Blog post by Esme Cormack of CXCS
Growing up, I was taught that dehorning calves was a safety precaution, not only for me and my family, but for the animals themselves. I remember the various ways my father and our vet would carry out the procedure, and grew to love the smell of disbudding. However, following the rumours that in my lifetime farmers will be banned from dehorning cattle, there has been a surge in breeding polled cattle.
In June of this year, I had the honour to join my Mum, the judge for the East Midlands Limousin Society herd competition, where I had my eyes opened to the difficulty breeding polled cattle brings to breeders. Within the Limousin breed, shape, confirmation, and size are some of the main qualities the breed prides itself on. However, not only do the breeders face difficulties keeping the breed’s standards, but they also have the Russian roulette of genetics.
One farmer we met on our journey had been breeding polled Limousins for over 40 years. Importing genetics from France (who offer a much larger range of polled animals), he said that he struggled with the lack of shape his polled bulls had to offer. This meant that although he had polled offspring, he was failing to meet high profit turnovers as they didn’t carry the desired qualities Limousin breeders search for. I was also baffled when I learnt that although he had been ‘experimenting’ with polled genetics for 40 years, only 25% of his 125-cow herd were homozygous polled.
Polling happens with the two genes – heterozygous and homozygous. The genetic mutation is very low – for every 20,000 calving cows put to a horned bull only one will be born polled. This means that natural polling is a very slow process. This has led to crossing in genetics from cattle that normally do not have horns such as Aberdeen Angus.
The presence or absence of horns is controlled by a major gene and there are two forms of the gene that control horn development. Each animal has two copies of the gene which are inherited from their parents. Offspring receive one copy from their sire and one from their dam. The two forms of the gene are:
P – This form causes polling, and the capitalisation of the letter indicates it is dominant over the other form
p – This form causes horns, and the lower-case styling indicates that it is recessive to the other form.
When the two copies (one from the dam and one from the sire) are combined in the offspring, we refer to the resulting combination as the genotype of the progeny. The physical appearance of the animal that can be observed is called the phenotype.
If a bull with two copies of the dominant polling gene (P) is bred with a horned cow with two copies of the recessive form of the gene (p) for horns, their offspring would all have the genotype Pp. The calves would all appear polled (though some may display scurs), but they would still have the potential to produce up to 50% polled offspring if they were mated with a horned animal because they are carriers for the p gene for horns.
Within the resultant offspring, 75% of the calves will be polled and 25% will have horns. Only 25% however will have two copies of the dominant polling gene (P) and therefore “breed true” producing only polled offspring. The half of the progeny that carry one copy of each gene (Pp) will still have the potential to produce both polled and horned offspring, and this is why it is difficult to eradicate horns altogether. Interestingly, 25% of the calves from these two polled animals will have horns as they receive a copy of the recessive form of the gene from each parent.
Dr Chad Dechow, an Associate Professor of Dairy Genetics at Pennsylvania State University, said the industry perception regarding polled genetics has generally been that selecting for the polled trait will cause other performance factors to suffer. “Both registered and commercial breeders generally do not seem to be opposed to polled genetics, but they will not breed for them if they perceive they will be chosen at the expense of other traits like reproduction and milk production,” he shared.
Within a single breed, Dechow said a herd could achieve 75-80% polled offspring over the course of 5-6 generations (10-15 years) by using mostly heterozygous polled sires. That rate could be increased rapidly via gene editing, although that technology has not yet been approved for commercial application. Dechow also noted that the same class of consumers concerned about dehorning would also likely be resistant to gene editing.
“If there are enough polled bulls in a single breed from which to choose, the trait would grow rather quickly, with little impact on long-term genetic merit,” said Dechow. “However, there is an initial investment in intentionally focusing on polled genetics.”
And, in the absence of an organised effort to advance polled genetics, it could happen organically if an outstanding sire emerges who just happens to be polled. “One really high-indexing polled bull could change the picture fairly quickly,” said Dechow.
This issue has also led to an increase in sales of naturally polled breeds such as Aberdeen Angus. The Angus are one of the very few breeds to be guaranteed to be homozygous and not lose their shape or milk production. There has also been a rise in polled Herefords, but as there aren’t many other breeds which are polled, this limits the selection that breeders can choose from if they want to go down this route.
So, with the rise of polling genetics in the UK, will farmers be more likely to gamble on the outcome and risk the losses in other areas, or will they continue to use current de-horning methods and hope these rumours aren’t true?
