Improving the effectiveness of gastrointestinal nematode control for meat-breed lamb production systems on the Northern Tablelands, New South Wales

The experiments reported in this thesis were designed to define and improve the effectiveness of ewe and lamb gastrointestinal nematode control in meat-breed production systems in a summer-dominant rainfall region of NSW Australia. The experiments (Chapters 2-7) reported in this thesis were written as a series of publications. The first step in defining the effect of gastrointestinal nematodes (GIN) on meat-breed lamb production under grazing conditions is the creation and maintenance of uninfected control groups. Experiments conducted under grazing conditions are challenging with difficulties encountered in maintaining uninfected control groups as GIN-free. One method is to serially treat sheep with a combination of short and long-acting anthelmintics to provide effective and continual GIN-suppression

Recent research into the Rispens vaccine: Transmission, protection and interaction with wild-type MDV

Internationally there is clear evidence of increased virulence of Marek's disease viruses leading to vaccine failure (Witter 1997, 1998). There is also evidence that vaccination with "imperfect" vaccines (which prevent disease but not infection) has contributed to this (Read et al. 2015). These findings warrant ongoing screening of isolates for virulence and attempts to improve our understanding of interaction between vaccine and wild-type viruses. In Australia we have a good understanding of the level of protection against Marek's disease provided by vaccination with HVT (Meleagrid herpesvirus 1) alone or in combination with MDV serotype 2 (Gallid Herpesvirus 3) vaccine virus (Renz et al. 2012; Walkden-Brown et al. 2013). These studies have also provided good insight into the kinetics and shedding of these viruses in co-infections with serotype 1 wild-type pathogenic MDV (MDV-1, Gallid Herpesvirus 2) (Islam and Walkden- Brown 2007; Islam et al. 2008). Our understanding of these phenomena with regard to the MDV-1 vaccine strain Rispens CVI988 has been held back internationally and in Australia by the apparent good efficacy of the vaccine in the field and the lack of an easy test to differentiate between the Rispens vaccine virus and wild-type MDV1 and provide virus quantification. In 2011 the Australian Egg Corporation Ltd (AECL) funded our research group to develop a qPCR test to differentiate between Rispens and wild-type MDV-1 and to use the test to address a range of issues. This paper summarises our findings over this whole area. Each component has reported separately in detail in journal papers and those papers are cited in this overview

Effect of host immunosuppression on response to infection with 'Haemonchus contortus'

The host immune response is strongly implicated in the pathogenesis of infection of sheep with the "scour worms" 'Trichostrongylus colubriformis' and 'Teladorsagia circumcincta' as determined by an experimental model enabling separation of the effects of parasitism and immunosuppression. We aimed to clarify the role of the immune response in the pathogenesis of infection by the more damaging haematophagous nematode 'Haemonchus contortus' (Hc) using the same experimental model

Marek's Disease in Australia - Developments in Monitoring and Control

Marek's disease (MD) is a common disease of chickens worldwide, including Australia, caused by the Marek's disease virus (MDV), a cell-associated alphaherpesvirus. The virus is lymphotrophic, but also infects cells of the feather follicle epithelium in which it replicates rapidly and is shed in feather dander, being transmitted laterally via inhalation of this material. The disease as first described by Josef Marek in 1907 was characterised by paralysis and lymphocytic infiltration of peripheral nerves in older chickens. This form of the disease, known as "classical" MD was superseded in the 1950s and 60s by "acute" MD characterised primarily by lymphomas in multiple organs in younger chickens. This development, associated with the intensification of the poultry industry, was a major threat to the industry until the concurrent discovery of the causative agent and development of live vaccines in the UK and USA in 1969. Since that time, there has been an ongoing evolution of virulence of MDV in countries such as the USA, associated with sequential vaccine failure and greater virulence in unvaccinated chickens with or without maternal antibody directed against MDV. Marek's disease vaccines are "imperfect" in that they protect against MD but not infection and shedding of virus, and as such are implicated in the evolution of virulence of the virus. Recent modelling work, based on our Australian research has shown that both vaccination and the reduced host lifespan that has occurred with the intensification of the chicken meat industry are implicated as causes of the observed increase in virulence

