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Breeding with Simmental Polled Cattle

The topic of polled/horned cattle has become increasingly topical in the seed stock industry in recent years, and even more so when the new legislation came into effect in October, mandating the use of local anaesthetic for the dehorning and debudding of any animals in New Zealand.

The reasons for wanting to eliminate horns from a beef herd, be it through breeding or via removal, are aplenty. The long and short of it is that breeding for polled cattle is a no brainer, and something the Simmental breed already is working towards.

Though it’s certainly the way forward, breeding for polled cattle is, however, a complex process requiring a dedicated effort – and can’t be achieved simply through the use of visually polled bulls and cows.

Polledness is a qualitative trait and therefore controlled entirely by genes.

In this article, we explore each of these points in more detail – looking at why the Simmental breed should be and is moving in this direction, how genetics dictate the presence or absence of horns, and what tools are available to help breeders transition to a polled breeding program as quickly as possible.

Why Polled Cattle?
The rationale is simple – the practice of dehorning cattle, usually as calves, is carried out to reduce the risk of injury to each other and to stock handlers. It does, however, come at a labour and monetary cost to ensure appropriate animal welfare standards. In a nutshell, it’s a job farmers would typically prefer to do without, hence the growing increase in demand for polled cattle we are seeing nowadays.

Governed by Genetics
Why isn’t a polled breeding program as simple as introducing a visually polled bull into a herd of polled cattle? The answer lies in the question of whether those animals are homozygous polled or heterozygous polled.

With Simmental, like most other cattle breeds, the polled/horned gene is simple recessive – the poll allele (P) is dominant to the horn allele (p). To keep the biology lesson as simple as possible, every parent has a pair of alleles at each gene and they pass on one of these alleles for each gene to their offspring. So, a calf will get one allele (P or p) from the Bull and one allele (P or p) from the cow. If it gets two polled alleles it would be classed as homozygous polled; if it gets one polled and one horn allele it would be classed as heterozygous polled; if it gets two horned alleles it would be classed as homozygous horned, and would present as a horned animal.

In a hypothetical situation, if a Bull and a cow are both visually polled but heterozygous for the gene (Pp) – there is a 50% chance the resulting offspring will be horned (pp).

Similarly, in a hypothetical situation looking at the herd level, if a heterozygous polled bull (Pp) is mated to a herd of heterozygous polled cows (Pp), you could expect that on average, 25% of the calves would be homozygous polled (PP), 50% will be heterozygous polled (Pp) and 25% homozygous horned (pp). So, even though the bull and all cows were phenotypically polled, the mating results in 25% of the offspring being horned.

From this we can infer that a manual process of breeding out the horned gene is a process governed, to some extent, by the law of probability, and very lengthy one at that.

DNA Testing to FastTrack the Process
There are a range of methods a breeder can adopt to increase the number of polled animals in their herd, though the method chosen will significantly impact the time taken and cost incurred to achieve the result.

As illustrated in the examples above, the manual process of breeding out the horned gene is a process governed, to some extent, by the law od probability, and a very lengthy one at that.

A number of DNA tests are now available, which enable breeders to determine whether a polled animal is homozygous or heterozygous polled. Armed with this information, breeders can use ensure they are using homozygous polled Sires which will significantly reduce the time taken to convert their entire herd.

Ask a progressive breeder about buying DNA tested polled Simmental bulls, or contact the Association for more information on the topic of breeding for polled cattle.