Dwarfism genetics question

[sweetheart]

Okay, so I have the opportunity to buy this beautiful mare, lovely confirmation, very refined. However, I know that her sire has had two dwarf foals with two different mares (but not the dam of this mare). The mare is definitely not a dwarf, and I've seen two other foals from this pairing of dam & sire and neither of them were dwarves. Is she more likely to have a dwarf foal because her sire had dwarves with other mares? What do y'all think, would you stay away or would you not worry about it?

Thanks!

 

[Ashley]

What is this mares foaling record if she has one? If she has had foals have any of them be dwarfs? Were the dams to the other dwarf foals related at all to the questioning mare?

I would look at all this before decideing.

 

[REO]

Her sire carries the dwarf gene. She has a 50/50 chance of also being a carrier depending if she inherited it from him or not. Some horses you can't tell by looking at them if they are carriers or not. If she is a carrier like her sire, 50% of her foals can be either dwarves or carriers. If she is bred to a stallion that is also a carrier, they can have some non carriers, some carriers and some actual dwarves.

Or she might be a non carrier. But there's no way to tell without there being a test for dwarfism.

 

[sweetheart]

One of the dams who had a dwarf was related to this mare's dam. The other dam who had a dwarf is completely unrelated. This mare is a maiden. But her dam has never had a dwarf, and has had 8 foals.

What is this mares foaling record if she has one? If she has had foals have any of them be dwarfs? Were the dams to the other dwarf foals related at all to the questioning mare?

I would look at all this before decideing.

Interesting! Do we know for sure that it is a single gene that causes dwarfism? Otherwise the probabilities wouldn't be as precise, right? (if it was multiple interacting genes that caused it?). I haven't kept up with the research, I know they were trying to isolate/identify the genetic cause of dwarfism.

Her sire carries the dwarf gene. She has a 50/50 chance of also being a carrier depending if she inherited it from him or not. Some horses you can't tell by looking at them if they are carriers or not. If she is a carrier like her sire, 50% of her foals can be either dwarves or carriers. If she is bred to a stallion that is also a carrier, they can have some non carriers, some carriers and some actual dwarves.

Or she might be a non carrier. But there's no way to tell without there being a test for dwarfism.

 

[REO]

It is said that it takes the dwarf gene from each parent to make an actual dwarf. If the sire has sired actual dwarves, then both he and the mares that he had the dwarves with carry the dwarf gene.

The mare you're thinking of buying may or may not carry the gene from her sire. (he has proven that he's a carrier) And if her dam is also a carrier, she may or may not carry it from her. But the mare herself not being a dwarf does not carry 2 dwarf genes, or she would be a dwarf herself.

So.....the mare you're thinking of buying (just like most minis!) either has one copy of the dwarf gene or none! No way to know since there is no test yet.

Sorry if I'm being confusing.

I was just trying to explain how it worked

 

[targetsmom]

I am certainly not going to advise you on whether or not you should buy this mare, and hope I am not going to add to the confusion. I imagine we would all love to buy only minis that were free of the dwarf gene, but at this point in time, that is just about impossible. So, if you don't buy this mare, do you think your chances of buying another mare free of the dwarf gene will be any better? Just something to think about. I am going to go out a limb here and say that I doubt if most breeders would tell you if a stallion sired a dwarf.

Some things I learned recently on this forum about dwarfs: over 40% of the 150 breeders who responded to a survey last November said they had a dwarf born on their farm. That does not mean 40% of minis carry the dwarf gene, but I think it does add some perspective to your question.

Another forum thread asked breeders who had stallions that sired 50+ foals, how many NEVER HAD A DWARF? The response was underwhelming. Among the very few responses happened to be the breeder of one of our mares!!! Does that mean our mare doesn't carry the dwarf gene because her sire never had a dwarf? NO, she could still have gotten the gene from her dam. (On the other hand, I do feel just a wee bit better knowing that!) See how complicated this is???

So as others said, she has a 50 percent chance of carrying the dwarf gene, but so does any other mare whose sire or dam ever produced a dwarf.

Good luck!

 

[Anne]

Ok, I'm just "thinking here."

I know that it "seems" to be accepted that both sire and dam must carry a "dwarf" gene to produce a dwarf, which gives the impression that there is just "one dwarf" gene.

I do not believe that has been proven.

There is not testing available for dwarfism.

I do tend to think (my humble opinion only) that this theory is being accepted and presented as fact without any real proof to back it up.

What if there is more than one genetic flaw that is needed to create a dwarf? There surely seems that there is more than one type of dwarfism and so more than one type of genetic issue.

