Bovine Parasitic Gastroenteritis (PGE)

What is bovine parasitic gastroenteritis?

Inflammation of the stomach and small intestine resulting in diarrhoea as a result of parasitic infection by a nematode (roundworm)

What are the clinical signs of PGE?

• Diarrhoea

• Weight loss

• Hypoalbuminaemia/hypoproteinaemia

What nematode species is most commonly responsible for PGE in cattle in temperature regions like the UK?

Ostertagia Ostertagi

What is the lifecycle of ostertagia?

1) Eggs are passed in faeces

2) Eggs hatch into L1 larvae

3) Larvae moult and progress to L2, L3, L3 larvae

4) L3 larvae are ingested and live within the abomasal glands

5) Adult ostertagia emerge onto the abomasal surface where they live and look for a mate.

What is the prepatent period?

The time interval between when the parasite initially infects the host and when the parasite’s reproductive stages become detectable. Essentially, the time taken to mature.

What is the prepatent period of ostertagia?

The time from when ostertagia are ingested to when the leave the abomasal glands. This is around 3 weeks but can take 6 months if development is arrested due to the time of year, for example.

What is the pathogenesis of ostertagia?

• Absomasal pH increases from 2 to 7 as less acid is secreted by affected gastric glands.

• Pepsinogen cannot be converted to pepsin due to the high pH, so protein digestion is impaired.

• Abomasal epithelium becomes leaky as emergence of adult ostertagia causes damage.

• Plasma proteins leak into the abomasum, leading to hypoalbuminaemia, weight loss, and osmotic diarrhoea.

What is ‘overwintering’ of nematode larvae?

The L3 larve survive the winter hidden in cowpats.

Why do levels of L3 larvae in the pasture decline when summer starts?

As the temperature increases, the larvae metabolism increases so energy reserves run out. The cowpats dry out creating a dry inhospitable environment.

Why is there a surge in L3 larvae in Autumn?

Cow which ingested the larvae in Spring are shedding eggs.

Why are nematode larvae numbers much lower when calves are turned out with their dams?

The calves are not weaned so are unlikely to ingest any larvae. The ewes ingest most of the larvae and are likely to have some level of resistance to them.

What is the autoinfection peak?

The time period when the number of auto infective larvae (L3) is greatest.

What is type I ostertagiosis?

Ostertagiosis which occurs in the same grazing period as when the nematodes are first ingested - late in the season.

This type is chronic but has a low mortality and causes persistent green diarrhoea.

What is type II ostertagiosis?

Ostertagiosis which occurs in the following grazing period/after the grazing period has ended. The larvae arrest inside the cattle (hypobiosis) and wait to all reproduce at the same time once environmental conditions are suitable for egg survival

This type is sudden onset and has a higher mortality. It causes sudden, profuse, watery diarrhoea.

How can ostertagia be controlled?

• Use clean pasture which was not grazed on the year before

• Delay turnout until summer, at which point larval count will be very low

• Strategic anthelmintic use

What is the appropriate anthelmintic dose period?

Prepatent period of the parasite + residual period of the individual drug (how long it is effective for)