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Rural Industries
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|| Introduction || Project listing|| Project Summaries ||
The following two projects, looking at ovarian regression in domestic hens and the development of Australian vaccines for controlling coccidiosis, have been jointly funded by the Chicken Meat and Egg programs, and hence are listed in this separate section.
OVARIAN REGRESSION IN THE DOMESTIC HEN AND ITS EFFECT ON PERFORMANCE IN LAYER AND BROILER FLOCKS
Objective
· To define the process of atresia of yolky ovarian follicles and relate these changes to those seen in true ovarian disease.
Background
Apparent abnormalities of the reproductive tract in layers/breeders that cease laying may be misdiagnosed as true ovarian disease when in fact they are going through normal ovarian regression.
Research
The process of bursting atresia in the hen's ovary was studied histologically and in vitro studies were undertaken to establish how excess yolky material is disposed of in the ovary. Surveys were undertaken of the prevalence of reproductive tract disease and ovarian regressiion in flocks of layers and broiler breeders.
Outcomes
The process of bursting atresia was defined in detail. Surveys revealed that most breeder birds culled for 'going out of lay' were probably going through normal ovarian regression, rather than as previously thought, being actually diseased.
Implications
This information may assist persons in industry responsible for investigating reproductive losses in broiler breeders to correctly diagnose ovarian disease and differentiate it from reproductive 'shutdown' and hence to devise appropriate control procedures.
RIRDC Project No: UQ-22CM / UQ-25E
RESEARCHER: Dr Roger Kelly
ORGANISATION: The University of Queensland ST LUCIA QLD 4072 PHONE: 07
3365 1111 FAX: 07 3365 1112
CHARACTERISATION AND ATTENUATION OF EIMERIA SPP. FOR USE IN A LIVING VACCINE FOR AVIAN COCCIDIOSIS
Objectives
· To isolate and purify field strains of E.maxima and E.acervulina.
· To attenuate these strains by selecting for precocious development.
· To characterise the precocious lines for pathogenicity and protection.
Background
Coccidiosis is an intestinal parasitic disease of poultry that causes significant economic loss to the intensive poultry industry. Drug treatment has proved convenient and cost-effective for the past 20 years and is still the most commonly used technique for control of coccidiosis. Resistance to available drugs is becoming a problem to industry.
Attenuated oocyst vaccines have been developed in the United Kingdom as an effective alternative to drug treatment. These provide protection provide a degree of immunity equivalent to natural infection. The aim was to develop an Australian version of these vaccines.
Research
Five potential vaccine strains have been isolated and purified by single oocyst passage: two strains of E.acervulina designated RA and NA and three of E.maxima designated RM, AM and KM. All strains were isolated from non-commercial flocks and purified by 3x single oocyst passage in susceptible chickens maintained in isolation. NA and KM strains were stored in liquid nitrogen as backups.
RA (E.acervulina), RM and AM (E.maxima) strains were passaged in susceptible chickens while selecting for precocious development and concomitant reduction in virulence. The precocious strains were then evaluated for reproductive output, pathogenicity, protection against virulent homologous and heterologous challenge, and drug sensitivity.
The RA precocious line of E.acervulina has been evaluated and found to have low pathogenicity, acceptable reproductive output, good protection against homologous and heterologous challenge, and is drug sensitive. Birds vaccinated with the RA strain have been shown to be resistant to virulent homologous and heterologous challenge (including strains isolated in Victoria and New South Wales). It was found to be a good candidate for use in a live vaccine.
The RM precocious line of E.maxima has been evaluated and found to have low pathogenicity, acceptable reproductive output, good protection against homologous and heterologous challenge, and is drug sensitive. This line is the most effective candidate for the E.maxima component of the proposed vaccine.
Implications and outcomes
The candidate E.acervulina and E.maxima vaccine stains developed in the course of this project will be incorporated in a coccidiosis vaccine to become commercially available to industry in the near future. As an outcome of a workshop attended by representatives from industry and Queensland DPI, a project proposal to develop attenuated lines of E.tenella and E.necatrix was developed and has subsequently received RIRDC support.
During the course of the project additional reference and challenge strains and species for intra and inter specific and biological comparisons and diagnostic test development were isolated and purified. A standardised and reliable technique to cryopreserve the different species of Eimeria was also developed.
RIRDC Project No: DAQ-25E / DAQ-29CM
RESEARCHERS: W K Jorgensen & N P Stewart
ORGANISATION: Queensland Dept of Primary Industries, Animal Research Institute,
Locked Mail Bag No 4, MOOROOKA QLD 4105
PHONE: 07 3362 9427 FAX: 07 3362 6429
Last updated: 25 October1997
Copyright © RIRDC
http://www.rirdc.gov.au/pub/97comp/jteggchk.html