Interesting facts about polled cattle

This topic needs a bit of introduction - I started raising Native Milking Shorthorns in 2016. This is a rare breed with some outstanding characteristics for homesteaders and I made it my project to create a Landrace of Native MS that are A2/A2 and Homozygous polled. The milk proteins gene comes in several varieties but basically, A1 milk causes a lot of allergy issues, A2 milk not so much. To get A2 milk requires 2 A2 genes. If a cow has 1x A2 gene and 1x A1 gene, the milk will give a mixture of A1 and A2 proteins. To know what genes your cow has, means genetic testing. I use UD Davis genetics lab to get this information. The other characteristic that I am selectively breeding for, is for polled cattle. I don't want horns in my herd for a variety of reasons - mostly to do with nearly losing a eye a few times.

Until a few weeks ago, I was only interested in whether polled animal was heterozygous polled (P/H) or homozygous polled (P/P). Obviously in my project I want to consolidate my breeding program on homozygous polled - though not to the exclusion of all the other great characteristics this breed exhibits. I had a bit of a revelation when the tests from my spring calves came back - one of those calves is homozygous polled, but has two different types of polled gene. I was previously oblivious to the fact that 'polled genes' come in two different flavors. The net effect is the same in that homozygous polled means the cow has no horned gene to give to its babies. When I initially started my project, UCD test results showed only polled versus horned, its only in the last two or three years they started reporting on which polled gene the animal carried.

To some extent, this is an academic discussion - one type of polled doesn't win over the other type of polled - but the origin of the gene comes from two different mutations in separate populations. So all my cattle until 2024 arose from Cantagree and JbarJ bloodlines - and the polled gene contributed from these sources were 100% Pf - that is, all my animals that carried the polled gene, arose from the Friesian mutation/population. Since then, I've bred several animals from the Eionmor Port-O-Call NP bull. His polled gene is of the Celtic variety. So I now have several animals that carry the Pc gene and one special heifer that is homozygous polled with a mix of the two polled genes. Some may find this a boring discussion, but discovering this, I found quite interesting.

Here is the explanation quoted directly from the UC Davis website:

"From the time when livestock was first domesticated, modifications to the wild types have been selected both for animal husbandry and aesthetic reasons. Unique and large horns define cattle breeds such as Texas Longhorn, Highland Cattle, and Ankole Watusi. However, in modern times many cattle are maintained in more crowded conditions such as barns and small fenced pastures where polled phenotypes are more desirable for both beef and dairy breeds.

Recently, candidate mutations associated with polled phenotype in European breeds of cattle were found. There are 2 independent origins of polled, one found in Holstein-Friesian and Jersey breeds (Pf), the other in many European breeds of Celtic origin (Pc) such as Angus, Blonde d’Aquitaine, Dexter, Limousin, Charolais, and Hereford, among others. Investigation of the polled mutation in Brahman cattle revealed the segregation of the Celtic polled variant (Pc) in the breed. Polledness is dominant; a polled animal can have one or two copies of the polled alleles. All offspring of a homozygous polled bull (2 of the same polled allele, Pc/Pc or Pf/Pf) will be polled. Additionally, offspring with one copy of each of the polled alleles (Pc/Pf, compound heterozygous) will also be polled. Genetic testing is a cost-effective means to determine if a polled animal has 1 or 2 copies of the polled alleles.

Testing for the polled gene assists breeders in selecting cattle that have 2 copies of Polled gene."

This parallels with coloured fleece in sheep, so I at least found it interesting.

In goats, the polled gene is linked with intersex.

Here's a useful article - Polled Intersex Gene in Goats

In short, it seems that in goats that carry one polled gene, the animal will be polled. But if they carry two, then the animal will be sterile intersex.

When breeding polled to polled over time you can expect 50% fertile polled offspring, 25% fertile horned offspring, and 25% non-breeding animals. When breeding polled to horned, you get 50% polled, 50% horned, and 100% healthy fertile offspring.

And for those who want a few more details...

The Polled Intersex (PIS) locus has been the subject of considerable scientific study. Both the wild type and mutated sequences have been determined, and it is known that the polled trait is due to a large deletion in an area of goat chromosome 1q43. The mutation is homologous to one in a similar region in humans responsible for a condition called blepharophimosis-ptosis-epicanthus inversus syndrome. It is also now known that the mutations disrupt the transcription of at least 3 genes, including the FOXL2 gene, which encodes a transcription factor required for correct ovarian differentiation.

The polled trait in goats is an autosomal dominant trait in both sexes; in other words, one copy of the gene results in the polled phenotype. However, if a goat is homozygous for (having 2 copies of) the polled allele, the result is either a pseudohermaphrodite (in XX, or what would normally be female, goats) and generally a reduction in fertility in XY, or male goats. Homozygous males usually suffer from a condition called sperm granulomas at a young age, which will generally render them infertile. The absence of correct production of the protein encoded by FOXL2 makes it impossible for a female goat to properly develop a functional reproductive system, and results in various degrees of masculinization of the fetus during development. A goat that is homozygous for the PIS allele cannot produce transcripts from the FOXL2 gene, and cannot develop as a normal female.

And here's another article, less technical but with some rather graphic photos - Hermaphroditism and Polled Goats

Here's one of the less graphic photos, just for fun...


And a quote from the article...

The gene for a goat to be hornless, or polled, is actually dominant to the gene for having horns. Therefore, if a goat gets a gene for being polled from one parent, but a gene for horns from the other, the goat will be polled. However, that goat can pass on either gene, and if it and its mate both pass on the recessive horned gene, they can have horned kids. While hornless goats would seem ideal, they, unfortunately, come with a downside. Apparently, either directly connected to or very close to the same chromosome is a recessive gene that causes hermaphroditism. It is very interesting that this gene is (fortunately) recessive while the polled gene is dominant. However, if you breed two polled goats together, and they both pass on that polled gene with its tag-along intersex gene, that recessive gene will affect the kid₂. If the kid is male, they will appear unaffected physically. Often, the fertility of that male is affected, but there have been cases of homozygously polled male goats siring many kids. However, if the kid is genetically female, there is a high probability of that female being a hermaphrodite with masculine characteristics and sterile.