Breeding myths...

[AndyPandy]

I thought I would post this to debunk some popular breeding myths before we get into the breeding season properly... please feel free to make any additions you like!

My mare absorbed the embryo

Sorry, but this one is a myth. Despite the fact that stud vets al over the globe still use the terms "absorb" and "resorb" and "reabsorb", it has been shown that this does not occur. Fluid associated with the embryo is absorbed by the uterus, but the embryo itself is aborted and is ejected through the cervix during the next estrus cycle, as the uterus is simply not capable of breaking down and absorbing embryonic tissue.

Mares have a 28 day oestrus cycle

Humans have a 28 day cycle. The typical mare’s cycle lasts for 21 days, although every mare is different and some mares may have shorter or longer than average cycles.

Old mares experience menopause

While it is true that some older mares are less fertile, there is no equine menopause, as such. Some mares may “shut down” after the age of 20, but this is not a universal occurrence.

Old mares have old, damaged eggs, and will produce foals with problems such as bad legs, deformities etc.

Eggs produced by a 20 year old mare, are themselves 20 years old, as each mare is born with a all the eggs they will ever have. These older eggs may not be as viable, and so may be less likely to produce pregnancies. However, DNA is DNA, and the genes in each egg remain unchanged, whatever the age of the mare (and the egg). Environmental factors and mare/stallion genetics cause these problems, not old eggs!

My mare cannot be successfully bred using AI, and must be covered naturally to become pregnant

There may be a variety of reasons why this may appear to be the case, but generally it is because the mare has delayed uterine clearance issues. During the teasing stages of natural covering, the mare releases oxytocin which helps to clear the uterus of any post breeding debris and fluid. Exactly the same results can be achieved with judicious use of AI and oxytocin administration.

Having a mare around a stallion will cause her to go into estrus

This myth stems from the fact that mares show signs of being in season when they are presented with the required stimulus (i.e. a stallion). Some mares cycle silently, and will only show any sign of being in estrus when a stallion is nearby. Stallion presence does NOT cause estrus.

My mare had a reaction to the semen extender

Extender is extremely unlikely to cause a reaction in the uterus of the mare. It is possible however, that if the mare is sensitive to a particular antibiotic, and that antibiotic is present in the extender, that it may cause excessive uterine inflammation. However, blaming the extender for failure to achieve a pregnancy is short-sighted and it is strongly suggested that all the other possibilities are investigated first.


I drove my mare to the stud and knocked off the follicle!

No you didn’t. Mares continue to show estrus signs for 2-3 days after ovulation in some cases. What probably happened is that the mare was taken to stud after ovulation, but while still showing this post-ovulatory estrus behaviour. It is not physically possible to “knock off” a follicle – otherwise everyone would drive their mares around in order to perfectly time ovulations.

X-rays kill sperm when they are scanned in airport security

There is no research that supports this theory. In fact, studies that have been undertaken show no reduced fertility of sperm exposed to x-rays.

Pregnancy rates are higher in the wild than they are managed breeding programmes

While this may be true in a poorly managed programme, in a well managed programme it is totally false. We manage to breed mares which, in the wild, could not be bred and would be driven out of the herd.

Wild stallions breed their own daughters, so inbreeding is totally natural

In New Bolton, Pennsylvania, the equine behaviour centre has studied a feral herd of ponies for over 9 years now. They have never had an inbred foal. When fillies become sexually active, they leave their birth herd, and seek new stallions. Inbreeding is man made, and is likely to be a significant factor in reduced fertility of modern animals.

It is dangerous for a menstruating woman to be in the presence of a stallion

There is no reason why this should be the case, and no evidence to support the hypothesis. It is likely to be a relic of the male-dominated breeding set-ups of the late 19th and early 20th century.

The foal’s umbilical stump should be treated with iodine after birth

Iodine has been shown to be far too astringent on neonatal umbilical tissue. It should in fact be treated with a 0.5% chlorohexidine solution, four times a day for the first 3 days after birth.

Foal heat scours are caused by the mare coming back into estrus

This was thought to be the case until one farm began worming the mares shortly after birth with an ivermectin based wormer – this almost completely eliminated the scours. It is now thought that the scours are due to the transfer of worm eggs in the mares milk.

I hope you find these interesting. Please let me know if you can think of anymore, or you disagree with any of them

[Bossanova]

[ QUOTE ]
Old mares have old, damaged eggs, and will produce foals with problems such as bad legs, deformities etc.

