“We are one ‘60
Minutes’ report away from rules against either leukosis or Johne’s.”
– MARK VARNER
A recently introduced technology to predetermine the sex of dairy cattle could also be the key to eliminating infectious diseases in dairy herds.
Sexed semen, in which sperm is sorted for gender, can help milk producers develop herds free of bovine leukosis and Johne’s disease, according to an American dairy specialist.
Sexed semen increases the incidence of heifers born to dairy cows. Having more heifers allows producers to cull infected cows more vigorously, said Mark Varner, a University of Maryland dairy scientist.
“Having more heifers coming into the herd allows you to then cull more for either of those diseases,” he said after speaking to the recent Manitoba Dairy Conference.
Varner said eliminating leukosis and Johne’s is important because of recently suggested links with human disease. He warned activists could seize on that as an opportunity to demand a crackdown on dairy cattle.
Leukosis is an infectious disease of cattle caused by the bovine leukemia virus. Johne’s is a chronic and sometimes debilitating disease affecting the intestines of ruminant animals. There is no treatment to prevent either one.
The Canadian Food Inspection Agency says there is no human health risk associated with bovine leukemia virus. However, some U. S. research suggests a possible connection between Johne’s and Crohn’s disease in humans, although definitive proof is lacking.
But that should still be enough to worry milk producers about unreasonable restrictions on their industry, said Varner.
“Not everyone in the scientific community believes that the links are true and are fully established yet. But there are people in animal rights groups who believe that no animal should be eaten and no animal products should be consumed. They will tell half truths to try to decrease consumption of animals and animal products. Because of that, they’ll use and exaggerate those facts,” he said.
“We are one ‘60 Minutes’ report away from rules against either leukosis or Johne’s.”
Sexed semen also gives producers an opportunity to cull for other diseases, such as mastitis, Varner added.
It could take up to 10 years to develop disease-free herds using sexed semen. So producers wanting to do that should start now, he said.
Sexed semen (also called sex-sorted or gender-enhanced semen) makes it possible to increase the rate of female calves born each year by screening for the X (female) chromosome.
The technology, developed in the late 1980s, has improved steadily since then. It can increase the chance of getting a heifer calf from about 50 per cent to as high as 90 per cent.
This can provide financial benefits to producers who are trying to expand their herds, who want to maintain closed herds or who have high-value animals, said Varner.
“If you can find a way to cull some extra heifers or you have a need on your farms for extra heifers to control disease or to help build the size of your farm, then it’ll work for you,” he said.
But in his presentation to producers at the conference, Varner also pointed out some drawbacks of sexed semen: it’s more expensive than conventional semen, conception rates are lower (because there are fewer sperm in a single dose) and it’s not 100 per cent foolproof in producing heifer calves.
For that reason, producers shouldn’t try sexed semen if their AI conception rate on heifers isn’t higher than 75 per cent, said Varner.
And if it’s lower than that, producers should work with veterinarians and AI technicians to get conception rates up before even considering sexed semen, he said. [email protected]