Testicles

[drmatthewtaylor]

I think we are mixing some information here as everyone is essentially right and wrong.

Testicular size does correlate to sperm production, but small testicles are not always infertile and huge testicles are not always fertile. There are more factors than size alone.

And although each egg can get fertilized by just one sperm, it takes more than one. 500 million is the lowest amount to have consistent pregnancies (and 1 billion is frequently used). But, a normal ejaculate has 5-20 times that number.

The reason testicular size is important is if a sire will have many females to impregnate in a particular year then maximal sperm production will be needed. But, unless you were going to breed 50 mares to a single stallion, then I doubt it will matter.

Dr Taylor

 

[Lindi-loo]

And although each egg can get fertilized by just one sperm, it takes more than one. 500 million is the lowest amount to have consistent pregnancies (and 1 billion is frequently used). But, a normal ejaculate has 5-20 times that number.

Dr Taylor

I disagree.. it takes just 1 sperm to fetilise the egg that developes into an embryo..yes many are released during ejaculation and yes if less than 500 million were released it would deff lower the chances of the mare becoming pregnant at all but still only takes 1 out of those millions to make a baby

 

[drmatthewtaylor]

I disagree.. it takes just 1 sperm to fetilise the egg that developes into an embryo..yes many are released during ejaculation and yes if less than 500 million were released it would deff lower the chances of the mare becoming pregnant at all but still only takes 1 out of those millions to make a baby

I'm not sure what you are disagreeing with, but unless in vitro fertilization is used, 1 sperm will never fertilize an egg. Less than 500 million may, but fertility will suffer.

Only a small fraction of the sperm deposited in the mare's vagina end up in the uterus. From those that make it to the uterus, only a small fraction of those find their way to the oviducts. Usually the egg is all the way up at the other end of the oviduct(fallopian tube). Of those that are in the oviduct only a small fraction make their way from the lower to the upper oviduct. So, in fact, the number of sperm successfully arriving at where the egg is located is actually very small and the journey requires many sperm pulling each other along. Another problem is that the egg is not just waiting to be fertilized by the first sperm to come along. The egg is usually covered by a thick layer of cells called the corona radiata that serve as a blockade to restrict sperm from getting into the egg. Sperm cells contain enzymes that break this barrier down. It may actually require an assault of many sperm to break down the corona sufficiently to let one sperm get through to the egg. So the whole process is somewhat like a marathon run in a maze filled with mucus followed by breaking into a fortress. That one sperm that finally makes it is the champion of Mother Nature's triathlon. If you don't have enough competitors to start, none are left at the finish.

Dr Taylor

 

[Charlotte]

Dr Taylor, thank you for a very clear and understandable explanation. That was great!

 

[Lindi-loo]

I wasnt diagreeing with how the egg is fertilized I was diagreeing that it takes more than 1 to create a new life..many make the journey possible but its 1 that makes the new life possible..we'r saying the same thing..only what im saying is that there is only 1 winner in the race

 

[rubyviewminis]

Thank you Dr. Taylor. Loved your *laymen's terms*.

 

[denny10012]

I'm not sure what you are disagreeing with, but unless in vitro fertilization is used, 1 sperm will never fertilize an egg. Less than 500 million may, but fertility will suffer.

Only a small fraction of the sperm deposited in the mare's vagina end up in the uterus. From those that make it to the uterus, only a small fraction of those find their way to the oviducts. Usually the egg is all the way up at the other end of the oviduct(fallopian tube). Of those that are in the oviduct only a small fraction make their way from the lower to the upper oviduct. So, in fact, the number of sperm successfully arriving at where the egg is located is actually very small and the journey requires many sperm pulling each other along. Another problem is that the egg is not just waiting to be fertilized by the first sperm to come along. The egg is usually covered by a thick layer of cells called the corona radiata that serve as a blockade to restrict sperm from getting into the egg. Sperm cells contain enzymes that break this barrier down. It may actually require an assault of many sperm to break down the corona sufficiently to let one sperm get through to the egg. So the whole process is somewhat like a marathon run in a maze filled with mucus followed by breaking into a fortress. That one sperm that finally makes it is the champion of Mother Nature's triathlon. If you don't have enough competitors to start, none are left at the finish.

