Exam 2 - Lecture 12

Question 1

Parasitisms in Small Ruminant Production Animals

Answer 1

-Haemonchus contortus is the most pernicious
Trichostrongylid parasite affecting Sheep & Goats

-Causative agent of Bottle Jaw Anemia

-Infections with large numbers of worms can bleed an animal to death

-Multi‐drug resistance is widespread

Question 2

Haemonchus contortus Barber Pole Worm

Answer 2

-Adult worms are parasitic in the abomasum

-Medium size worms, sexually dimorphic: males (10 to 20mm) and females (18 to 30mm)

-Adult worms with single tooth in small buccal capsule

-Blood filled gut spirally encircling white ovaries distinctive “Barber Pole” appearance

-Most economically significant parasitism of small ruminants

Question 3

Haemonchus contortus Barber Pole Worm

Answer 3

-Direct life cycle:
-Prolific egg producer, single female 1000’s of eggs/day
-Animals infected while grazing
-Prepatent period ~ 21 days

-Larvae on pasture are sensitive to environmental conditions:
-Little development below 48o
-Sensitive to desiccation & dry pastures
-Disease outbreaks predominate in Late Spring & Summer w/ optimal temperature/moisture
-Susceptible to “hard freeze” in (Nov/Dec)

-Parasites likely over‐winter in host by “arrested development” or hypobiosis:
-Seed pasture for next season

Question 4

Clinical Signs of Haemonchosis

Answer 4

-Anemia:
-PCV < 15%
-Pale Mucous Membranes

-Hypoproteinemia Submandibular edema (Bottle Jaw)

Question 5

Why are Goats so Susceptible to Worms?

Answer 5

-God never intended for goats to live in a humid subtropical climate !

-Never had to evolve the ability to acquire strong immunity to parasite challenge: goats are preferential browsers (avoid worm‐ infested grass). inhabitants of arid desert & steppe regions
and mountains (relatively worm free
environments)

Question 6

Host Adaptations for mitigating Parasite
Disease Risk - Sheep

Answer 6

-Predominately grazing animals: appear to be a higher risk when grazing rough range land compared to goats

-Degree of acquired immunity to regulate parasite numbers

Question 7

Host Adaptations for mitigating Parasite
Disease Risk - Goats

Answer 7

-Preferential browsers

-Ability to de‐toxify ingested plants: tannin enriched plants may have inhibitory effect on parasite infection

-Relative absence of acquired immunity

Question 8

Teladorsagia circumcincta (aka Ostertagia)

Answer 8

-Less Pathogenic than in Cattle

-Disease associated with emergence of large numbers of worms following hypobiotic arrest

Question 9

Trichostrongylus sp.

Answer 9

-Less Pathogenic

-Disease associated with large numbers (10,00 to 100,00 worms) in nutritionally stressed animals

Question 10

Nematodirus sp.

Answer 10

-Less pathogenic

-10,000 worms considered significant

-Seasonal concentration of infective larvae in Spring

-Disease typically associated with lambs and kids during late Spring

Question 11

Basic Principles of Parasite Control

Answer 11

-Reduce pasture contamination to prevent hazardous reinfection of grazing animals: don’t overstock/over‐graze (~5 sheep/goats per acre)

-Appreciate risk of disease as a function of: age and susceptibility of host and acquisition of large parasite burdens & disease potential

-Use effective anthelmintics & know the resistance status of drugs at the herd‐level: fecal Egg Counts to determine which drugs work and which don’t and discontinue use of dewormers with demonstrated resistance

-Mixed (Cross) species/alternate grazing: equines & ruminant do not share parasites and mixed forage in pasture for parasite inhibitory effects

Question 12

Mean FEC of Treated Goats w/ Doramectin
at 200, 300, 400, and 600 g/kg

Answer 12

-FECR was ~ 68% at all dosages

-Drug performance not affected by increased dose &
suggest worms have been selected for resistance

Question 13

Fecal Egg Count Reduction Test

Answer 13

-Fecal egg counts performed on 10% of herd, or 6 animals (more is better!)

-Eliminate all animals with FEC < 100 EPG

-Kit w/2 slides @ $60 obtained from Chalex Corporation

-Treat animals with preferred deworming
drug

-Follow up with FEC (7‐10 days later):
Pre Tx EPG ‐ Post Tx EPG / Pre Tx EPG X 100

-Drugs with FECR’s < 90% should be discontinued

-Widespread multi‐drug resistance ~ 75 to 80% FECR is common

Question 14

Applications of Fecal Egg Count Results

Answer 14

-Use FEC w/FAMACHA as basis for Selective Deworming of “wormy‐high egg shedding animals”

-Prevent hazardous re‐infection from hyper-contaminated pastures

-Identifying “genetically resistant” animals for breeding replacement hoof stock

-Cannot be used to predict worm burden of clinically affected animals!

-Should not be used alone to make treatment decisions on individual animals

Question 15

FAMACHA Scoring Rubric

Answer 15

-Qualitative scale for visually assessing anemia in sheep and goats

-Highly correlated with hematocrit & disease risk when used by trained observers

-Used as a practical basis for prescribing anthelmintic treatment to at risk animals

Question 16

Why Selective Deworming (or letting a few worms live) Doesn’t Seem As Bad As it Sounds

Answer 16

-Worms on most farms are moderately to very susceptible to the commonly used anthelmintics

-Killing some worms will relieve disease symptoms and slow re‐infection: just removing 50% of worms can result in clinical improvement most of the time and treating only the high FEC animals can reduce pasture contamination by 80%

-With strong drug selection eventually most worms become resistant and when treatment fails:
-Animals often die
-Producers suffer economic loss
-Emotional distress

Question 17

Benefits of Selective Deworming

Answer 17

-Selective deworming of high FEC animals maintains genetic diversity (drug susceptibility) in worm population

-Maximize Refugia for preserving drug effectiveness: portion of the parasite population not subjected to drug selection pressure

-Reduces pasture contamination w/ less out of pocket cost for Tx of entire herd/flock

-Allows animals to develop and maintain natural immunity

Question 18

Use FEC for “Identification of Resistant Livestock”

Answer 18

-Able to reject parasitic challenge and minimize associated disease and production losses

-Resistance is evident in certain breeds and in individuals within a breed

-Worm resistance is heritable (~0.25) and may be used as a criterion for selecting breeding stock

Question 19

Effective Management of Parasitism in Production Animals

Answer 19

-Decreasing reliance on pharmacologic control

-Provide “safe” pastures (i.e., little immediate risk of parasitic disease): hay aftermath; crop stubble; temporary, small grains; pastures ungrazed since mid‐summer, and pastures grazed by other species, or by adult animals (mixed species grazing schema)

-Reserve safest pastures for young animals at highest risk