Biosecurity on sheep farms

Biosecurity refers to the management practices taken to prevent the introduction and spread of diseases.  Healthy animals are the cornerstone of a successful sheep enterprise, regardless of the reasons for sheep ownership.

These days, there is a heightened awareness of biosecurity due to the risks of bioterrorism and the fear of introducing foreign diseases such as foot-and-mouth disease to the United States.  Individual states are also interested in keeping diseases from within their borders.  Biosecurity is important no matter what size flock or farm you have. It only takes one sheep to introduce a new disease and one farm to start a disease epidemic.

Purchasing sheep from sale barns increases the risk of introducing new diseases to your farm and flock.

Acquisition of new sheep
Introduced sheep pose the greatest risk of disease introduction. While they may appear healthy, they could be carrying a wide variety of diseases. Anytime a new animal is introduced to the flock, there is a potential risk of that animal introducing a new disease.

Before adding new sheep to your farm/flock, it is important to know the health status of the flock(s) from which you are buying or receiving animals. Don't be afraid to ask questions about the farm's health program and disease status of the flock. Only buy sheep from reputable breeders. Ideally, you should purchase sheep from a closed flock. A closed flock is a flock that has not introduced new animals for the past three or more years. It is best to buy sheep from as few sources as possible. It is not recommended that breeding stock be purchased from a sale barn (stockyard, public livestock auction).

You should not purchase animals from flocks or farms in which you observe lameness, abscesses, soremouth, or other clinical signs of disease. While healthy-appearing animals may still be harboring these disease organisms, many diseases can be avoided by thoroughly observing and inspecting the animals you purchase.

When purchasing mature ewes, be sure to palpate their udders to make sure they don't have any lumps, scar tissue, or hard spots, which could be indicative of mastitis. If both halves of the udder are "hard," the likely cause is ovine progressive pneumonia (OPP). Examine their teeth to determine their age and soundness. Palpate the testicles of rams. Do not purchase rams with reproductive abnormalities or structural defects.

To prevent the introduction of OPP to your flock, try to purchase animals from OPP-free flocks. Unfortunately, there aren't many flocks that have tested and culled for OPP -- despite a study showing that 26 percent of sheep in the U.S. are infected with the OPP virus. Cross transmission is possible between OPP and CAE (caprine arthritic encephalitis) so make sure if there are goats on the farm that the goat herd is CAE-free.

To prevent the introduction of scrapie to your flock, try to purchase animals from USDA certified scrapie-free flocks or enrolled flocks. The purchase of sheep with scrapie-resistant genotypes (RR or QR) will also help to prevent scrapie from occurring on your farm. While the prevalence of scrapie in the U.S. sheep flock is only 1 in 500 sheep, it is 1 in 100 Suffolk or black-faced sheep.

Isolate new sheep
Newly purchased sheep should be isolated for at least 2 weeks, preferably 30 days, before being co-mingled with other animals on your farm or being turned out to pasture. A period of isolation provides an opportunity to detect a disease problem before the rest of your sheep or premises are exposed. Isolation/quarantine areas should not same the same airspace with the rest of the flock. A distance of at least 100 feet is recommended. The farther the isolation pen is from the rest of the flock, the better it is. The isolation area should be confinement, ideally another building. If another building is not an option, you should select a corner of your barn for isolating new animals. Isolated animals should not have nose-to-nose contact with the rest of your flock.

While in isolation, new animals should have their hooves trimmed and inspected for footrot and other hoof problems. Making the sheep stand in a footbath of zinc sulfate is a good preventative measure to keep footrot off a farm. Koppertox can be used on individual animals. Footrot is usually introduced to a farm through the introduction of infected animals.

To prevent the introduction of drug-resistant worms, new animals should be dewormed and have their fecals checked. It will probably take the use of anthelmintics from a least two different chemical families to prevent the introduction of drug-resistant worms to your farm. It will be helpful to learn the deworming history of the farm from which you purchase or receive new animals.

Buying animals at a sale barn
Purchasing animals at sale barns (or stockyards) greatly increases the risk of a new disease entering your farm. When you buy animals at a sale barn, there are no guarantees, written or otherwise, that the animals are free from contagious diseases. Since there are no health requirements to sell at a sale barn, it is possible to take animals infected with soremouth, pinkeye, caseous lymphadentis, footrot, or other contagious diseases to a sale barn. These animals can expose healthy animals at the sale barn. Many producers take their cull animals to sale barns. An animal that looks okay may actually be harboring a disease or other problem that will prevent it from being a productive animal. Buyer beware!

The risk of showing
Taking your animals to shows and other exhibitions increases the risk that you will introduce a new disease to your farm. Contact with other animals at a fair can expose your animals to infectious agents. Try to minimize the nose-to-nose contact your animals have with other animals at the fair. While at the fair, try not to share equipment, waterers, or feeders with other exhibitors. If you loan your equipment to someone, make sure it is disinfected before you use it on your animals. When you return from a show, isolate your show animals from the rest of your flock.