Dr Taylor

Thank you for that wonderful explanation

 

[Becky]

Thank you, Dr Taylor! Excellent explanation and very informative.

 

[Nathan Luszcz]

YES. Testicular size DOES correlate to fertility. More precisely, larger testicles produce more sperm cells. Larger testicles won't make bad sperm good, and they can certainly be infertile due to injury, fever, or genetics. But the larger testicles will produce more sperm.

 

[rubyviewminis]

I think anyone wanting information on horse testicles has it permanently emblazoned on their memory cells, over and over.

 

[Nathan Luszcz]

I am only guessing, but

1) Could it have been age? Meaning was he young when they were smaller and he just matured over time?

2) Hormones. I imagine that breeding and being with mares in season caused some hormones to be secreted. Perhaps that continued stimulation caused increased hormone release which in turn caused an increase in testicle size. I just did a google search on this subject, but most of the articles were not exactly scientific, lol! I guess that's what happens when you type in 'testicles enlarge after sex'!!!

Believe it or not, but stallion's testicles DO change size!!! In the spring, they will enlarge, and in the fall/winter they will shrink (vica versa for you southern folks). Stallions react to daylight just like mares do. In their case, the light tells them when to start producing testosterone. This happens through stimulation of the laydig cells, which enlarge, making the testicles larger!

You are definately correct! Age is a big part of it too. Testicles will grow larger until sexually mature (around age 5) then shrink slowly when they hit their late teens.

 

[Nathan Luszcz]

Internet giving fits, double post!

 

[Riverrose28]

Believe it or not, but stallion's testicles DO change size!!! In the spring, they will enlarge, and in the fall/winter they will shrink (vica versa for you southern folks). Stallions react to daylight just like mares do. In their case, the light tells them when to start producing testosterone. This happens through stimulation of the laydig cells, which enlarge, making the testicles larger!

You are definately correct! Age is a big part of it too. Testicles will grow larger until sexually mature (around age 5) then shrink slowly when they hit their late teens.

Nathan, or Dr. Taylor, both of you have given us great information, I have a differnt question. One of my stallions that had two now only has one. Reason he was being shown and not bred for two years as we were promoting him to earn Championships to enhance his offspring. He got strangles and had a very high fever. Before he got sick he had two, I didn't notice he only had one till several weeks after the illness and I was bathing him and discovered he only had one left. I called my vet and she said the other must have atrophied because of fever. I asked if she thought he was still fertile, as I had just spent thousand of dollars having him promoted. She said well breed him next year and find out. Well I did and he settled all his mares. My question is, should I be concerned about his future, health wise? He is so special to us, and if we had to geld him it would be OK. What do you think is best for him? Also the one that is remaining seems to have gotten larger, could it be more testosterone?

 

[drmatthewtaylor]

One can atrophy, but I don't think you know yet. Have him ultrasounded to find out then go from there.

Yes, remaining teste does increase in size and fertility is usually not hurt by the loss of one teste.

Dr Taylor

 

[Nathan Luszcz]

Fever destroys germ cells (sperm stem cells), so instead of dividing into two cells, one of which becomes another germ cell, and the other becomes a sperm, the cell dies. Eventually (in a matter of 72+ hours) with a high enough fever, all the germ cells are dead. Within two months, the stallion will no longer produce sperm.

However, at the same time, Laydig cells continue to produce testosterone. They will not atrophy and are not effected by temperature. Germ cells take up very little space in the testicle, most of the tissue is made up of other types of cells.

Moral of the story is even infertile testicles will not "disappear". They may get a spongy consistency to them, but they will not go away.

As far as YOUR horse, you do not need to breed him to make sure he is still producing sperm. A BSE (breeding soundness exam) or a semen collection would show you the same thing. Fever doesn't make the sperm infertile, it causes sperm to not be produced. So if there is sperm there, fever hasn't destroyed the cells

And of course everyone knows that sperm =/= semen, right? Just because a stallion is infertile doesn't mean he can't breed or ejaculate, just that there may not be any sperm in the fluids.

