PGE epidemiology Flashcards
When does PGE affect lambs?
Late summer
August-September
Which 3 parasites are involved?
T.circumcincta
Trichostrongylus spp
Cooperia spp
What does the severity of PGE depend on?
- concurrent infection
- nutritional status
- development of immune response
How do worm burdens affect first season lambs?
- Depressed appetite which reduces feed intake and growth rates
- Permanent damage to the gut which reduces the absorption of nutrients and causes diarrhoea
- Impaired mineral retention causing a small skeleton
- Reduced protein metabolism reducing muscle growth and carcase quality
What are the sources of PGE infection?
- peri-parturient rise in ewes
- hypobiosis of larvae
- overwintered L3
What is the main source of contamination of pasture, and why?
Peri-parturient rise
- leads to increased egg output by ewes
- increased egg output just prior to and for several weeks after parturition
- causes seasonal hypobiosis of larvae
Describe hypobiosed larvae
Temp drop in the autumn triggers L3 on pasture to hypobiose in the sheep if ingested
stays there over winter and extends to the pre-patent period
What happens to overwintered larvae if there are no animals on the pasture?
Gradually die out
What is the development of the free living stages (L1-3) dependant on?
- temperature
- humidity
- dispersal from the faeces
Why is survival of L3 important?
- it is the infective stage
- survive on pasture until eaten
- limited life span, limited food reserves
Describe the spring time in the life cycle of T.circ
- overwintered L3 on grass
- ewes turned out with their lambs
- ewes contaminate pasture with eggs from the peri-parturient rise
At which point are there the highest numbers of L3 on pasture?
Mid July - August
What happens throughout June/July in the life cycle of T.circ
- As the day/night temperatures increase, the development of eggs speeds up
- Eggs shed onto pasture in May take longer to develop than eggs shed in June
- By mid-summer (mid-July), large numbers of L3 appear on pasture
