Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 2. Weather variables associated with development

Long-Term Climatic Changes in Small Ruminant Farms in Greece and Potential Associations with Animal Health

The objectives of this work were (a) to present the changes in climatic parameters from 1989 to 2019, in 444 locations throughout Greece, where small ruminant farms have been based and (b) to present associations of the changes in the climatic parameters with clinical data related to small ruminant health. Climatic variables (1989–2019) were obtained for 444 locations with small ruminant farms throughout Greece. During this period, significant increases were noted in temperature-related parameters (annually 0.05 °C for average temperature and 0.14 °C for temperature range) and precipitation (annually 0.03 mm). There were significant differences in climatic conditions between locations of farms in accord with the management system applied therein, as well as in accord with the breed of animals on the farms (e.g., higher average temperature in locations with Greek breeds, higher temperature range in locations with imported breeds). There were significant associations of temperature-related parameters with the annual frequency of cases of neonatal hypothermia seen at a veterinary teaching hospital, as well as with the average proportion of Haemonchus contortus larvae in faecal samples and the frequency of cases of H. contortus resistance reported by a veterinary parasitology laboratory.

Infective larvae of Haemonchus contortus found from the base to the top of the grass sward

The resistance of gastrointestinal nematodes (GIN) of sheep to anthelmintic treatment has motivated researchers to seek alternatives to reduce the use of these drugs in sheep farming and decontaminate pastureland based on knowledge about the survival dynamics of larvae. The aim of this work was to evaluate the migration of the infective larvae (L3) of Haemonchus contortus at different times of the day, strata, and sward heights, with and without shade after the deposition of contaminated sheep feces. The grass species used here was Cynodon dactylon cv. Tifton 85 in four treatments: low sward height shade; low sward height sunshine; high sward height shade; and high sward height sunshine. The number of L3 recovered from the pasture at different times of the day did not differ. The highest number of L3 recovered was in shade. The number of L3 at different times and strata occurred uniformly, confirming that L3 remain in the same place after migrating from dung at the hottest times of the day. Infective larvae of H. contortus were able to migrate across all the strata regardless of the time of day in the summer season in humid subtropical climate.

Long spelling periods are required for pasture to become free of contamination by infective larvae of Haemonchus contortus in a humid subtropical climate of São Paulo state, Brazil

The objective of this trial was to evaluate the period of spelling necessary for a pasture to become free of contamination by infective larvae of gastrointestinal nematodes (GIN) of sheep, in different seasons of the year, as well as to determine when the greatest pasture contamination occurs and how long it lasts. An area was divided into four paddocks, one for each season (spring, summer, autumn, and winter). In order to contaminate the paddocks with free living stages of GIN, eight ewes, naturally infected, grazed on each paddock for 14 consecutive days, starting on the following dates: autumn, on April 4, 2017; winter, on July 4, 2017; spring, on September 26, 2017; summer, on January 2, 2019. At the beginning and end of the grazing period, faecal samples were taken directly from the rectums of the ewes to count eggs per gram of faeces (EPG) and for faecal cultures. Every 14 days pasture samples were collected to assess the number of infective larvae (L3) per kilogram of dry matter. At the end of the 14 day ewe grazing period, 21 stakes were placed where there were faeces on the paddock. Subsequently, every 14 days, the faeces located at three of the stakes were collected and the L3 were recovered. After the exit of the ewes, monthly, two tracer lambs, free of helminth infection, were allocated into the paddock for 14 days. At the end of this period they were housed in covered stalls for 28 days. Faeces from the lambs were collected for individual EPG counting and faecal culture at 21 and 28 days after grazing. Infective larvae recuperation was observed from faeces and pasture in all seasons. In the autumn, spring, and summer, high EPG counts were observed in the first tracer lambs (8521, 4800, and 8064 EPG, respectively), while in winter, high infection (14132 EPG) of the animals was observed only from the second pair of tracer lambs. For a pasture to become "clean", 322 days, 350 days, 294 days, and 182 days following contamination were necessary, respectively, in the autumn, winter, spring, and summer. In autumn, spring, and summer, massive contamination of the pasture with L3 occurred soon after an area had been grazed by infected sheep, while in winter this took a little longer. The contamination persisted, approximately, from a minimum of six months post contamination in summer to up to almost one year post contamination in winter.

