Don't stallions determine the sex of the foal?

[nnadams]

I feel really stupid for asking this question, but over the last few years of being on this forum, I have heard so many refer to how many fillies their mare has had. I cannot figure out whether they are just stating how many fillies the mare has had or they are giving credit to the mare for the sex of the foal? I assumed that the male determines the sex as in humans, but is it different in equine?

 

[disneyhorse]

Yes, it is the male who determines the sex of the offspring.

Andrea

 

[Bess Kelly]

When I was breeding for 20-30 foals a season, years ago, the ratios of filly/colt for my stallions was of concern as I found it to carry through within a small percentage of change. None of my original stallions were purchased as young stock, so there was stud book backgrounds to check. There are times when a mare's PH will influence her ability to maintain live filly/colt sperm for a different period of time but, ultimately I have always felt the stallion was producing more filly/colt sperm and determined the percentage of outcome.

I did have one mare who broke all rules -- blessed are the mares -- and seemed to prefer to carry only colts. In 8 foals, different stallions 6 times, she gave me ONE filly...next to last foal. Heck, I had to keep checking that one to be SURE I was seeing things correctly!!! Bless her heart. The same mare also passed genetics for downsizing to every foal she had.

If you look at mating, growth tendancies, conformation tendancies, you will see that those can be guestimated to a fairly good amount based on past production. One of my guys, Indian Snow, felt it was his job to populate the herd with boys, apparently. 75% + were colts...one of his sons has taken pitty on me and given me 80% fillies!

Another guy I bought a few years back for conformation, bloodline, etc. is also a high filly producer. In fact, I would love a colt by him.

IMO -- the boys determine the sex, and I believe medically it's true but don't know all the reasons -- more one kind of sperm, longer lived sperm, etc, etc, or why it is that way. Maybe one of our doctors will give us the actual medical answer.

 

[nnadams]

When I was breeding for 20-30 foals a season, years ago, the ratios of filly/colt for my stallions was of concern as I found it to carry through within a small percentage of change. None of my original stallions were purchased as young stock, so there was stud book backgrounds to check. There are times when a mare's PH will influence her ability to maintain live filly/colt sperm for a different period of time but, ultimately I have always felt the stallion was producing more filly/colt sperm and determined the percentage of outcome.

I did have one mare who broke all rules -- blessed are the mares -- and seemed to prefer to carry only colts. In 8 foals, different stallions 6 times, she gave me ONE filly...next to last foal. Heck, I had to keep checking that one to be SURE I was seeing things correctly!!! Bless her heart. The same mare also passed genetics for downsizing to every foal she had.

If you look at mating, growth tendancies, conformation tendancies, you will see that those can be guestimated to a fairly good amount based on past production. One of my guys, Indian Snow, felt it was his job to populate the herd with boys, apparently. 75% + were colts...one of his sons has taken pitty on me and given me 80% fillies!

Another guy I bought a few years back for conformation, bloodline, etc. is also a high filly producer. In fact, I would love a colt by him.

IMO -- the boys determine the sex, and I believe medically it's true but don't know all the reasons -- more one kind of sperm, longer lived sperm, etc, etc, or why it is that way. Maybe one of our doctors will give us the actual medical answer.

So it does work the same as in humans. The mare produces an egg that can go either way based on whether the stallions sperm that reaches the egg first is male or female. And supposedly in humans, male sperm is faster, but female sperm can live longer, so that based on the timing of ovulation to intercourse you can maybe sway the outcome a little.....

Of course, my oldest sister was not able to sway the outcome of any of her human babies. She married a man who only had male children born to his family for as many generations back as could be traced. My sister researched and tried every possible method

offered to increase the chance of having a girl and she still ended up with 4 boys!

 

[Michelle@wescofarms]

Bess is right, we've seen the same results over the years.

BTW Bess - totally jealous that you owned Indian Snow and his sons. Still very very envious. : )

You will see some stallions really have a high production of one sex over the other. Yeah for the registry studbooks.

 

[Songcatcher]

Bess is right, we've seen the same results over the years.

