So I have two full siblings one is at 10 months about 15.1h and his sister at 22 months is about 15.2h, roughly how tall do you think they will end up and has anyone else had such large differences between full siblings?
It would help to know what they are (breed) and how tall their parents (dam/sire) are.
I’ve had a 3 inch difference between full siblings. Remember that there is variation which is why breeding is so much fun!
Both WB sire 16.3 dam 16.1
How much info do you have on what the sire and dam typically produce? If they have a lot of offspring, you may have an easier time predicting this. I’m not a breeder, but I know many people who are. After a while you will get a feel for what the sire and dam will produce.
I have a friend who has a very small mare, 15:2, and she was bred to a stallion who is 16:3 and the resulting colt ended up 17:1 at age 4 and might still be growing. I think the stallion was known for throwing tall babies.
I know another person who owned a mare who wasn’t super tall, just average at 16:2 and no matter who she was bred to, her babies were all over 17hh. The owner eventually stopped breeding her because she didn’t want big babies and that seemed to be what she produces.
There are a lot of thoughts on how to do estimates, like measuring from the coronet band to the middle of the knee. Every inch supposedly represents 1 hand. There are other ways to estimate if you do a search on the internet. I don’t know how accurate those are.
Different horses mature at different rates. A friend of mine has a colt who was nearly 160 lb at birth and was HUGE!! A few months later many of her other foals had caught up.
Doing the string test, near or after growth plates in the knee have closed (which is a guess)- around 20 to 26 months of age, (string from elbow to ergot, then turn the string so that it runs from the elbow “up” the side of the horse to where the wither will be) will give you your best guess on final height. Before that age, you are really only guessing.
And yes, there can be HUGE differences in size of full siblings. I’ve had six inch differences between full siblings. Full TBs. And sometimes, full siblings are far more identical. “It Depends”, on what comes through, and where it comes from. You neva no nothing for sure when it comes to breeding horses.
I think there will be more variability when you’re breeding horses from registries than if you’re breeding purebreds. Regardless as those have said breeding is still a gamble…Staying with a section of a breed, in my case, has made predicting foals’ adult height far easier and my full siblings have been very close in size. I still won’t/don’t guarantee that anything will be x or stay under y…
i’m interested to see how my full siblings turn out - one is 6 and about 15.1, the other is 2 and perhaps 14.3/15 (need to stick her). i’m surprised that she’s almost as tall as her gelding brother at this age. always fun to see what you get!
Measure both at 12 and 24 months, then add 2h and 1h, respectively, for a decent prediction.
String test the 22 month old now, and the 10 month old at 12 months, for another decent prediction.
The 10 month old is tall for his age, and will likely be in the 16.3+ range.
The 22 month old is in a pretty typical range for her age, and will probably end up in the 16.1-16.2 range.
Often the first foal will be smaller than subsequent.
Thankyou for all the info everyone, its very interesting to watch them grow 
I bred 2 full siblings. The first was a chestnut filly who topped out at 16.1. The second was a grey gelding who finished at a solid 18.1…a full 2 hand difference. The mom was about 16.2 and the sire about 16.3 if I remember correctly. Hanoverian.
2 hands difference? Yikes! 18.1 is HUGE
Just out of curiosity were there any really tall offspring by the same sire or out of the same mare?
[QUOTE=arenabound;8917097]
I bred 2 full siblings. The first was a chestnut filly who topped out at 16.1. The second was a grey gelding who finished at a solid 18.1…a full 2 hand difference. The mom was about 16.2 and the sire about 16.3 if I remember correctly. Hanoverian.[/QUOTE]
[QUOTE=arenabound;8917097]
I bred 2 full siblings. The first was a chestnut filly who topped out at 16.1. The second was a grey gelding who finished at a solid 18.1…a full 2 hand difference. The mom was about 16.2 and the sire about 16.3 if I remember correctly. Hanoverian.[/QUOTE]
Sounds like what Big Ben did! Is there big height back in the pedigree anywhere?
I’ve known multiple pairs of siblings with at least a full hand difference in height between them. The biggest gap was a 15.1h TB mare bred to a 16.2h TB stallion who together produced both a 15.2h mare and an 18+h gelding.
Full sibling geldings belonging to a friend. They are 8 and 12.
Gelding A is a very refined, super modern 16.1
Gelding B is older style and every bit of 17.3
I’ve seen horses from different breeds look more alike than these two do.
Breeding is a crap shoot
Thane everybody, amazing to see that there can be so much difference between full siblings!
Foal 1- bay, 16.2
Foal 2- bay, 17.1 + but pinto markings
Foal 3- chestnut, barely 16.1
Same as siblings in any family. 
Full brother/ sister:
Brother looks like uncles tall leggy bright bay 16.2+ and ADD goofey
Sister looks like grandma! black bay full figured 16.0 - serious, focused, a woman on a mission.