My opinion is that the generally held and spoken opinion that there is "a" dwarf gene, that both parents must carry to present a dwarf, or carrier, or one parent will /can pass along the gene to an offspring to create a "carrier", may be an over simplification of the issue.

 

[horsehug]

If you go to the "Dwarfism in Miniatures" Forum right here on Lil Beginnings, John Eberth answers many questions we all have/had about dwarfism.

He alone has studied this far more than any other person, and while not isolating any specific genes so far to develop a test, (due to lack of funding in large part) he has found in his extensive research so far that in the 4 main kinds he has found, they follow the genetic laws (which he has spent his life studying) for it to take two parents to produce a dwarf.

The questions and answers on that forum are very interesting and informative.

I wish I could have been at his dwarf seminar he gave in Toronto today!

Susan O.

 

[MiLo Minis]

Her sire carries the dwarf gene. She has a 50/50 chance of also being a carrier depending if she inherited it from him or not. Some horses you can't tell by looking at them if they are carriers or not. If she is a carrier like her sire, 50% of her foals can be either dwarves or carriers. If she is bred to a stallion that is also a carrier, they can have some non carriers, some carriers and some actual dwarves.

Or she might be a non carrier. But there's no way to tell without there being a test for dwarfism.

Having just freshly arrived home from our club's clinic on dwarfism with John Eberth, which was actually just north of the 401 near the Mohawk Racetrack and was VERY good, I can tell you that if she is a carrier and is bred to a non carrier there is a 50% chance of producing a carrier, 50% chance of producing a normal foal and NO chance of producing a dwarf - it takes 2 carriers to produce a dwarf. If she is a carrier and is bred to a carrier she has a 25% chance of producing a dwarf, 50% chance of producing a carrier and 25% chance of producing a non carrying normal foal. She herself could easily be a carrier OR a non carrier. John is the world's leading expert on dwarfism in Miniature Horses and this is what his research has shown to be true.

Sorry - it didn't seem to want to let me edit my post so I just wanted to add:

John has so far recognized that there are at least 4 types of dwarfism in our breed and it seems that although there is the rare chance of dwarfism resulting from an anomoly, or freak chance, it is more likely that it takes one gene from each parent to cause any of the 4 types.

 

[REO]

Thanks Lori, that's what I meant to say.

I knew I was messing up my wording somewhere!

 

[Contessa]

IF I were in your shoes I would run, not walk away from this mare especially if you ever plan to breed her. At least you were given the knowledge that her sire has had dwarves in the past so put that knowledge to use and just say no.

 

[MiLo Minis]

Thats okay Reo - I was just hoping to clarify your reply which was correct

I wouldn't necessarily run from this mare. She could easily be a non carrier completely normal horse. I would look at her conformation very closely and be sure that she is as close to perfect as possible before considering her though. If you breed her and produce a dwarf then you will know that both she and the stallion you bred her to are carriers but there is only a 25% chance of getting a dwarf - thats one in four each time you breed. Don't breed her to that stallion again. If we were to give up on any well conformed horse that might be a carrier there would certainly be a LOT less breeding going on in Miniatures and we would lose a lot of very good bloodlines. Do breed her wisely and carefully. The quickest way to find out if she is a carrier would be to breed her back to her sire who you know is a carrier.

 

[Sue_C.]

The quickest way to find out if she is a carrier would be to breed her back to her sire who you know is a carrier.

I am CERTAINLY hoping this isn't something you would ever consider??

And NO...this still wouldn't tell you, unless she had a dwarf foal right off. She COULD produce several carriers FIRST...which may go on and continue to scourge the gene-pool even more.

I too, would walk away from this mare. I am one who thinks that there ARE enough GOOD horses without taking chances that you KNOW are already high. I do not care HOW "great" the conformation of this mare is...I am sure there is another one just as good, or better, who doesn't come from dwarf-producing parents.

I say hedge your bets-- and leave her. I have seen and read here on this Forum, just too many bad outcomes of dwarf producing horses, to KNOWINGLY take that chance. Yes, I know...it is true that any breeding IS a chance taken...but I will do my utmost to ensure I've taken what precautions I CAN.

 

[yankee_minis]

It is possible to find a stallion with very little history of dwarfs in their pedigree. I learned a lot with the dwarf forum. Some specific things were unsaid, but I was able to learn a lot.

If you want this mare-- whether she can be bred or not-- then by all means, buy her.

I commend the seller for being honest.

 

[Jill]

How many foals has her sire produced? If it's 10, I may pass, but if it's a substantial number, it would make me question more if it was the mares vs. him.

 

[sweetheart]

Thanks for the replies! I will think about it some more.

~Allisa