Flock use of the range is associated with the use of different components of a multi-tier aviary system in commercial free-range laying hens.

1. The objective of this study was to investigate the association of using a multi-tier aviary system and access to range on flock uniformity in free-range laying hens, and to determine whether the extent of range use or flock uniformity can be predicted from the use of different levels of the aviary system.2. A total of 13,716 Lohmann Brown hens from five commercial free-range flocks housed in identical houses on the same farm were individually weighed at 16 weeks of age and allocated to five replicate areas within each house. Hen movement in the multi-tier aviary system and on the range was individually monitored using radio frequency identification (RFID). All hens had access to the range from 18 to 22 weeks of age and were exposed to the same management conditions.3. Whilst only one flock significantly changed its flock uniformity with time, they differed from each other in uniformity and body weight (P = 0.001).4. Hens spent most of their available time on the lower aviary tier (7.29 ± 0.029 h/hen/day) and on the upper aviary tier (4.29 ± 0.024 h/hen/day) while the least amount of time was spent on the range and in the nest boxes (0.93 ± 0.005 h/hen/day and 1.48 ± 0.007 h, respectively, P = 0.001).5. Range use was negatively correlated (r = -0.30) to the time spent on the upper aviary tier and positively correlated (r = 0.46) to the time spent on the lower aviary tier (P = 0.001). Bivariate analysis revealed that range and upper aviary resp. lower aviary tier usage had a significant curvilinear association.6. In conclusion, the study showed that range use was associated to the time hens spent on the different tiers of the aviary system. Flock uniformity varied between flocks but was not associated with either range and aviary system usage.

Viability and development of Ascaridia galli eggs recovered in artificial media followed by storage under different conditions.

Eggs oviposited by Ascaridia galli females in artificial media are commonly used as a source of infective material. We investigated the rate of egg production by cultured mature females (n = 223), and changes in egg viability under different storage and incubation conditions. Eggs recovered after 1, 2 or 3 days of culture were subjected to either (1) storage in water at 4°C (1, 4 or 8 weeks) followed by incubation in 0.1 N H2SO4 at 26°C (2, 4 or 6 weeks); or (2) prolonged storage at 4°C (up to 14 weeks). Egg development and viability was assessed by morphology coupled with a viability dye exclusion test of hatched larvae. Of the 6,044 eggs recovered per mature female 49.2, 38.5 and 12.3% were recovered on days 1, 2 and 3 of worm incubation respectively with similar initial viability (≥99%) between days. Eggs recovered on different days had only minor differences in viability after storage. The prolonged storage period at 4°C significantly affected both viability and embryonation ability resulting in decline in viability of 5.7-6.2% per week. A smaller but significant decline in egg (2.0%) and hatched larval (1.4%) viability per week of incubation at 26°C was also observed. We conclude that storage and incubation conditions, not the day of egg recovery, are the main factors affecting A. galli egg viability. Our findings indicate that under aerobic conditions storage at 26°C may be preferable to 4°C whereas other studies indicate that under anaerobic conditions storage at 4°C is preferable.

Pathogenicity, tissue distribution, shedding and environmental detection of two strains of IBDV following infection of chickens at 0 and 14 days of age.

Infectious bursal disease virus (IBDV) is endemic to most poultry-producing countries worldwide. Immunosuppressive classical and variant IBDV strains endemic to Australia are genetically distinct from other international strains. We report the results of infection experiments with Australian classical strain 06/95 and variant strain 02/95 in SPF chickens. We tested the effects of strain and age of infection on bursal atrophy, viral RNA (vRNA) load in bursa of Fabricius (bursa), spleen, thymus, caecal tonsils, faeces, litter and exhaust dust as determined by real-time reverse transcriptase polymerase chain reaction. The two IBDV strains did not differ in the degree of bursal atrophy induced, lymphoid organ distribution and faecal shedding but variant strain 02/95 induced a greater antibody response to the infection than classical strain 06/95 which was associated with a more rapid decline in IBDV vRNA genome copy number (VCN) in lymphoid organs and faeces. Infection at 14 days of age induced greater bursal atrophy and higher vRNA copy number in lymphoid tissues than infection on the day of hatching, indicating true age susceptibility independent of maternal antibody (Mab) status. The direction of the association between rankings for IBDV vRNA load in bursa and relative bursal weight changed from positive at 3 and 6 days post-infection to negative at 28 days post-infection. Intra-tracheal administration of dust collected from chickens infected with IBDV resulted in successful transmission of IBDV. IBDV vRNA was detected successfully at high levels in the environmental litter and dust samples.