Shearing
Some diseases can be introduced and spread by shearing. Of particular concern is caseous lymphadentis, an infectious, contagious disease that is the third leading cause of carcass condemnation (in cull ewes). To prevent infections from being introduced and/or spread, shearers should disinfect their equipment between flocks and between sheep. Shearing the youngest sheep first will also prevent the spread of diseases.

Limiting access to your farm
Some diseases can be spread by contaminated footwear and vehicles. By limiting access to your farm and sheep, you can limit the risk of introducing and spreading diseases. When people are given access to your sheep flock, they should not have been on another sheep operation for several days. They should be required to wear plastic boots or clean their shoes before entering your sheep-raising areas. Persons who have been in foreign countries within the prior 5 days should be denied access to your farm and sheep. If you travel to a country that has foot-and-mouth disease, it is best to leave your protective clothing and shoes there.

Good farm management
Rodents, cats, and other wildlife can harbor infectious agents. Some method of rodent control should be employed on the farm. Usually, this is cats. To prevent ewes from becoming infected with Toxoplasmosis, one of the leading causes of abortion in sheep, young cats should be kept away from stored hay and grain. It is best to neuter and vaccinate any cats on the farm and maintain a healthy, stable, adult population of cats.

The best way to maintain a healthy flock is to maintain a closed flock.

Dead carcasses, and placenta and fetal tissues should be removed immediately from the sheep-raising areas to prevent the introduction and/or spread of diseases. The ewe should not be permitted to eat her placenta, as this can spread diseases, such as scrapie and abortion. Composting is often the best way to dispose of waste products. Under no circumstances should carcasses and other waste products be left for dogs or wild animals to eat. This attracts predators and scavengers and can spread diseases. Sheep measles (cysts in the meat) is perpetuated when dogs and other canines are allowed to consume sheep carcasses. Dogs which eat infected placentas can pass the infective organism in their feces, further infecting the premises and other sheep.

Preventative health management
A vaccination program provides cheap insurance against common sheep diseases. It is generally recommended that all sheep and lambs be vaccinated for clostridium perfringins type C & D (overeating disease) and tetanus. The use of other vaccines will depend upon the perceived disease risk and diagnosis of particular diseases in the flock. Vaccines are available for soremouth, caseous lymphadentis, footrot, vibrio and chlamydia abortion, epididymitis, and rabies. Many of these vaccines (e.g. soremouth, caseous lymphadentis) should not be used unless the disease is already present on the farm because vaccination will introduce the disease to the farm. Such vaccines are advocated to reduce the incidence of disease, not prevent it in its entirely.

Gastro-intestinal parasites are the primary health problem affecting sheep and goats raised in warm, moist climates. An parasite control program that integrates pasture and grazing management and selective deworming (using the FAMACHA© system) should be implemented. Regular deworming of all animals in the the flock is NOT advocated due to the widespread emergence of drug-resistant worms. Fecal testing (fecal egg count reduction test or DrenchRite®) should be conducted to determine which anthelmintics are effective on the farm. Natural dewormers should not be trusted to control parasitism until their effectiveness has been proven under controlled circumstances.

When a ewe experiences an abortion, she should be isolated from the rest of the flock. The dead fetus(es), placenta, and fetal tissues should be removed immediately and buried or composted. The lambing area should be disinfected. Antibiotics should be given (fed or injected) during an abortion storm to prevent further losses. Chlorotetracycline is FDA-approved for this purpose. Including monensin (Rumensin®) or Decoquinate (Deccox®) in the feed or mineral during the last third of pregancy may help to prevent abortions caused by toxoplasmosis.

Maintaining a closed flock
The best way to maintain a healthy flock is to maintain a closed flock. Once the ewe flock has been established, replacement females should be selected from within the flock and new acquisitions should be limited to rams. Unfortunately, artificial insemination is generally not a practical option for most U.S. shepherds, making ram introduction usually necessary. It may be possible for large flocks to select their own ram replacements, but for most shepherds, outside ram purchases are necessary to avoid unacceptable levels of inbreeding. Fortunately, rams spread considerably fewer diseases than ewes. While rams can still introduce soremouth, footrot, pinkeye, or caseous lymphadentits to a flock, they are not likely to introduce vibrio or chlamydia. They are not believed to transmit scrapie, though the use of RR rams will ensure the birth of lambs that are scrapie resistant.

You should not loan rams to another flock, unless the health status of their flock is equivalent. You should not allow other producers to bring ewes to your farm for breeding, unless the health status of their flock is equivalent. There are other ways to help new shepherds besides making your farm and animals available to them.