of MVD at approximately age 5 as well. And this ALSO means that if both parents develop mitral valve disease BEFORE age 5, close to 86-88% of their offspring will ALSO develop MVD BEFORE age 5. BUT, approximately 10-15% of their offspring will not follow in their parents footsteps and may develop MVD earlier or later.
Below is a graph showing the results of this study. The chart on the left explains what intensity murmur each color represents. No murmur is what is hoped for. The higher the grade, the worse the murmur. The chart on the right shows the comparison of the mean parental grading. *Mean parental grading* is the average of the murmurs of the two parents. If both parents were grade 1, then the mean parental quality would be 1 + 1 divided by 2 = 1. If one parent was a grade 1 and the other a grade 2 then 1 + 2 divided by 2 = 1.5. The graph clearly shows the parents that were most affected (had a higher grade MVD murmur) produced more affected offspring (by age 5) than did the parents less affected.
Due to this evidence, the geneticists proposed a voluntary protocol which aims to delay the onset of MVD in offspring. This protocol asks for breeders to breed only:
(1) Individual Cavaliers that have attained the age of 5 and are SUBSEQUENTLY (AFTER age 5) found to still be clear of MVD (regardless of parental status);
(2) Cavaliers that have attained the age of 2.5 years and are subsequently found to still be clear of MVD, AND whose parents BOTH attained the age of 5 years and were subsequently found to be still clear of MVD;
in a way that puts emphasis on long-lived, delayed onset ancestors.
The cut-off age of 5 was chosen for two reasons: (1) Dogs that attain the age of 5 still free of MVD are already in the upper 50th percentile--or are in the *better half*, the half which we WANT to use in our breeding programs. (2) Since the gene pool for the Cavalier is small, eliminating only the *worst* half of the population will still allow us to maintain a decent-sized gene pool and progress slowly towards a later and later onset of MVD.
Although the protocol is voluntary, it is hoped that as time goes by, more and more breeders will be able to follow this protocol.
BEFORE you buy a puppy from ANY breeder, please ask for copies of the current cardiologist heart clearances of BOTH parents. Because MVD is a developmental fault, it simply canNOT be checked for in a puppy. It is the parents that need the clearance form. Look any forms you receive over well. Virtually all of them, even if they vary from the examples shown, will state the name of the dog that was examined, the date of examination somewhere on the form and clearly state the name of the Board CERTIFIED veterinary cardiologist. Please look for these specifics. A vet signed statement is NOT acceptable. The vast majority of veterinarians CANNOT hear low grade murmurs (grades 1 and 2), so ONLY Board Certified Cardiologist clearances are acceptable.
more on MVD, please go to this site: www.ckcsc.org.
This is the Cavalier King Charles Spaniel Club, USA, Inc., site. Click on
Health and then MVD to read more. You can also view and/or download
the Transcript from the Atlanta Heart Symposium in 1998, which presented the
Swedish study and proposed the heart protocol, at the CKCSC site also.
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