Sheep farmers are being urged to work closely with their vets to test for infectious diseases and to invest in post-mortems on animals that die from no obvious cause.
Maedi visna (MV), Border disease and other iceberg diseases are caused by viruses or bacteria and are spread from sheep to sheep or dam to offspring.
One or more are likely to be present in a big percentage of flocks, but quite often farmers will be unaware of that, according to sheep vet Phillipa Page, who told farmers at a recent webinar.
This is because they are challenging to diagnose and control as early symptoms are typically vague and lead to loss of body condition.
It means they spread unnoticed, resulting in persistent subclinical infections and so reduce production efficiency, mainly due to their impact on body condition score (BCS), Ms Page, from Flock Health, said.
“These aren’t easy diseases to deal with as there is often more than one involved and they are very good at hiding from the immune system at certain times which makes them difficult to find.
“When we do find icebergs, they are usually not something we can solve in a season or in a year, they take a while but we can deal with them."
Strategic post-mortems can provide important clues: “Don’t waste an opportunity to post-mortem a dead ewe, it is worth investing in that because guessing will ultimately cost you more money," said Ms Page.
“I’m not saying that we find the definitive answer with every post-mortem, we don’t, but it will start to build a picture of your flock."
Flocks that have dealt with these diseases notice a lift in other areas such as colostrum quality and lamb vigour so they are worth looking for, she added.
“And from an efficiency point of view, efficient ewes are good for the environment and that has got to be a good story."
Any flock with a replacement rate exceeding 20% should question if iceberg diseases could be a cause.
Body condition score (BCS) is a good indicator of their presence therefore monitoring is key – no ewe should be less than BCS 1.5, Ms Page advised.
For lowland breeds, the minimum BCS is 2.5, for upland 2 and for hill 1.75.
Although there are many reasons why sheep lose weight, from tooth loss, poor nutrition and trace element deficiencies to parasite infection and lameness. Thinness can also indicate the presence of iceberg diseases in a flock.
“One of the more subtle signs are that the ewes are not gaining condition. Ask yourself how many in your flock are leaner than they should be," advised Ms Page.
“We need to know what percentage are leaner than they should be and in which age group, so document this as it’s important to have a record because we can then measure whether the situation is getting worse, whether it is getting better."
Establishing at which point in the year ewes become lean can indicate which disease might be present.
If testing does show the presence of one or more, what happens next will often depend on the type of flock or system.
“Do we want to eradicate the disease, can we eradicate it, are we going to monitor its impacts, try and reduce it or try to protect other sheep from bringing it in again? Every flock will have a different aim," Ms Page noted.
A pedigree flock might target eradication, for example gaining MV-free status and accreditation.
But that is unlikely to be cost effective or achievable in a commercial flock, especially if it is not a closed flock.
In this instance, disease monitoring or removing animals that are clinically affected might be a more suitable approach.
“The aspiration is that we eradicate these diseases from all flocks but that isn’t realistic," said Ms Page.
If testing shows these diseases are not present, the ambition should be to protect the flock from future infection. It often takes time to detect infectious diseases.
“This is not a one visit thing, it will involve ongoing discussions but don’t be afraid of that because it’s good to invest in somebody to help you work out what might be going on and to take it forward," said Ms Page.
If investigations establish the presence of one or more of these disease, she said farmers shouldn’t panic.
“We can manage what we find, it might be through treatment or vaccination or working out how they might have arrived."
For example, there are vaccines available for Ovine Johne’s disease and Caseous lymphadenitis (CLA) and thoracic ultrasound for detecting Ovine pulmonary adenocarcinoma (OPA).
Ignoring the problem is not the answer: “The worst thing you can do is bury your head in the sand and go merrily on because that will really affect your bottom line, ignoring the problem can lead to big flock issues."
