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Animal health and welfare

A GENERIC MODEL FOR JOHNE'S IMMUNODIAGNOSIS AND VACCINATION

Project leader: Prof Frank Griffin
Research organisation: Otago University
Project number: 98MN05
Phone number: 03 479 7710
Location: Otago
Fax number: 03 477 2160
Email: frank.griffin@stonebow.otago.ac
Funders: Meat & Wool Innovation, Meat New Zealand

Project outline: The primary goal of this project was to establish an experimental infection model for Johne's disease, using oral exposure to virulent Mycobacterium paratuberculosis. It has been established that continuous culture of the bacteria causes them to lose their virulence, so animals were challenged with bacteria isolated directly from infected lymphatic tissues from sheep with clinical disease. This strategy produced Johne's pathology in the intestine of lambs within four to six months. Infection could also be established by challenging animals via the tonsil. A wide range of cellular and antibody responses were seen in the infected animals within two months. The immune reactions in infected animals tended to be highly cross-reactive and not specific for Johnin antigens. Animals vaccinated with an attenuated strain of Mycobacterium paratuberculosis (316F) produced strong immune reactions that were generally specific for Johnin. Now that the experimental model is working efficiently it will be used for further studies on immunodiagnosis and to test vaccine efficacy.

CONTROL OF VAGINAL PROLAPSE IN EWES

Project leader: Dr Richard Hilson
Research organisation: Veterinary Services (HB) Ltd
Project number: 99VS01
Project number: 06 858 9060
Location: Waipukurau
Fax number: 06 858 9062
Contact: Veterinary Services (HB) Ltd
P O Box 503, Waipukurau
Funders: Meat & Wool Innovation, Meat NZ, AGMARDT

Project outline: The project is an intensive epidemiological study of vaginal prolapse in ewes on up to 70 farms in both Central Hawkes Bay and Central Southland. The objectives are to improve understanding of vaginal prolapse in ewes, and to identify environmental, animal and management risk factors associated with the occurrence of the disease, which may be altered in a practical manner to minimise the problem.

Vaginal prolapse in ewes is a continuing seasonal frustration for all sheep breeders and has serious welfare and financial implications for the whole industry. At a 1% incidence of disease (and some flocks suffer up to 10% prolapse) the estimated direct cost to our industry is $23 million per annum. If suitable practical and proven advice can be generated from this trial, a reduction in disease of just 10% would provide direct annual savings of $2.3 million.

On each participating farm, data has been collected from the start of joining until lambing for a wide range of animal factors, management procedures and physical farm features. In addition, 200 ewes have been individually tagged to allow more powerful analysis of disease occurrence in the mixed age ewes. Data has been collected during four visits through the breeding season and analysed at these levels: individual farm, regional and overall. Appropriate reproductive and descriptive data has been reported back to participating farmers throughout the trial.

The trial began in autumn 2000 and is to run for two consecutive sheep- breeding seasons. Farmer diaries recording ewe feeding levels and bearing histories have recently been collected.

This data is being made computer ready, and initial analysis is expected to be completed by August 2002.

Refer to Wool Grower Summer 2001 (issue #12, p. 11): 'Bearings project nears end' - Results due out in April; Autumn 2001 (issue #9, p. 9): 'Bearings and the rest' - Research sheds new light; Spring 2000 (issue #7, p. 20): 'Bearings' - Like a cheque lying ripped up on the ground; Autumn 1999 (issue #2, p. 21): 'Bearing down'.

FERNMARK SHEEP

Project leader: Dr David Scobie
Research organisation: AgResearch
Project number: 01AR56
Phone number: 03 983 3921
Location: Lincoln
Fax number: 03 983 3946
Email: scobie@agresearch.co.nz
Funders: Meat & Wool Innovation, AgResearch

Project outline: Fernmark sheep will be a polled sheep with a genetically short bare tail, no fleece covering the head, legs, or belly, and a large patch of bare skin surrounding the breech.

The majority of flystrike begins around the backside, where the blowflies are attracted to dags or urine-stained wool. Flystrike will be reduced on Fernmark sheep by crutching them permanently using breeding. Less flystrike will mean a reduced need to use chemicals, which will appeal to organic consumers. Without the need for docking, and with less chance of shearing cuts on the ears, eyelids, teats and pizzle, Fernmark sheep will be more appealing to consumers concerned for the welfare of animals. Shearing Fernmark sheep will be faster, safer and easier, without much loss of fleece wool, and oddment wools will virtually disappear. Oddment wools are the most difficult to harvest with conventional shearing equipment, and are a source of fibre contaminants like stains, grass seeds and kemp fibres. Overall, Fernmark sheep will appeal to producers, shearers, processors and discerning consumers.

So far, researchers have shown that it is very simple to reduce tail length by selection and cross breeding. They also have evidence that increasing bareness of the backside will reduce flystrike around the breech in lambs. This is consistent with the effectiveness of manual techniques such as dagging, crutching and mulesing that produce similar bare patches around the backside. The Meat & Wool Innovation sheep production officers and shearing instructors, and commercial farmers have been enthusiastic about the concept, which has had good publicity through Wool Grower. The Sheep Council has been supportive of the aims of the project, provided that it does not sacrifice too much production. The SPCA, National Animal Ethics Advisory Committee and other animal welfare bodies are very supportive of the breeding programme.