A mathematical model to predict the risk arising from the pasture infectivity of four nematode species in Australia

Gastrointestinal parasites cost the Australian sheep industry AU$436 million annually. Early warning of impending worm risk may reduce this cost by providing producers with sufficient time to implement control strategies. A biophysical model was developed to simulate the on-pasture lifecycle stages of the four predominant nematode species in Australia (Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis and Trichostrongylus vitrinus). The influence of climatic variables (temperature and water availability) on the survival, development and migration of each lifecycle stage was incorporated and parameterised to available point estimates (H. contortus: R2 = 0.88, n = 1409; T. circumcincta: R2 = 0.56, n = 243; T. colubriformis: R2 = 0.61, n = 355; T. vitrinus: R2 = 0.66, n = 147). Constant fecundities (eggs/worm.day) provided the daily quantity of eggs deposited per sheep (H. contortus = 3275; T. circumcincta = 140; T. colubriformis = 300; T. vitrinus = 300). Farm management practices were considered via the specification of stocking rates (sheep/ha), and the administration of anthelmintic treatments (reducing egg deposition by a defined efficacy and duration for each nematode species). Pasture infectivity per nematode species was calculated as the quotient of larvae on herbage and herbage availability (t/ha). Risk was calculated as the product of pasture infectivity and the potential productive impact of each nematode species (H. contortus = 3.9%; T. circumcincta = 9.22%; T. colubriformis = 9.31%; T. vitrinus = 9.31%), and then summed across nematode species. This predictive model has been incorporated into the Sheep CRC’s ‘ASKBILL’ application (www.askbill.com.au, verified 13 April 2018), which uses 90-day weather forecast data (5-km grid resolution) provided by the Australian Bureau of Meteorology.

Prevalence of Ostertagia ostertagi lesions in slaughtered dairy cattle from São Miguel Island, Azores, Portugal

Ostertagiosis caused by Ostertagia ostertagi is considered the most important parasitosis in dairy cattle raised in temperate areas. The aim of this investigation was to determinate the prevalence of ostertagiosis in cattle slaughtered in São Miguel Island (SMI), Azores, the geographical distribution of positive cases, its economic impact and farmers awareness regarding preventive and control measurements against this parasitosis. From the 2000 animals sampled, 1282 presented lesions compatible with ostertagiosis representing a prevalence of 49.0% in young animals and 75.7% in adults. Positive animals had significantly worse carcass rating when slaughtered and the fat rating of positive uncastrated males older than 24months was also significantly lower. The presence of lesions compatible with ostertagiosis resulted in a total weight loss of 2.810.89kg (2.19kg mean weight loss per animal - 1.07% carcass weight drop), which extrapolating to the total of animals slaughtered in SMI in 2014 corresponds to a value of losses of roughly about 91.000.00€. Our data also indicate that ostertagiosis has a widespread distribution throughout the Island and that 85.7% of the farmers dewormed calves and 42.9% dewormed cows (only one administration was provided for each deworming). Data shows that ostertagiosis represents an important economical lost in dairy cattle from SMI and a significant lack of knowledge by farmers about the benefits of deworming and preventive management practices.

The Pathophysiology, Ecology and Epidemiology of Haemonchus contortus Infection in Small Ruminants

The parasitic nematode Haemonchus contortus occurs commonly in small ruminants, and it is an especially significant threat to the health and production of sheep and goats in tropical and warm temperate zones. The main signs of disease (haemonchosis) relate to its blood-feeding activity, leading to anaemia, weakness and frequently to deaths, unless treatment is provided. Due to the high biotic potential, large burdens of H. contortus may develop rapidly when environmental conditions favour the free-living stages, and deaths may occur with little prior warning. More chronic forms of haemonchosis, resulting in reduced animal production and eventually deaths, occur with smaller persistent infections, especially in situations of prolonged, poor nutrition. The global distribution of the main haemonchosis-endemic zones is consistent with the critical requirements of the egg and larval stages of H. contortus for moisture and moderate to relatively warm temperatures, but the seasonal propensity for hypobiosis (inhibition of the fourth-stage larvae within the host) largely explains the common, though sporadic, outbreaks of haemonchosis in arid and colder environments. The wide climatic distribution may also reflect the adaptation of local isolates to less favourable ecological conditions, while an apparent increase in the prevalence of outbreaks in environments not previously considered endemic for haemonchosis - especially cold, temperate zones - may be attributable to climatic changes. Although the risk of haemonchosis varies considerably on a local level, even where H. contortus is endemic, the extensive range of ecological investigations provides a sound basis for predictions of the relative geographical and seasonal risk in relation to climatic conditions.

Moisture requirements for the migration of Haemonchus contortus third stage larvae out of faeces

The abomasal nematode Haemonchus contortus causes severe disease and production loss in small ruminants in warmer regions and is also an emerging threat in many temperate climates. Specific knowledge of the effects of climate on the epidemiology of H. contortus is needed to effectively apply sustainable control strategies, which rely on prediction of infection risk. Although the effects of temperature and rainfall on larval development in this species have been characterised, much less is known about migration out of faeces and onto herbage. This is an important deficit in our understanding of the epidemiology of haemonchosis in regions with relatively low and particularly erratic rainfall. Methods were developed to assess the migration of third stage larvae (L3) out of faeces under simulated rainfall in the laboratory. These were applied in a series of experiments, which showed that rainfall is required for migration. However, a single rainfall event was not sufficient for migration from faeces of which the crust has hardened after having been kept in dry conditions. Light and regular rainfall resulted in rapid emergence from moist faeces kept in humid conditions, but much slower emergence from dry faeces in dry conditions. Ambient relative humidity therefore appears to act through faecal moisture content to modify the effect of rainfall on larval migration. Larvae survived well in dry faeces for a number of days, but did not migrate in the absence of rainfall, so sheep faeces could potentially act as a larval reservoir in dry conditions, with peaks of infection following rainfall. Rates of faecal desiccation and rehydration on pasture could therefore be highly relevant to temporal patterns of larval availability.

