Bernie BECKMAN
Doug GRIEVE
Kenton KREAGER
Hy-Line International
(1) Peritonitis caused by E. coli
One of the most challenging causes of mortality in adult layer birds is E. coli peritonitis. Birds die quite suddenly, usually in good body condition and high rate of lay. Peritonitis mortality occurs either during the peak of egg production or in older flocks. Fecal dust and respiratory infections might be affecting younger flocks, while vent trauma and scratching from poor feather cover may affect older flocks. Lesions consist of a serous to caseous yolk-colored exudate in the abdominal cavity.
E. coli is most frequently isolated, although other bacterial types can be found including salmonella, pasteurella, staphylococcus, streptococcus, and enterococcus.
Primary respiratory pathogens such as IB, MG, MS, etc. also need to be evaluated as a contributing factor in peritonitis breaks.
(2) MG – Mycoplasma gallisepticum
MG is a primary respiratory pathogen that continues to be a challenge to control in some cases. MG has been controlled with the use of 6/85 or Ts-11, however recently these vaccines have lost effectiveness. F-strain has been the next choice for control because of its ability to readily spread bird to bird and displace field MG. Additional vaccine control measures that have been used with some success have been the Vectormune FP-MG and the killed MG product. Chemical control with Tylan with any of the above programs has also worked to stabilize production.
MS – Mycoplasma synoviae
Most layer flocks on multi-age farms are MS positive. Alone MS is not considered a primary pathogen but may act in concert with IB, ILT, E. coli and other respiratory pathogens. Little is done for MS prevention and control.
(3) Bronchitis
Infectious bronchitis (IB) continues to be one of the most important diseases causing losses in egg numbers, shell and internal egg quality. Despite the widespread use of live and killed IB vaccines, variants continue to emerge, decreasing the effectiveness of control strategies. Attention to the details of vaccine timing, strain selection and administration of pullet vaccination programs is still our main approach to control of IB.
(4) Gout or Urolithiasis
Pullets and layers are susceptible to kidney damage that results in mortality with lesions of urolithiasis or gout. Young growing birds are more susceptible to kidney damage from various causes, but the mortality resulting from kidney failure usually occurs when the flock is mature and consuming a high calcium layer feed. Gout, in most cases, is caused by abnormal intakes of calcium or phosphorus. In addition, kidney damage can result from nephropathogenic strains of IB, certain mycotoxins, and water deficiency.
Feed phosphorus has a protective effect against high calcium-induced damage. Grower and layer feeds with low available phosphorus tend to have more gout-related mortality during the production period.
Kidney damage cannot be reversed, but mortality can usually be reduced by acidifying the diet with ammonium sulfate or ammonium chloride at gradually increasing levels up to 1% of the diet.
(5) Osteomalacia (soft bones)
Layers are susceptible to two bone conditions that are related and often confused. Early in the egg production cycle, layers may not consume sufficient calcium or phosphorus to supply their daily needs for eggshell formation and bone regeneration. The result is a soft bone condition called osteomalacia. Osteomalacia is characterized by very pliable bones, crooked keels, collapsed ribs, birds going down in the cage, reduced production, and increased mortality. It is difficult to distinguish between calcium, phosphorus, and vitamin D3 deficiency at this stage. Close attention to daily intake of these nutrients should prevent development of osteomalacia.
The second bone condition is osteoporosis, and is defined as a decrease in the amount of fully mineralized structural bone. Early problems with osteomalacia may cause a flock to be more susceptible to osteoporosis later in life. Between the two bone conditions, osteomalacia is the more significant production problem.
(6) Wet Pox / Dry Pox
Wet pox and dry pox outbreaks continue to occur in vaccinated flocks at a low incidence. In areas/companies having outbreaks, the following program helps correct the problem:
- Use of both pigeon and fowl pox at 1.25 doses of each per bird.
- Increase the number of times the skin is punctured during vaccination from 1-2 to 4 times.
- Check “takes” 7 days post-vaccination. Flocks should score 99-100%.
- Rechecking 300-500 birds on flocks that have a pox break to determine the % of susceptible birds. (Non-vaccinated and non-exposed birds should demonstrate a “take” 7 days post vaccination.)
