08: Control of Ruminant Nematodes

By numbers what is the major target of deworming and why

Subclinical cases because of the hidden economic loss

Diagnostic method used for trichostrongyles

Quantitative methods (McMaster or Wisconsin, as appropriate)

How do we test the efficacy of deworming in most species

Do a FECRT 14 days after treatment

How do we test the efficacy of deworming in small ruminants

FAMACHA test 14 days after treatment

Benchmark FECRT for an effective dewormer in ruminants

>/= 99% reduction

Benchmark FECRT for a dewormer with resistance in ruminants

<90%

What do we do with a FECRT between effective and resistant

Considered equivocal; test result is inconclusive and you may need to retest

How many animals should you do a FECRT on in a large herd to evaluate resistance

At least 15 animals

Which cattle in a large herd should you prioritize testing

Animals <16 months old because they shed more

How do parasites develop resistance to drugs

Genetic mutations selected for over time as the population is exposed to treatment

T/F: some drug A historically does not work at all for parasite X and it still doesn’t work today, so we say that parasite X is resistant to drug A

F; a parasite had to have been susceptible at one time to a drug in order to develop resistance

Where do genes for drug resistance come from

Could be a result of randomly generated mutations or be a trait that was always in the population but at low numbers

How does resistance to fenbendazole affect the rest of the benzimidazoles

Usually if a parasite is resistant to one drug, it is resistant to the whole drug class

Which ruminant parasite is among the hardiest and hardest to treat

Cooperia spp.

Strategies to delay the onset of resistance

1. Treat at certain times

2. Selective treatment of individuals

3. Increase refugia

4. Integrated drug and non-drug strategies

Refugia

A population of parasites that have not seen the drug due to location, life stage, or untreated animals

Why does refugia work

Most genes for resistance are recessive, so genetic dilution with non-survivor worms works well

Things to consider other than resistance if your FECRT is high

• Diagnostic failure: improperly run test

• Treatment failure: Drug given incorrectly, drug inactivated, wrong drug

What is the gold standard for how often we should determine resistance profiles in a herd

Every 2-3 years

Assay that evaluates resistance profiles and can ID specific species

Drenchrite

Key concepts in controlling GIT nematodes

• Reduce parasite exposure: pasture management, screen new arrivals

• Selectively deworm

How does nutrition play into parasite control

Animals in a nutrient deficiency are less able to fight off parasites and are more likely to show clinical disease

How do breeding programs play into parasite control

Can make breeding/culling decisions on whether the animal is a high shedder or naturally more resistant to parasites

Options for pasture management to decrease environmental contamination

• Mow or harrow pasture: lets the enviro kill larval stages

• Clean pastures

• Pasture rotation

Options for grazing management to decrease environmental contamination

• Co-grazing

• Prevent overgrazing: keep them eating grass farther from any feces

• Incorporate a small percentage of forages high in tannin (inhibits gut parasites)

Gold standard for how long a pasture should rest during rotational grazing

One year

Minimum amount of time a pasture should rest during rotational grazing

60 days

Purpose of co-grazing

Gets the parasites in a non-DH/IH

Successive grazing

AKA pasture flip; successive grazing of different host species

Types of parasiticide usage

• Therapeutic

• Prophylactic

• Strategic treatment

Why can prophylactic use of parasiticides be a problem

interfered with the development of acquired resistance

Benzimidazole commonly used in ruminants

Albendazole (± fenbendazole)

Imidazothiazole commonly used in ruminants

Levamisole

MCL commonly used in ruminants

• Ivermectin

• Doramectin

• Moxidectin

• Eprinomectin

Why are MCLs liked by producers

Persists in the tissues, providing an extended effect

Most important GIT parasites in cattle

Ostertagia ostertagi (type II dz) and Cooperia spp. (dose limiting parasite)

Most important parasites in nursing calves

Toxocara vitulorum and stongyloides

When should we deworm nursing calves

2-3 weeks before weaning

Why do we focus a lot on deworming stocker calves and replacement heifers

They are highly susceptible to parasitic infection because they don’t have a lot of acquired immunity and they are the largest risk for production loss

Why do we deworm feedlot cattle on arrival

Increased stress and increased stocking density results in higher incidence of disease

Parasiticide of choice for feedlot cattle

MCL to kill arrested ostertagia

Recommendation (debated) for deworming mature beef

Annually

When would you treat a mature beef cow

Near freshening to maximize milk production

Drugs used to deworm adult beef cattle

MCL ± benzimidazole

Treatment criteria for bulls

May treat up to 2-3x/year; before breeding season and with herd in fall/winter if there is high stocking density

Why do we treat bulls more frequently

Intact males are more susceptible to parasites and disease than females

Why are dairy replacement heifers very susceptible to parasites when first put on pasture

They are hutch raised and have essentially no acquired immunity

How are replacement heifers managed while on pasture

They aren’t :)

How are producing dairy cows managed

There is no consensus on whether to treat

Arguments against treating producing dairy cows

They are largely confined and kept in good health; they have low exposure and good ability to fight GIT parasites

Arguments for treating producing dairy cows

Treating at calving can reduce parasite related stress and increase milk production

Drugs that are ok to use in producing dairy cattle

Pour-on moxidectin and eprinomectin

When do we combine drugs in treating cattle

If a treatment with one drug gets no response, use a combo

Primary parasite of concern in small ruminant

Haemonchus contortus

How do we give small ruminant parasiticides labeled for oral use

PO

How do we give small ruminant parasiticides labeled for injectable use

PO

Treatment of choice for H. contortus

Moxidectin

When to treat for H. contortus

Before and after parturition

Treatment protocol for small ruminants with severe clinical signs

Moxidectin and some other drug class that works on the farm

Protocol for using combined drug classes in small ruminants

• Don’t mix them in one syringe!

• Observe the longest withdrawal

How to determine who to treat in small ruminants

FEC and FAMACHA

When to treat adult small ruminants

FAMACHA score 4 or 5; treat 3’s if >10% of herd is 4 or 5

When to treat young small ruminants

FAMACHA score 3-5

How often do we check FAMACHA score

Every 2 weeks during H. contortus season, 4-6 weeks during the cooler season