Evaluation of high dietary inclusion of distillers dried grains with solubles and supplementation of protease and xylanase in the diets of broiler chickens under necrotic enteritis challenge.

A 2 × 2 × 2 factorial experiment was conducted to investigate the effect of a high level of sorghum distillers dried grains with solubles (DDGS; 20%), with or without a combination of protease and xylanase in broiler chickens, under a necrotic enteritis disease challenge. A total of 576 male broiler chicks were randomly assigned to 8 experimental treatments, each replicated 6 times, with 12 birds per replicate for 35 d. Oral inoculation of the challenged group with Eimeria spp. occurred on d 9, followed by 3 consecutive inoculations of Clostridium perfringens from d 14 through 16. The disease challenge and DDGS inclusion significantly (P < 0.01) interacted, depressing BW gain and feed conversion ratio only in wk 3. Disease challenge adversely influenced (P < 0.01) BW gain and feed conversion ratio of the birds in the third week and across the 35-d study. Over the last 2 wk and across the 35-d trial, the interaction between DDGS and enzyme supplementation showed a tendency (P = 0.09) to gain more BW in birds regardless of the disease challenge. Inclusion of 20% DDGS markedly (P < 0.01) interacted with disease challenge, accelerating the proliferation of C. perfringens in the ceca at d 17. Inoculation of birds with C. perfringens resulted in higher (P < 0.01) counts of C. perfringens in both ileal and cecal contents. The necrotic enteritis-related lesions (d 17) were more severe (P < 0.05) in the intestine of infected birds fed DDGS diets than in birds fed the control diet. Incorporation of DDGS to the diets improved (P < 0.01) the IgA and IgG titer at d 13 but interacted with the disease challenge, reducing the concentration of IgA at d 21 and IgM at d 35 in the infected birds. In conclusion, incorporating a high level of DDGS in the diet of broiler chickens may increase susceptibility to necrotic enteritis. Supplementation of enzymes did not reveal significant mitigation effect in infected birds but helped the birds fed DDGS to maintain feed intake and BW gain.

A cost-benefit analysis of foot and mouth disease control program for smallholder cattle farmers in Cambodia.

The Cambodian government is attempting to mobilise government, donor and private sector funding to implement a coordinated FMD vaccination program (FMDVP). A necessary first step is to convince the farmers of the benefits of participating in and potentially financially supporting this program. Information was collected from 300 farmers in order to estimate the on-farm benefits and costs of their participation in an FMDVP. Implementing a successful vaccination program is difficult, and farmers understand from previous experience that there may be institutional, social, technical and financial constraints which limit its success. A benefit-cost analysis needs to take into account that outbreaks do not occur every year, not all cattle will be successfully vaccinated, not all sick animals successfully treated and sometimes sick animals simply sold. This study sensitises these variables in order to give a realistic estimation of the farmer participation benefits in an FMDVP. A general result is that it is worthwhile for farmers to participate in the FMDVP if there are average annual outbreaks, or at least two major outbreaks, in the ensuing 5 years. However, the results are influenced by the interaction of vaccination success and treatment success and coverage. Ineffective coverage and poor treatment of sick animals reduce the benefits of an FMDVP. It is also important that farmers do not sell sick stock and, if they do, that they are able to breed replacements rather than purchase replacements. There are many factors in the smallholder cattle farming system that will influence the success of an FMDVP; farmers will only choose to participate if they can be convinced of the short and long-term economic benefits.

Australian surveys on incidence and control of blowfly strike in sheep between 2003 and 2019 reveal increased use of breeding for resistance, treatment with preventative chemicals and pain relief around mulesing.

