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ANSC 420: Critical thinking in Animal Science Susan Schoenian Sheep and Goat Specialist Western Maryland Research & Education Center University of Maryland Cooperative Extension –

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ansc 420 critical thinking in animal science

ANSC 420: Critical thinking in Animal Science

Susan SchoenianSheep and Goat SpecialistWestern Maryland Research & Education CenterUniversity of Maryland Cooperative –

Critical thinking is learning to think for yourself and to develop your own independent opinions, backed by sound reasoning and support.

Critical thinking is the process of evaluating what other people say or write to determine whether to believe their statements.


Critical thinkers gather information from all senses, verbal and/or written expressions, reflection, observation, experience, and reasoning.

. . .to form a solid judgment that reconciles scientific evidence with common sense.

small ruminants

Even-toed hoofed animal


4 compartment stomach

Bovidae (hollow horns) family

Caprinea sub family

Ovis aries (54 chromosomes)

Capra hircus (60 chromosomes


sheep, goat, cervids (deer)

Small ruminants
sheep and goats
Multi-purpose animals




Vegetation control

Research and biomedical


Youth projects (4-H, FFA)


Sheep and goats
sheep vs goats
More similarities than differences.

Same problems, same opportunities

Mostly the same diseases and health issues.

Sheep vs. goats
sheep and goats in maryland
Some large farms

200-300 females

Over 500

Largest farm has 1,600 sheep for bleeding

Only 4 certified dairy goat farms; no sheep dairies

A lot of small fiber flocks

Mostly small farms

Average flock size is less than 30

A lot of niche marketing of lamb and wool products.

Some commercial production

Mostly hobby, 4-H, tax advantage

Sheep and goats in Maryland

2002 Ag Census: 22,702 sheep (655 farms) and 9,601 goats (702 farms)


An animal or plant that lives in or on a host (another animal or plant) and obtains nourishment from the host without benefiting or killing the host.

Internal parasite

An organism which lives in an animal and derives its nutriment from the host animal oftencausing death or damage to the host. This term is usually reserved for worms.

internal parasites worms
Primary health problem affecting small ruminants in warm, moist climates like Maryland.

Sheep are goats are more susceptible to the effects of internal parasites than most other livestock.

Internal parasites (worms)
why more susceptible
Close grazing

Goats forced to graze

Small fecal pellets

Graze close to feces and each other.

Slower to develop immunity

Incomplete immunity (goats)

Temporary relaxing of immunity at lambing/kidding.

Lack of veterinary expertise

Lack of FDA-approved drugs

Worms have become resistant to most dewormers (drugs).

Main parasite is a blood sucker and killer!

Why more susceptible?
lack of veterinary expertise
Many veterinarians will not work with farm livestock.

Many veterinarians lack technical and/or practical knowledge of sheep and goat health issues.

The cost of treating a sheep or goat often exceeds its value.

There is often a disconnect between veterinarians and producers.

Most sheep and goat producers learn to do their own veterinary work.

They are often in violation of extra-label drug laws (they have no choice!).

Lack of veterinary expertise
lack of fda approved drugs
Three families (chemistries) of anthelmintics.


Nicotinic agonists

Macrolytic lactones

1-2 drugs in each family are FDA-approved for use in sheep.


Levamisol ®

Ivermectin ® and Cydectin ®

Only two drugs are FDA-approved for use in goats.

Safeguard ®

Rumatel ®

U.S. Organic standards do not permit deworming of meat animals.

There is growing public scrutiny regarding the use of drugs in food animal production.

