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Farm Tech1. ANIMAL HEALTHControl of Vaginal Prolapse in EwesProject leader: Dr Richard Hilson 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 our 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 will be 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 will be individually tagged to allow more powerful analysis of disease occurrence in the mixed age ewes. Data will be collected during four visits through the breeding season and analysed at these levels: individual farm, regional and overall. Appropriate reproductive and descriptive data will be reported back to participating farmers throughout the trial. The trial began in autumn 2000 and will run for two consecutive sheep breeding seasons, with complete analysis and information dissemination expected by mid 2002. Raw data collected to date has yet to be analysed, as key information on the occurrence of bearings on participating farms is still being collected, but farmers involved have received individual and group weight and condition score data in graphic form for their general information. Calcium and Bearings in EwesProject leader: Dr Greg Lambert Project outline: This project is investigating the influence on bearings incidence, of manipulating calcium supply to multiple-pregnant ewes in late pregnancy. Bearings (vaginal prolapses) occur mainly in multiple-pregnant ewes. Bearings lower profitability, cause significant psychological stress for farmers, and lead to animal welfare concerns. Management practices that reduce this problem are the desired outcome from the project. Following on from farmer experience overseas, and some preliminary trial work in New Zealand, we are investigating the effect of manipulating calcium status of ewes during pregnancy. A trial last winter was not conclusive, as bearing incidence was very low. However we did establish that of ewes that had a bearing the previous year and survived, about 20% had a repeat occurrence the next year. This emphasises that it is critical to permanently identify and cull all ewes treated for a bearing. Pregnant ewes use more calcium than they can consume during late pregnancy. To offset this negative balance, ewes mobilise calcium from bone and increase absorption from the diet. When the ewe’s demands for calcium increase initially, prior to lambing, blood calcium concentrations decrease leading to physiological changes that subsequently increase calcium supply. It is possible that in some ewes, changes in calcium supply with increasing demand are slow or incomplete and this could result in chronic depletion of calcium which may predispose the ewe to bearings. In the 2000 lambing season we are conducting trials on several commercial properties in Southland, and one in northern Wairarapa, that have chronic bearing problems. Untreated ewes are being compared with ewes exposed to various treatments that might influence calcium status. These are: supplementation with anionic salts (to reduce calcium status) eight to four weeks before lambing, and injection with vitamin D (which increases bone calcium mobilisation) or supplementation with dietary calcium, up to four weeks before lambing. Subclinical Johne’s DiseaseProject leader: Assoc Professor K G Thompson 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 1,800 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 are being compared. During the first two-and-a-half 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 is either not having an impact on productivity, or that it is too early for any measurable effect to become apparent. However, since Johne’s disease is a chronic condition, and tends to affect adult animals, its impact may not be noticed until the ewes are three to four years of age. 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 7 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 to 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. The principal benefit 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. Development Of A Defined Subunit Vaccine Against Johne’s DiseaseProject leader: Dr Alan Murray Project outline: Year 1 (1998/99) To prepare a collection of genes from Mycobacterium avium subsp. paratuberculosis (M.ptb), that code for secreted proteins and to express these genes in E. coli and the fast growing mycobacterial species Mycobacterium smegmatis. The genes will be sequenced and the encoded proteins purified. Year 2 (1999/2000) Sheep will be vaccinated with the live M.ptb vaccine Neoparasec and their white cells will be used in an in vitro assay to identify which of the secreted proteins stimulate a cell mediated immune (CMI) response. Year 3 (2000/01) Sheep will be immunised with pools of secreted proteins selected in year 2 and those proteins that stimulate a CMI response in the animal will be selected for further study as potential vaccine candidates. Industry issue addressed and desired outcomes: The current vaccines against this disease contain whole organisms (either dead or alive), which can cause unacceptable lesions at the injection sites. A subunit vaccine containing only 'protective' antigens can avoid excessive hypersensitivity responses and may not interfere with TB control programmes. Also, being non-infectious it:
Approach used and any interim results/trends: Mycobacterial proteins located on the surface or secreted from the organism are promising candidates for vaccine development. We have recently demonstrated that a ‘protective-type’ of immune response is generated when sheep blood cells from Neoparasec-vaccinated animals are mixed with secreted proteins from M. paratuberculosis. The response was dependent on the amount of protein added to the cells. Blood from unvaccinated animals did not respond to the secreted proteins. This demonstrates that secreted proteins are an important component of the vaccine. We are currently investigating the nature of the immunoreactive proteins, with a view to producing a subunit vaccine composed only of secreted proteins. Novel Johne’s VaccineProject leader: Dr Colin Mackintosh Project outline: A long-term trial is being carried out by AgResearch scientists and staff at the Woodlands research station in Southland, to test a new vaccine and novel methods of administration to prevent Johne’s disease in sheep. The trial will also measure production losses associated with Johne’s disease and subclinical infection. Johne’s disease, which causes wasting and death in adult sheep, is estimated to be present in over 50% of New Zealand sheep flocks and cause losses of over $6 million annually. The only vaccine currently available in New Zealand significantly reduces the incidence of Johne’s disease but causes severe lesions at the site of injection and/or abscesses in the shoulder lymph node. These side-effects cause losses at slaughter due to carcass trimming and have limited the use of the vaccine. The lesions look unpleasant, but neither the vaccine nor the disease presents a proven food hygiene