Polled Intersex Syndrome: Why we don't breed polled to polled

Polled Intersex Syndrome (PIS) is something about goats that comes up every so often in various goat discussion forums. There is a lot of debate back and forth, but in the scientific literature things are more clear. I have attempted to write here in simple terms what PIS is.

Something that isn’t obvious from our farm page is that there are two people behind Floof Farm. Kate who does most of the goat care and Chris who is the builder as well was went back to school to study Biology. We already had information on PIS but more learning towards the scientific definitions. Let’s break it down into more simple terms.

What is a polled goat?

Polled goats (and other horned animals) mean genetically the animal is born without horns. Each parent of a goat carries one gene for polledness and polledness is a dominant trait. If one gene of the two is for the goat to not have horns then it will not have horns, it needs two genes for horns to be horned. If both genes say the goat won’t have horns then it also won’t have horns, though we will get into why this is difficult later.

Farmers and vets remove horn buds early in life to prevent horn growth. Nobody really enjoys disbudding goats. People start out and look for ways to avoid disbudding. At first polled goats seems to be a solution.

Heterozygous vs Homozygous

A trait for hornedness comes from each parent. With a dominant gene like polledness the concept of heterozygous vs homozygous comes into play. Heterozygous means each genetic trait inherited from each parent is different and homozygous means that each is the same. So theoretically if you had a heterozygous polled goat they would pass on the polled gene half the time when breeding, but if they were homozygous they would ALWAYS pass it on. That would mean every kid produced from a homozygous parent would always be polled.

Then often the question is:

Why not breed polled to polled?

Polled Intersex Syndrome is why.

Polled Intersex Sydrome or PIS

The genetics for expression of sex are tied together to genes for polledness are tied to some of the genetics for expression of sex. Genes are much more complicated than I’ve been describing in this post. I’m being hand wavy about details for the sake of simplicity. That said there are deep definitions and information published in multiple journals, but this article is more practical for the goat breeder. The way PIS manifests is if a genetically female goat inherits two genes for being polled.

Female goats with two polled genes

According to the research that has been done any female goat that it homozygous for polledness will be intersex. This means they will not be fertile and will have both female and male sex characteristics. So if you breed 2 goats together that are both polled you will roughly get the following breakdown. You might remember doing Punnet Squares in school for this type of inheritance. Below is all the options for both polledness and sex.

Each option has a 12.5% chance of happening. Meaning if you bred a statistically significant quantity of goats 12.5% of them would be female with Polled Intersex Syndrome. There are other potential combinations as well for example what if you had a male goat with homozygous polled genes and a female goat with heterozygous? Then the chance of female goats from that breeding having PIS would be even higher as the chance of a kid having both polled genes would be higher.

Why does Polled Intersex Syndrome matter?

Well there are a few reasons it matters to me. The first is that I breed dairy goats. I believe 12.5% of the potential goats from a breeding being infertile is too many. Second while having a homozygous polled buck seems like a great option. Some would tolerate the infertile females, but there is no way to tell if a buck if homozygous polled. Because of the even greater chance of PIS I would not be able to breed them to polled females as the majority of the females born would be intersex from such a breeding.

But someone says they have been breeding polled to polled for YEARS

Often when breeding polled to polled comes up in a discussion forum things get heated. Someone will say they have never had issues breeding polled to polled. The only time they got intersex goats was from breeding horned to horned. I have a few different things to say about that.

They won the genetic lottery

Genetics are random and you have to breed a lot of goats to get the percentages I calculated above. It is possible they have just been very lucky. Let’s say you did five polled to polled breedings. This is not enough to prove anything, that would be like flipping a coin five times and getting heads. This is less probably, but certainly possible.

Polled Intersex Syndrome goats have other issues

I think some of the PIS impacted goats are dying early in gestation. When this happens perhaps they are reabsorbed. I have even heard of at least one case where such a goat died at a few days old due to complications. If a herd has been breeding for years many many goats I would be curious about their ratio of male to female goats and if it is skewed male.

Goats can have other sex expression issues not caused by polledness

There are any number othe reasons a goat could have sex expression issues that have nothing to do with polledness. A horned breeding could have free martins or some other mutation. In those cases they we just unlucky in another way that was not PIS.

Maybe….maybe there are some breeds of goats that don’t have this issue

There is a slim chance there might be a breed of goats or a pool of genetics that don’t have this issue. I’m not planning a Phd in goat genetics, so someone else will have to do the science to figure this out.

Summary of Polled Intersex Syndrome

Based on what I know about the polledness triat in goats I don’t breed polled to polled. My opinion is heavy in this article and I have simplified a lot of the concepts. Draw your own conclusion. For now I’ll continue my breeding plans as I have been.