Therapeutic  Medical use

Lack of FDA-approved drugs
lack of anthelmintic efficacy
Lack of anthelmintic efficacy
  • Overuse (therapeutic) and sometimes misuse (e.g. pour-ons and injectables, underdosing) has lead to the emergence of drug-resistant worms in all three anthelmintic classes.
  • Highest levels of resistance have been reported in the benzimidazoles and ivermectins.
  • Drug resistance is determined using a fecal egg count reduction test or DrenchRite® larval assay test.
  • Resistance is permanent (levamisole ?).
slowing drug resistance
Slowing drug resistance

The FAMACHA© system

  • A color eye chart showing varying degrees of anemia (symptom of barber pole worm infection).
  • Identifies animals that require deworming and those that do not.
  • Results in fewer animals being treated.
  • Results in more refugia (worms that have not been exposed to the drug).
  • Slows the development of drug-resist worms and prolongs the effectiveness of anthelmintics.
non chemical dewormers
Non-chemical “dewormers”
  • Nematode-trapping fungus
  • Copper oxide wire particles
  • Condensed tannins (Sericea lespedeza)
  • Natural dewormers are currently be evaluated by researchers:
    • Garlic juice
    • Pumpkin seeds
    • Wormwood
    • Diatomaceous earth
    • Oregano oil (coccidiosis)
  • A vaccine is under development.
the internal parasites of sheep and goats
The internal parasites of sheep and goats
  • Stomach worms
  • Tapeworms
  • Lungworms
  • Liver flukes
  • Coccidia
  • Meningeal worm
the other parasites these parasites tend to cause less problems than the others

Tend to be non-pathogenic

No beneficial effect of treatment


Difficult to diagnose

Liver fluke

Not thought to be a problem in Maryland

Meningeal worm

Parasite of the white tail deer (sheep and goats are abnormal hosts)

Requires intermediate host (snail, slug)

Causes neurological damage.

The “other” parasitesThese parasites tend to cause less problems than the others
coccidia eimeria sp
Single-cell protozoa


Permanently damages lining of the small intestines.

CoccidiaEimeria sp.
coccidia life cycle
Coccidia life cycle

2 to 3 weeksoxygen, moisture, warmth

diagnosing coccidia
Affects mostly young lambs and kids, 1 to 6 months of age.

Diarrhea is the most common symptom. It often contains blood or mucous.

Other symptoms: loss of appetite, rough hair coat, poor growth, ill thrift, loss of body condition, dehydration.

Fecal egg flotation*

Diagnosing coccidia
treating coccidiosis
Treating coccidiosis
  • Amprolium (Corid)*
  • Sulfa drugs*
  • Must individually treat each animal.
  • Must treat each animal in pen.
  • Cannot reverse permanent damage.

* Not FDA-approved for goats

prevention of coccidiosis
Some level of “infection” is normal.

Most fecal tests will be “positive” for coccidia eggs.

Young animals require low level of exposure to develop immunity.

Prevention starts with good sanitation and management.

Clean pens

Feed and water that is free from fecal matter

Avoid overstocking

Prevention of coccidiosis
prevention of coccidiosis24
Prevention of coccidiosis
  • Coccidiostats aid in the prevention of coccidiosis and can be put in the feed, mineral, or drinking water.
    • Monensin (Rumensin®1)
    • Lasalocid (Bovatec®2)
    • Decoquinate (Deccox®12)
    • Oregano oil (experimental)
    • Amprolium (Corid)


Drinking water

1 FDA-approved for goats2 FDA-approved for sheep

coccidiostats inhibit growth but do not kill coccidia
Reduce coccidia in the environment

Start 30 days before lambing/kidding

Continue through weaning

Include in lamb and kid rations

Have many other beneficial effects

Feed efficiency, rate-of-gain, aid in prevention of toxoplasmosis and bloat

Can be toxic to equines

CoccidiostatsInhibit growth but do not kill coccidia
gastro intestinal worms the barber pole worm and its relatives
Gastro-intestinal wormsThe barber pole worm and its relatives
  • Haemonchus contortusBarber pole worm
  • Ostertagia circumcincta Medium or small brown stomach worm
  • Trichostrongylus Bankrupt or hair worm
barber pole worm
Barber Pole Worm

Rough hair coat


  • Pale mucous membranes
  • Edema (bottle jaw)
  • Not diarrhea (scours)
  • Sudden DEATH
  • Fecal egg flotation (?)

Is difficult to control because . .

  • Short, direct life cycle
  • Prolific egg producer
  • Can go into “hypobiotic” (arrested) state during winter to survive.
  • Can survive on pasture for a long time.