risk. AgResearch have developed a modified vaccine that avoids serious side-effects. Alternative administration methods may also reduce carcass damage. The development of an effective vaccine that causes minimal carcass damage should lead to high levels of uptake by the sheep industry, leading to a dramatic reduction in wastage due to Johne’s disease and increased productivity and profitability. For the last three years, the lambs in two Johne’s infected flocks at Woodlands have been randomly divided into three groups: one getting the conventional vaccine, one getting the new vaccine and the third being unvaccinated controls. The flocks are closely monitored for four years to measure the vaccine efficacy and to measure the effects of Johne’s disease and subclinical infection on productivity. Progress to date shows that vaccination with the novel vaccine causes minimal carcass damage and produces significant immune responses, indicating that the vaccinated sheep should be better able to resist Johne’s disease. Molecular Genetic Fly ControlProject leader: Dr Max Scott Project outline : The aim of our programme is to facilitate the use of the sterile insect technique (SIT) for area-wide control of sheep blowfly by using genetic engineering to make an all-male population of flies which would be sterilised before release in the field. The sterile males mate with fertile female flies in the field producing no viable offspring (blowfly females only mate once). There are several on-going SIT programmes in other parts of the world. Successful past SIT programs 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. There were four main tasks that had to be achieved in order for us to accomplish our aim:
We have accomplished the first three tasks and are making progress on the fourth:
The development of a strain of the Australian sheep blowfly suitable for a Sterile Insect Technique programme would mean that this technique could be used for an area-wide control programme for this pest. Novel Actives and Formulating Agents For Control Of Flystrike On SheepProject leader: Mr Simon Causer Project outline : Previous studies conducted at WRONZ and funded by WoolPro have identified a compound able to improve the penetration and uptake of some ectoparasitic formulations. However, this previous work highlighted a number of other questions that need to be answered before commercialisation can be considered. In conjunction with WoolPro , WRONZ is currently collaborating with a major ectoparasiticide manufacturer to trial and develop a formulation incorporating this agent. The development course will be dictated by whether any proposed formulation change is classified as ‘major’ or ‘minor’ (less than 5% change) by the relevant registration authorities. Initially however, this project will involve collating all available ecotoxicity data for the chemical, preparing a dose-effect curve describing the improvements in formulation uptake and retention achieved using differing amounts of the chemical (by in vitro trialing using greasy fleeces), investigating the compatibility of the chemical with flystrike formulations (including evaluating the effect of temperature and water hardness on formulation stability), and determining the effect addition of the chemical has on the half-life of existing active ingredients. The project will also examine leaching of ectoparasiticide formulation from fleeces and determine whether addition of the chemical alters where pesticide resides in the fleece. Ewe Immunology and ProductionProject leader: Prof A Sykes Project outline: The first year of the trial has been completed successfully. The studies have confirmed that improved protein supply during the peri-partum period assists the ewe in maintaining her immunity and preventing major increase in nematode egg output, and therefore contamination of pasture for her lambs. The work also confirmed our suspicions that the effect of protein nutrition, and the response of the ewe around lambing, may be very dependent on whether she is exposed to nematode larvae during late pregnancy. Ewes which experienced larval challenge while receiving the protein supplement maintained much lower egg output and worm burdens during early lactation than sheep supplemented but without larval exposure, or sheep which were unsupplemented. Current studies are testing which is the optimum pattern or minimum exposure needed to stimulate immunity. Farmers Farmers in many situations have the option of grazing ewes in late pregnancy on contaminated or clean pasture. This work suggests that clean pasture may not be the best choice at this time in the reproductive cycle, if the aim is to limit the ewe’s subsequent contribution to contamination of pasture for the lamb. This is important information as we seek systems which are sustainable with minimum anthelmintic use. ADD GENERAL INFO FROM LAST YEAR’S Sheep Louse ImmunologyProject leader: Dr Alex Pfeffer Project outline: Economic losses experienced by the New Zealand sheep industry due to the louse, Bovicola ovis , result largely from the costs of control and reduced quality of the fleece. These losses may be proportionally similar to the $169 million annually estimated for the Australian sheep industry. In New Zealand, losses due to the pelt defect, cockle, associated with louse infestation, amount to $10 to $15 million annually and this also must be included. Additional to the direct costs of infestation are market-related concerns over insecticide residues and developing resistance by the louse to commonly used insecticides. The objective of this project is to use our increasing understanding of the antigens of the louse and the immunological response of sheep, to control louse infestation and reduce reliance on chemical insecticides. Work on this project is progressing well with several confidential approaches being pursued that should lead to effective control of louse infestation with reduced chemical insecticide usage. Development of A Sustainable Method of Natural Footrot ControlProject leader: Dr Jon G H Hickford Project outline: Footrot results in significant economic losses to New Zealand. In sheep it has been estimated to cost $20,000 per outbreak, per farm, per annum. There are several ways of controlling the disease, but none of these affords lasting assurance against re-infection and all are subject to increasing cost. The possibility of controlling footrot in sheep by exploiting naturally occurring resistance to the disease offers a new and sustainable way of limiting its economic impact. It could also lessen dependence on agrichemicals, antibiotics and vaccines, which is desirable for the future of animal production. In this proposal, gene markers associated with increased resistance to footrot will be developed as a commercially available test. This test will underpin the creation of a ‘best practice’ approach to breeding sheep for increased footrot resistance. |
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