Leading the way in Agriculture and Rural Research, Education and Consulting

SAC Consulting is a division of Scotland’s Rural College

Emerging diseases… but don’t forget the old ones!Lynn Batty

What barren rate at scanning should be investigated?

When should abortions be investigated?

Cause of increased barren rate at scanningTup factors• Tup infertility• Poor body condition/lameness• Incorrect ewe to tup ratioEwe factors• Poor nutrition ( trace element deficiencies)• Concurrent disease causing ill thrift including parasitism,

lameness, Johnes, Maedi visna, Caseous lymphadentis and Ovine pulmonary adenomomatosis.

Infectious disease• Toxoplasmosis• Border disease• Schmallenberg?

Common infectious cause of embryo loss, abortion and still birth

Enzootic abortion (Chlamydophila abortus)

Toxoplasmosis

Campylobacter

Salmonella sp

Listeria

Border disease

Schmallenberg

These can also cause the birth of weakly lambs

Schmallenberg virus

• Orthobunyavirus identified in 2011• First identified in the UK in January 2012• Infection of susceptible sheep usually subclinical.• Causes abortions and stillbirths with foetal deformities including

immobile joints, brain abnormalities and narrowing of spinal cord. Dummy lambs born on farms with abnormalities.

• Spread by midges• Risk period 20-60 days gestation.• Variable dates quoted as risk period.

Schmallenberg virus – Does previous infection

on the farm mean the flock is immune?

• No- The degree of exposure to SBV cannot be predicted by location and history.

• The proportion of sheep in a flock that become infected and develop immunity following natural infection via midges is more variable than in cattle.

• Recent studies have suggested that flocks can contain a significant population of susceptible sheep even after two

seasons of exposure.

Schmallenberg virus – Does previous infection

on the farm mean the flock is immune?

• Flocks in Sussex, Essex and Kent that were previously exposed had varying seroprevalence from 8% - 73%. [Study by Nanajiani et al (2013)]

• Another study in SW England looked at seven flocks with previous exposure. Lamb losses from Schmallenberg ranged from 4-40%. Seroprevalence varied in these flocks from 35% to 94%. [Study by Glover (2013)]

NATURAL IMMUNITY CANNOT BE RELIED ON TO COMPLETELY PROTECT A FLOCK FROM LOSSES FROM SBV.

Schmallenberg virus- is there a vector free period?• Cases of deformed calves confirmed to be caused by SBV

seen in Aberdeenshire in June suggesting that midges were circulating in late autumn- early winter.

• Cases of active infection in adult sheep in Dartmoor managed outdoors in mid March.

• Risk periods:Danger period (20-60d gestation)

Date served Date start Date end

August 1st 21st August 29th September

September 1st 21st September 30th October

October 1st 21st October 29th November

November 1st 21st November 30th December

December 1st 21st December 29th January

DON’T ASSUME ALL DEFORMED AND DUMMY LAMBS ARE DUE TO SCHMALLENBERG!!!!

Border disease

• Pestivirus related to BVD virus.

• Sheep to sheep contact principal mode of transmission. Bought in carriers likely source of infection

• Adults and healthy lambs exposed to Border disease only have mild clinical signs.

• Sheep are potential low risk for spreading Border disease to cattle. A higher risk is cattle spreading BVD to sheep

• Serious consequence if sheep are naïve and infected during pregnancy

Border disease

Clinical signs:• Poor scanning percentage• Increased abortions and stillbirths• Weakly lambs born • “Hairy shakers”

Border disease

Infection Infection Conception 60 85 Birth

Days

Possible outcome of border disease virus infection before and after the fetus gains immunological competence

between approximately 60 and 85 days gestation.

Fetal death

Resorption Mummification Abortion Stillbirth

Fetal survival ‘Hairy-shaker’ Weak or normal lambs which are persistently infected with virus No antibody detectable

Fetal death Abortion Stillbirth

Fetal survival Weak or normal lambs with antidody to BD virus No virus detectable

Border disease: Why should you worry?• SAC study 2006:

125 flocks in Scotland tested1 in 3 flocks there was evidenceof exposure to Border disease.

? An increasing threat to the sheep industry ?

Consequences to the pedigree flock

if Border disease introduced:• Losses at lambing• Potential loss of reputation

if persistently infected(PI) lambs sold• Cost of testing to find PI animals

What can be done?

• Investigate increased abortion/ still births, deformities or dummy lambs.

• Screening tests involve antibody testing of young sheep e.g. hoggs/gimmers to assess the flock status.

• If positive consider virus testing to find a PI

• Consider testing of replacement breeding stock.

• Reduced lambing percentages?• Poor lamb growth rates?• Lower weaning weights?

CONSIDER MAEDI VISNA

Maedi visna

• Virus infection• Maedi – pneumonia• Visna – wasting

• Persistent, lifelong infection• Long incubation period• Often fatal• No cure or vaccination

Clinical signs

• Weight loss• Pneumonia• Mastitis• Arthritis• Hindlimb paralysis

Flock example

• 1500 Masham ewes

• Single bearing ewes in poor body condition

• Lower lambing percentage

• Increased no. of thin ewes & deaths

• Smaller lambs & lower milk yield => poorer lamb growth rates, lower weaning weights

Flock example

• 4 out of 6 ewes positive for MV

• Difficult to fatten cull ewes

• Higher replacement rate in recent years

• Suspect bought in ~ 8 years earlier

Flock example - economic effects

• 20-40% reduction in productivity

• £30-50k cost p.a. & ongoing

Aug 2012 update:

• Losing an average of a ewe a day

• Low milk yields

• Very uneven lamb crop

SAC/AHVLA Maedi Visna survey findings

- funded by EBLEX & HCC

Within national flock

1995-6 Current Change

No. of flocks tested 2277 726

No. of sheep tested 41,593 11,757

Flock seroprevalence 1.4% 2.8% Doubled

Individual seroprevalence

0.19%(2 in 1000)

0.74%(8 in 1000)

Fourfold increase

Mean % of infected sheep within positive flocks

13% 24% Doubled

Estimated no. of positive ewes in national flock

39,000(based on 20.5 million ewes)

109,000(based on 14.75 million ewes)

Summary

1. Consider investigating: Lower scanning rate percentages (<5% barren)

Abortion and still births (<2%)

2. Discuss appropriate investigation with your vet.3. Reach a diagnosis and instigate appropriate

treatment or eradication.4. Prevent the disease from entering the flock by

health planning.5. If you don’t have a disease keep it out by

quarantine of new stock and testing for disease where appropriate.

Any questions?

Leading the way in Agriculture and Rural Research, Education and Consulting

SAC Consulting is a division of Scotland’s Rural College