California Poultry Letter

University of California - Cooperative Extension - May/June 1999


The Poultry Symposium and Egg Processing Workshop previously scheduled for June 29 and 30 have been cancelled and will be rescheduled in the Fall.


C. Riddell

Western College of Veterinary Medicine

University of Saskatchewan

Saskatoon, Canada


Avian leukosis is caused by a group of viruses called the avian leukosis/sarcoma retroviruses. These viruses can cause a wide range of tumors. Until recently the most common tumor caused by these viruses has been lymphoid leukosis which is characterized by massive enlargement of the liver due to infiltration of cancerous lymphoid cells. In lymphoid leukosis other abdominal organs and, in particular, the bursa of Fabricius are also often involved. Other tumors caused by this group of viruses have been rare. They include myelocytoma, erythro-blastosis, fibrosarcoma, nephro-blastoma and osteopetrosis. This group of viruses is split into subgroups on the basis of coat differences. These subgroups vary in occurrence, pathogenicity and tumor types produced. Subgroups A and B have been the most common and generally cause lymphoid leukosis. Subgroups C and D are rare while Subgroup E is very common but rarely causes tumors. Subgroup J is a new subgroup which has recently been recognized. It has been associated with a wide range of tumors including myelocytoma, erythro-blastosis and fibrosarcoma.

It should be noted that infection with these viruses does not always result in tumors but that infection can result in a reduced number of eggs over a production cycle. These viruses are spread by egg transmission and can also spread laterally from bird to bird. They are relatively fragile and will not survive for long in the environment. By selecting hens which are not transmitting the viruses to their eggs and raising progeny from these hens in isolation with good biosecurity it has been possible to eradicate subgroup A from some flocks of chickens. Primary breeders have been working on such eradication programs.


In 1989, a new avian leukosis virus was isolated from meat type chickens in the United Kingdom and was designated J on the basis of its coat properties. It was associated with myelocytomas and other tumors. Research in the United Kingdom suggests that this new virus arose from a recombination of parts of other avian leukosis viruses. In 1996, a similar virus was isolated from broiler breeder chickens dying from myelocytomas in North America. Since then increased mortality due to myelocytomas and other tumors has been reported in broiler breeder flocks throughout North America. Another term which has often been used to describe myelocytomas in these flocks is myeloid leukosis. The other tumors which have been recognized include erythroblas-tosis, sarcomas, and hemangiomas.

Increased mortality in these flocks does not usually start until after 17 weeks of age and the severity can vary greatly. The mortality may be double or triple the normal in the laying house and a high of 6 percent per month has been reported in some flocks. J viruses have been isolated from several of these flocks. Research on these isolates indicates that the properties of the virus are often different. This indicates that the virus is not very stable. It has been suggested that the virus may be becoming more virulent and as a result may cause more severe losses.

Recent observations and experimental work indicate that J viruses as well as causing mortality will affect breeder flock performance with reduced numbers of eggs and reduced egg size. A recent study found that these smaller eggs contained the virus. This explains uneven broiler flocks and mortality in some broiler flocks due to J virus. Though it was originally thought that Leghorn chickens were resistant to J virus this may be incorrect. Mortality due to tumors which may have been caused by J viruses has been recognized recently in leghorn chickens. Stress may be important in the severity of disease caused by J virus. A recent experimental study demonstrated an interaction between J virus infection and Marek=s disease.


As this is a viral infection it cannot be treated. No vaccines against J virus are available. Correct diagnosis is important. Isolation and identification of the virus can only be done by a very few laboratories. However, the pattern and types of tumors in an affected flock is generally very suggestive of J virus infection. Sometimes to correctly identify the type of tumor, microscopic studies in a laboratory are needed.

Primary breeders are working to eradicate J virus from their stocks using the methods described in the introduction but this is not a simple task. The tests required to identify infected hens are complex and expensive. There may be inter-ference with the tests by other subgroups of avian leukosis viruses. The testing may be complicated by changes in the virus. However, if breeder chicks free of J virus can be obtained it should be possible to keep them free of infection if good biosecurity is practiced on a farm.

