During the last year, further research work has gone on to see how widespread spirochaetosis is in the UK laying flock, both in caged and free-range flocks and what affect it can have on production.

Previous studies in Australia and Italy have shown that 70% of flocks have spirochaetes but only 30% have pathogenic or disease-causing strains B. pilosicoli and B. intermedia. A pilot survey of 10 free-range farms with reported sub-optimal production and laying percentage peaks of between 60-90% instead of the expected 94% showed that 60% of the flocks had a B. intermedia infection and 10% had B. pilosicoli. Ninety per cent had B. innocens but this is considered non-pathogenic. Three farms had concurrent worm infections and two had raised serological titres to infectious bronchitis (IB) variant virus strains showing that the diagnosis can be complicated involving a mixture of infections. One farm with 46 week old birds, where only B. intermedia was found as a cause, showed a 12.6% drop in egg production and a 4% increase in mortality in comparison with the breed standard. This represented a 20 eggs/hen housed drop in production, which cost approximately £1.00/hen, assuming an egg cost of 5p/free-range egg.

Brachyspira intermedia is meant to be the more severe infection than B. pilosicoli and when the original case's (April 2005) production was compared with the breed standard, in fact, the egg production was reduced by only 6% but the mortality was still over 8% higher by 72 weeks of age. Brachyspira colonise the caeca and attach to the epithelial (lining cell) surfaces (see Photo 1) in patches or almost sheets. The severity of the disease depends on the damage and invasiveness of the spirochaete. Infections with B. intermedia are reported to be more severe and cause epithelial cell erosions and even destruction of the caecal epithelial surface, whereas it is less common with B. pilosicoli and thought not to occur with B. innocens the non-disease causing species. All Brachyspira infections appear to be chronic in nature and last for several months, hence their debilitating effects on production over a long period.

Recent findings in a small survey of six caged-hen flocks with depressed production showed different results to the free-range flocks. One flock had pale eggs, thought to be associated with high avian pneumovirus (ART/TRT) titres and only B. innocens was isolated. In the other 5 flocks, B. pilosicoli were cultured and only one of these flocks, with the most severe performance drop, showed rising IB titres as well. It is important to carry out a number of tests to obtain a correct diagnosis, as it may involve more than one causal agent.

Findings	Free-range flocks	Caged flocks
No of Flocks	10	6
B. innocens	90%	17%
B. intermedia	60%	0%
B. pilosicoli	10%	83%
Worms	30%	0%
Virus infections	IB 20%	IB 17%
	ART 0%	ART 17%

Treatment of laying hens is limited to two antibiotics in the UK, because of the necessity for a zero withdrawal period in eggs. Both tiamulin and chlortetracycline have been used separately and in combination to control these spirochaete infections and tiamulin has been shown to be effective where chlortetracycline resistance occurs. Both are antibiotics and must be used under veterinary supervision. It is important to treat early on in the infection to obtain the best results, before chronic caecal damage occurs and production is adversely affected (see Graph 1).

especially in free-range flocks where B. intermedia appears to dominate. Caged flocks can be infected but B. pilosicoli appears to be more common. Calculations of the potential losses to the laying industry if 30% of laying flocks are affected could amount to over £4.1 million/year.

October 2009