Blowfly strike or cutaneous myiasis, caused principally by the Australian sheep blowfly Lucilia cuprina is endemic to Australian sheep producing areas and is a major cause of suffering and economic loss. This article reports incidence and control practices as determined by three cross-sectional surveys of Australian sheep farmers covering the years 2003 (n = 1365), 2011 (n = 575) and 2018 (n = 354) with more questions relating to blowfly strike in the latter two surveys. Breech strike was reported at a higher rate than body strike in all survey years. Reported annual incidence of breech strike ranged from 2.2 to 4.7% of sheep nationally with minor differences between ewes and lambs. The incidence of body strike ranged from 1.0 to 7.1% with higher incidence in younger sheep in all years. The use of fixed time routine preventative chemical treatments increased during the survey period (43%, 46% and 66%, in 2003, 2011 and 2018 respectively) with dicyclanil (54%-58%) and cyromazine (23-36%) the main insecticides used for control since 2011. The use of the Mules operation (mulesing) to remove skin wrinkles from the breech area as a preventative modification did not change between 2011 and 2018 (47% in both), however, the use of pain relief at mulesing of replacement ewe lambs increased substantially between 2011 (59%) and 2018 (87%). The most commonly used methods to assist with flystrike control were timing of crutching (clipping of wool from susceptible areas) and shearing, with few respondents destroying maggots from treated sheep (21-26%) and very low use of fly traps (5-8%). Phenotypic selection of ewes for reduced susceptibility to flystrike based on visual traits was practiced by 61% of respondents in 2011 and 56% in 2018. Selection of rams for reduced susceptibility using estimated breeding values increased from 10% in 2011 to 17% in 2018. Breeding for resistance was the most commonly nominated (21%) most important change made to flystrike management in 2018. The results indicate that concern for sheep welfare has increased with almost universal use of pain relief at mulesing. Increased use of selection for blowfly resistance indicates farmer commitment to planning for a future without mulesing, although the practice remains prevalent. An increase in the reliance on preventative chemical treatments increases the risk of insecticide resistance.

Prevalence of sheep lice and trends in control practices across Australia - Australian sheep parasite control surveys from 2003 to 2019.

The sheep body louse (Bovicola ovis) is a parasite of major economic concern in Australia. This article reports lice incidence and control practices on Australian sheep farms as determined by three cross-sectional surveys of the years 2003, 2011 and 2018. The incidence of live lice detected within a flock was similar across the survey years with a slight decline in 2018 (2003: 20%, 2011: 18.6% and 2018: 13.9%). In an average year, most farmers did not see any direct or indirect evidence of lice infestation (2011: 59.3% and 2018: 69.5%), however, over a five-year period 38.9% (2003), 66.3% (in 2011) and 55.8% (in 2018) reported seeing evidence of lice infestation at least once with significant variation between sheep producing regions in 2011. In an average year, nearly three quarters of respondents treated for lice (2011:73.5% and 2018: 73.3%) with the majority treating immediately following shearing and very few treating sheep with long wool. Even higher percentages treated for lice at least once in the preceding five-year period (2011: 86.2% and 2018: 87.5%). Backliner was the most popular method of chemical application for lice control in sheep off-shears or with short wool (2003: 77%, 2011: 73% and 2018: 74.3%). For long wool treatments, hand jetting declined in popularity from 2003 (64%) to 2011 (54%) and 2018 (8.6%) as backliners became more popular (2003: 36%, 2011: 51% and 2018: 60%). The use of benzoylphenyl urea insect growth regulators (IGR) for off-shears/short wool treatment declined from 2003 (92.8%) to 2011 (51%) and 2018 (2.9%) and were largely replaced by neonicotinoids and spinosad for backliner/spray-on products. The use of organophosphates declined for plunge dipping (2003: 83.8%, 2011: 83% and 2018: 7.7%). Spinosad use for plunge dipping off-shears/short wool increased over the survey years (2003, 0%, 2011: 9% and 2018:46.2%). The use of IGRs declined for backliner application on long wool and were mainly replaced by spinosad in 2011 and 2018. Fewer respondents reported suspected resistance to lice control products in 2018 (8%) compared with 2003 (26%) and 2011 (13%) with most reporting suspected resistance to IGR and synthetic pyrethroids and emerging suspicions of resistance to neonicotinoids in 2018. Resistance to lice control products also reduced in importance as a reason for recurring lice infestations between 2011 (ranked 2nd) and 2018 (ranked 6th). Biosecurity was important to sheep producers with the highest ranked reason for recurring lice infestations being from stray or purchased sheep.