Weight loss, unthrifty

Bottle jaw

Pale membranes

stomach worm life cycle
Stomach worm life cycle

2-3 weeks

Eggs require warmth (60°F) and humidity to hatch to first stage larvae.

fecal egg counts
Fecal egg counts






















integrated parasite management ipm
Integrated Parasite Management (IPM)

Goal is not to create parasite-free animals. It is normal for sheep and goats to have parasites. Goal is to prevent clinical disease and production losses.

parasite control begins with good management and common sense
Parasite control begins with good management and common sense
  • Good sanitation
  • Feeders which prevent wastage and contamination.
  • Clean water, free from fecal matter.
  • Not overstocking pens and pastures.
  • Isolation and deworming of new animals.

The primary cause of internal parasitism is overstocking.

use clean or safe pastures
Use “clean or safe” pastures

What is a safe pasture?

  • New pasture
  • Pasture that has been renovated with tillage
  • A pasture that has not been grazed by sheep or goats for the past 6 to 12 months.
  • Pasture grazed by horses and/or cattle for the past 6 to 12 months.
  • Pasture in which a hay or silage crop has been removed.
  • Pasture that has been rotated with row crops.
  • Burnt pasture
  • Severely overgrazed pasture????

Cleaner, safer pastures are a more realistic goal for most producers.

graze multiple species
Graze multiple species
  • Sheep and goats share the same internal parasites, but they are different from the parasites that affect cattle and horses.
  • Producers who graze multiple species of livestock report fewer parasite problems.
  • Cattle and horses“vacuum” sheep/goat pastures.
  • There are other benefits to mixed species grazing, such as complimentary grazing habits.
pasture rest and rotation
Pasture Rest and Rotation
  • Pasture rotation is a recommended strategy for controlling internal parasites because it allows the use of safe or safer pastures.
  • BUT, intensive rotational grazing generally does not help to reduce parasitism unless rest periods are long enough.
  • In a rotational grazing system, ideally, sheep/goats should not be returned to the same pasture for 2 to 3 months.
  • Due to increased stocking rates, management intensive grazing may increase internal parasite problems in sheep and goats.
alternative forages
Alternative forages
  • Livestock that browse have fewer parasite problems.
  • Livestock grazing tall-growing forages will have less parasite problems.
    • 80% of parasites live in the first 2 inches of the vegetation.
  • Grazing some high-tannin forages may reduce the effects of parasitism.

Forage Chicory

Sericea Lespedeza

Birdsfoot Trefoil

Chicory, birdsfoot trefoil, and Sericea Lespedeza have been shown to reduce fecal egg counts and/or larval development.

nutritional management
Nutritional Management
  • Animals on a high plane of nutrition and in better body condition are better able to withstand worm burdens.
  • Nutrition in early pregnancy (fat stores) can affect the immune response to internal parasites.
  • Sheep receiving higher levels of protein prior to lambing have lower fecal egg counts.
  • Supplementing lambs with protein has been shown to reduce fecal egg counts.
zero grazing
“Zero” grazing
  • Sheep/goats raised in confinement or dry lot (zero grazing) have fewer stomach worm problems.
  • Sheep/goats put in confinement or dry lot do not usually get re-infected with stomach worms.
  • Coccidiosis could still be a problem.
genetics and worms two important traits resistance and resilience
Genetics and wormsTwo important traits: resistance and resilience


  • Ability of host to limit infection
  • Assessed by fecal egg counts (FEC)


  • Ability of host to withstand challenge and/or infection, and thus maintain health and productivity.
  • Assessed by blood hematocrit/packed cell volume (PCV) and eye anemia score.

Moderately heritable – 20-40 percent

resistant breeds some sheep and goat breeds are more resistant to worms

Gulf Coast Native

Hair sheep

Barbados Blackbelly

St. Croix


Royal White (?)

Select populations of other breeds(?)


