Fri, 02 Feb 2018
DENMARK - Within Danish cattle breeding, the semen of one breeding bull is used to inseminate a lot of cows. Due to the multiple inseminations, one bull can thus sire thousands of calves. It is, therefore, vital to determine whether breeding bulls carry hereditary diseases.
This is exactly what researchers at the University of Copenhagen have done. In a study among Holstein calves published in the scientific journal BMC Genetics, they have discovered a hitherto undescribed disease among animals - a facial deformation they have chosen to call Facial Dysplasia Syndrome.
The researchers have discovered the genetic mutation that is the cause of the disease among calves and traced it back to one particular breeding bull. The bull has now been put down to prevent further cases of the disease among new-born calves.
"We discovered that one breeding bull had developed a mutation in the cells of the semen-producing tissue, which led to the deformation among the calves. The bull passed the mutation on to 0.5 per cent of its offspring, which does not sound like much. But this bull had already fathered more than 2,000 calves and could potentially have come to father even more.
"All the deformed calves died or had to be destroyed because they were suffering. Therefore, it was important to discover the cause," said Professor Jørgen Agerholm from the Department of Veterinary Clinical Sciences.
After having received information from veterinarians of calves with facial deformations, Professor Agerholm went looking for more cases in his network of cattle veterinarians, including on Facebook. He then received more calves for examination.
DNA from the deformed calves was subjected to genetic studies, and here the researchers identified the overall part of the genome which contained a mutation not found in normal Holstein DNA. This was possible due to thorough previous mappings of normal Holstein DNA.
The researchers then learned that similar facial deformations are found among humans, and these are caused by mutations in the same part of the genome, more specifically the FGFR2 gene among new-born babies. This gene was sequenced in the calves' genome, and the researchers were then able to determine that a mutation in this gene had caused the disease among the calves. The human disease thus helped the researchers in the process of identifying the gene mutation.
The researchers also examined DNA from the calves' parents and siblings and learned that the mutation also dominated here. This means that the calves developed the deformation when the mutation was passed on from either parent and not from both the parents, which is the case with many hereditary diseases.
"Our aim was always to lower the number of sick and dead calves, as some hereditary diseases are very painful and invalidating. In this case the eyes hung down from the heads of the calves, and the facial deformations caused them to have severe breathing problems. It is not difficult to imagine the pain this caused.
"Research results like these will heighten the animal welfare by limiting the spread of such diseases. And of course it also improves the financial situation of the cattle owners, who are able to minimise losses," explained Jørgen Agerholm, who is also Head of the Section for Veterinary Reproduction and Obstetrics.