I hope I didnt miss the already posted topic..) : But I need some information.Ive been told by a reputable Breeding Consultant that the sex is determined by the ph balance in the mares reproductive organs. I know some mares have tons of fillies and very few colts and some have tons of colts and visaversa Some argue that its the stallion that determines this... Fact or fiction? ( :
its obviously the stallion that determines whether its a colt or a filly But I am not sure if the mares ph balence may have some affect of the sperm I have read that a mare that is at a good weight will when bred will more often have a filly and a mare that is under weight or gaining at the time of conception will have colts more often. There was a reason too but I cannot remember where I read it OR if its true
I've read that about the mares weight contributing to that factor too. I have yet to rememebr to ask my vet to get his opinion..are they all only opinions or are there concrete facts to support this, Im wondering ......
I did some research on the topic because I had never heard any science based theory of predicting the sex of a foal. This was the only published research I found and it does not support the theory - I would love to know if there is any research that countradicts this article because it is an interesting concept http://beheco.oxfordjournals.org/cgi/content/abstract/10/5/472
There has been some more recent research - published last year, but I can't remember by whom - that confirmed the research by Cameron et. al. that you have cited.
Actually - when one thinks about it, it's pretty logical. Just think like nature for a moment...
If food is scarce, then the mares will be thin, but nature wants to produce as many female foals as possible because the attrition rate is going to be higher - hence, production of the fillies is greater (meaning that in the event of high death rates due to starvation, the population will be replenished). OTOH, if food is plentiful (and mares are therefore fat), then nature wants to be careful that overpopulation doesn't occur, so it limits production of female foals (that will subsequently be available to reproduce). Remember too that thinner mares are more likely to lose the pregnancy due to EED, so again, nature is bumping the odds of increasing replication in hard times by increasing the number of filly foals.
Often when one looks at things from nature's perspective, it suddenly becomes obvious! Nature really is smart - and don't ever forget that and lose your respect for nature, or your horse breeding career is going to be very frustrating!
Thanks, that makes alot of sense. I found a later published article by Cameron (probably the one you refernced. It references a notable difference in offspring percentage based on whether the mare is gaining or losing at the time of conception - not for those that are stable. Biol Lett. 2007 Apr 17; Extreme sex ratio variation in relation to change in condition around conception.
Cameron EZ, Linklater WL.
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.
Adaptive theory predicts that mothers would be advantaged by adjusting the sex ratio of their offspring in relation to their offspring's future reproductive success. Studies investigating sex ratio variation in mammals have produced notoriously inconsistent results, although recent studies suggest more consistency if sex ratio variation is related to maternal condition at conception, potentially mediated by changes in circulating glucose level. Consequently, we hypothesized that change in condition might better predict sex ratio variation than condition per se. Here, we investigate sex ratio variation in feral horses (Equus caballus), where sex ratio variation was previously shown to be related to maternal condition at conception. We used condition measures before and after conception to measure the change in condition around conception in individual mothers. The relationship with sex ratio was substantially more extreme than previously reported: 3% of females losing condition gave birth to a son, whereas 80% of those females that were gaining condition gave birth to a son. Change in condition is more predictive of sex ratio than actual condition, supporting previous studies, and shows the most extreme variation in mammals ever reported.
(Message edited by katheekj on March 22, 2009)
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