1. Preventative Medicine in the Older Horse
Vaccination and Deworming
Frank M. Andrews, DVM, MS
Diplomate ACVIM
Professor of LA Medicine
The University of Tennessee, CVM

2. Activities of the Older Horses
Equestrian Sports
Reproduction
Broodmare, Stallion
Pleasure Horses

3. Demographics of the older horse
Increase in geriatric horses presented to veterinary hospitals (4 to 6 fold, up 55%)
NAHMS*-7.5% of horse population is ≥ 20 yrs
75% between years (old horse)
25% ≥ 30 years (very old horse)
Average age = 25 years (71 human years)
1 horse year  2.85 human years
*NAHMS=National Animal Health Monitoring System, 1988, USDA

4. Demographics (as of January 1, 1999)
Equine population in US: 5.32 million
~400,000 old horses and ponies in the US
Tennessee 3rd in horse inventory behind Texas and California, 190,000 (7th in value of horses sold)
14,250 old horses in Tennessee
10,688 old horses
3,572 very old horses
Economic impact: $189.3 million ($2,711/head)

5. Changes with Advancing Age
Decline in body condition
Decreased muscle tone
Decline in immune system
Increased susceptibility to infections
Decreased antibody production
Decreased immune response to vaccines
Vaccine failure rate ~50%

6. Vaccination

7. Variation in Vaccine Response
Genetic variation with age
Health status
Parasitism
Equine Cushings Disease
Dental disease
Arthritis
External stress factors
Weather
Nutrition

8. Vaccination – General No vaccine offers absolute protection
Lessen the effects of disease
Shorten duration and signs of disease
Good vaccine will stimulate immunity while minimizing secondary reactions
Swelling at site of injection
Injection site abscesses
Anaphylactic reaction
Fever and illness with loss of appetite

9. Vaccine Older Horses and Ponies
Relative risk of exposure
What diseases will your horse be exposed to?
Pastured horse vs. Stabled horse
Use attenuated vaccine products
Inactivated and killed vaccines
Likely to be safer in older horses

10. Eastern and Western Encephalitis (EEE, WEE) West Nile Virus
Important Diseases
Tetanus
Rabies
Influenza
Eastern and Western Encephalitis (EEE, WEE)
West Nile Virus
Rhinopneumonitis (Equine Herpes Virus 1)

11. Caused by Clostridium tetani Abundant in environment, manure
Tetanus
Caused by Clostridium tetani
Abundant in environment, manure
Often fatal
Infection through wounds
Yearly booster
New study suggests that yearly booster is essential for protection in horses

12. Always fatal in infected horses Humans can get disease from horses
Rabies
Caused by a virus
Always fatal in infected horses
Humans can get disease from horses
Infection from bite of infected animal
Skunk, raccoon, bats, etc.
Yearly booster-Pastured horses??

13. Endemic in the US, stabled horses? New horses brought onto premises
Influenza
Caused by a virus
Endemic in the US, stabled horses?
New horses brought onto premises
Respiratory disease, 3 day incubation
Booster every 6 to 12 months
Depending on exposure
Killed vs. Modified live vaccine

14. Eastern and Western Equine Encephalitis
Caused by a virus-”sleeping sickness”
Spread via mosquitoes
Regional areas
WEE-West of Mississippi
EEE-East of Mississippi (2003 outbreak in SE US)
Fatality- EEE=75-100%; WEE=25%-50%
Boosters every 4-6 months during mosquito season in endemic areas

15. Eastern Equine Encephalitis
Over 200 cases reported this year in ten US States
Florida, Alabama, Georgia, Tennessee, North Carolina, South Carolina, Mississippi, Virginia, Indiana, and Wisconsin
Florida outbreak = 66% fatalities
All have residual neurologic deficits

16. West Nile Virus Caused by a virus Spread via mosquitoes
Throughout the US
2003 – over 4,000 cases in horses
2002 – over 14,000 cases in horses
Fatality-30%, 40% may have lasting deficits
**Horses over 18 years had a 2.8X greater likelihood of dying or being euthanatized

17. Incubation period -- 3 to 15 days
West Nile Virus Transmission Cycle
Mosquito vector
Incidental infections
West Nile
virus
Incidental infections
Bird
reservoir hosts
Incubation period -- 3 to 15 days

18. Spread of West Nile Virus: Birds

19. Epidemiology
Horses cannot spread West Nile Virus to other horses, people, or pets
Dead-end Host

20. Prevention of West Nile Virus
Client Education a must
Not just a source of vaccine and meds
No stagnant water
4 days required for mosquito breeding
Old tires--and other Redneck landscaping materials
Gambusia fish eat larvae in tanks and ornamental pools
Topical spraying on horse—permethrins
Mosquito Magnet (
Stalls at night
fans in stalls
Mosquito Magnet

21. West Nile Virus Vaccines (USDA Approved)
New Vaccine
“Innovator vaccine is 92% effective”

22. Rhinopneumonititis Latent infections in horses
Caused by a Equine Herpes Virus 1
Respiratory disease is most common
Neurologic, abortion, and weak foal forms
Latent infections in horses
May be reactivated by vaccination in older horses
May precipitate neurologic disease
Not recommended in older horses because most horses have been exposed to virus
**Broodmares should be vaccinated during pregnancy to prevent abortion

23. Vaccine Protocol: Older Horse
Spring: (March 15-31)
4 – Way Vaccine
Tetanus
Eastern Equine Encephalitis
Western Equine Encephalitis
Influenza
Rabies
West Nile Virus
Summer: (July 31-August 15)
West Nile Virus (most cases in Sept. and Oct.)

