Switch to a closed flock brings health improvements for sheep breeder

Lleyn sheep

© Wayne Hutchinson/FLPA/Rex/Shutterstock

Running a closed flock can have its challenges, but the health benefits more than outweigh the problems, writes Jeremy Hunt.

Monitoring ewe health and performance by running a closed flock can bring long-term benefits, however maintaining adequate genetic diversity remains a major challenge.

Six years ago West Country sheep breeder George Cullimore decided to change his sheep enterprise from running about 500 commercial ewes to establishing a closed flock of 120 Lleyns – and he’s convinced the health benefits he’s achieving could easily be replicated by larger commercial flocks.

See also: Make the most of flock health forms

Although using AI had initially enabled him to achieve the biosecurity and genetic progress he wanted, and while it remains a vital part of the flock’s breeding policy, a compromise had to be made.

Over the years a small number of rams have been used to provide natural service, but strict biosecurity procedures are maintained and rams are always bought from a known source.

However, the benefits of running a closed flock far outweigh the negatives.

“You’re able to keep the best of everything you’re breeding in your own flock year after year while reducing the risk of introducing diseases – and there are now so many health issues that can seriously undermine a flock’s performance.

“Having to buy-in replacements continually throws a whole new set of challenges at any sheep business year on year. Once you’ve taken the decision and started to run a closed flock you ask yourself why you hadn’t done it years ago.”

Setting up a closed flock

For the first four years of running the closed flock Mr Cullimore didn’t even buy-in any rams and relied completely on AI.

Because it was difficult to depend totally on semen for the quality of rams he wanted he began carefully selecting a few ram lambs for natural service. However, but he was very strict about biosecurity and kept them in isolation before using them.

“We still don’t want anything to jeopardise the health status we’ve achieved over the last six years,” says Mr Cullimore of Kelston, near Bath.

Maintaining sheep health by avoiding introducing diseases with bought-in replacements was the main reason for setting up the flock.

Benefits of a closed flock

“In our previous commercial flock we’d had Maedi visna so operating a system that enabled us to avoid health issues was very important. We have maintained a strict culling policy and as an example of what we have achieved, we have had no foot-root in the closed flock for five years – apart from an occasional case of scald.”

When the flock was established all ewes were vaccinated against enzootic abortion for two years but haven’t been vaccinated since.

Artificial insemination

The flock has relied on buying semen from a bank of AI rams and selects on performance, but also on worm resistance. “We achieve a conception rate of around 80% but now also run some ram lambs to catch any females that don’t hold to service.

“Yes, there is a risk bringing rams into the flock, but we need to introduce new genetics and so have to weigh up the pros and cons. But we’ve only bought three tups in six years.”

Breeding for health

The flock undertakes faecal egg counts (FEC) to aid the selection of females with a high resistance to worms and to maintain an ongoing improvement in resistance in future generations – as well as reduce pasture contamination.

Saliva swabbing to measure antibody levels as a means of assessing worm resistance is also being carried out in the flock. It’s part of research under way with AHDB Beef and Lamb and Glasgow University into an alternative method of assessing worm resistance in individual sheep.

“What we are finding is there are certain ewes that are producing large amounts of worm eggs so we need to make sure we aren’t breeding from these females. Our ultimate aim is not to need to dose the flock for worms.

“We have proved we can maintain genetic diversity within a closed flock, but we can now capitalise on the opportunity to apply health monitoring such as identifying sheep with a high level of worm resistance.

“By sampling all our ewe lambs we know that we have the potential to benefit the flock in the long term through selection of our home-bred replacements with worm resistance. The aim is to breed more sheep that are resistant to worm infestation.”


A tough culling policy is applied and any ewes showing health issues or other problems are removed from the flock.

“It means we have a have a fairly quick turnover of sheep. We base our culling policy on health as well as performance, but it also means we aren’t carrying any problems or poor performers. We’re replacing a third of the flock annually.

“The savings we are making aren’t just based on not having the actual cost of buying replacements, but also on the fact we aren’t introducing females that may have health issues that could lower their performance and so reduce flock’s profitability.”

Expert view on maintaining a closed flock

Better biosecurity and having total control of your sheep’s genetic progress are the two main advantages for running a closed flock, according to sheep specialist John Vipond of Scotland’s Rural College.

