Allow mares to LOSE condition at conception ...

[TrueColours]

If you are trying for a filly ... and to GAIN condition if you want a colt ...

Interesting study coming out of New Zealand and you have to admire the odds with their findings:

http://www.horsetalk.co.nz/breeding/foalsex-121.shtml

And also interesting on the elevated glucose levels and more colts as a result as well

Comments? How valid do you feel these findings are?

[Dalemma]

Interesting..............I know I had my mare on a diet (so loosing condition) when she conceived and delivered a filly.

Dalemma

[DancingAppy]

The statistician in me (I'm a STATS major) is going "hold on, lets wait a second." I really want to see their sampling methods and their statistical data. What is their population? It sounds like from that news article was that the population was wild, feral horses in Australia. You cannot expand those results to all horses, especially domesticated horses, because they are not part of the population of the study.

Other than my nerdy-ness coming out, if you really want a filly, might try it. However, I wouldn't want to have the mare lose too much weight to increase the chance of a filly.

However, I did just get a good idea for a study for my senior project or master's....

[amdfarm]

That is interesting. Here I'm always blaming my stallion for the colt/filly offness. I've had WAY more colts than fillies, that's for dang sure. I did have a mare on a diet and she foaled a filly at 363 days. She'd had colts prior to that and was always a chunky monkey (her nickname) at conception through til delivery. But then I have another mare that never really changes, except for gaining late gestation as the foal grows, and she's always given me fillies (3 so far.)

And by that study, the maiden that gave me a filly last year should have given me a colt. She was in great condition at conception and then just bloomed right up until she foaled at 403 days. Going that long I also expected a colt, but nope, she sure surprised me.

It seems my mares gain condition once bred and still I get BOYS!! :)

[Edgar]

"It seems my mares gain condition once bred and still I get BOYS!! "

Well, that seems consistent with the study. (read OP's first sentence)
On the clear cases where we knew that mares were skinny and gaining we got all colts. I am not aware of many that were losing but we had skinny mares shipped in for breeding multiple times and the rule seems to apply.

[Rendaivu]

So how long does the mare have to be not gaining condition for? Doesn't the sperm decide the sex based on whether its carrying an x or y? So if a mare is losing condition there is more chances of a female sperm making its way up there? Interesting.

[Fairview Horse Center]

This is the other thread on this topic. http://www.chronicleforums.com/Forum/showthread.php?t=172534

[Fairview Horse Center]

The research http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2390657

[Signature]

I had always heard thinner for conception and fatter for delivery... but never this theory. Our mares are always very plump just because I like to see fat shiny horses running around :), so I probably couldn't bear it to attempt this theory. LOL :)

In our experience it seems to be related to insemination timing for colt vs. filly. Last year was a good example - we bred 5 mares. We usually bred well ahead of ovulation as that's what our vet likes and is very successful with, and we almost always get fillies, loads and loads of fillies. This particular time the three fresh semen breedings were fillies and the two frozen breedings were colts (done with one dose right AT ovulation). The year before we had three foals and all fillies. We'll see this coming year what the statistics are! :)

But, I'm sure there can be many other factors!

[Iron Horse Farm]

100% of our frozen semen and ET foals have been colts! Coincidence?

[ellebeaux]

100% of our frozen semen and ET foals have been colts! Coincidence?

Are you talking 300 mares or 7? Big difference statiscally.

Actually, this could've been due to the level of glucose in the culture media. There's evidence in cattle IVM/IVF for this.

[ellebeaux]

If you are trying for a filly ... and to GAIN condition if you want a colt ...

Interesting study coming out of New Zealand and you have to admire the odds with their findings:

http://www.horsetalk.co.nz/breeding/foalsex-121.shtml

And also interesting on the elevated glucose levels and more colts as a result as well

Comments? How valid do you feel these findings are?

I have to tell you that I think these findings are 100% valid - Wayne's my PhD advisor. I do think there are several steps that need to be taken before we can routinely use this information for sport horse production.