Effects of challenge level and vaccination with HVT on rate of MDV transmission

Two experiments investigated the rate of MDV transmission in unvaccinated and HVT-vaccinated broiler chickens exposed to various levels of environmental contamination with MDV. Expt. 1 was in positive pressure isolators with continuous airflow of approx. 12-23 air changes/hr (14-27 m3/hr) and Expt. 2 used floor pens with no artificial ventilation. Chickens in Expt. 1 had air from infected shedder chickens containing 106.07 to 109.01 MDV copies per m3 of air ducted into their isolators for 21 days. Chickens in Expt. 2 inhaled air containing 106 to 107.5 copies of MDV per m3 generated by in-contact shedder chickens. In Expt. 1, 54 (range 40-70)% of unvaccinated chickens were MDV positive at day 7 whereas in vaccinated chickens only 7 (0-20)% chickens were positive. At day 21, 100% of unvaccinated chickens were positive but only 67 (50-80)% of vaccinated chickens were positive. By day 56 post-exposure, 50 (43-66)% of unvaccinated and 11 (9-14)% of vaccinated chickens showed gross MD lesions depending on group. In Expt. 2, 8, 50, 92 and 100% unvaccinated chickens were positive for MDV at days 5, 10, 15 and 20 post exposure whereas a maximum of 14% of vaccinated chickens were positive by day 20 post-exposure. Daily infection rate (%/day) was calculated in Expt. 2 and ranged from 6-10 in unvaccinated and 0-2.8 in vaccinated groups. Vaccination with HVT reduced the rate of lateral infection markedly in both experiments. Rate of transmission in Expt. 2 was significantly correlated with level of MDV exposure in vaccinated but not unvaccinated chickens

Effects of full litter reuse with or without chemical amendment on measures of welfare and performance on three Australian broiler farms

There are pressures on some sectors of the Australian broiler industry to reuse poultry litter for multiple batches of chickens. We investigated the effects of reused litter on bird performance, welfare, litter pH and moisture, and air ammonia concentrations on three commercial farms (A, B, and C) across NSW, Australia. On each farm, the litter inside six sheds was assigned to one of three treatments: 1) a full cleanout replenished with new litter (NL); 2) litter reuse in the entire shed following heaping and turning (RL); and 3) RL plus the addition of a commercial acidifying litter amendment (RL+A). In the RL and RL+A sheds, chicks were placed directly on reused litter. Bird performance, welfare, and litter measurements were made on days 0, 7, 14, and 35. Feed conversion ratios (adjusted to 2.45kg) on a whole farm basis were 1.868, 1.839 and 1.920 for farms A, B, and C, respectively. Day 35 weights were highest on RL on all 3 farms but the effect of litter treatment on mortality varied between farms, with some indication that placing chicks on reused litter less than 3 days after re-spreading increased early mortality. On all three farms, welfare measures provided no evidence of sustained reduction in welfare status of birds on reused litter, nor any clear benefits or disadvantages of litter amendment. Litter moisture content and pH varied significantly with treatment and time on all farms. On the reused litter treatments, moisture content increased steadily on all farms between placement and day 35, with no effect of litter amendment. The litter amendment also failed to lower the pH of the reused litter at any time; however, it did appear to have a reducing effect on air ammonia concentrations relative to the RL treatment on farms B and C. In conclusion, bird performance and welfare can be maintained on reused litter if managed properly

Routine monitoring of Marek's disease virus in poultry dust in Australia

Since 2004 a major Australian poultry company in has used routine monitoring for MDV serotype 1 (MDV1) in poultry dust using serotype-specific real-time quantitative PCR (qPCR) as part of their MD management strategy, particularly in one production region. Dust samples are collected from one house for each farm batch at approximately 6 weeks of age. Combined with standard PCR monitoring of in ovo HVT vaccination in spleen samples, the monitoring program allows assessment of broiler vaccination value, assessment of the seasonal pattern of MDV1 presence and evaluation of MDV1 challenge levels over time. In the one region monitored consistently over the period MDV levels in dust have fallen to very low levels in the last two years. Monitoring has also allowed a rapid comparison of MDV1 status in new sections of the operation. Between 2005 and 2011 1487 shed dust samples were analysed for MDV1 by qPCR with 22.5% being positive for MDV overall. The positive rate ranged from a low of 6% in 2007 to 40% in 2010. Mean (±SD) MDV copy number per mg of dust in positive samples was 4.51±3.2 x 105 on the untransformed scale or 3.96±1.14 on the log10 transformed scale. The range in annual averages on the two scales was 0.091 to 13.2 x 105 with peak levels in 2009 reflecting samples from a new region with very high counts. The experience has been that routine monitoring of MDV by qPCR is a useful tool in managing cost effective control of MD in broiler operations

Field Studies on the Rispens CV1988 Vaccine Virus in Layer and Unvaccinated Broiler Chickens