Investigation of the combined efficacy of two Haemonchus contortus vaccines in weaner Merino sheep.

This study was conducted to investigate whether co-administration of Barbervax® (Bvax) with Haemonchus contortus surface larval antigen (HcsL3) would increase the protective efficacy and duration of protection against H. contortus infection in weaner Merino sheep. A total of 132 10-month-old weaned Merino ewe lambs were randomly allocated into six treatment groups (n = 22). Sheep were vaccinated four times with either Barbervax® (Bvax), H. contortus L3 surface larval antigen (HcsL3), combined vaccination (Bvax + HcsL3), Bvax + AlOH, HcsL3 + Saponin or remained as unvaccinated controls. Aluminium hydroxide (AlOH) and saponin adjuvants were included in HcsL3 and Bvax vaccines respectively. The first three vaccinations were given at 4 week intervals and the fourth vaccination provided as booster, 9 weeks later. All animals were treated with Zolvix™ (monepantel 25 mg/mL, Elanco) at the third vaccination and commencing two weeks later, artificially trickle infected with H. contortus L3. Worm egg count (WEC), packed cell volume (PCV), antibody titre and bodyweight were measured throughout the study as was specific antibody directed against each antigen using ELISA. The administration of Bvax and HcsL3, alone or in combination, induced an antibody response against HcsL3 but only the Bvax and the combined treatment elicited an antibody response to the Bvax antigen. The targeting of HcsL3 by each vaccine was confirmed by immunofluorescence staining of H. contortus L3. However, only the booster vaccination in the Bvax treatments reduced WEC to levels below untreated controls. The HcsL3 vaccine did not reduce WEC in this experiment and co-administration with Bvax did not improve the efficacy and duration of protection against H. contortus infection.

Benchmarking Australian sheep parasite control: Changes in gastrointestinal nematode control practices reported from surveys between 2003 and 2019.

Cross-sectional surveys of sheep parasite control practices in Australia were conducted in 2004, 2012 and 2019 to document parasite problems, control practices and measure change over time. This article reports the results pertaining to gastrointestinal nematode infection; comparisons between years are mostly descriptive and not based on statistical inference. There was a general increase in the use of grazing management to prepare clean pastures for sheep to control gastrointestinal nematode infections with the largest increases in the use of: cropping, long acting anthelmintics to prepare clean pastures, feeding strategies, selecting rams for resistance to nematodes, and leaving some sheep untreated. The proportion of respondents using faecal worm egg count monitoring (WEC) and the number of WEC monitors per year were similar in 2003 (weaners: 3.0 WEC/year, adult ewes: 2.6 WEC/year) and 2018 (lambs and weaners and adult ewes both 3.1 WEC/year) but lower in 2011(lambs and weaners: 2.0 WEC/year, adult ewes: 2.9 WEC/year), whilst there was a higher number of anthelmintic treatments given in 2011 than 2003 and 2018 which were similar. There was an increase in the proportion of respondents carrying out WEC monitors themselves from 2011 (21%) to 2018 (30%) and a corresponding reduction in the use of private laboratories, government laboratories and veterinarians with regional differences in who carried out WECs. The top three anthelmintic groups used did not differ between the three survey years with macrocyclic lactones the most used followed by benzimidazoles (BZ) and levamisole (LEV) although the percentage of MLs used in 2011 and 2018 was lower than in 2003 with higher proportions of respondents using BZ and LEV groups in the latter two survey years. Moxidectin was in the most commonly used active in all survey years. There was an increase in the use of combination of anthelmintics from different groups, especially for a combination of three anthelmintics (2003: 4.4%, 2011: 19.1%, 2018: 21.5%), with lower use of single anthelmintics in 2011 (57.0%) and 2018 (55.4%) compared with 2003 (74.5%). The use of testing for anthelmintic resistance was generally low across the survey years with a lower proportion of respondents using tests in 2011 and 2018 than in 2003 (2003:48%, 2011: 29%, 2018: 37%). Time of year, results from WEC and seasonal weather condition were the most important factors when deciding when to apply anthelmintic treatment.