BTW Bess - totally jealous that you owned Indian Snow and his sons. Still very very envious. : )

You will see some stallions really have a high production of one sex over the other. Yeah for the registry studbooks.

I hesitate to rely too much on the percentages in the registry studbooks as I feel there are far more boys who go unregistered than girls.

 

[Sandee]

From different sources that I read while the stud determines the sex, the mare has an influence on it only from the fact the ph in her system creates a "friendly" or not ground for the male or female sperm. I don't remember exactly how it goes but I do remember the article saying that because the ph in most mares tend to be hard on the sperm that there is a better sucess of getting a filly by "catching" the mare at the end of her cycle. I suppose because the male sperm is often more virulent (stays "active" longer) and in a race to the egg the female type sperm don't make it.

 

[Jill]

While it is the stallion's sperm that determines the sex of the foal, there have been studies that indicate that a big factor is actually the "environment" within the mare. Certain conditions favor the survival colt creating sperm, while others favor the survival filly creating sperm.

 

[Al B]

We are the only ones that have that "Y" chromosome.

 

[Reignmaker Miniatures]

I vaguely recall reading a few years back that studies suggest that environmental conditions can also affect the % of male to female offspring in animals. Such things as amount of food available can mean more females (nature determines the greater ability of that particular ecosystem to support a larger population) and how nature strives for balance so if there are already lots of males available then more females will be born to balance the male to female ratios. Hard to compare wild animals to domestic ones of course but I've always rather wondered if this was true.

 

[Carolyn R]

All valid points, and, as already said, if they are anything like humans, it is based on ph, what stage of the cycle the mare is in, the sperm responsible for the coding of males and females swim at different rates, one swims faster but dies quicker, the other is a slower swimmer but is hardier. Not to mention outside factors like diet and nutrition, some mares are quicker to be receptive than others, some stallions need to be smacked in the head with a cave man club as the mare says "My lord :arg! this is your last chance, I've been throwing myself at you all week", in which case those faster swimmers may be the only hope left before the window of opportunity closes. And through all of this and many more factors, it is still all a crap shoot in the end, LOL.

 

[Nathan Luszcz]

All of this is true, in various degrees

Only the stallion can determine sex, but the mare can influence which sperm survives.

 

[Genie]

All of this is true, in various degrees

Only the stallion can determine sex, but the mare can influence which sperm survives.

Sorry for not understanding your comment "but the mare can influence which sperm survives

I must have missed something.

I hate to break a pattern here on our farm, or give us bad luck by saying this, but so far the three studs we use are producing a high percentage fillies and one is 100% so far in his fourth year of siring foals for us.

I did state that our recent foal was the third filly for this mare but was also aware that the stud was responsible.

 

[champsmom]

All I know is I am praying for a filly this year. Had 2 colts last year. I only rebred one mare . Same stallion for all three. I really want a filly!

 

[Nathan Luszcz]

The mare can help decide by her uterine environment. X sperm are heartier and live longer than Y sperm. So if the mare ovulates well after copulation, only the X could possibly survive.

Please note

NONE of this is "usable" as far as choosing your foal's sex. The only way to "choose" which gender you have is to use sex-sorted semen, and that is very rare in the horse world (and even then, not 100% reliable).

 

[Riverdance]

I have read many studies regarding fillies verses colts (because I always seem to have colts).

When wild horses were studied it showed that if the mare came out of a hard winter she would produce more fillies because her condition was not good. When it was a good winter and their body condition was good when bred, they tend to have more colts. This is perhaps that more horses would die of starvation during harsh winters and so nature needed more fillies to be born to continue the breed. Since one only needs one colt per so many mares, only when they had feed well during a winter, would nature allow more boys to be born. I also have a theory that the colts, having different personalities than the fillies and take more chances become more fodder for the pray animal.

Also, as was mentioned the male sperm swims faster than the female sperm, but does not last as long. When I had Morgans all of my sperm had to be shipped in, so the sperm was 24hrs old by the time I got it and maybe a few hours more before the vet could inseminate the mare. I always had fillies then.

Maybe I should either starve my mares, or start to inseminate them.