He advises anyone considering setting up a closed flock to firstly assess the disease status of the sheep.

“A farm needs to be biosecure and some thought should be given to the suitability of the existing enterprise if it is to be run as a closed flock. It may be that a change of breed is necessary so that a closed flock could also bring advantages in reducing labour as well as saving on replacement costs and achieving better flock health,” he says.

While strict selection and quarantining of bought-in rams must be undertaken, some closed flocks are now running a system based on several “families” within the flock so that rams can be used across females from different family groups.

“There’s an increasing interest in setting up closed commercial flocks of Romneys and I know some breeders who can’t keep up with the demand for females needed by new flocks starting up.

“And across a range of breeds there are flocks that now feel – because they are clear of major health problems – they should capitalise on that are become a closed flock.”

But Mr Vipond says it’s important  a closed flock must also be totally contained. “It’s no good being in a situation where a neighbour’s sheep may end up in your fields because boundaries aren’t secure.”

Five most common sheep diseases that can be bought in

1. Contagious Ovine Digital Dermatitis (Codd) – causes severe lameness and can affect a large proportion of the flock. Lesions begin at the coronary band of the hoof and run downwards to the toe often resulting in the loss of the whole hoof.

2. Sheep scab – caused by Psoroptes ovis mites and results in intense itching.

Repeated rubbing and skin damage leads to wool breakage and eventual complete loss of patches of fleece. Interruptions to feeding leads to dramatic weight loss and the irritation can lead to fitting behaviour. Spreads rapidly through the flock.

3. OPA (Ovine Pulmonary Adenocarcinoma or Jaagsiekte), is a contagious lung cancer caused by jaagsiekte sheep retrovirus. Overproduction of fluid in the lung causes liquid to run from the nose when the animal lowers its head. Typical clinical signs of OPA are progressive respiratory disease that resembles pneumonia.

4. Enzootic abortion – caused by bacterial type organism and spread from sheep-to-sheep via birth fluids and placentas from infected ewes. Lambs are either dead or weakly and do not thrive and may die. The ewe will excrete the organism in her afterbirth and fluids for many days after lambing.

5.  Maedi visna – a chronic viral disease which is highly contagious. Causes lamb mortality and reduced growth rates, leads to an Increase in the culling rate and Increased incidence of arthritis, premature birth and reduction in conception.

Case study: Colin Forsyth, Dumfriessshire

Scottish sheep producer Colin Forsyth runs around 2,000 Lleyn ewes as a closed flock and retains around 500 as replacements each year.

The Dumfriesshire-based flock has been closed for 11 years and was set up to give more control over flock health.

“Dealing with lame sheep and lambing problems is ongoing when you have to buy-in replacements and I wanted to overcome that. We don’t record individual ewes but we do cull very hard so the ewe lambs we retain are constantly helping us to improve the type of sheep we keep and the health of the flock.

“We chose to work with the Lleyn but the principles are the same whatever the breed and I believe flocks can achieve massive improvements irrespective of the type of sheep being farmed,” says Mr Forsyth.

He says he established the closed flock to give more control over health and performance. “I wanted to improve fertility and longevity and eradicate lameness. And I think we have done that.

“But there are challenges particularly at tupping time. You have to be careful about what rams are run with which ewes to avoid in-breeding.”

The flock runs around 50 tups but there are strict biosecurity procedures for all newly purchased tups. “One of the biggest disadvantages of a closed flock is the risk of losing hybrid vigour, particularly if you become too pure. So tup purchases are very important to us.

“A few years ago we assessed where we wanted to go with the flock. The Lleyn was doing really well for us and although lambing, fertility and health were good, we were losing growth rate. We needed to find a terminal sire that wouldn’t compromise what we had achieved and set us back with lambing problems and lameness.

“Now we’re using 15 Abertex tups from Innovis alongside 30 Lleyns to give us a wider genetic base in our females. The Abertex-sired females will go back to Lleyn tups.

“I don’t think I am compromising any of the gains I’ve achieved from being a closed flock just because I have to buy-in rams. The strict levels of biosecurity we operate have so far been successful.”