As far as the other part of your question, the other testicle went SOMEWHERE. Either what you originally felt wasn't actually a testicle, or it was so small it retracted back up into the body, or SOMETHING, it wouldn't just disappear

Since he is (apparently) a crypt, you need to consider whether or not you want to breed him. If he is a genetic crypt, there is a good chance you could pass that trait on to the next generation. It is also equally possible it was a fluke, and that he isn't a genetic crypt. But its an ethical question whether or not you feel its best for the breed to breed a *possibly* genetic crypt. Having just one will not diminish his fertility (other than producing LESS quantity of sperm). It WILL hypertrophy (get bigger) to compensate for testosterone production (those laydig cells again! They enlarge to produce more testosterone. A monorchid (single testicle) stallion will have the same or similar testosterone compared to a normal stallion.) So it is very possible that the one testicle is bigger than normal. But I still wonder where the other one went! Its there somewhere!

 

[Riverrose28]

One can atrophy, but I don't think you know yet. Have him ultrasounded to find out then go from there.

Yes, remaining teste does increase in size and fertility is usually not hurt by the loss of one teste.

Dr Taylor

Thank you Dr. Taylor, you just confirmed what my Vet told me. He is still fertile even though I'm not breeding at the present time, but may do so in the future. MOst appreciated!

 

[Riverrose28]

Fever destroys germ cells (sperm stem cells), so instead of dividing into two cells, one of which becomes another germ cell, and the other becomes a sperm, the cell dies. Eventually (in a matter of 72+ hours) with a high enough fever, all the germ cells are dead. Within two months, the stallion will no longer produce sperm.

However, at the same time, Laydig cells continue to produce testosterone. They will not atrophy and are not effected by temperature. Germ cells take up very little space in the testicle, most of the tissue is made up of other types of cells.

Moral of the story is even infertile testicles will not "disappear". They may get a spongy consistency to them, but they will not go away.

As far as YOUR horse, you do not need to breed him to make sure he is still producing sperm. A BSE (breeding soundness exam) or a semen collection would show you the same thing. Fever doesn't make the sperm infertile, it causes sperm to not be produced. So if there is sperm there, fever hasn't destroyed the cells

And of course everyone knows that sperm =/= semen, right? Just because a stallion is infertile doesn't mean he can't breed or ejaculate, just that there may not be any sperm in the fluids.

As far as the other part of your question, the other testicle went SOMEWHERE. Either what you originally felt wasn't actually a testicle, or it was so small it retracted back up into the body, or SOMETHING, it wouldn't just disappear

Since he is (apparently) a crypt, you need to consider whether or not you want to breed him. If he is a genetic crypt, there is a good chance you could pass that trait on to the next generation. It is also equally possible it was a fluke, and that he isn't a genetic crypt. But its an ethical question whether or not you feel its best for the breed to breed a *possibly* genetic crypt. Having just one will not diminish his fertility (other than producing LESS quantity of sperm). It WILL hypertrophy (get bigger) to compensate for testosterone production (those laydig cells again! They enlarge to produce more testosterone. A monorchid (single testicle) stallion will have the same or similar testosterone compared to a normal stallion.) So it is very possible that the one testicle is bigger than normal. But I still wonder where the other one went! Its there somewhere!

Thanks Nathan, very goon info!

 

[valshingle]

I'm not sure what you are disagreeing with, but unless in vitro fertilization is used, 1 sperm will never fertilize an egg. Less than 500 million may, but fertility will suffer.

Only a small fraction of the sperm deposited in the mare's vagina end up in the uterus. From those that make it to the uterus, only a small fraction of those find their way to the oviducts. Usually the egg is all the way up at the other end of the oviduct(fallopian tube). Of those that are in the oviduct only a small fraction make their way from the lower to the upper oviduct. So, in fact, the number of sperm successfully arriving at where the egg is located is actually very small and the journey requires many sperm pulling each other along. Another problem is that the egg is not just waiting to be fertilized by the first sperm to come along. The egg is usually covered by a thick layer of cells called the corona radiata that serve as a blockade to restrict sperm from getting into the egg. Sperm cells contain enzymes that break this barrier down. It may actually require an assault of many sperm to break down the corona sufficiently to let one sperm get through to the egg. So the whole process is somewhat like a marathon run in a maze filled with mucus followed by breaking into a fortress. That one sperm that finally makes it is the champion of Mother Nature's triathlon. If you don't have enough competitors to start, none are left at the finish.

Dr Taylor

That's a great visual! It sums up what I've read in the repro books.