Just to clarify - the mares that lost body condition in the 3 weeks PRIOR to conception continuing to the 3 weeks after conception were the ones that gave birth to more fillies.

[Edgar]

a little over one third of our ET's have been fillies.

[amdfarm]

" "

Well, that seems consistent with the study. (read OP's first sentence)
On the clear cases where we knew that mares were skinny and gaining we got all colts. I am not aware of many that were losing but we had skinny mares shipped in for breeding multiple times and the rule seems to apply.

You're right, it does. Wonder if I can change those stats some, but it's probably too late now. They're fat and sassy on their round bales.

[ellebeaux]

On the clear cases where we knew that mares were skinny and gaining we got all colts. I am not aware of many that were losing but we had skinny mares shipped in for breeding multiple times and the rule seems to apply.

This is an area I'm hoping to study in the future with farms that do live cover. I'd like to start with a retrospective study reviewing farm records.

One of the things that I'm wondering is when you hear rumors of a stallion siring mostly males is how much feeding practices play into this. If you move a mare to a farm and start increasing her diet (for whatever reason) this may influence birth sex ratios.

Another factor is stress - perhaps due to increased cortisol levels around the time to breeding. In other species, it appears that the stress of translocation can cause the next several calves to be males. Moving a mare to a new farm can be a stressful event!

So I'm hoping I can collaborate with breeders and review their records for this information. It wouldn't involve any animal manipulation and would just be costs for my time and travel. And we may get something useful out of it.

Once we validate that this does occur in a horse farm situation under current management practices, then we can start doing prospective studies where we weigh and body condition score the mares when they come in, then monitor them weekly until 2 weeks post-conception. And do feeding and breeding trials.

But I gotta finish this degree first!

[JackSprats Mom]

If you think about the biology of this it makes sense. If a mare is losing condition it would be biologically better for the species existence to have a filly and continue the breeding- the body losing condition would be a good indicator of lack of food hence produce a filly as there would be an increased number of deaths so a filly would help repopulate.

This happens alot in nature.

[Donella]

So what is the physiology behind this? It is the male (hence the sperm) that contributes the sex of the foal, so how is weight loss or metabolic rate at the time of conception affect the sperm? This is obviously what is happening right? But how?

We used a Friesian stallion a few years ago for which you could select the sex of your foal because the owners used a process by which semen would be sex selected. I wonder why this is not more popular amoung warmblood breeders?

[ellebeaux]

So what is the physiology behind this? It is the male (hence the sperm) that contributes the sex of the foal, so how is weight loss or metabolic rate at the time of conception affect the sperm? This is obviously what is happening right? But how?


There's 2 main theories for the mechanism:

1) steroid hormones during follicular maturation: So steroids (i.e. progesterone, estrogen etc.) in the follicular fluid are causing a change in the egg cell surface that make it receptive to either X or Y- bearing sperm.

2) glucose concentrations around the time of conception/before blastocyst hatching. So there are sex-differentiated differences in glucose metabolism during early development that cause females to lose one sex embryo or the other. You would never know because the fertilized embryo would be too early to detect before it's absorbed/repelled by the dam.

Metabolic changes due to change in body condition could cause either one of these situations to occur. There's evidence for both occuring in vivo and in vitro in other species (i.e. cattle and mice). Right now, I think both of these are possible with the steroid hormones being more influential since they occur earlier in the developmental sequence. But I reserve the right to change my opinion as more studies occur!

I do think that the timeline for the mechasnisms affecting sex selection in the mare are within one or two follicular waves and before blastocyst hatching.

[twistoffate]

I had the opposite result... I bought a rescue TB in AWFUL condition and put weight on her for 3 months before breeding her and she had a filly. I had seen this study and was expecting a colt.... Just my experience...

[Edgar]

put weight on her for 3 months before breeding her

That is not opposite results. It would have been if you bred her during the 3 months she was gaining a lot of weight.

