College Farm Project Introduction
There are many conditions that can cause ill thrift in sheep flocks, such as liver fluke, worm burdens and trace element deficiencies. Ill thrift can also be caused by the presence of the following diseases –
- Ovine Pulmonary Adenomatosis/ Jaagsiekte (OPA)
- Maedi Visna (MV)
- Caseous Lymphadenitis (CLA)
- Ovine Paratuberculosis/Johnes (OJD)
- Border Disease (BD)
These diseases are termed ‘iceberg diseases’ as they are reported in fewer numbers than actually exist. Only the clinically diseased ‘tip’ are obvious, but the true size of the problem can be greatly underestimated. This is mainly due to the diseases being very hard to diagnose and can exist in a flock for a number of years before any clinical signs are seen. These iceberg diseases pose significant challenges to the productivity of sheep flocks (higher mortality and morbidity in lambs due to lower milk yield and poor colostrum), and can prove very costly to the farmer. This means that the diseases can often spread significantly before it has been detected, therefore controlling the diseases can then be difficult. Clinical signs are often not seen until around 50% of the flock is infected and at that stage eradication is very difficult, if not impossible. It is very important to know which ones are present so that they can be tackled appropriately.
Following a survey carried out by veterinarian and researcher Fiona Lovatt in 2016 from over 800 UK farms (who were finishing an average of 670 lambs a year); 94% of farmers claimed to have never seen the five ‘iceberg disease’, however irrefutable evidence collected from fallen stock centres show the true extent of these diseases. These diseases are increasing in prevalence with an estimated 37,000 ewes in the UK reported to have Maedi Visna in 1995 in commercial flocks. This has risen to 109,000 by 2011. Part of the problem is the UK stratified breeding system with draft ewes and cross bred ewes being widely sold as replacements to farmers, who also buy in rams.
Following the sudden death of a 3 year old, good condition ewe back in 2017 at College Farm, a post mortem was carried out to identify the cause of death. Severe pleurisy pneumonia was identified as the cause of death, however solid tumour lesions were also found on the lungs. Samples sent to the lab for histology confirmed the presence of OPA (Ovine Pulmonary Adenocarcinoma/Jaagsiekte) which would have been the trigger for pneumonia. Although OPA has been discovered in the flock at College Farm previously, the scale of the disease is very much unknown.
What will be done:-
Flock Health Plan
The farmer and vet will review and update the farm’s current flock health plan. This
will be vitally important to maintain the best possible health and welfare standards of
the sheep flock, as well as developing a collaborative working relationship between
the vet and the farmer.
Blood Samples
Whole flock health status will be measured and monitored using blood samples.
Following body condition scoring of ewes for tupping groups, a group of 28 of the
thinnest ewes have been pulled out to a separate group. Blood samples from 12 of
these ewes will be taken to sample for the following diseases: MV, Johnes, CLA,
Borders Disease.
Faecal Samples
A group Coproantigen test will be carried out on these 12 ewes to test for fluke
presence. Although this project hopes to concentrate on identifying ‘iceberg
diseases’, testing for fluke in this way will allow us to see if fluke is in fact the
underlying issue for causing these ewes to be on the thinner side.
Liver Biopsies
Liver biopsies will be taken from any post mortems that will be carried out on dead
ewes. This will be done to test for trace element issues that could also be an
underlying issue for why these ewes have underperformed.
Post Mortem
From the group of thin ewes drafted out following body condition scoring at tupping
time, two of the thinnest ewes will be sacrificed to send for post mortem at the
WVSC. Detailed post mortems will be carried out which will give us a good starting
point to knowing what we’re working with. Following this, a post mortem will be
carried out on any ewes that die without any obvious reason.
Ultrasound Scanning
Ultrasound scanning is currently the best way to manage and identify the infectious
and fatal lung disease Ovine Pulmonary Adenocarcinoma (OPA). The technology,
which is similar to pregnancy scanning for lambs, works by locating tumours (2cm or
bigger) and can identify 98% of cases. The group of 28 ewes that have been
identified as being below the optimum BCS prior to tupping will all be scanned for
lung lesions. Following on from the findings of these scans, a whole flock scan will
be carried out whenever all ewes are handled and is convenient for the farmer (i.e.
pregnancy scanning/ weaning time etc.)
Culling
Following the above tests and test results, a stricter culling protocol will be
developed to reduce the number of PI individuals identified within the flock.