Chapter 19 Flock and Herd Health

Patty Scharko, Jason Johnson, Seyedmehdi Mobini, D.G. Pugh

Sheep Flock Health

Definition of Flock Health

The aim of a flock health program is to improve the overall health and welfare of the sheep in the flock, decreasing losses from disease, increasing productivity, and maximizing the profitability of the flock. The use and analysis of production, health, and financial records are excellent ways to measure the success of the program. Regardless of the approach used, flock health programs should include a written component that addresses all aspects of the production unit, time of year, vaccination, nutrition, reproduction, and parasite control, as well as overall productivity.

Flock health programs are developed for multiple applications. They may be used by an individual producer or incorporated into initiatives for the control and eradication of specific diseases through either voluntary or mandatory cooperation with state and federal animal health officials. Programs used by individual operators generally are planned annual approaches that address the following:

• Prevention of common disease conditions through the use of appropriate vaccination schedules (Table 19-1)

• Management strategies that minimize risk factors for disease occurrence

• Provision of appropriate levels of nutrition for the stage of production

• Assessment of metabolic status and productivity

TABLE 19-1 Basic Vaccination Program for Sheep

Timing	Immunization/Scheduled Management Practice(s)/Intervention(s)
PREGNANT EWES
• Midgestation	In endemic areas, vaccinate ewe lambs or previously vaccinated animals against Campylobacter and Chlamydia (Chlamydophila) abortion.
• Last month of pregnancy	Vaccinate for Clostridium species (C. perfringens type C and D, C. novyi, C. sordelli, C. chauvoei, C. septicum, C. tetani)
• 2 to 4 weeks after birth	Repeat Chlamydophila and Campylobacter vaccinations for previously unvaccinated animals and give yearly booster to other ewes
LAMBS
• 1 to 2 months • Repeat immunizations in 3 to 4 weeks	Immunize lambs from immunized dams for Clostridium species (C. perfringens types C and D, C. novyi, C. sordelli, C. chauvoei, C. septicum, C. tetani)
• 1 to 3 weeks • Repeat immunizations twice at 3- to 4-week intervals	Immunize lambs from nonimmunized dams for Clostridium species (C. perfringens types C and D, C. novyi, C. sordelli, C. chauvoei, C. septicum, C. tetani)
RAMS AND YEARLINGS
• As for ewes	Vaccinate at the same time as for ewes, with an emphasis on Clostridium species. Vaccines against rabies should be given in endemic areas.

In order to provide correct advice, the veterinarian must have a sound knowledge base regarding the sheep industry and the individual production system. The client and the veterinarian should work together in order to outline all pertinent details of a record-keeping system.

Veterinary visits usually are scheduled in accordance with timing of major production events (e.g., before breeding; in midpregnancy; before, during, and after lambing; in midsummer). During the first visit, the veterinarian assigns a body condition score (BCS) to the ewe flock, which is imperative for making nutritional and feeding management recommendations. Evaluation of the rams should include both a general physical examination and fertility assessment (see Chapter 8). A written record should indicate the ram’s BCS and weight, problems identified on the physical examination, and an action plan to address any problems that are crucial to breeding. The midpregnancy visit focuses primarily on ultrasound pregnancy determination and fetal counting and aging. On the basis of these results, the veterinarian can develop a plan for feeding ewes appropriately and economically as appropriate for fetal numbers and stage of pregnancy (see Chapter 2). This visit can be crucial in preventing metabolic disease in late pregnancy. The visit, examination, and herd/flock recommendations for the ewe in late pregnancy entails a review of the nutrition of the late-gestation ewe so that she can perform up to her genetic potential at lambing.

Properly fed ewes produce maximal amounts of colostrum and milk, give birth to thrifty lambs with minimal difficulty, and demonstrate excellent mothering abilities. The final 2 months of pregnancy are crucial to successful lamb growth and survivability. During this visit, the veterinarian can review strategies to prevent disease such as vaccinating against clostridial infections 4 weeks before lambing and providing a clean environment. The management plan at lambing time, including the layout and use of facilities, also should be reviewed. This plan should include education of farm personnel to recognize the need for intervention for lambing problems (Tables 19-2 and 19-3).

