This is an interesting study that just came up on FB, that the age of the mare influences the gender of the foal.
My own experiences do not jive with these findings though -
What are your thoughts?
This is interesting.
I think it’s tough to draw conclusions without more information about how the mares were bred. I think it’s doubtful that all of these mares were bred live cover to the same sire in a herd environment. So what WAS done? I can certainly see possibilities that a young maiden mare would be treated differently than an experienced middle aged mare (potentially with some $$$$$ offspring) vs an aged mare. Even the sires used on those specific mare populations might impact the sex ratios.
Was this result inadvertently caused by differences in the way the mares were managed through breeding? Tough to determine, perhaps.
I also saw that study and thought that much information about how it was conducted was left unshared. My experiences do not jive with the findings either.
142 mares is a relatively small sample.
Was this charted over the same mare’s lifetime production or a single season?
No mention of actual breeding dates vs. ovulation dates within the mare’s cycle.
No mention of sex ratio within the stallion’s sperm.
No mention of the mare’s hormonal state or uterine environment.
And that is just the things that leap out.
Meh.
Now, if they took an entire sporthorse database over the lifetime production of mares that began young and continued in production throughout life: tens of thousands of mares and foals, especially where it is important to register each foal vs. not registering the ‘wrong sex’ euthed or unrecorded foal, then I might find interesting coincidences or correlations.
From my own mares here ( since 1999…15 foaling seasons)
Maiden mares: no, did not get more fillies. Actually mostly colts.
Old mares: going by the last foal for each of my geriatric mares: yes they were actually all fillies except one… And she was a maiden too.
There have been several human studies that have found various things like the more sons a woman has, the more likely the younger ones are to be gay. Something about hormone flooding in the womb. It doesn’t seem to actually affect sex, though. Just orientation. The finding seems plausible, but the study group was relatively small and limited to a single registry. I’d want to see if this holds true across other breeds.
My experience is limited to about 26 foals, but I had over half as colts out of maiden mares (and most of my mares were maiden OR I knew their prior foals and know what they produced in their maiden year). And I bred one mare into her 20s and after 20, she produced 1 colt, 2 fillies, and a couple of colts in her late teens and a single filly. Her last foal was a colt. So again, limited, but doesn’t hold up to the findings.
Doesn’t jibe with my experience breeding live cover by same stallion in a herd environment over the last 14 years. The colts are 66% and the fillies 33% in a group of 40 odd foals. The age of the mare makes no difference. I don’t think my results proves or disproves anything.
I agree that statistics apply to large numbers. A small sample size is not particularly helpful as an indicator and the results should not be generalized.
My own experience based on small number of mares I bred multiple times…
Mare #1, age 7 filly, age 8 colt, age 10 filly, age 11 colt, age 12 filly, age 13 colt.
Mare #2, age 8 filly, age 14 filly, age 16 filly, age 18 filly.
Mate #3, age 13 filly, age 17 colt.
Jennifer