Refer to Wool Grower Autumn 2001 (issue #9, p. 21): '2001 Sheep Odyssey' - The low-input sheep of the future?; Summer 2000 (issue #8, p. 25): 'Worrying wrinkles' - Why wrinkly sheep are all screwed up.


MOLECULAR GENETIC FLY CONTROL

Project leader: Dr Max Scott
Research organisation: Massey University
Project number: 97MU18
Phone number: 06 350 5515 X2586
Location: Palmerston North
Fax number: 06 350 5688
Email: M.J.Scott@massey.ac.nz
Funders: Meat & Wool Innovation

Project outline: The aim of this project is to facilitate the use of the sterile insect technique (SIT) for area-wide control of the Australian sheep blowfly Lucilia cuprina. Genetic engineering will be used to make an all-male population of flies that would be sterilised before release in the field. The sterile males mate with fertile female flies (blowfly females only mate once) in the field, producing no viable offspring. There are several ongoing SIT programmes in other parts of the world. Previous successful SIT programmes include the eradication of screwworm from North America, tsetse fly from Zanzibar, melon fly from the Okinawa islands, Queensland fruit fly from Western Australia and medfly from Mexico. SIT is most effective if only sterile males are released in the field.

L. cuprina is the most important pest species involved in cutaneous myiases (flystrike) of sheep in Australia and New Zealand. The annual cost of flystrike in lost production and control measures has been estimated to be NZ$37 million in New Zealand. In New Zealand, L. cuprina is a relatively recent introduction, first detected in the North Island in 1988. However, the species is now found throughout the North Island and much of the South Island. It is the species most commonly associated with flystrike. The desired long-term outcome of our research would be to use SIT to eradicate L. cuprina from New Zealand. In the medium term SIT could be used to suppress L. cuprina populations, which should significantly reduce flystrike caused by this species.

Over the past four years researchers have made significant progress towards making a transgenic or genetically modified (i.e. GMO) strain of L. cuprina suitable for a male-only sterile-release programme. Researchers have developed a method for making transgenic L. cuprina, which was a major milestone for the project. However, since the current success rate is low, they are now working on improving the method so that they can routinely genetically modify L. cuprina. Researchers have also developed a genetic system for controlling the viability of female flies. The system has been tested in the vinegar fly Drosophila melanogaster, as researchers can routinely genetically modify this species. Female D. melanogaster that carry the female-killing genes die unless small amounts of the antibiotic tetracycline are added to their diet. Work is now underway on optimising the genetic system for L. cuprina. To date three publications from this project have been published in prestigious international science journals.

Refer to Wool Grower Summer 2001 (issue #12, p. 19): 'You only mate once' - Massey research to offer 'green' solution to flystrike; Spring 1999 (issue #4, p. 11): 'Sterile males needed' - Massey fly research shows promise.


SUBCLINICAL JOHNE'S DISEASE
Project leader: Assoc Prof Keith Thompson
Research organisation: Institute of Veterinary, Animal & Biomedical Sciences, Massey University
Project number: 98MU21
Phone number: 06 356 9099
Location: Palmerston North
Fax number: 06 350 2270
Email: K.G.Thompson@massey.ac.nz
Funders: Meat & Wool Innovation, Massey University

Project outline: The purpose of this project is to obtain quantitative data on the effects of subclinical Johne's disease in sheep, and the benefits that can be expected from vaccination. At present, the true cost of the disease to farmers with infected properties is unknown. As such, it is impossible to provide objective advice to farmers on the likely benefits of a vaccination programme.

A total of approximately 1800 replacement ewe lambs, on two commercial properties, have been vaccinated with either a killed or live Johne's disease vaccine, or included as unvaccinated controls. A range of production parameters, including growth rate, wool production, reproductive performance, and survival, are being measured in these animals over a four-year period. In addition, the size of the lesions associated with the two vaccines is being compared.

During the first four years of the trial, no significant differences have been detected between vaccinated and unvaccinated groups in liveweight, fleeceweight and reproductive performance on either property. This suggests that subclinical Johne's disease in sheep, unlike in cattle, is not an important cause of production loss.

On one property, the size of vaccination-site lesions induced by the live vaccine were significantly larger than those induced by the killed vaccine. This difference was apparent after seven months and was even more marked after 13 and 25 months. This could be associated with the persistence of live organisms at the vaccination site, or with the presence of a more irritant and persistent adjuvant. Interestingly, there was no significant difference in the size of vaccine-site lesions on the other property.

Blood-testing of a sample of sheep from each group throughout the trial has shown a good initial humoral immune response to both vaccines, but there was a more rapid decline of titres in animals vaccinated with the live vaccine. Interestingly, the live vaccine appeared to induce a better cell-mediated immune response than the killed vaccine.

The principal value of this project, together with related projects at Invermay and in Australia, will be to determine the actual cost of subclinical Johne's disease to sheep farmers, and to show the benefits that can be expected from vaccination. Meanwhile, efforts to produce a new vaccine with fewer side-effects are proceeding at Massey University.

 

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