TABLE 19-2 Generic Management Calendar for Spring Kidding and Lambing

January	Evaluate range and forage conditions; monitor body condition of does and ewes and supplement if necessary; ensure adequate intake of minerals, salt, and water; vaccinate during the final month of gestation for clostridial disease and any other endemic diseases.
February	Begin supplemental feeding of pregnant females and consider prebirthing shearing; begin birthing; check teats for milk and identify lambs and kids; ensure ingestion of adequate colostrum by lambs and kids; institute pre- and postbirthing strategic deworming; maintain an ionophore in feed or mineral mixture before and after birthing to decrease coccidial contamination of pasture.
March	Separate singles from twins; confine and feed females with their lambs and kids as needed; feed does and ewes to maintain milk production; continue strategic deworming program.
April	Continue to feed a supplement to lactating does and ewes; monitor for parasites with FAMACHA scoring and “smart drenching.”
May	Wean small, stunted lambs and kids; discontinue supplemental feeding of does and ewes; monitor internal parasites (with FAMACHA and fecal egg counts using McMaster technique).
June	Continue parasite control program with FAMACHA monitoring.
July	Monitor internal parasites; watch for signs of heat stress; wean lambs and kids.
August	Continue parasite control program; continue weaning lambs and kids; supplement replacement does, ewes, bucks, and rams; select replacement males and females; identify and cull unsound and inferior animals; perform breeding soundness evaluation in males. Criteria for culling include the following: • Poor or slow growth • Barren status in females (missed one season) • Unsound teats or udders (too big or too small) • Poor dentition • Structural defects (feet, leg, or back abnormalities) • Testicles that are small or soft or have other abnormalities (so that animal fails a breeding soundness evaluation) • Unthriftiness (caused by old age or chronic disease)
September	Begin supplemental feeding of females and males on fresh green pasture with ½ lb feed/head/day for 2-3 weeks before and after males are placed with females; continue parasite control program.
October	Begin breeding; maintain good male-to-female ratio, depending on pasture size and conditions; continue supplemental feeding of females for 2-3 weeks after start of breeding season.
November	Evaluate range and forage conditions; determine females’ body condition and plan winter supplemental and feeding program; control internal and external parasites; remove some of males’ feed to regain body condition; determine pregnancy status and number of fetuses.
December	Evaluate body condition of does and supplement feed if needed; monitor internal and external parasites.

TABLE 19-3 Seasonal Veterinary Management

Period in Seasonal Cycle	Veterinary Visit Assessments
Prebreeding	BCS in ewes Nutrition and feeding recommendations for flushing Ram breeding soundness exam
Midpregnancy	Ultrasound pregnancy exam: fetal counting and aging BCS
Prelambing	Vaccination for clostridial diseases Review of nutrition Lambing management plan Review of intervention criteria BCS
Midsummer	BCS FAMACHA scoring and “smart drenching”

BCS, Body condition score.

Minimum standards and target production parameters should be set for morbidity, mortality, culling, and growth rates (Table 19-4). A quality assurance program also should be designed for the flock. To date, the sheep-packing industry has not required producers to participate in flock quality assurance programs, but such programs exist and will become more common in the future as a result of consumer demand. Quality assurance programs educate producers in good production practices and encourage cooperation between practitioners and area producers. Table 19-2 presents a sample management calendar for spring lambing.

TABLE 19-4 Production Targets

Production Parameter	Target
PREGNANCY
Ewes	More than 95%
Ewe lambs	More than 75%
Visible abortion	Less than 5%
LAMBING
Ewes	More than 90%
Ewe lambs	More than 70%
Stillbirths	Less than 2%
Weaning	More than 95%

Biosecurity Aspects of Flock Health Programs

Biosecurity programs are a critical element in the control of infectious disease. Such programs include management steps to reduce the likelihood of introduction of a new disease from an external source.

Another benefit of a biosecurity program is that it has the potential to reduce the spread of infectious disease already present in the flock. Scientifically sound approaches regarding the introduction of sheep into a flock are required to prevent the introduction of new diseases into the resident sheep population. Practical biosecurity principles include purchasing animals directly from the farm of origin, transporting them in clean and disinfected transport vehicles, housing them in true isolation facilities while following practical isolation practices for 1 month, and regularly observing for conditions such as pruritus, lameness, external lumps, and unexplained weight loss. In addition, isolated sheep should be integrated into the flock’s regular vaccination program, dewormed with an effective anthelmintic, and have their feet trimmed and visually inspected for footrot.