Translation of H. contortus and T. colubriformis from egg to establishment in grazing sheep is unaffected by rainfall timing, rainfall amount and herbage height under conditions of high soil moisture in the Northern Tablelands of NSW

A field experiment was conducted at Armidale in the Northern Tablelands of NSW, Australia to determine the effects of simulated rainfall amount (0, 12 and 24 mm), rainfall timing (days -1, 0 and 3 relative to plot contamination) and herbage height (4 and 12 cm), on translation of Haemonchus contortus and Trichostrongylus colubriformis from egg to established stages in grazing sheep under conditions of high soil moisture (22-23%). The experiment was conducted in summer when temperature was not anticipated to be a limiting factor for development success. Development success was assessed using tracer sheep and expressed as percentage recovery of parasitic stages relative to egg output on pasture (translation%). For both species, translation (0.11% H. contortus; 0.55% T. colubriformis) was observed in the absence of simulated rainfall and was unaffected by treatment effects of rainfall amount and timing, and herbage height. We suggest that soil moisture (>20%) alone was sufficient to support development and translation (from eggs to parasitic stages in the gut of tracer animals) of these species which contrasts with expectations for development success on dry soils. These findings identify the importance of taking soil moisture into account when predicting the likely effects of rainfall and herbage height on development to L3 and ultimately in predictive epidemiological models of ovine gastrointestinal nematodiasis.

Soil moisture modulates the effects of the timing and amount of rainfall on faecal moisture and development of Haemonchus contortus and Trichostrongylus colubriformis to infective third stage larvae

Recent experiments on the effects of rainfall and/or soil moisture (SM) on development of sheep gastro-intestinal nematodes to infective L3 stage have used soil of relatively low moisture content in small experimental samples that dry out faster than field soil. To determine whether higher and more sustained SM content modulates the effects of rainfall amount and timing on faecal moisture (FM) and development of H. contortus and T. colubriformis to infective third stage larvae (L3), a climate-controlled chamber experiment was conducted. It was designed to test the effects of rainfall amount (0, 12 and 24 mm), rainfall timing (days -1, 0 and 3 relative to faecal deposition) and soil moisture maintained at 10, 20 and 30% on these variables. Total recovery of L3 14 days after faecal deposition was significantly affected by SM, rainfall timing and their interaction (P<0.01), but not by rainfall amount or species or other two-way interactions. Recovery of L3 was maximal (28%) with a SM treatment of 30% and simulated rainfall on day 3. Faecal moisture was significantly affected by collection day, SM treatment, rainfall amount and rainfall timing with significant interaction between many of these effects (P<0.05). A positive linear association between FM and total L3 recovery was strongest on day 4 after faecal deposition (R(2)=0.64, P<0.001) for H. contortus and day 6 (R(2)=0.78, P<0.001) for T. colubriformis. Overall the results show that SM is able to modulate the effects of rainfall timing and amount with increased SM acting to broaden the window of opportunity for the free-living stages to respond to post deposition rainfall to complete development to L3. If SM is maintained in the range 10-30%, the reported benefits of early rainfall (days -1 and 0) of up to 24 mm appear to be negated with later rainfall (day 3) proving more beneficial. These results require field confirmation.

Effect of simulated rainfall timing on faecal moisture and development of Haemonchus contortus and Trichostrongylus colubriformis eggs to infective larvae

Three climate-controlled chamber experiments were conducted to determine the effect of 32 mm simulated rainfall applied prior to (days -4 to -1) or after (days 0-7) faecal deposition and as a single (32 mm) or split (2 × 16 mm) application on faecal moisture (FM) and development of H. contortus and T. colubriformis to third stage infective larvae (L3). The timing of simulated rainfall regulated extra-pellet L3 recovery for H. contortus (P<0.05) but not T. colubriformis. Recovery of L3 was highest (P<0.05) when simulated rainfall was applied on the day of deposition followed by days -1, 1 and 2, which resulted in similar but lower development success rates. Recovery of intra-pellet T. colubriformis L3 was two-fold greater (P=0.008) than for H. contortus and was higher (P=0.007) following simulated rainfall on days 0 and 1 than on other days. There was a positive association between FM and total L3 recovery indicating the importance of FM in the period 48-72 h (H. contortus) and 72-96 h (T. colubriformis) after deposition. Simulated rainfall on the day prior to deposition was as effective in supporting total L3 recovery as application on days 1 or 2 and this effect could be predicted through FM. This highlights the importance of soil in transferring moisture to the faecal pellet. The importance of precedent rainfall and soil moisture in determining the development success of H. contortus and T. colubriformis, in addition to the general effects of the timing of simulated rainfall, need to be accommodated in grazing management programs to combat these species.