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Leukosis: The disregarded, yet devastating disease

The prevalence of leukosis within the Holstein breed in Canada is beyond what anyone would expect. It has been found that 12-15% of all Holstein animals in Canada are tested seropositive.  It is a disease within a group of ‘production limiting diseases” – a sickness caused by a pathogen that is both untreatable and life-long.  In Canada, there are only 26 out of 12,746 milking dairy herds that are certified leucosis free.

We’ve brought together a panel of respected industry members, all with very different roles within the Holstein industry, but consistently affected by the presence of this disease within their jobs.  Hear what each has to say about not only the disease itself, but what it will take to make Canada more leukosis-free, both on a certification level and just in having increased farm awareness.

Dr. Gordon Atkins (Sr. Instructor of Veterinary Medicine, University of Calgary)

Rick McRonald (Executive Director, Canadian Livestock Genetics Association)

Brian and Erik Leach (Brilea Holsteins, CHAH Certified, Master Breeder Herd)


What percentage of leukosis positive animals will develop symptoms?

GA: There is very little actual data available on this, what we do know is that the percentage of animals that develop symptoms depends on the age of the population at risk, as well as the definition of ‘symptoms’. We know that a greater percentage of older positive animals develop clinical lymphosarcoma when compared to younger positive animals.  However, it has been recognized recently that many positive animals (even young animals) that are clinically normal have significantly elevated lymphocyte counts in the peripheral blood and this should be considered as a definitive symptom even though it is rarely counted.

 

At what age is an animal most prone to show symptoms?

GA: We rarely see animals less than 3 years of age with full blown lymposarcoma. My clinical impression is that animals greater than 5 years of age have a greater likelihood of developing lymphosarcoma.

 

What effect of leukosis do you notice on the Holstein industry?

GA: The impact of leucosis on the Holstein industry is far greater in the elite purebred industry where producers are selling cattle for export and selling bulls to AI centers.  In the commercial Holstein industry, I feel that producers need to be much more concerned since the prevalence of positive animals has increased greatly over the past 10 years and the negative impact of this disease is like far greater than appears on the surface.

 

RM: I don’t believe that the impact of EBL on the dairy industry has been fully appreciated.  I look at it from the standpoint of exports of live animals and (to a lesser extent) embryos and semen.  It isn’t just loss of- or limited – market access; it is that Canada is falling behind some of our competitors.  We can do better.  The US and Mexico have the same status and attitude as we do so (along with Libya, Mongolia and Panama) they have no requirement at all for EBL when importing live animals.  That is a total of 5 countries out of 39 countries where we have live cattle access (counting the 27 EU members as one).  The EU 27 and Macedonia require CHAH and all the others require at least one test of the animals to be exported.  This is usually a compromise after being asked to supply animals from a negative herd or at least from a herd that meets the OIE recommendation. The available tests are not as accurate as we would like and if any animals are positive when retested at destination, it will give Canada a black eye. 

In these post-BSE years, we are seeing an increase in market diversity for live cattle.  This is a very good thing BUT in order to capitalize on it, we will need to pay more attention to diseases including EBL.  We can’t keep shipping the negative animals and do nothing to stop the spread of the disease inside Canada.

On the semen side of things, if the EBL status of the uterine dam is not negative, the EU will not import semen until the bull has tested negative after reaching 2 years of age.  That might not have mattered much before the genomic revolution, but, it does now.

 

BEL: In order to export out of the country and into the EU the animals must beleukosis free. The presence of leucosis in the Canadian herd limits themarketing potential of Canadian Holsteins.

 

 

What big changes would there need to be to have more CHAH certified herds?

GA: Producers with CHAH herds need to be rewarded for the effort they make to keep their herds leucosis free.  At the present time the market advantage of a leucosis free herd does not compensate producers for the effort and cost to remain leucosis free.

 

RM: The CHAH program is REALLY out-of-date and CLGA has been involved with other industry partners in efforts to modernize it for a number of years.  We believe that using DHI milk samples for EBL testing will be a critical element if the CHAH program is going to survive and grow.  There are other program elements that need to change but, we need to keep in mind that whatever we do, the program has to have the scientific integrity for CFIA to support and “sell” it to the EU as equivalent to their EBL-Free herd program.

 

BEL: From a CHAH producer standpoint, it would require CFIA to approve milk tests preformed by DHI to qualify herds. This would make it much easier for herds to be able to test, so more herds would be likely to take part.

 

In your opinion, why are so few herds certified leukosis free?