Even before performing a visual examination and obtaining the history of the flock of origin, the producer or the clinician may wish to use a foot bath (15 minutes in a 10% zinc sulfate solution) for footrot control. During isolation, the sheep may be serologically tested for diseases of concern to the buyer. If the sheep were tested for various diseases before purchase, the buyer should request the official test forms and results to check the results and test dates. Incoming sheep should be thoroughly examined for obvious clinical manifestations of contagious or infectious diseases such as contagious ecthyma (“soremouth” or orf), keratoconjunctivitis (“pinkeye”), external parasites, caseous lymphadenitis, scrapie, footrot, strawberry footrot, ulcerative dermatosis, and other contagious diseases of concern.

Barnyard Biosecurity

Producers should be educated regarding the following practices and principles as key to an efficacious biosecurity program for farm animals:

• Do not haul disease home or to the market. Table 19-5 lists some of the diseases that should “stay home” on the farm until the animal fully recovers.

• Isolate new animals for 2 to 4 weeks. Have no contact between new animals and the resident farm herd or flock animals during this time. Prevent introduction onto farm by keeping a closed herd or flock, and purchase animals from known sources (Table 19-6).

• Restrict access to the farm: post signs for vehicle and foot traffic control; keep a visitor log; don’t track disease in—wear different shoes, clothes, and hat to livestock auction market or public area and change before working with livestock.

• Provide good nutrition (water, feed, and minerals) and management plan (including vaccination, deworming, and the like) to maintain a healthy herd or flock.

• Report animals with unusual illness or those that are not responding to treatment to a local veterinarian, the state veterinarian, or the U.S. Department of Agriculture (USDA) Veterinary Services. Early detection may save animal lives.

TABLE 19-5 Diseases That Need to Stay Home on the Farm Until Animal Recovers

TABLE 19-6 Diseases Without Clinical Manifestations That Can Cause Abortion^*

Vaccination Programs

Through regular and correct usage, vaccines are designed to reduce the incidence and severity of a specific disease. Few, if any, vaccines are 100% efficacious in preventing disease. When vaccines are used properly, however, in most instances their beneficial effects will far outweigh their drawbacks. Area veterinarians can provide advice on prevalent diseases that should be used regionally, because farms in different areas have different needs. The local veterinarian should work with the producer to design a farm-specific vaccination program for ewes, young lambs, market or feedlot lambs, replacement breeding stock, and rams. Knowledge of prevalent diseases in the area and of diagnostic laboratory data is the best basis for developing a vaccination program. Vaccination should proceed according to label directions, because the timing of doses is crucial to optimal protection.

Clostridial diseases are the only universal group of diseases for which all sheep should receive vaccinations. Decisions regarding the inclusion of other vaccines in an individual flock health program should be based on knowledge of prevalent diseases in the area and the needs of the particular flock. In areas in which a disease is known to occur but no vaccine is available, risk factors for that disease should be controlled with proper management. Sheep that are frequently exhibited (as in, FFA, 4H, or breed shows) are at greater risk for contracting contagious and infectious diseases. For this reason, show sheep usually should be vaccinated against more diseases than is usual for sheep in a closed flock.

Other diseases that have an available vaccine labeled for use in sheep in the United States include some infections associated with abortion such as those caused by Campylobacter spp. and Chlamydia (Chlamydophila) psittaci; multisystem diseases such as caseous lymphadenitis, musculoskeletal diseases such as footrot, neurologic diseases such as rabies, and integumentary diseases such as contagious ecthyma (soremouth). If past history indicates that the flock is at risk for a disease, such vaccines can be included in an immunization program (see Table 19-1), which can be modified for the individual farm.