Protective efficacy of Barbervax® in Merino weaner sheep trickle infected with five doses of Haemonchus contortus infective larvae.

Barbervax® protects sheep against H. contortus infection; however, the level of protection afforded by the vaccine at different levels of larval challenge under field conditions has not been reported. Therefore, this study was designed to investigate the protective efficacy of Barbervax® at increasing doses of trickle infection with H. contortus third stage larvae (L3). Merino lambs (220) were randomly allocated to challenge treatment groups and received Barbervax® vaccinations at approximately 8, 11, 15 and 22 weeks of age or not vaccinated (control group). Animals within each treatment group were subjected to one of five levels of H. contortus L3 trickle infection (0, 300, 600, 1200 and 2400 L3/week in two split doses). Trickle infections started two weeks after the third vaccination (week 0). Worm egg count (WEC), packed cell volume (PCV), antibody titre and bodyweight were measured at week 2 (start of trickle infection), week 5 and then every two weeks for 11 weeks. Vaccinated weaners had a significantly (P < 0.0001) lower faecal WEC than unvaccinated control animals. Vaccination induced significant specific antibody responses that were not influenced by level of trickle infection. Vaccination significantly reduced the number of weaners requiring salvage anthelmintic treatment (9.4% vaccinated weaners versus 33.6% unvaccinated). Vaccine protective index based on WEC was similar at all challenge levels (overall mean> 60%) and at the higher challenge levels did not reduce H. contortus infection to levels that would not require anthelmintic treatment. Therefore, it is suggested that under conditions of high larval challenge the use of Barbervax® should be integrated with other control methods.

A quantitative trait locus for faecal worm egg and blood eosinophil counts on chromosome 23 in Australian goats.

Three microsatellite markers on goat chromosome 23 adjacent to the MHC were used to test for quantitative trait loci (QTL) affecting faecal worm egg count (WEC) and leukocyte traits in ten Australian Angora and twelve Australian Cashmere half-sib families (n = 16-57 per family). Data were collected from 280 Angora and 347 Cashmere kids over a 3- and 4-year period. A putative QTL affecting trichostrongyle WEC was found in two small families at the 5% chromosome-wise threshold level. The biggest QTL effect for WEC of 1.65 standard deviations (sigma(p)) was found within the region of OarCP73-BM1258. A significant QTL affecting blood eosinophil counts at the 1% chromosome-wise threshold level was detected at marker BM1258 (at 26 cM) in two Angora and Cashmere families. The magnitude of the putative QTL was 0.69 and 0.85 sigma(p) in Angora and Cashmere families, respectively. Due to the comparatively low power of the study these findings should be viewed as indicative rather than definitive.

Evaluation of Barbervax® vaccination for lambing Merino ewes.

The Barbervax® vaccine, directed against Haemonchus contortus, has been commercially available in Australia since 2014. However, to date the optimal timing for booster vaccination of lambing ewes has not been identified. Therefore the aim of this experiment was to compare the efficacy of Barbervax® when administered to ewes one week prior to the commencement of lambing versus at lamb marking 7 weeks later. A total of 400 single bearing Merino ewes, run on a commercial sheep property in the New England region of New South Wales, previously primed with Barbervax® were enrolled in the project. The experiment incorporated a cross-over design with two treatments imposed pre-lambing; Barbervax® booster vaccination with anthelmintic (n = 200) or anthelmintic alone (n = 200). At lamb marking, there were four treatment groups (n = 100) and anthelmintic was administered to all treatment groups. The four treatment combinations were Barbervax® booster vaccination at pre-lambing and lamb marking (V-V), booster vaccination only at pre-lambing (V-A), booster vaccination only at lamb marking (A-V) or anthelmintic only at both at pre-lambing and lamb marking (A-A). Pre-lambing Barbervax® booster vaccination of ewes induced an antibody response and, when used in conjunction with anthelmintic, significantly reduced worm egg counts (WEC) assessed at 7 weeks (lamb marking) and 13 weeks later, relative to treatment with anthelmintic alone. Booster vaccination plus anthelmintic treatment at lamb marking was not effective at reducing WEC compared to anthelmintic treatment alone. Body weight and packed cell volume did not differ between the treatment groups throughout the trial. In conclusion Barbervax® booster vaccination at pre-lambing provides additional protection for reproducing ewes given an effective short acting anthelmintic at this time.