24. Vaccine Protocol: Optional for Older Horse
Spring: (March 15-31)
Potomac Horse Fever
Pastured horses on endemic farms
Questionable effectiveness
Summer: (July 31-August 15)
Influenza
Stabled horses with new arrivals

25. Deworming

26. Deworming-General
Resistance-Many of today’s parasites are resistant to some dewormers
Adaptation: faster reproduction, environmental changes, to dewormers
Parasites must pass into environment to complete life cycle
Infection in related to quantity of parasites in environment that horse is exposed to!!
Older horses are more susceptible to infections

27. Parasites- What problems do they cause??
Colic
Diarrhea
Poor hair coat
Weight loss
Suboptimal performance

28. Minimize environmental contamination of the parasite offspring
Deworming-General
Minimize environmental contamination of the parasite offspring
Treatment vs. Prevention
Preventing infection of larval stages is key
Killing adult parasites important because it prevents them from laying eggs

29. Specific Parasites
Large Strongyles
Small Strongyles
Bots
Tapeworms

30. Large Strongyles (blood worms)
Strongylus vulgaris
Most common large strongyle
Larva stages lodge in main blood vessel that supplies the small intestines
Strongylus equinus
Triodontophorus spp.
Discovery of avermectins (Zimecterin®, Equvalan®, Quest®) have pushed to near extinction

31. Bots Gastrophilus intestinalis Gastrophilus nasalis
Larva stages live in stomach and small intestine
Larva released in manure in spring and become flies
Flies lay nits (eggs) on front legs of horses
Not a big problem in horses
Associated with ulcers?

32. Small Strongyles (most important)
Cyathostomum spp.
Affect all grazing horses
Infections are acquired from pasture only not stalls or dry lots
Eggs hatch at temperatures 45 F to 85 F
Temperatures > 85 F larva die
Horses are safe from infection during summer in Southeastern United States
Eggs resistant to freezing
Encyst in large intestine

33. Normal Large Intestine wall Inflamed Large Intestine Wall
Small Strongyles
Normal Large Intestine wall
Encysted Stage
Inflamed Large Intestine Wall

34. Tapeworms Anoplocephala perfoliata Anoplocephala magna
Most common tapeworm
Can reach up to 3” in length
Ileocecal junction
Anoplocephala magna
Paranoplocepha mamillan

35. Tapeworms
Life Cycle:

36. Tapeworms Clinical signs, What to look for in your horse? Colic
Spasmodic – 22% associated with tapeworms
Ileal impaction – 80% associated with tapeworms
Intussusception – blockage associated with telescoping intestines
Weight loss
Abnormal hair coat

37. Tapeworms: Where are they found?

38. Tapeworm Treatments
All are FDA approved

39. Specific Deworming Agents
Benzimadazoles
Fendbendazole (Panacur®) - Resistance
Pyrantel pamoate (Strongid®) - Resistance
Avermectins
Ivermectin (Zymecterin®), moxidectin (Quest®)
Cestode dewormers
Praziquantel (Contained in Zimectrin Gold®, Quest Plus®, and Equimax®)
Daily dewormers
Pyrantel tartarate (Strongid-C®)

40. Don’t be fooled – Read the label!!
These all contain Ivermectin and Praziquantel
Get all parasites including Tapeworms

41. Suppressive Deworming
Deworming should be based on:
Egg Reappearance Period (ERP)
Length of time in which the eggs appear in the manure after deworming
Panacur and Strongid = 4 weeks
Ivermectins = 6 to 8 weeks
Moxidectin = 8 to 10 weeks
Scheduling deworming based on ERP

42. Protocol for Strategic Deworming
September 1st
Ivermectin + Praziquantel (Zimecterin Gold)
October 24th
Moxidectin (Quest)
December 17th
Ivermectin (Zimecterin)
March 1st

43. Protocol for Strategic Deworming (cont)
May 1st through August 31st
Limited exposure to develop immunity
Parasites cannot live on pastures in summer
Fecal egg counts can be done to determine resistance of parasites
Egg count before treatment
Egg count 7-10 days after treatment
Deworming can be adjusted based on egg counts

44. Strategic Deworming-Alternative 2
September 1st
Moxidectin + Praziquantel (Quest Plus)
November 1st
Ivermectin
December 25th
Strongid Paste
January 20th
Panacur
February 15th
Ivermectin + Praziquantel (Zymectrin Gold)

45. Strategic Deworming-Alternative 2 (cont)
March 1st through August 31st
Limited exposure to develop immunity
Take advantage of summer heat

46. Strategic Deworming-Alternative 2
September 1st through August 31st
Strongid C daily dewormer
Colic protection policy by Pfizer
Farnham

47. I am vaccinated and I have no parasites
When horses dream??
I am vaccinated and I have no parasites