GA: The disease is a sleeping giant that is not often recognized clinically since so many cows leave dairy herds at such a young age.   Therefore there are not adequate signs to raise the awareness for producers and there is not a significant financial benefit for the effort and expense to maintain a leucosis free herd.

 

RM: The current CHAH program is too difficult and too expensive.  Right now, only the EU and Macedonia REQUIRE animals to come from an officially EBL-free herd.  The EU alone is 27 countries that would probably buy some fairly high value animals but, if a producer doesn’t have the genetics they want, he may not see the return on his investment in CHAH.  The number of herds on the program dropped dramatically during the BSE ban on exports to the EU and during that time, the market changed.  When it re-opened, too much energy was wasted on trying to get around the rules instead of complying with them.

 

BEL: As a closed herd it is difficult to add animals into the herd with the CHAH status. As a manager and milk producer you can’t just add animals to the herd when you need it. Instead, extra consideration must be made in order to bring new animals into the herd. It is difficult to find non-Leucosis animals. It forces breeders to manage livestock inventory differently. The cows that don’t breed or don’t

 give as much milk are kept in the herd longer because they can’t be replaced

 as easily. We have used embryo transfer as a way to qualify animals immediately but there is a two year wait to have them putting milk in the tank. We also run a herd bull as clean up to make sure that we have enough livestock. It takes more management. On top of that, CHAH certification also incurs a yearly cost in testing.

 

 

What will it take to have a more concerted approach to be leukosis free in each herd? And nationally?

GA: It will take either a marketing crisis such as elevated consumer fear of human health risk from consuming milk from positive cows or a significant marketing and financial benefit for producers that maintain a leucosis free herd.  We need an extensive research project to accurately identify the prevalence and the subclinical costs as well as a reasonable and properly communicated and funded national control program.

 

RM: We need to realize that there are 2 issues:  one of them is  a herd that is certified by CFIA as free of EBL (CHAH) and the other one is the reduction of the overall incidence of EBL in our dairy cattle population.  CHAH will not be for everyone but, I do hope that producers will address EBL – either on its own or as part of an overall biosecurity program whereby the individual producer monitors the status of his herd and can demonstrate to buyers that it is free from EBL and/or Neospora and/or Q fever and/or whatever.  There are new, emerging or re-emerging diseases coming at us with greater frequency and the scientists tell us that it’s going to get more complicated as time goes by.  Some of those diseases will be zoonotic and most of them have the potential for negative impacts on trade.  Furthermore, the world has changed and we have to be able to PROVE our disease status to trading partners.  I think that Canadian producers will use the same “smarts” with which they created the world’s most profitable cow to address disease issues – through tools like genomics and the implementation of on-farm biosecurity programs that ensure healthy food from healthy animals and provide the basis for profitable trade in live animals, semen and embryos.

 

How does the presence of leukosis in Canada impact domestic and international sales?

RM: It probably has very little impact on domestic sales right now.  For too long, many in Canada didn’t take EBL seriously and they scoffed at the EU and other countries for their control/eradication programs.  However, the fact that a growing number of breeders are testing for EBL (via DHI) is an indication that some are now taking it seriously and may require that animals which they purchase be negative.  The coming implementation of the national dairy biosecurity standard will (I hope) provide further impetus for producers to address disease in general – including EBL.  It will need to be packaged along with CQM or another program to reduce the burden on producers.  If a producer is on a Johne’s program, he is already doing most of what he needs to do to control EBL.

For comments on international sales, see my response to question #1.

 

And finally the most important question of all – what are some preventative measures to avoid the spreading of leukosis?

GA:1. Feeding young calves colostrum from leucosis negative cows

2.       Using single use individual needles for all injections including vaccinations

3.       Proper sanitation of tagging, dehorning, and tattooing equipment

4.       Avoiding palpation of leucosis negative cows with the same glove used for leucosis positive cows

It is consistent that something needs to change in leukosis prevention practices.  If the industry continues on this path, the rate of leucosis among Holsteins will surely rise. The apparent costs of becoming a CHAH-status herd are discouraging what should be the real priority: to have a clear herd health strategy to reduce and limit leukosis spreading in herds. Clinical leukosis affects all types of dairy the same, from big-time show cows, to high genomic champions, to just good milking cows that fill the tank. Have the talk with your veterinarian about biosecurity and best management practices to control these ‘production limiting diseases’ like leukosis. When it comes to higher profitability from production and good herd health among the animals, it becomes a real win:win situation.

By: Lorene Vanderwal, BC


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