A simplified Barbervax® vaccination regimen in lambs to evoke immunological protection to Haemonchus contortus.

This study assessed the feasibility of altering the pre-weaning vaccination schedule of the commercially available Barbervax® vaccine directed against Haemonchus contortus, to avoid the 2nd priming vaccination which typically falls between lamb marking and weaning. Merino lambs (n = 175) born to maiden ewes, located in the Northern Tablelands, New South Wales, were randomly allocated to treatment groups (n = 35) and subjected to five different vaccination regimes. One group remained as unvaccinated controls and another had the full set of three priming doses. The other three groups were vaccinated only at marking and weaning receiving a double dose of vaccine at marking and/or weaning. The hypothesis tested was that reducing the interval between lamb marking and weaning to 6 weeks, and providing a double dose of vaccine at marking, weaning or both would remove the need for the second priming vaccination between lamb marking and weaning. This priming vaccination in the vaccination protocol necessitates an additional mustering of ewes with young lambs at foot and is a time consuming and costly exercise which increases the risk of mis-mothering. Blood and faecal samples were collected at frequent intervals for worm egg count (WEC), larval differentiation and H. contortus vaccine specific ELISA antibody analysis. Overall, the results supported the hypothesis, and it was found that antibody titres and WEC reductions equivalent to the registered vaccine regimen were achieved by the alternative regimens. This finding requires further investigation under a wider range of conditions. Deviation from the registered vaccination protocol would constitute off-label usage, and at this time and until further evaluations are done these deviations are not recommended.

Genetic mapping of quantitative trait loci for resistance to Haemonchus contortus in sheep.

This paper presents results from a mapping experiment to detect quantitative trait loci (QTL) for resistance to Haemonchus contortus infestation in merino sheep. The primary trait analysed was faecal worm egg count in response to artificial challenge at 6 months of age. In the first stage of the experiment, whole genome linkage analysis was used for broad-scale mapping. The animal resource used was a designed flock comprising 571 individuals from four half-sib families. The average marker spacing was about 20 cM. For the primary trait, 11 QTL (as chromosomal/family combinations) were significant at the 5% chromosome-wide level, with allelic substitution effects of between 0.19 and 0.38 phenotypic standard deviation units. In general, these QTL did not have a significant effect on faecal worm egg count recorded at 13 months of age. In the second stage of the experiment, three promising regions (located on chromosomes 1, 3 and 4) were fine-mapped. This involved typing more closely spaced markers on individuals from the designed flock as well as an additional 495 individuals selected from a related population with a deeper pedigree. Analysis was performed using a linkage disequilibrium-linkage approach, under additive, dominant and multiple QTL models. Of these, the multiple QTL model resulted in the most refined QTL positions, with resolutions of <10 cM achieved for two regions. Because of the moderate size of effect of the QTL, and the apparent age and/or immune status specificity of the QTL, it is suggested that a panel of QTL will be required for significant genetic gains to be achieved within industry via marker-assisted selection.

Availability of gastro-intestinal nematode larvae to sheep following winter contamination of pasture with six nematode species on the Northern Tablelands of New South Wales.