Traditional wooled breeds









Boer goats

Dairy goats

Angora goats

“Resistant” BreedsSome sheep and goat breeds are more resistant to worms.
resistant individuals parasite resistance varies between individual animals of the same breed type
“Resistant” IndividualsParasite resistance varies between individual animals of the same breed type.
  • 20-30 percent of flock shed most of the parasite eggs.
  • Focusing deworming on susceptible animals will significantly reduce pasture contamination.
  • Culling worm-susceptible animals will increase flock resistance and reduce pasture contamination.
heritability of fec and pcv
Heritability of FEC and PCV

2004, Vanimisetti, Andrew, Zazac, Notter

Selection for parasite resistance is possible and will not adversely affect growth of lambs and fertility of ewes.

comparison of genetic and non genetic control strategies
Comparison of Genetic and Non-genetic Control Strategies

Australia, 2002

  • Monitor sheep, run in the plots after the end of the experiment had lower FEC’s when run in the plots previously grazed by supplemented sheep (35%) or selected sheep (46%).
  • The largest and most persistent effect on FEC’s and worm contamination of pasture was achieved by genetic selection.
maximize the effect of a single treatment
Maximize the effect of a single treatment
  • Give proper dose;do not underdose.
  • Dose orally (all formulations)
  • Put dewormer in back of mouth behind tongue.
  • Restrict feed 12-24 hours before administering a benzimidazole or ivermectin or administer two treatments 12-24 hours apart.
  • Use higher dose for goats than listed on label. Goats usually require 1.5-2X the sheep/cattle dose. (Consult with veterinarian for proper dose for goats).
  • Use two different drugs.
slowing down drug resistance
Slowing Down Drug Resistance
  • DO NOT overuse drugs, especially Levamisole and Moxidectin.
  • DO NOT introduce resistant worms to your farm
    • Isolate new animals and deworm them aggressively
  • DO NOT underdose
    • Weigh animals or dose for heaviest animals in group.
  • DO NOT rotate dewormers after each treatment
    • Rotate dewormers annually
    • Rotate among drug families
    • Use specific dewormers for specific situations.
  • DO NOT treat everybody
    • Leave some animals untreated
refugia in refuge from the drug
“Refugia” – in refuge from the drug

What is refugia?

  • Worms not exposed to drug;therefore still susceptible to treatment.

The goal

  • Increase the population of susceptible worms.


  • Selective treatment – leave some animals untreated.
  • After deworming, do not move animals to a clean pasture.

You do not have to deworm every animal.


How We Select for

Drug resistance


Next Generation

Drug Treatment





Treatment RecommendationsDeworm adults at scores 4 and 5*Treat lambs and kids at categories 3, 4, and 5

*South Africa recommends goats be treated at categories 3, 4, and 5

using the famacha system to control internal parasites in grazing lambs















Using the FAMACHA© system to control internal parasites in grazing lambs
  • 84 hair x wool crossbred lambs, 3 months old
  • June 10-Sept 30 (112-day grazing period)
  • Lambs scoring 3, 4, or 5 on the FAMACHA© scale were dewormed with moxidectin or levamisole
  • Lambs gained 0.3 lbs. per day, 57 lbs. → 87 lbs.

% Lambs/No. times treated

Western Maryland Research & Education Center, Keedysville, MD

fecal egg counting
Fecal Egg Counting

Qualitative Analysis

  • Shows presence or absence of eggs
  • Identify egg types
  • Shows general trends

Quantitative Analysis

  • Shows specific number of eggs per gram of feces (epg)
  • Use known quantity of feces and flotation solution.
what do fecal egg counts tell you
What do fecal egg counts tell you?
  • Potential pasture contamination
  • Fecal egg counts are not mathematically correlated to worm numbers or the severity of parasitic disease.
  • Monitor and maintain low egg counts; deworm when appropriate to keep contamination of pasture low.
  • Determine the efficacy of anthelmintic treatment by comparing paired samples from the same animals (treatment and control group).
next wednesday s farm visit
Next Wednesday’s farm visit
  • Small meat goat farm in Clarksburg(typical operation for Maryland)
  • Evaluate overall health management, with specific attention to the control of internal parasites (worms and coccidia).
    • Reduce morbidity and mortality
    • Minimize cost
    • Minimize use of drugs


Pasture and grazing management


Internal parasites



Equipment and facilities

Genetics andselection

Feeding and nutrition