Technical resources; and
Availability of effective vaccines and treatments.
Diseases gain entry into and spread within flocks by various routes. Most commonly, they are brought in by the introduction of new animals or by animal contact at points of concentration such as shows, sales, fairs, and sale barns. Disease can also be spread by vectors that include visitors, equipment, feed, and insects. Good hygiene and biosecurity measures are important methods of preventing the spread of disease into and within a flock. Although there are costs associated with biosecurity measures, they have the potential to halt the entry of pathogens that may result in disease. As stated previously, the costs associated with disease are both direct (treatment and mortality losses) and indirect (production losses) and usually are higher than the expense of prevention.
Biosecurity refers to measures taken to keep diseases out of populations, herds, or groups of animals or to limit the spread of diseases. Successful biosecurity measures must address isolation of new animals brought to the farm; isolation of sick animals; regulation of the movement of people, animals, and equipment; correct use of feed; and procedures for cleaning and disinfecting facilities. The responsibility for a successful biosecurity program falls on the owner (European Community, 2007). The American Sheep Industry Association (ASI) has a fact sheet on biosecurity that provides useful advice.1
The 2001 National Animal Health Monitoring System (NAHMS) study (USDA, 2002) found that more than one-half of the sheep operations with 100 or more head added replacements from the outside in 2000. This was also true for approximately 25 percent of operations with 1–24 sheep and close to 40 percent of the operations with 25–99 head. Approximately 80 percent of all operations added sheep in the last 9 years (USDA, 2003a).
New replacements from other flocks pose a risk of introducing a disease into an existing flock. Certain precautions may be taken to minimize this risk. Effective prevention measures may include obtaining a complete history of the flock of origin, testing for certain diseases prior to and after movement, isolation and quarantine on the new farm, vaccination, treatments such as medicated foot baths, and deworming. When introducing/ purchasing animals from another farm a good practice is to investigate the health status of the flock of origin. This inquiry should include a discussion