This experiment was designed to determine the infective consequences of winter pasture contamination by sheep infected with 6 species of trichostrongylid gastro-intestinal nematode (GIN) at Armidale in the New England region of NSW. Ten helminthologically inert pasture plots were contaminated using 'donor' sheep harbouring artificial infections of Haemonchus contortus, Trichostrongylus colubriformis, Trichostrongylus vitrinus, Trichostrongylus axei, Nematodirus spathiger and Teladorsagia circumcincta. A single plot was contaminated in March to serve as a positive control and three plots in each of the winter months of June, July or August of 2007. Weekly assessments of 24 h faecal output and worm egg count of all donor sheep, combined with differentiation of larval cultures enabled calculation of total egg deposition per plot for each GIN species for each month of contamination. All plots were provided with supplemental spray irrigation sufficient to remove desiccation as a cause of non-development. The infective consequence of each monthly contamination was assessed by grazing each plot with two tracer sheep for the last 14 days of each month following contamination until a final grazing in November. Translation for each GIN species was expressed as the percentage of eggs deposited translating to worms counted in tracer sheep. The GIN parasites fell into two distinct groups differing greatly in translational success. Translation of egg to establishment in the tracer host was ineffective for H. contortus, T. axei and T. colubriformis but effective for T. vitrinus, T. circumcincta and N. spathiger. Overall mean total translation for each of these species throughout the experiment was respectively 0.00%, 0.00%, 0.00%, 0.34%, 0.45% and 0.48%. We conclude that winter contamination of pastures in this region with eggs of the latter 3 species is capable of impacting on the health of sheep subsequently grazing these pastures. Where H. contortus and T. colubriformis predominate, paddocks selected for spring lambing may be grazed safely over the winter months without contributing significantly to pasture contamination. These findings are particularly relevant to the preparation of clean spring lambing paddocks in this region using grazing management.

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 2ha paddocks was designed to compare the efficacy of 3 management strategies to prepare spring lambing paddocks of low gastro-intestinal 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 2 weeks 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.

Intensive rotational grazing assists control of gastrointestinal nematodosis of sheep in a cool temperate environment with summer-dominant rainfall.

While rotational grazing methods have an accepted role in the management of gastrointestinal nematodosis (GIN) of small ruminants in humid tropical regions, their efficacy and application in cool temperate regions is more controversial. This study evaluated GIN over 2 years in three classes of fine wool Merino sheep (lambs, hoggets and ewes) under three different sheep management systems in a cool tableland environment near Armidale NSW Australia (950m altitude, 30 degrees 31'S, 151 degrees 39'E). The management systems were High input (HI) with high fertiliser inputs, a target of 100% sown pasture, high stocking rate (13.4 dry sheep equivalents/ha) and relatively long grazing periods; Typical (TYP) New England management system with moderate fertiliser inputs and stocking rate (9.3DSE/ha) and relatively long grazing periods; and Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate (8.8DSE/ha) but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. Twenty sheep of each class in each management treatment were sampled monthly for faecal worm egg counts (WEC, followed by larval differentiation), and body weights with a blood sample taken for haematology every second month. The proportion of sheep with WEC above zero did not differ between management systems but the magnitude of WEC did, with sheep under IRG displaying lower mean WEC than those on the other treatments (IRG: 326, HI: 594, TYP: 536, eggs/g P<0.0001). This was despite a significantly longer mean interval between anthelmintic treatments (IRG: 144 days, HI: 77 days, TYP: 78 days, P<0.0001). The IRG management system also influenced the composition of the infections with sheep on this treatment having a significantly lower proportion of Haemonchus contortus in their faecal cultures (IRG: 59.7%, HI: 79.4%, TYP: 80.9%, P<0.05) and a significantly higher proportion of Trichostrongylus spp. Sheep on the IRG treatment also had a significantly higher haematocrit (HCT) than those on the other management systems. Despite the lower WEC and higher HCT, sheep under IRG also had significantly lower bodyweights and fleece weights overall, although this was only evident in sheep raised to adulthood prior to the experiment, not those raised during the 2-year experimental period. The results demonstrate that IRG systems with short grazing periods and long rest periods between grazing events can assist with control of GIN in cool temperate climates where H. contortus is the dominant parasite.

Tissue distribution, shedding and environmental detection of infectious bursal disease virus genome following infection of meat chickens at two ages.

