22 October 1999

Infectious arthritis a pain in pigs

FINISHING pigs in a straw-based system appear more likely to contract a form of infectious arthritis than pigs housed on slats. Larger group numbers on straw-based systems means the disease spreads more rapidly through these animals.

There are several forms of arthritis in pigs, some infectious and some non-infectious. As signs of arthritis are not always apparent in live animals, the cause in a particular herd can usually only be found by analysing material taken from slaughtered stock. Arthritis can lead to parts of or the entire pig carcass being condemned.

In a letter to Vet Record (Oct 9) Aberdeen-based SAC vet Bill Smith reports differences in abattoir condemnations for an infectious form of arthritis – Mycoplasma hyosynoviae – between two groups of pigs housed on straw-based and slatted systems. Pigs were fed the same diet.

Of one batch of 190 pigs slaughtered, 83 (44%) were detained by meat hygiene inspectors for arthritis; one carcass was totally condemned and 82 carcasses were partially condemned.

The total weight of meat rejected averaged 10kg a pig – about £8 a pig on current prices. None of these pigs showed any signs of lameness and all passed the pre-slaughter inspection at the abattoir.

Only five of 178 pigs (3%) from slatted accommodation, slaughtered on the same day as the straw-based group, were detained for arthritis.

"An assumed high welfare system resulted in much higher prevalence of the disease," he reports.

The straw-based system was run on an all-in, all-out basis. In the slatted system, although individual pens were all-in, all-out, the houses themselves were not. This means that the straw system should have resulted in a lower prevalence of the disease, says Dr Smith.

But the bug causing this strain of arthritis can easily be passed from pig to pig. Because pigs on straw-based systems tend to be in larger groups than those on slats, the disease transmission risk increases dramatically. Dr Smith believes this is why pigs on straw-based systems had a higher incidence of arthritis.

Addressing the problem means finding the cause of arthritis, according to SAC vet David Strachan. "Where pigs have been detained for arthritis, information from the abattoir will not usually reveal the cause. A vet must be involved to determine the cause and advise on treatment."

Pigs with this form of arthritis can be treated with lincomycin. Dr Smith reports that when lincomycin was added to the feed of pigs on the straw-based unit at 2.5 kg/t of feed to control a low grade swine dysentery problem, the arthritis condemnation rate fell to 3%. But lincomycin is ineffective in the treatment of some other forms of arthritis, says Dr Strachan.

As the problem appears to be connected with large group sizes, reducing group sizes where pigs are on straw-based systems may help but is impractical in most cases, according to Dr Strachan.

However, mixing different groups should be minimised, he advises. This avoids pigs introduced to the group – possibly infected with the disease – from spreading it to the rest of the group.

Marianne Curtis

PIG ARTHRITIS

&#8226 Losses up to £8 a pig.

&#8226 Find cause.

&#8226 Slats better than straw?

PIG ARTHRITIS

&#8226 Losses up to £8 a pig.

&#8226 Find cause of problem.

&#8226 Slats better than straw?