14 February 1997

Abortion caution paid off

By Sue Rider

STEPS taken to control abortion in ewes are now paying dividends for one West Sussex flockmaster.

John Olphert, who runs 1150 ewes at 162ha (400-acre) Marden Farm, East Harting, suspected underlying infectious abortion in his flock two years ago.

"Abortions were edging up to about 3% – which starts to feel very high," he says.

Blood samples from 10 aborted ewes showed on analysis that the ewes had been exposed to toxoplasma and enzootic infections.

Working with vet Jonathan Harwood, of St Peters Veterinary Group, Petersfield, Mr Olphert embarked on a programme of vaccinating bought in flock replacements against the abortion-causing bugs.

At about £3.50 a dose for the enzootic, and £2 a dose for the toxoplasmosis vaccine – its not cheap, admits Mr Olphert. "It was a question of weighing up the losses due to abortion against the vaccination costs – and vaccination made sense."

For either vaccine to be effective Mr Harwood emphasises that ewes must be injected before they become infected.

Although Mr Olphert buys most of his replacements from high health status flocks, these replacements would come into contact with aborting ewes carrying EAE infection in the existing flock. Ewes which had aborted in the past may also excrete infection at the next successful lambing.

Mr Harwood recommends vaccinating three to four weeks pre-tupping to allow immunity to develop before pregnancy, and ensuring vaccines for the two diseases are given one month apart.

All flocks should monitor abortion throughout the season, he suggests. "When over one in 50 ewes abort theres likely to be infection," he warns. "Early diagnosis is important so that appropriate control measures can be implemented for short and longer term."

To diagnose the type of infection, he advises delivering aborted material, both the foetus and cleansing, promptly to the local veterinary investigation centre. Then, once infection is identified, seeking vet advice on possible control measures. "Aborted ewes must be kept away from pregnant ewes," he adds.

Antibiotics can be given to limit EAE abortion in the face of infection – but this treatment is expensive and there is also the effect of stress induced by handling the ewes to consider, says Mr Harwood.

For long-term EAE and toxoplasmosis control, vaccinate, he says. On a farm contaminated with toxoplasma, vaccination is the only way to ensure ewes become immune before they have their first lamb.

"Left to nature, build up of immunity is a bit hit-and-miss, with many ewes not becoming infected in the safe period outside their pregnancy. Some infected ewes do not abort, but instead produce weakly lambs that often die despite careful nursing which can take up valuable time at lambing." Toxoplasmosis can also cause a high number of barreners when the abortion occurs in early pregnancy, he adds.

Main causes of infectious abortion

Enzootic abortion – cause is Chlamydia bacteria. Occurs in last month of pregnancy or at lambing. Infection spread by cleansing and discharge. Keep aborted ewes separate for 1-2 months. Infected females, including ewe lambs at foot, may become carriers and abort in next pregnancy. Hence bought in ewes often abort at their second lambing. Once aborted ewes will not abort again due to this cause and can be retained in the flock unless an active eradication programme is being considered.

Toxoplasmosis – toxoplasma can cause abortion at any stage of pregnancy. The environment – feed and bedding – contaminated with cats faeces is the source of infection. Safe to return aborted ewes to group of lambed ewes. Once infected ewe will be immune for rest of her life. Ewe-to-ewe spread of infection is very unlikely.

Producer John Olphert (left) and vet Jonathan Harwood now vaccinate flock replacements to control enzootic abortion.


Main causes of infectious abortion

Enzootic abortion – cause is Chlamydia bacteria. Occurs in last month of pregnancy or at lambing. Infection spread by cleansing and discharge. Keep aborted ewes separate for 1-2 months. Infected females, including ewe lambs at foot, may become carriers and abort in next pregnancy. Hence bought in ewes often abort at their second lambing. Once aborted ewes will not abort again due to this cause and can be retained in the flock unless an active eradication programme is being considered.

Toxoplasmosis – toxoplasma can cause abortion at any stage of pregnancy. The environment – feed and bedding – contaminated with cats faeces is the source of infection. Safe to return aborted ewes to group of lambed ewes. Once infected ewe will be immune for rest of her life. Ewe-to-ewe spread of infection is very unlikely.