OBJECTIVE: To compare the effects of infectious bursal disease virus (IBDV) infection of commercial meat chickens at 0 and 16 days old (d.o.) and determine if IBDV vRNA is quantifiable in litter and dust samples. METHODS: Ross meat chickens (n = 60) were orally infected or not with IBDV at 0 or 16 d.o. Blood and faecal samples were collected longitudinally to 28 days post infection (dpi) from six chickens and tissues collected weekly from three euthanased chickens. Relative bursal weight was recorded postmortem. IBDV antibody titres in sera were measured using ELISA and VCN was determined in tissues, faeces, litter and dust using qRT-PCR. RESULTS: Chickens infected at 16 d.o. had earlier and more severe bursal atrophy, earlier and higher IBDV vRNA load in lymphoid organs and an earlier and greater antibody response to infection than those infected at 0 d.o. Faecal shedding of IBDV between 2 and 6 dpi was observed in both groups followed by cessation with the 0 d.o. group and re-initiation of shedding at 28 dpi. IBDV was readily detected and quantified in litter and dust samples. CONCLUSIONS: The presence of significant maternal antibody (MAb) titres in 0 d.o. chickens provided protection against IBDV replication and bursal atrophy at 7 and 14 days post infection. The reduced titres of MAb present at 16 d.o. did not prevent rapid IBDV replication and early marked bursal atrophy. The observed resistance of 0 d.o. chickens is likely to be a combination of MAb inhibition of IBDV and true age resistance of neonatal chicks. Measurement of IBDV in litter and dust may have research or diagnostic application.

Trapping efficacy of Duddingtonia flagrans against Haemonchus contortus at temperatures existing at lambing in Australia.

The aim of this study was to determine the trapping efficacy of Duddingtonia flagrans against Haemonchus contortus at the temperature ranges experienced around lambing in the major sheep producing regions of Australia. Faeces were collected from Merino wethers, maintained in an animal house and which had received either D. flagrans chlamydospores for a 6-day period (DF) or not (NIL). Faeces were incubated at one of four daily temperature regimens which were composed of hourly steps to provide 6-19 degrees C, 9-25 degrees C, 14-34 degrees C and 14-39 degrees C to mimic normal diurnal air temperature variation. Enumeration of the number of preinfective and infective larvae that had migrated from or remained in faecal pellets was used to calculate percentage recovery and trapping efficacy of D. flagrans. Recovery of H. contortus larvae of both stages was significantly lower in DF faeces but the magnitude of the effect was considerably greater for infective larvae. Mean recovery of infective larvae from NIL and DF faeces was 10.6 and 0.4%, respectively, indicating a mean trapping efficacy of 96.4%. The lowest trapping efficacy (80.7%) was observed at 6-19 degrees C but total recovery of infective larvae, from DF faeces, was greatest at the two highest temperature regimens, although still less than 0.9%. The results of this study indicate that typical Australian lambing temperatures should not be a barrier to the use of D. flagrans as an effective biocontrol of H. contortus in Australia.

Twin efficiency for reproductive variables in monozygotic twin sheep.

The aim of this study was to determine whether the number of animals used in experiments examining reproductive variables could be reduced without loss of statistical efficiency by using monozygotic twin (MT) sheep. In a series of four experiments, we measured the reproductive responses to changes in nutritional, opioidergic, and calcium status and calculated values for twin efficiency (TE) for each variable. In Experiment 1, we monitored the changes in gonadotrophin and testosterone secretion, scrotal circumference and live weight, of MT rams after an acute change in nutritional regime. In Experiment 2, we examined the changes in ovulation rate and gonadotrophin secretion in MT ewes following treatment with bovine follicular fluid. In Experiment 3, we determined responses to naloxone and exogenous calcium on gonadotrophin secretion in MT rams. In Experiment 4, we investigated the effects of naloxone and exogenous calcium on the hypothalamus-pituitary-ovarian axis of MT ewes. The TE values were high only for live weight and scrotal circumference; the other reproductive traits had less variation between than within MT pairs, suggesting that randomly selected animals were just as efficient as genetically identical twins in experiments examining physiological reproductive traits.