The Milk Producer - August 2009 - (Page 37)

RUMINATIONS By Ann Godkin Balancing act Culling highly infected cows has a big role to play along with other key factors to combat Johne’s disease W hen it comes to Johne’s disease control programs, culling tends to stir up the most discussion. No one wants to dispose of cows that still have years of valuable production ahead of them—even if they are infected. On the other hand, no one wants to keep cows with declining milk production that are actively infecting young replacements. Culling high-risk cows to prevent the disease’s spread is one of three main elements in the on-farm portion of the Ontario dairy industry’s recently proposed Johne’s program. The other two elements are a veterinarian’s on-farm risk assessment and cow testing to classify herds as negative, or low-, medium- or high-prevalence for Johne’s infection. Johne’s programs used around the world initially varied widely, but have become similar during the last 10 to 15 years due to experience and research. These programs always include some form of culling. The Ontario program’s design freely takes advantage of this experience. In the early 1990s, the first Johne’s programs focussed on testing. Once producers and their vets received herd test results, test-positive animals were frequently culled. Often little else was done. Over time it became clear a test-and-cull prevention program, which had been used success- fully against other contagious diseases like Brucellosis in Canada, won’t work for Johne’s. Test-and-cull only doesn’t work Infected cows could not be identified soon enough or accurately enough to remove them in time to stop them from infecting young cattle. By the time mature infected cows were discovered and removed, infection had started all over again in the young stock. The infection and disease cycle continued in the herd. Today’s Johne’s knowledge shows cattle are most likely to be infected well before they are one year old. However, infected animals don’t shed or pass on infection until they are more than four years old on average. As they age, they shed more and more bacteria. Cattle that actually get sick with Johne’s do so years after infection and months to years after they start shedding the bacteria. This time lag means paying closer attention to finding the optimum time for each herd owner to remove cows for effective Johne’s prevention. Culling cows for Johne’s can be an expensive proposition if done too early or too late. The objective is to pick the right time to remove animals to achieve the best results for both disease control and economic benefit. Calf management that animals Calf management that protects young animals from infection allows culling in a more orderly traditional manner. culling allows Ruminations is prepared by Ontario Ministry of Agriculture, Food and Rural Affairs livestock technology specialists to provide information you can use on your farm. MilkPRODUCER | August 2009 | 37

Table of Contents for the Digital Edition of The Milk Producer - August 2009

The Milk Producer - August 2009
Contents
Editor's Notes
DFO Chair's Message
Dairy Update
Industry Roundup
DFC Promotion
Our Readers Have Spoken
Issues Update
Research
Applied Science
Ruminations
Markets
New 'n' Noted
Back Forty

The Milk Producer - August 2009