It isn't health problems, it is the potential for female offspring to be hermaphrodites. But there are people out there breeding polled to polled with no problems.
Interesting. I can't wait to see what I get from my one polled goat. Hoping for polled anything....which will be kept, maybe. Will there be a chance of it being a hermaphrodite if the buck was horned? Will I be able to tell externally?
I'm really excited to try breeding to a polled buck that my breeder is getting!! All of my does are disbudded, and we have a 50/50 chance of polled babies!! Can't WAIT!! lol
With polled goats, if you breed polled to polled, you have a ONE in FOUR chance of a hermaphrodite offspring. So saying that people are breeding polled to polled with no problems is highly unlikely - more likely is they don't realize they're selling hermaphrodite babies or they cull the hermaphrodites and cover the evidence.
As far as my research can find - breeding polled to horned is safe. I do have one customer who is reporting difficulty settling her polled doe from one of these breedings - but I think they're missing her cycle rather than there being a genetic issue with her fertility. Her dam was very difficult to read when she was in heat, too.
A hermaphrodite doe should have an underdeveloped vulva...and they often act bucky and grow the buck hair around their neck and shoulders. I've seen one in doe like this...I can dig up a picture...
Gypsy Moon Nigerians has a photo of a hermaphrodite vulva posted on their website.
I have horned & polled nigerians. It seems like we get more horned kids than polled no matter how you cross them. Either that or I just haven't found the right cross. I have only crossed polled on polled 1 time and was blessed to have no problems. I discontinued this cross as I came across more information discouraging this practice.
So is the polled gene is dominant? If breeding polled to polled you have a 25% chance of a sterile baby, that would indicate the polled gene is dominant and receiving two copies of the polled gene leaves the offspring sterile. If that is true, than all fertile polled goats are heterozygous polled (One polled gene, one horned gene: PH), all non fertile polled goats are homozygous polled (2 polled genes: PP)and all horned goats are homozygous horned (2 horned genes: HH). The Punnet square than says this:
Polled to polled
P H
P PP PH
H PH HH
25% chance of a hermaphrodite, 50% chance of polled and 25% chance of horned.
Polled to horned
H H
P PH PH
H HH HH
50% chance of polled and 50% chance of horned.
To the o.p. -- It is just different in sheep. (For one thing in sheep there is also a version that causes only males to be horned, females to be polled). Here is some info on the polled gene in Shetland sheep: http://www.shetlandsheepinfo.com/CONFORMATION/polled.htm I do not know how different it is in other sheep breeds)
Basically, different critter, somewhat different genetics.
Supposedly water buffalos are like goats, where individuals with two copies of the polled allele tend to be hermaphrodites.