This is also posted in the genetics board so pardon if you have answered this on this board.
OK, we've all had sex ed and know that the stallion determines the actual sex of the foal by contributing the x or y chromosome. BUT, I've also heard that the mucous thickness & hormone levels in the mare are also a contributing factor in gender determination. Is that true? Reason that I'm asking is that I've heard of a piece of equipment that you can buy that will monitor hormone/mucous levels in the mare and tell you when to breed a mare for the desired sex foal that you want. I'm also curious because a breeder friend of mine in Kentucky has already had 5 colts and no fillies yet this year. That's not a normal occurance for them. All their mares have gone about 2 weeks past due too. The owner tried to explain this stuff to me but as I'm a novice, I didn't want to sound dumb and I'm interested in what this forum can tell me.
I have no information about hormone or mucous levels. It was explained to me in this way - "colts swim faster but die sooner, fillies are slower but live longer". In other words, the timeing of when the mare is bred in relation to when she ovulates can determine the sex of the foal. The best way to get a colt is to breed the mare every day she is in heat so the fast swimmers can get there first. I know, to simplistic, but it works for me.
Actually, there is no scientific proof of the "colts=faster swimmers/less longevity; fillies=slower swimmers/greater longevity" theory in the equine. It has been seen in other species (elk in particular), but those other species naturally have multiple sexual partners, whereas the equine of course is naturally a herd animal with a single dominant stallion. Hence, there are significant sexual differences between elk and equine, and the general consensus among researchers is that this is one area so affected.
You will undoubtedly hear that the slow/fast swim theory holds true from some people, but the problem is that one is usually looking at small numbers of "research animals" with those individuals, or [scientifically] uncontrolled situations. It is not until one looks at significant numbers that a true statistical analysis can be made.
There are almost certainly other factors that will influence the fetal sex though. We do know that some stallions will sire more colts than fillies (or vice versa), so the sire is obviously a proven factor. At the moment though, the only proven way to sway the odds in favour of one sex or the other is to use flow cytometry. This service is provided by x-y inc. in Colorado.
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