Cattle breeding: Sunglasses for cooler cows

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For Simmental cows, dark circles around the eyes are likely to be a sign of health in the hotter countries. They provide protection from UV rays and eye cancer. Researchers in Munich have decoded the hereditary pattern of the bovine eyespots. The data will be of particular interest for breeders in sunnier countries. Source: Bayern-Genetik GmbH

23.01.2013  - 

The Simmental cow is an institution not only on the Bavarian pastures. Also in Africa and South America, the ‘Pied’ breed of cattle are prized for their milk yield and meat quality. In these countries, however, the intense sunlight can place a significant strain on the animals, as their characteristic white head fur offers no protection from UV rays. As a result, in sunny countries every second animal suffers from malignant tumours of the eye. Animals that carry brown spots around the eyes are much better protected. Animal geneticists in Munich have now deciphered the hereditary pattern of these brown circles. This is a prime example of the possibilities of modern livestock genetics. The results will be of particular interest for breeders in the southern countries. The BMBF is supporting the work of the research cluster ‘Synbreed’ with €1.8 million.

 The breed of cattle is synonymous with Bavarian pastures. Today, about 3.6 million of the ruminant animals can call Germany their home. The Simmental has long been an export success, thanks both to its good milk-providing abilities as well as its good quality meat.

Breeding specialists Bayern Genetik estimate that there are about 41 million of the animals around the world, and the breed of cattle is especially popular in Africa and South America. However, away from the frequently shady Alps, the cattle have frequently serious health issues. The Simmental typically has a white fur on its head, making the animals defenceless against UV rays in the sunnier regions. Very frequently, the result is eye cancer for the hapless cows. But there is a natural defence mechanism: A small proportion of Bavarian Simmental exhibit dark colours around the eyes and on the eyelids. The dark eyespots function not unlike sunglasses and protect the animals from eye tumours. 

Numerous genes involved in the hereditary pattern

A team of livestock geneticists headed by Ruedi Fries and Hubert Pausch of the Technical University of Munich are now shedding some light on the hereditary pattern of this brown eye patch. The pigmentation pattern, i.e. the colour and size of the protective eye circles, is determined by many, perhaps even several thousand segments of DNA. As they report in the journal PLOS One (2012, online), the geneticists have successfully identified twelve DNA segments in the hereditary pattern of the dark circles, which account for up to 57 percent of the heritability. “Even at birth, it is easier than before to forecast whether the descendents of a calf are more likely to carry the protective eye circles,” says Fries. This knowledge will definitely be of assistance for breeders in sunnier countries: For years is has been standard practice to create a ‘genetic fingerprint’ for breeding bulls. These can now be examined for the hereditary pattern of the protective eye circles, thus delivering stronger foundations for the selection of suitable breeding animals than was previously available.

Fries is sure that “This approach can quickly reduce the number of cases of ocular tumours in the animals”.

Scouring the genetic fingerprints of bulls

To decrypt the inheritance pattern of the eyes, the researchers combined statistical prediction models with the latest methods in DNA analysis. To do this, they must first create ‘genetic fingerprints’ for the individual bulls. For each animal, this means the detection of several hundred thousand of tiny variations in the DNA strand, giving an aggregated and unique profile. Scientists have collected such fingerprints from around 3,400 bulls. Using statistical methods the scientists then link DNA profiles with information about the appearance of the offspring of the breeding bulls, in this case the eye patch. Combining these two values provides a probability for the inheritance of the dark spots. The approach used by Ruedi Fries and Hubert Pausch, i.e. ‘genomic selection’, is suitable not only for the selection of suitable bulls; it is also used for yield increases in corn- or chicken breeding. The animal scientists Fries and Pausch are thus working closely together with plant scientists and bioinformaticians in the research Cluster ‘Synbreed’. Their common objective is to make breeding successes more predictable. Synbreed is being funded by the Federal Ministry of Education and Research (BMBF) as part of the initiative ‘Competence Networks in Agricultural and Nutrition Research’.

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