Rispens CVI988 (Rispens) is a widely used serotype 1 Marek's disease virus (MDV) used as a Marek's Disease (MD) vaccine worldwide. In this study we used Rispens and wild type MDV specific real-time quantitatfge PCR (qPCR) tests to investigate a) vaccination success using qPCR of feather or dust in comparison to enzyme-linked immunosorbent assay (ELISA) b) whether vaccinated chickens are persistently infected, c) whether vaccinated chickens are coinfected with wild-type MDV and d) presence of Rispens in unvaccinated broiler flocks. Feather and dust samples for qPCR and serum samples to detect antibody using ELISA were collected from birds aged 1-91 weeks from three layer farms. DNA extracted from 100 broiler shed dust samples positive for MDV, were re-tested using the Rispens qPCR. Overall 66% of 498 feather samples from vaccinated layers were positive for Rispens. The mean Rispens viral load in feather peaked at 8 weeks. Of 120 feather samples from vaccinated layers tested for wild-type MDV, 8 were positive (6.7%). Of 42 layer dust samples, 93% were positive for Rispens. Viral load in dust peaked around 4 weeks. Anti-MDV antibody was highest at week 8. Antibody levels and virus in feather and dust persisted at variable levels to 91 weeks. Of 100 dust samples from unvaccinated broiler flocks, 7 were positive for Rispens. We conclude that vaccine take can be measured by Rispens-specific qPCR of feathers or dust from 3 weeks post vaccination and infection with Rispens is lifelong. Infection of vaccinated chickens with wild-type MDV was low and there was evidence of escape of Rispens vires to unvaccinated flocks

Spatial landscape utilisation by sheep and its relationship to individual productivity and health

This study explores the relationship between individual animal performance, health and spatial landscape utilisation. Individual animals are known to vary in the way they use landscapes for grazing, camping and travelling activities. There is also clear evidence of variability in production traits between individual animals. However there are few studies linking these two traits and no known studies in sheep. To explore these issues a study is being undertaken in a 46 Ha paddock at Kirby Research Station, Armidale, NSW, Australia. 20 individuals from a mob of 346, 18-month-old fine wool merino wethers, were selected based on race order and weight and UNEtracker GPS collars attached to log their position at 5 minute intervals. The collars were deployed in mid-February 2012 and will remain on the wethers until mid-August 2012. Once a month the sheep will be brought back to the yards where they will be weighed, have mid-side dye-bands put in their wool and have individual faecal samples collected to perform a faecal worm egg count (WEC) for gastrointestinal nematodes followed by a pooled larval differentiation test

Comparison of strategies to provide lambing paddocks of low gastro-intestinal nematode infectivity in a summer rainfall region of Australia

A replicated field experiment using nine 2 ha paddocks was designed to compare the efficacy of 3 management strategies to prepare spring lambing paddocks of low gastrointestinal nematode (GIN) infectivity. The management treatments were designed to provide the same overall stocking rate over the lambing paddock preparation period (Phase 1, 16 January–9 June, 2006). The first treatment involved two 21-day periods of intensive grazing with drenched wethers in Jan–Feb, and in late March (Smartgraze summer rainfall, SGSR). The second treatment was industry standard practice of continuous grazing of adult sheep over the entire preparation period (continuous sheep, CS) and the third treatment was industry best practice of continuous grazing of adult cattle (continuous cattle, CC). Phase 2 of the experiment (14 August–12 December, 2006) tested the efficacy of the paddock preparation treatments. Single-bearing ewes (n = 10 per paddock) were introduced on 14 August following an effective short acting anthelmintic treatment. Lambing commenced 2weeks later on the 25th of August with lamb marking at 7 weeks and weaning at 15 weeks when the experiment was terminated. Tracer sheep (n = 2) were run in each of the paddocks for 2 weeks at the start of Phase 1, and at the start and conclusion of Phase 2 to assess pasture GIN contamination. Total worm counts in tracers were reduced by 97.7% (SGSR), 96.9% (CC) and 88.5% (CS) between the start of the experiment and the introduction of lambing ewes. Between the start of the experiment and weaning, total reductions were 87.9% (SGSR), 85.6% (CC) and 26% (CS). Worm egg counts of ewes and lambs grazing SGSR or CC paddocks were significantly lower than those grazing CS paddocks. As a consequence ewes grazing CS paddocks required anthelmintic treatment at both marking and weaning and their lambs at weaning, whereas no anthelmintic treatments were required for ewes or lambs on SGSR paddocks. Ewes and lambs grazing paddocks prepared with SGSR and CC were significantly heavier at weaning than those grazing paddocks prepared with CS, despite requiring fewer anthelmintic treatments. This experiment demonstrates that an understanding of regional GIN epidemiology can be employed to prepare pastures of very low infectivity in sheep only systems (SGSR) providing parasitological and production benefits equivalent to those obtained by grazing non-host species, in this case mature cattle (CC). Implications of these strategies for the development of anthelmintic resistance are discussed