The most harmful effects of infection with J virus appear to occur if infection occurs by egg transmission or within the first 6 weeks of life. In a breeder flock, males and females should be reared separately for at least 6 weeks. Strict sanitary precautions should be taken to avoid possible spread of infection between sexes. Infection can be spread by needles used for vaccination or collecting blood samples. Needles should be changed between sexes when using them at an early age. Any stress, particularly during this early period should be avoided. Circumstantial evidence suggests that overheating and/or crowding may increase the severity of the disease. It may also be increased by any form of immuno-suppression. Proper con-trol of diseases such as Marek=s disease and infectious bursal disease which cause immuno-suppression is important.



California Egg Quality Assurance Plan (CEQAP) Progress Report

Most of our readers should be aware that the program now requires environmental sampling of laying flocks. The last training workshop on environmental sampling was completed on May 6th. Plan participants now have 60 days to submit updated quality assurance plans. Updated plans should be mailed or delivered to the appropriate Regional CDFA office. This means that all updated plans are due by July 6th. If participants need help with plan development they can contact David Goldenberg at 916/985-0675 or e-mail

If you want training on environmental sampling so that you are certified to collect and submit your own samples and you did not participate in one of the workshops, you must employ a certified veterinary consultant to train you. Under some circumstances certified State or University veterinarians may volunteer to provide you this training, but this is not part of their usual responsibility. CDFA veterinarians are now sampling many ranches as part of a field study assessing the incidence of Salmonella enteritidis on California egg ranches. Some ranchers may be able to get hands on training while this sample is being collected. A partial list follows of veterinarians who have been certified to collect environmental samples and instruct industry clients.

Certified private veterinary consultants:

1. Mark Bland

2. Gregg Cutler

3. Marian Hammerlund

4. Fausto Manotok, III

5. Mike Martin

6. Steve Spellman

Certified CDFA and University veterinarians:

1.  David Castellan, CDFA, Sacramento

2.  Chrisin Charlton, CDFA, Sacramento

3.  Joan Jeffrey, UC Tulare

4.  David Kerr, CDFA, Ontario District

5.  Gene Little, CDFA, Ontario District

6.  Sarah Mize, CDFA, Fresno District

7.  Dan Rolfe, CDFA, Modesto District

8.  Robert Tarbell, CDFA, Fresno District

9.  Pat Wakenell, UC Davis

10. David Willoughby, CDFA, Modesto District

New professionally produced video tapes for the CEQAP are becoming available as follows:

Flock Health Management (12 minutes) Tape #14P; sponsored by USDA, FSIS.

Cleaning, Disinfection and Biosecurity (19.5 minutes) Tape #15P; sponsored by USDA, FSIS.

Invertebrate Pest Management (22 minutes) Tape #16P; sponsored by Bayer Corporation; available soon; check with the PePa office for availability.

Rodent Control (46 minutes) Tape #17P; sponsored by Bayer Corporation, USDA & CDFA

The cost is $11 per tape which includes shipping and handling. To order contact the Pacific Egg & Poultry Association, 1521 I St., Sacramento, CA 95814, phone 916/441-0801.


June 22-25, 1999

Oregon Poultry Industries Council/Washington Poultry Industries Association Joint Poultry Convention, Eagle Crest Resort, Redmond, Oregon. For information contact Jim Hermes 541/737-2254 or Steve Wagner 541/484-6511.

August 8-11, 1999

Poultry Science Association Annual Meeting, Springdale, Arkansas. For information contact the PSA Office at 217/356-3182.

August 15-19, 1999

12th European Symposium on Poultry Nutrition, Veldhoven, The Netherlands. Organized by the WPSA Working Group No. 2, Secretariat WPSA 12th European Symposium on Poultry Nutrition, c/o Wageningen Agricultural University, Animal Nutrition Group, Dr. Rene P. Kwakkel, P.O. Box 338, 6700 AH Wageningen, The Netherlands. Telephone: +31 317 482468/ 484082; Fax: 31 317 484260.

May/June Editor:

Ralph A. Ernst, Extension Poultry Specialist, Animal Science Department, University of California, Davis, CA 95616-8521

Tel. (530) 752-3513, Fax (530) 752-8960, e-mail: