BREEDING FORUM

Posted: **Thu Feb 08, 2024 10:07 am**

It’s a horrible wet and not so warm day here so I am confined to the office for the morning at least. I was thinking about inbreeding and how inbreeding to some horses appears to be very negative yet to others it is less of a problem.
I read somewhere that inbreeding is really a negative thing because it leads to loss of vigour and poor fertility. When it comes to inbreeding, the data is fairly clear. The more inbred a horse is, the less likely it is to race and also race at the highest level. As I am no geneticist I really don’t have any arguments with that.
Now I have noticed in the course of the work I do, that inbreeding to Danehill is a very low percentage play, and that is despite the fact that it has been and still is being done quite a lot in the Southern Hemisphere (particularly in Australia) simply because he is such a presence in so many pedigrees its very difficult to avoid.
This would make the statistical analysis of the inbreeding look better than it should do simply because there are so many horses inbred to Danehill that they are going to win a higher proportion of the races they run in than would be the case here.
Maybe there is a very simple explanation, if there is that might be a first for anything to do with breeding racehorses. But I noticed that Danehill, who is closely inbred himself, has a very high coefficient of inbreeding (COI). His COI is 3.61%. So if you inbreed to Danehill the progeny is also going to have a higher than normal COI.
Northern Dancer who is found in multiples in nearly all pedigrees has a COI of 1.07% significantly lower than Danehill. Mr Prospector has a COI of 0.41% less than half of that of Northern Dancer and about a ninth of that of Danehill.
That inevitably brings me to the question what is likely to be the results of inbreeding to Galileo. Well surprisingly his COI is quite similar to that of Mr Prospector at 0.49% so am I possibly doing clients a disservice when I advise against.