Raising livestock for a living means that they have to be productive. They must reproduce, be healthy, and not be labour-intensive. Nobody makes a profit raising sick animals.
The University of Guelph and Semex have been moving forward studying this from a genetic standpoint. This is exciting because with the increase in prevalence of Johne’s, producing healthy animals with a strong immune systems is a must. Johne’s disease is a contagious chronic progressive bacterial infection of the digestive tracts of cattle, sheep, goats, deer, bison, llamas and alpacas.
The infection occurs in the layer of cells of the digestive tract that are responsible for absorption. This area becomes thickened as the body’s immune system attempts to control the infection. The thickening prevents the digestive tract form absorbing nutrients, which creates a chronic diarrhea that does not respond to treatment and subsequently leads to a loss of body condition in spite of a normal appetite. There is no cure for Johne’s.
Animals that develop clinical signs will eventually die from the disease. Clinical signs usually do not develop before two years of age. However, the range is six months to 12 years with five years as the average. The long incubation period of this disease makes it a herd problem as well as an individual animal problem. Many animals can become infected before any in the herd show clinical signs. The primary way any herd becomes infected with Johne’s is through the purchase of infected animals.
When we started with small ruminants the major economic health concerns of producers were Caseous lymphaditis, Caprine arthritis ancephalitis virus (CAE) (goats), Maedi-Visna virus (MVV) (sheep). Johne’s, CAE and MVV all fall under the umbrella of small ruminant lentiviruses (SRLV).
Nancy Stonos, a PhD candidate from the University of Guelph, researched the prevalence of SRLVs in Ontario and the number of goats infected with both diseases. Research results showed the prevalence of SRLVs is 80 per cent and Johne’s-causing bacteria (Mycobacteria avium subsp. Paratuberculosis MAP) is 79 to 80 per cent. She found that 14.3 per cent of animals tested had both MAP and CAE infections and 71.4 per cent of farms tested had both diseases present in the herd. This was a single test so Stonos cautions producers that there could be false negatives.
The bacterium which results in Johne’s is resistant to most disinfectants, including bleach. Pouring formalin, cresylic and phenolic disinfectants on the area and letting them sit for more than 10 minutes is reported effective. It is resistant to most antibiotics, including those used to treat tuberculosis in humans. It does not survive well in very alkaline soils (high pH), dry conditions or when exposed to sunlight (UV radiation). Broadcast spreading of the dry compost manure is excellent for killing Johne’s.
Keep it clean
The best offence in this case is a good defence against these very hard-to-eradicate diseases. Stonos’s research shows that breeding for disease resistance is the way of the future. There are no pharmaceuticals that will stop these diseases. There are good farming practices that can keep livestock that is exposed to them healthy, though, and the most obvious is selective breeding for immunity.
Selective breeding programs for animals with enhanced immunity/disease resistance are being promoted in the cattle dairy industry already. Research is being done to test genes so that breeders will be able to select animals resistant to a specific disease, or select animals that have an improved immune system, or that may help combat many diseases at once. This is a long way off for small ruminant breeders so until then we can depend on the guidelines produced by the dairy cattle industry to show if an animal has a low, average or high immune response.
High immune response animals have the following traits in common:
- Decreased occurrence of mastitis, metritis, ketosis and retained placenta.
- Improved response to vaccine (this one is hard to gauge without blood work).
- Better hoof health (reduced digital dermatitis).
- Beneficial associations with herd life and some reproductive traits.
- Improved milk and colostrum quality.
It is very easy to understand why establishing a disease-resistant herd has to start with clean stock. The first step to this is to educate yourself before you purchase stock. When we started with livestock we booked a two-hour meeting with our local veterinarian. He could guide us and teach us because he knew what the dangers were. He could recommend vaccination programs and what testing he thought was necessary, etc. He also took the time to recommend textbooks for us to purchase and taught us how to do different procedures such as castrating.
It is also important to understand that most of these conditions can lay dormant for an animal’s entire life and never become active. The usual trigger is stress so once a healthy flock of females is in place only purchasing in new males is a way to reduce the risk of bringing home a problem.