Internal Parasite Control Programs

The epidemiology of pathogenic sheep nematodes and protozoal species depends on the climate of the region; therefore internal parasite control must be tailored to the region of the country in which the flock resides. Parasite control programs also must take into account whether the flock is confined, pastured, or rotationally grazed. Successful programs implement regular monitoring of the efficacy of anthelmintics, sheep-friendly handling equipment for anthelmintic delivery such as well-designed pens and chutes, and use of automatic syringes or drench guns. Other components of a parasite control program include the use of multiple strategies to minimize the buildup of nematode eggs on pasture; this aim can be achieved by deworming ewes with larvicidal doses during winter housing, at 4 weeks after spring turnout, and at 3 weeks into lambing. Control also is enhanced by the use of management practices that reduce reliance on chemical anthelmintics, such as FAMACHA “Smart Drenching,” grazing clean ground with weaned lambs, “vacuuming” nematode eggs by grazing the previous year’s sheep pastures with cows or horses, and selecting for and breeding nematode-resistant sheep (see Chapter 6).

When the flock must graze close to the ground and nutritional input is marginal, nematode infestation may escalate, typically with development of clinical parasitism in stressed sheep. The veterinarian and the producer should create an annual calendar that details the entire flock health program. The producer should record details about any procedures performed in the production groups. Box 19-1 summarizes recommendations to improve parasite control. Table 6-1 shows some commonly used anthelmintics and coccidiostats useful in parasite control for sheep and goats.

BOX 19-1 Summary of Recommendations for Parasite Control ^*

1. Make certain that the anthelmintic or combination of anthelmintics used on the farm actually works (kills at least 90% of the viable worms). Check for resistance with fecal egg counts before and after deworming.

2. Utilize FAMACHA “smart drenching” in the spring and continue to assess every 2-4 weeks until the hazard of Haemonchus infestation no longer remains in cold weather.

3. Use strategic deworming. Deworm the flock while the parasites are in hypobiosis and are being transmitted at low levels (i.e., the winter). This strategy reduces the frequency of exposure to deworming products.

4. Employ pre- and postbirthing deworming starting 1 month before birthing at 2- to 4-week intervals and ending 2-4 weeks after the final lamb or kid is born.

5. Tactical dewormings (based on increased levels of parasite eggs or 10-14 days after rainfall) enhance the effectiveness of a parasite program.

6. Graze above 4 inches; use “clean” or safe pastures when possible (aftermath of crops, annual forage such as chicory); utilize rotational grazing or cograzing with cattle or horses. (Beware: Permanent pastures promote parasites.)

7. Deworm new animals and place them in a nonpasture environment such as a dry lot or barn after treatment for as long as 72 hours before moving them to a safe pasture. Check fecal egg count 10-14 days after treatment for fecal egg shedding

8. Rotate anthelmintics yearly if effective drugs are available.

9. Do not underdose. Determine dose for the heaviest animal in a production group.

10. Identify and select individual animals resistant to internal parasites for flock/herd retention and breeding.

^* More in-depth recommendations are available in Chapter 6.

External Parasite Control Programs

Keds and biting lice are the prevalent external parasites of sheep. Many sheep flocks have not introduced these parasites. In these flocks, all newly purchased sheep should be treated prophylactically while they are in isolation to prevent parasite introduction. In flocks in which either parasite is endemic, all sheep on the property should be treated at the same time, so that one group does not serve as a reservoir for reintroduction. Treated sheep should be kept out of any contaminated buildings for 2 weeks, because buildings also can serve as reservoirs during this time. Further treatments should not be necessary after the whole flock is properly treated. The flock should be monitored for ectoparasite infestation after reintroduction from carrier sheep or after improperly applied whole flock treatment. An external parasite control program is described in Chapter 6.

Flock Health Monitoring

Program records should contain a flock inventory divided into production groups. Important information gained from the records can include:

• Ram-to-ewe ratios at breeding

• Pregnancy rates

• Lambing percentages

• Ewe and ram mortality numbers and reasons

• Pre- and postweaning lamb mortality rates and reasons

• Ram morbidity and treatment outcomes (especially those that pertain to breeding use)

The average BCS of the ewe flock should be recorded at breeding, lambing, and weaning (see Chapter 2). If target scores are not achieved, the producer and the veterinarian need to determine why and make appropriate management changes. If the correct changes are implemented, future scores should improve, with consequently enhanced production.

If mortality rates exceed targets, necropsy should be performed in representative sheep to determine cause of death. Gross findings can be further investigated with ancillary laboratory-based tests.