Emerging diseases but don t forget the old ones! Lynn Batty SAC Consulting is a division of Scotland s Rural College Leading the way in Agriculture and Rural Research, Education and Consulting
What barren rate at scanning should be investigated? When should abortions be investigated?
Cause of increased barren rate at scanning Tup factors Tup infertility Poor body condition/lameness Incorrect ewe to tup ratio Ewe 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 virusis 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 1 st 21 st August 29 th September September 1 st 21 st September 30 th October October 1 st 21 st October 29 th November November 1 st 21 st November 30 th December December 1 st 21 st December 29 th 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 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 Possible outcome of border disease virus infection before and after the fetus gains immunological competence between approximately 60 and 85 days gestation.
Border disease: Why should you worry? SAC study 2006: 125 flocks in Scotland tested 1 in 3 flocks there was evidence of 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 No. of flocks tested 2277 726 1995-6 Current Change No. of sheep tested 41,593 11,757 Flock seroprevalence 1.4% 2.8% Doubled Individual seroprevalence Mean % of infected sheep within positive flocks Estimated no. of positive ewes in national flock 0.19% (2 in 1000) 0.74% (8 in 1000) 13% 24% Doubled 39,000 (based on 20.5 million ewes) 109,000 (based on 14.75 million ewes) Fourfold increase
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?
SAC Consulting is a division of Scotland s Rural College Leading the way in Agriculture and Rural Research, Education and Consulting