VLA: Coccidiosis Reported in Young Caged Layer Flock

UK - Two flocks of caged layers were found to have coccidiosis and unusually high mortality of unknown cause(s) was reported, while leg problems affected a broiler flock, according to the Veterinary Laboratories Agency (VLA) Monthly Scanning Surveillance Report for February 2011.

12 April 2011

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Europe

Commercial Layers and Layer Breeders

Coccidiosis

Haemorrhagic typhlitis due to Eimeria tenella was seen in two unrelated flocks of 22-week-old caged layers. Post mortem examination revealed carcass pallor and markedly distended caecae containing fibrinous-haemorrhagic luminal casts. Impression smears of caecal wall and wet smear examination of luminal contents revealed large numbers of oocysts and schizonts consistent in size and location with those of E. tenella.

Early brooding mortality

Two separate houses of approximately 14,000 layer chicks each had experienced higher-than-usual losses during the early brooding period, with around three per cent mortality by day 5. (First week mortality should normally be less than one per cent.) At post-mortem examination chicks showed little or no sign of growth, most weighing around 30g or less (expected c. 50-60g) and they were dehydrated, often with visceral gout. Other chick placements on the same premises at the same time, with the same brooding conditions, but usually from different hatches and housed in different sheds, were not affected.

Possible reasons for the increased losses in some hatches included egg age – the eggs were thought to have been stored for longer than usual prior to incubation in some affected flocks – time from hatching to delivery and chick factors. Brooding conditions and management and drinker systems were the same in affected and unaffected houses and were not thought to be contributory.

Broilers and Broiler Breeders

Rickets

Rickets was diagnosed in two submissions of 29- and 34-day-old broilers and tibial dyschondroplasia was seen in 42-day-old broilers with a history of uneven growth. In the birds with rickets, findings at post mortem examination were of slight reduction of bone strength, linear widening of the tibio-tarsal growth plates and a prominent enlargement of parathyroid glands. Histological examination of undecalcified sections of growth plates stained by Von Kossa's method confirmed osteodystrophic changes consistent with an earlier episode of hypocalcaemic rickets with mineralisation of the growth plate already resolving.