8 March 2002

Closing a herd difficult – and no guarantees

By Richard Allison

MANY cattle and sheep producers are reassessing their herd disease prevention policy, but those contemplating a closed herd or flock may find it difficult to implement.

Since the foot-and-mouth outbreak, nearly 70% of dairy producers questioned in a recent survey reported changes in their attitude to disease prevention, says Antecs Mark Blackwell.

"A total of 62% of respondents said they wanted to close their herd. A similar number stated they would be more selective on the source of purchased animals, but only 20% will quarantine them before introduction to the herd."

However, Shropshire vet Clive Norrell warns it is difficult to close a herd and does not always prevent disease. "One local herd recently reported a TB breakdown with more than 10 infected cows, despite being virtually closed for several years."

All replacements were bred and reared on farm and a bull was occasionally bought, the last one six years ago, he says.

With livestock markets re-opening, producers will again be buying one or two milking cows instead of batches of dry cows, as during the F&M outbreak. "But these need milking, which makes it difficult to isolate them from the herd for three weeks."

When closing a herd, Mr Norrell advises installing a double fence with a 2m (6.5ft) gap because cows rubbing noses with stock on neighbouring units can transfer infectious bovine rhinotracheitis (IBR). A stream flowing from a neighbouring unit can also be a source of leptospirosis infection when cattle drink from it.

"One of the main economic benefits of closing a herd is low somatic cell counts. Breeding replacements avoids the risk of bringing new strains of Staph aureus and Strep uberis into the herd and increasing mastitis rates."

Notts producer and Farmer Focus contributor Andy Guy believes operating a closed herd system is cost-effective, including benefits of reduced mastitis and lower culling rates. "Our 76-cow high health status herd has been closed for nearly six years. Vaccination is a big cost, but having a high health herd does not always mean high vet and medicine costs. These are £22 a cow including additional F&M expenses. Instead, be choosy about who to allow on the unit and always ensure they follow disinfection procedures."

Mr Guy questions whether the full benefit of closing a herd will be gained when using existing animals instead of buying high health status stock. Some herds already have IBR and bovine viral diarrhoea infection and will see little benefit, he says.

"A major part of operating a closed herd is heifer rearing, which can be costly and not something to do in your spare time. It is an enterprise on its own which requires building space and forage area."

In addition, producers with below average milk yields must think carefully before rearing replacements. Good cow genetics are essential to enable continued genetic progress and low merit heifers cost the same to rear as high merit animals.

For sheep producers, operating a closed flock raises even more practical problems, says National Sheep Association chief executive John Thorley. "One important difference is that sheep are moved to feed, instead of feed being moved to cows."

He believes the most practical approach is to obtain replacements from accredited flocks in the Sheep and Goat Health Scheme. "This ensures the main sheep diseases are not introduced via replacements."

The survey also revealed that a proportion of dairy producers would stop grazing tack sheep in winter to avoid disease risk.

But Mr Guy says sheep grazing is still possible, despite having a closed herd. "To minimise risk, sheep are taken away in early January and they only graze silage areas, allowing a three-month break until cows graze the area." &#42