In search of cows that fight off mastitis better than others
Wednesday, August 10, 2011
Scientists are using molecular research to find animals that show a superior immune response to disease challenges – and perhaps in the long-term to reduce the need for antibiotics
by DON STONEMAN
Mastitis control isn't just about udder management. Some cows simply fight off disease better than others.
Now, using molecular research, veterinarians and animals scientists are trying to develop screens to find the animals that mount a superior immune response to disease challenges.
The near-term goal is to reduce the incidence of mastitis. A single case costs a Canadian dairy producer between $110 and $320, according to a paper presented by Prof. Bonnie Mallard of the Ontario Veterinary College at the National Mastitis Council annual meeting in Arlington, Va., last January.
The longer-term goal is to reduce the need for antibiotics in general. The emergence of antibiotic-resistant pathogens is of increasing concern to producers as well as consumers, Mallard noted.
But, says Ken Leslie, a professor at the Ontario Veterinary College, practical applications for the dairy farm using molecular research are likely to be years away. Leslie says that, for now, vets are still focused on reducing genetic predisposition to mastitis by emphasizing genetic merit for somatic cell score, one of the traits accounted for when the Canadian Estimated Breeding Value (EBV) of sires is published. (see Table 1).
The somatic cell score doesn't get the attention it should, a prominent American dairy scientist asserts.
In a report presented at the 2007 National Mastitis Council conference, George Shook, professor emeritus, dairy science department, University of Madison-Wisconsin, noted that bull stud operators and breeders face a dilemma when they choose a bull. He cited the example of the U.S. bull Tres and the Canadian bull Goldwyn. Both produce daughters with a low predilection to mastitis and a tendency to produce high-quality milk.
However, breeders using these bulls are giving up 28 pounds and 16 kilograms of protein production per daughter per lactation, respectively, compared to higher-producing bulls like the American bull Jet Stream or the Canadian bull Lomax, whose daughters, statistically, are much more likely to get mastitis.
Shook asserts that operators of herds with excellent mastitis control might choose the latter bulls, while those with a poor milk quality track record may not be able to afford to or they will face milk quality penalties.
Mallard says the patented High Immune Response Technology test she has developed at Guelph will improve on this. The test was used on 690 cows from 58 herds across Canada to measure their response to a variety of diseases. About 15 per cent of cows were high responders, 15 per cent were low, and 70 per cent were average immune responders.
Her January paper cited other studies which have shown that high immune response cows have the lowest disease occurrence. Mallard's paper says: "Results to date have shown that breeding for optimal high immune response based on both antibody and cell-mediated immune responses would not compromise production."
David E. Kerr, associate professor of animal science at the University of Vermont, favours another genetic testing system (also still under development) to test fibroblasts, individual cells in connective tissue that secrete proteins. Fibroblasts might be tested in vitro (before birth) or when heifers are at a young age to select herd replacements. BF
(With files from Susan Mann)