(7) LT– laryngotracheitis
Seasonal outbreaks of ILT continue to occur in some areas of the country. C.E.O. and T.C.O. vaccines are still considered the standard method of vaccination, but the use of Vectormune POX-LT also appears to be an alternative vaccination method. Mass application of vaccine and unwanted spread of vaccine virus account for many of the outbreaks. Mixing of vaccinated with unvaccinated pullets account for other outbreaks.
Diseases under control and considered a non-issue, but need to be monitored:
Marek’s Disease
Farms with a history of Marek’s are using Rispen/HVT vaccine for control.
Farms with no history of Marek’s are using HVT/SB-1 vaccine for control.
IBD – Gumboro
Always present and flocks need to be monitored for signs of subclinical IBD along with any breaks of IBD that may cause mortality. Thorough cleaning and disinfecting between pullet flocks and a properly timed vaccination program with appropriate products and routes of administration are needed for IBD control. IBD outbreaks in properly water vaccinated flocks are rare; most problems have occurred with spray-administered IBD vaccine.
Coryza
No confirmed cases in the Midwest, but coryza continues to be persistent and prevalent in Southern California. Vaccination programs, controlled exposure and strategic antibiotic treatments limit the economic loss.
Spirochaetes
Sometimes spirochaetes are found when there is an increase in dirty eggs. Treatment with tetracyclines help if spirochaetes are the problem. Histopathology of the digestive tract (cecum) is needed to confirm if spirochaetes are present, as dirty eggs can be caused by other factors.
Cocci
Generally considered to be a mortality problem, cocci breaks are mostly seen shortly after housing in layer houses equipped with manure belts. Some poor performing pullets or flocks after housing have responded to Amprol treatment. This suggests that, under certain conditions, cocci could be having a subclinical affect on performance.
SE - Salmonella enteritidis
Farms having positive SE isolations from tracebacks or environmental testing should use killed SE vaccines. Various programs including no vaccines, live only vaccines, or live and killed vaccines are being used on farms negative for SE. How the new FDA proposed program, “Prevention of SE in Shell Eggs During Production”, announced September 22, 2004, would affect each farm will need to be determined.
FDN – Focal Duodenal Necrosis
In Pennsylvania in 1996, an enteric condition was found in layers that seemed to be associated with some performance problems. The only notable gross lesion was ulcers and/or raised gray/green patches in the duodenum, and rarely in the proximal jejunum. Microscopically, there are ulcers on the tips of villi, populated with large Gram-negative rods. A number of bacterial types have been isolated from affected gut tissue, but there is no proven cause of the disease. The only significant clinical effect is a reduction in egg weight for several weeks compared to normal. Egg weight may be slow to increase early in production or may temporarily fall later in production. The rate of egg production is generally normal, but rarely may show a slight decline. Affected birds may appear to have slightly pale combs, but droppings are normal and mortality is not elevated. All strains of layers seem to be equally susceptible to FDN and it most often is found in multi-age layer complexes. The condition does respond to antibiotics, such as tetracyclines, neomycin, bactracin, tylosin, and erythromycin. Recurrence after treatment is possible.
It may be more common than realized, as it is only diagnosed by necropsy of average-appearing layers, and grossly inspecting the duodenum for typical lesions. FDN has been found in complexes throughout the Midwest.
PN – Peripheral Neuropathy
In recent years, a neurological disease has been recognized in layer pullets that closely resembles Marek’s disease, but is not caused by the Marek’s disease virus. The syndrome has been termed “peripheral neuropathy” and the cause is not known at this time.
The clinical symptoms associated with PN are paralysis of the leg muscles and birds unable to stand, as seen with nerve involvement in Marek’s disease (MD). Pullets in the age range of 6 to 16 weeks are most often affected. Mortality is elevated in typical commercial conditions and can reach 2-5% of the flock. Postmortem lesions consist only of slightly enlarged sciatic nerves in the legs of some affected pullets. Grossly visible nerve enlargement may be seen in only 15-25% of affected pullets.
Experimental evidence suggests this syndrome may be an autoimmune reaction against nerve tissue, triggered by the bird’s immune reaction to other common vaccinations. It also appears there is a genetic aspect, as it is recognized only in certain strains of layers and is more prevalent in birds with certain blood types within those strains.
Marek’s disease vaccination neither prevents this disease nor appears to cause it. At this time, there is no known method to prevent or treat the condition. Layer strains known to exhibit this condition should be expected to have some mortality from PN in the growing period.
From Proceedings of the “Midwest Poultry Federation Convention”, St. Paul, Minnesota, U.S.A.