Eggs produced by a 20 year old mare, are themselves 20 years old, as each mare is born with a all the eggs they will ever have. These older eggs may not be as viable, and so may be less likely to produce pregnancies. However, DNA is DNA, and the genes in each egg remain unchanged, whatever the age of the mare (and the egg). Environmental factors and mare/stallion genetics cause these problems, not old eggs!


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I only disagree with this one. DNA suffers damage as time goes on. As egg cells are essentially the same as normal body cells bar the number of chromosomes, their DNA can also be damaged. As the mare gets older the repair mechanism cannot always repair DNA damage sufficiently so mutations can occur.
Also, as DNA goes through the cycle of damage-repair-damage-reapir, it shortens and if shortended to a significant level, genetic material is lost.

[Shilasdair]

[ QUOTE ]

Foal heat scours are caused by the mare coming back into estrus

This was thought to be the case until one farm began worming the mares shortly after birth with an ivermectin based wormer – this almost completely eliminated the scours. It is now thought that the scours are due to the transfer of worm eggs in the mares milk.


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Interesting post, thank you.
I have my doubts regarding the wormer one above, and would like more information (if you have it). What sort of parasites are involved, and are there any scientific studies to back up the stud's experiences?
S

[AndyPandy]

[ QUOTE ]
Eggs produced by a 20 year old mare, are themselves 20 years old, as each mare is born with a all the eggs they will ever have...

I only disagree with this one. DNA suffers damage as time goes on. As egg cells are essentially the same as normal body cells bar the number of chromosomes, their DNA can also be damaged. As the mare gets older the repair mechanism cannot always repair DNA damage sufficiently so mutations can occur.
Also, as DNA goes through the cycle of damage-repair-damage-reapir, it shortens and if shortended to a significant level, genetic material is lost.

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Well, I would agree with your disagreement if oocytes were "normal" cells which underwent mitosis throughout the mares life. However, they do not.

The mare is born with a set number of primary oocytes on each ovary. The primary oocytes remain dormant until they are recruited for maturation (ootidogenesis). They are therefore not under the same aging stresses that normal cells are under (no real metabolic activity, no mitosis, no changes to the DNA). Even when they do mature, their meiosis is halted at metaphase II until fertilisation takes place.

Normal cellular aging does not effect oocytes because there is no telomere shortening, because their is no cellular reproduction. So 20 year old oocytes are not any different to 3 year old oocytes.

[AndyPandy]

[ QUOTE ]
Interesting post, thank you.
I have my doubts regarding the wormer one above, and would like more information (if you have it). What sort of parasites are involved, and are there any scientific studies to back up the stud's experiences?
S

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I believe the first study was Ludwig et al, 1984, but many subsequent studies have shown this to be the case. Direct administration of ivermectin to the neonate can cause severe toxicity which can lead to blindness and other complications.

There is still debate over whether the ivermectin prevents transfer of eggs/worms in the milk, or whether is does something else to alter the way the foals gut deals with new pathogens in the first fortnight.

If I find any more info, I will let you know Try it and see what happens though.

[machannah]

AP - what wormer do you recommend to stop scouring? My chap didnt have anything last time, so i may have done something right by accident!!

[KarynK]

Re what sort of parasites:

I believe that the two species involved in foal scours would be Intestinal Threadworms and Large Roundworms. But I would put my money on the Threadworms as they are passed through the mares milk and they have a short lifecycle so this is probably the culprit, which would make the ivermectin dose on foaling effective at preventing the scours at a young age along with loss of appetite and dullness. Natural immunity is acquired at around 6 months of age with these beasties so they do not affect juveniles or adults.

With the Roundworms the eggs have a sticky coating and no matter how clean the stables and equipment the eggs of these little suckers will be there waiting for years, even on the mares udder!!! And of course when your foal starts eating ma’s dung to get its bacteria hey presto a perfect oportunity!

[CrazyMare]

When you say worm on foaling with an ivermectin, what time frame are you looking at? Worming within an hour of foaling? 4-6 hours of foaling?

[AndyPandy]

I would go for Eqvalan. Interestingly enough, Eqvalan was also shown to improve sperm quality in stallions about 20 years ago! It's good stuff (always consult your vet, and the wormer vendor before use etc.)

[machannah]

Interesting, I primarily used Eqvalan when I had my ponies etc, and then the market changed and people recommended others so I havent used in a while

I shall go purchase some for my lady and put it my box of important things! Thank you