Elevated temperatures and long drought periods have a negative impact on survival and fitness of strongylid third stage larvae.

In grazing cattle, infections with gastrointestinal nematodes pose some of the most important health threats and subclinical infections result in considerable production losses. While there is little doubt that climate change will affect grazing ruminants directly, mean temperature increases of ∼ 3°C and longer drought stress periods in summer may also influence the free-living stages of parasitic nematodes. Hostile climatic conditions reduce the number of L3s on pasture and therefore the refugium, which is expected to result in a higher selection pressure, accelerating development of resistance against anthelmintic drugs. The aim of the current experiments was to investigate the effects of drought stress and different temperature/humidity ranges over time on the survival and fitness of Cooperia oncophora L3s and their distribution in grass and soil under controlled conditions using a climate chamber. Grass containers inoculated with L3s were analysed after 1-6weeks using descriptive statistics as well as linear models. A large proportion of L3s was recovered from soil where fitness was also better preserved than on grass. Numbers and fitness of recovered L3s declined with duration in the climate chamber under both temperature profiles. However, the results of the linear models confirmed that higher temperatures (20-33°C versus 17-22.6°C) significantly impaired survival, distribution and fitness of L3s. Application of drought stress, known as another important factor, had a surprisingly smaller impact than its duration or higher temperatures. The climate chamber enabled exclusion of confounding factors and therefore accurate interpretation of the investigated climatic aspects. The obtained results highlight the relative importance of those factors, and will help to design better models for the population dynamics of L3s on pasture in the future. Additionally, the outcomes of these investigations may offer explanations regarding interdependencies of development of anthelmintic resistance and the presence of hot/dry weather conditions.

Rapid selection for ß-tubulin alleles in codon 200 conferring benzimidazole resistance in an Ostertagia ostertagi isolate on pasture.

Resistance to benzimidazoles (BZs) is widespread in sheep nematodes and increasing in those of cattle. Several reasons including the predominant use of pour-on anthelmintics and lack of scales in field conditions lead to under-dosing of cattle and therefore to increased selection pressure. In an field experiment the frequency of BZ-resistance associated allele (TAC) in codon 200 in the ß-tubulin isotype 1 gene of Ostertagia ostertagi was monitored over one grazing season (approximately 30 weeks). Group 1, consisting of four calves, was experimentally infected with a pure O. ostertagi population displaying ∼50% of the TAC allele. The subsequently following groups of calves (four groups of two calves each) acquired natural infections by grazing contaminated pastures. Each group was treated with increasing percentages of sub-therapeutic dosages of albendazole (35-65%). Larvae obtained from faecal cultures pre and post treatment were subjected to species/genus-specific PCR as well as pyrosequencing to determine allele frequencies. PCR revealed the presence of Ostertagia, Trichostrongylus, Haemonchus and Cooperia in pre-treatment samples and predominantly Ostertagia as well as some Trichostrongylus in post treatment samples. Faecal egg count reduction was always less than 90% 7-10 days post treatment. In naturally infected calves TAC allele frequencies were significantly increased (p<0.05) after treatment and they also rapidly increased during the grazing season (pre: 15-63%; post: 55-89%). The more than 4-fold increase in resistant genotypes before treatment indicates how fast selection for BZ resistance can occur when sub-therapeutic dosages are combined with a high treatment frequency, even under moderated climatic conditions and in the presence of a refugium.

Assessment of the impact of plant species composition and drought stress on survival of strongylid third-stage larvae in a greenhouse experiment.

Grazing livestock is always exposed to infective parasite stages. Depending on the general health status of the animal, the farm management, environmental conditions and pasture exposure, the impact ranges from non-affected to almost moribund animals. The greenhouse experiment was performed to investigate how climatic changes and plant composition influence the occurrence/survival of strongylid third-stage larvae (L3) on pasture. Ten different types of plant species compositions (eight replicates for each) were inoculated with approximately 10,000 Cooperia oncophora L3. The different plant compositions can be assorted to two groups: without legume content and with legume content (52-62% legume content). Half of the replicates were watered adequately, while the other half was hold under drought stress (DS), mimicking longer dry periods. During the DS cycles, the respective containers were not watered until they reached the wilting point. Grass samples were taken 1, 4 and 6 weeks after inoculation, soil samples were taken only once after 6 weeks and all samples were examined for occurrence of L3. After the second DS cycle, the number of L3 present on herbage samples was reduced significantly. The higher the legume content of the pasture composition, the higher is the L3 occurrence on pasture. Independent of the watering scheme, the soil served as the most important reservoir with consistently higher numbers of L3 in the soil compared to herbage.

Rapid method for recovery of strongylid third stage larvae of parasitic nematodes from small soil samples.

Livestock with access to pasture is generally exposed to infections with parasitic nematode species by uptake of infective third stage larvae (L3) with the grass. L3 can survive on pasture and particularly also in the soil up to several months and sometimes even longer, depending on temperature and humidity. As indicators for health and productivity of grazing animals it is important to determine the intensity and species spectrum of parasitic nematode larvae by analysing grass as well as soil samples. A rapid method for the recovery of L3 using a centrifugal-flotation technique from soil samples of 50-500 g was developed. The method takes advantage of the low specific weight of larvae to separate them from equal sized soil and debris particles by centrifuging them in a saturated sugar solution. A stack of differently sized sieves is used to achieve elimination of larger particles, dust and sugar from the sample to enable easy counting of larvae. Independent of the number of larvae used for inoculation of the samples a mean recovery of 75.3% was obtained. The recovery rates obtained ranged between 60.8% and 88.0% which demonstrates a considerably lower variability compared to earlier approaches and therefore a more precise estimation of the actual numbers of parasite larvae in soil is achieved. Further advantages over already developed methods are the use of easy, affordable and eco-friendly materials, the simplicity of the procedure and a faster processing time with the possibility to examine up to 20 samples per day.