A number of papers of significance to the egg industry were presented at the 61st Annual Meeting of the North Central Avian Disease Conference held concurrently with the 2010 Midwest Poultry Convention.
Beak deformation investigated
Dr. Robert Porter and colleagues at the Minnesota Veterinary Diagnostic Laboratory investigated a case of beak deformation in battery-housed hens ranging in age from 25 to 60 weeks. Approximately 5% of birds in a flock were affected.
Characteristic lesions involved small scabs on the comb and the lower beak. In severe cases loss of beak tissue was evident together with osteomyelitis (inflammation of the bone structures) of the mandibular (lower) and maxillary (upper) bones in which the beak is inserted.
The organism responsible for the infection was identified as Staphylococcus hyicus. Although this organism is commonly isolated from the skin of normal chickens it is possible that lesions may develop in immunosuppressed flocks or where skin or beak tissue is damaged by feeders or by pecking.
It is noted that the hens in the affected flock were not beak trimmed.
Pullet mortality examined
Dr. Ian Rubinoff of Hy-Line International Laboratory and Dr. Daniel P. Shaw of the University of Missouri described a case of tracheal aspergillosis responsible for 2% mortality in a flock of 3-week-old pullets.
Initially diphtheritic pox and ILT were considered as differential diagnoses but microscopic examination of the occluded tracheas confirmed aspergillosis.
In this case, immunosuppression predisposed the flock to clinical disease after exposure to Aspergillus spp spores. Peritonitis attributable to E.coli was also observed in the flock and by 16 weeks of age mortality from secondary infection exceeded 9%.
Why delay vaccinations?
Dr. Kenton Kreager of Hy-Line International reviewed protection against infectious bursal disease. Based on extensive epidemiologic studies and experience in both broiler breeder and egg production flocks, a successful program of vaccination has been developed which appears to be protecting the industry.
Hy-Line recommends vaccinating flocks using an intermediate strain of live attenuated IBD vaccine initially at 18 to 20 days of age with two consecutive doses at 1-week intervals.
The reason for delaying the first vaccination is that there is considerable maternal antibody transfer which interferes with the live vaccine. High maternal titer is due to the fact that parent flocks are primed with live attenuated vaccine and receive an inactivated booster prior to onset of production.
Aggressive IBD programs
In Europe, Africa, and Asia where highly virulent IBD strains occur it is necessary to apply more aggressive vaccination programs. Dr. Kreager discussed injecting killed IBD vaccine at 12 to 16 days of age. In some areas an intermediate-plus vaccine such as strain 228E is usually administered after flocks receive a priming dose of a mild or intermediate strain.
In some locations hatcheries inject a mild live IBD vaccine at a day old in an attempt to block IBD receptors in the bursa of Fabricius to be followed at approximately 14 to 20 days with an intermediate-plus strain vaccine.
Currently in the U.S. flock survival is regarded as a measure of successful vaccination. This however discounts the immunosuppressive effect of field challenge. Damage to the immune system by field strains of IBD will compromise the development of antibodies following vaccination against Newcastle disease, infectious bronchitis, laryngotrichitis and mycoplasmosis.
Focal duodenal necrosis (FDN) in egg producing flocks was reviewed by Dr. Eric Gingerich of the University of Pennsylvania. The condition was initially recognized and described by Dr. Patricia Dunn of the Diagnostic Laboratory at Pennsylvania State University in 1997. Since this time the infection has been observed in both caged and non-confined flocks.
The initial signs of the condition include depressed peak production (2% to 5%) and lower egg weight (1 lb to 2 lbs per case) accompanied by mildly elevated mortality frequently accompanied by as much as a 10% post-peak depression in production. Characteristic lesions are noted in the duodenum and proximal ileum but are best observed in sacrificed hens.
Post mortem decomposition obscures recognition of the individual or confluent ulcerations when reviewing collected dead birds. The causal organism is now regarded as Clostridium colinum, a pathogen responsible for ulcerative enteritis in game birds and occasionally in chickens.
Antibiotics which suppress gram positive bacteria in the intestinal tract will prevent clinical focal duodenal necrosis. Addition of bacitracin at 25 grams per ton of feed is frequently administered as is tylosin which is used to suppress mycoplasmosis.
Withdrawal of antibiotics from feed results in a proportional increase in the incidence rate of FDN in the flock.
A number of producers have administered probiotics - live direct fed cultures (Primalac) - or prebiotics (Bio-Mos or XPC). Botanical products (Apex or Regano) have been introduced to the market but have not been adequately evaluated under field conditions.