Disease is present in every flock and can reside in the animals, soil, air, and water. Producers don’t often talk about illnesses affecting their sheep because they don’t want the stigma of disease to reflect negatively on their flock. But producers shouldn’t have to deal with the problem alone. Let’s accept the fact that disease is inevitable, remove the stigma, and learn how we can prevent or mitigate disease transmission in our flocks.

Disease is defined as “a condition of the living animal that impairs normal functioning and is typically manifested by distinguishing signs and symptoms.” Unfortunately, sheep can’t tell us how they feel or what symptoms they’re experiencing so it often becomes a guessing game for both producers and their veterinarians. Since healthy sheep are resistant to many of the pathogens already present on their own farm, they often don’t get clinically ill unless they are under stress. Previous exposure to these pathogens prepares the immune system to attack the disease in a timely manner.

Newly purchased animals can be ‘asymptomatic carriers’ of a disease your sheep have never been exposed to. This is why quarantining new animals is so important. Young lambs (and adults without previous exposure) are therefore more susceptible to novel diseases. In addition, stressors such as transportation, feed changes, weather events, weaning or lactation can weaken the immune system and increase susceptibility to infection.

Climate change is impacting the occurrence and prevalence of infectious disease. Like humans, livestock are now being exposed to novel diseases or new strains of a common virus or bacteria. Diseases in sheep that were once limited to specific regions of the country or even to another continent are now spread more easily through the shipping of goods, the transporting of animals to and from sales and exhibitions, and by changes in global wind patterns. There is also an increased prevalence in cross-transmission of zoonotic diseases among different species of livestock. Vector-borne diseases, spread by mosquitos, midges, ticks and fleas, are also on the rise due to the migration of disease-carrying insects to a more hospitable environment. Changes in farming practice, land use and extreme weather patterns have also created new microenvironments that destroy beneficial plants and animals and allow harmful organisms to flourish, including disease-causing fungi and molds.

The Disease Triangle above illustrates how the transmission of disease is dependent on the interaction between a virulent pathogen, a susceptible host and a favorable physical, chemical or biological environment. Interruption or manipulation of any part can significantly reduce further development and transmission of disease.

Since diseases can spread rapidly, implementing good biosecurity practices, protecting susceptible animals or just altering the environment can help to mitigate the spread of infections. Some management practices that can help reduce disease transmission include:

1. Inspect and quarantine new animals for at least 30 days before comingling.
2. Isolate and treat animals with obvious signs of disease: limping, nasal discharge, fever, cough, scours, abscesses, or skin/oral lesions.
3. Test new animals for communicable disease such as Ovine Progressive Pneumonia (OPP), Caseous Lymphadenitis (CL) or Johne’s disease.
4. Restrict access to wet pastures, stagnant water, moldy feed/hay. Avoid grazing sheep on pastures with high levels of parasite larvae. Lung worm and meningeal worm are more common in wet or wooded areas frequented by deer.
5. Vaccinate against Clostridial diseases and Tetanus. Consider vaccinating against abortion diseases (Chlamydia, Vibriosis), bacterial pneumonia (Pasteurella/Mannheimia) and/or sore mouth (Contagious Ecthyma).
6. Reduce stress during pregnancy, lactation, weaning and transport.
7. Provide good nutrition, good minerals and a clean, fresh water source
8. Improve soil and forage health. Manage or eliminate poisonous plants/weeds.

The majority of infectious diseases are introduced by newly purchased animals and are then spread throughout the flock because the animal was not adequately quarantined. It is important to note that 75% of diseases are also transmissible to humans. Wear gloves when handling sick animals, disinfect equipment and properly dispose of any contaminated instruments, needles, syringes and bandages. Not all diseases can be avoided, but reducing the likelihood of transmission, protecting susceptible animals and improving environmental conditions can significantly reduce risk.

By: Roxanne Newton, Hound River Farm

EAPK Communications Committee