[Tango14]

My stallion has produced only 1 colt out of 12 foals from 3 different mares. I was always lead to believe that the sire is solely responsible for the sex of the offspring but it seems there is no conclusive proof or short answer that this is indeed the case?
If so, Henry VIII really was barking up the wrong tree:)

[TrueColours]

ellebeaux - thanks for lending your insights to this as well. Not saying I understand any of it fully, but I find it fascinating all the same ... :)

[ellebeaux]

ellebeaux - thanks for lending your insights to this as well. Not saying I understand any of it fully, but I find it fascinating all the same ... :)

Hey, I don't understand it fully either, and I've been thinking about it every day for the past two years!

But the evidence is building and I think in the next 5-10 years, we'll have enough information that we will be able to develop dietary and husbandry approaches for significantly increasing the odds of producing one sex or another. And I like this idea as it would be a potentially no-cost, no medication approach that takes advantage of the horse's normal physiology.

[ellebeaux]

My stallion has produced only 1 colt out of 12 foals from 3 different mares. I was always lead to believe that the sire is solely responsible for the sex of the offspring but it seems there is no conclusive proof or short answer that this is indeed the case?
If so, Henry VIII really was barking up the wrong tree:)

Yes, you are correct! Just to help you understand:

In horses, as in all mammals, the sex chromosomes are called X and Y. Females produces eggs that all carry X chromosomes. Males produce sperm that carry either X or Y chromosomes.

So, yes, it is the sire that is solely responsible for the sex of the offspring. In general, sex ratios at birth are about 50:50. However...

It's been observed for years that in certain conditions, females tend to give birth to one sex or the other. Conditions at the time of conception, such as famine or drought or even seasonal differences between wet and dry periods can influence birth sex ratios. This observation is what this area of research is all about.

There is an apparent advantage for females to produce one sex under certain conditions and the other under different conditions. Imagine a horse in the wild - in the winter, when the grass is all dried up and food is scarce, the are going to lose body condition and become skinnier. In spring and summer, when the grass is flush and there's plenty to eat, they are going to gain condition. Wayne's research in horses found that as the mares lost condition, and bred, they tended to conceive female offspring. When times were good and they were gaining condition, they tended to conceive males.

There's a social advantage to this: horses are polygynous. One male breeds many females. If a mare can produce the fittest (biggest, baddest) male of his peers, he stands a better chance of producing offspring. Producing a filly is good too, but not as advantageous, since females can't breed willy nilly, they can only produce 1-2 foals every 2-3 years, whereas a male can produce as many foals as he can breed mares. So in good times, a female 'wants' to produce colts and in leaner times, fillies.

See how it works now?

So our work is figuring out how to duplicate this observation to produce the sex of offspring we want.

[twistoffate]

That is not opposite results. It would have been if you bred her during the 3 months she was gaining a lot of weight.

I guess I didn't word that correctly.... She was still gaining weight when I bred her but it took 3 months before she had enough condition on her for me to feel comfortable TRYING to breed her. I was actively putting weight on her for about 6 months total.

Here is a pic from when I got her...
http://i279.photobucket.com/albums/kk150/TwistofFateEventing/Marcy7.jpg

The picture doesn't do justice to how bad she looked but you can see she had a lot of weight to gain.

[Hampton Bay]

I read this study right after I bred my mare, and I got the filly I should have gotten. My mare had lost weight after being moved north, and I struggled to get her to gain. She was at a steady (though too low) weight when she conceived. About 2 weeks later she blew up like a balloon when the grass came in, but by then I already had my filly!

[Dalemma]

My stallion has produced only 1 colt out of 12 foals from 3 different mares. I was always lead to believe that the sire is solely responsible for the sex of the offspring but it seems there is no conclusive proof or short answer that this is indeed the case?
If so, Henry VIII really was barking up the wrong tree:)

Interesting as the stallion I picked had only sired 2 fillies in about 24 different mares.

We got the third filly and last filly before he was sold.

Dalemma