Project goals
Since parasite infestation in sheep farming represents a significant economic factor, strategies should be developed to minimize the economic damage. While until a few years ago the entire flock was regularly dewormed several times a year, this practice has been abandoned in recent years, and deworming is now limited to a portion of the flock as needed. "As needed" means that the infestation level is determined via fecal samples, and deworming is then carried out accordingly. Another option is breeding for potentially parasite-resistant or more resilient animals. If this trait is to be included in breeding value assessments, a practical method of data collection is essential. Measuring the number of parasite eggs would be one such method. However, determining the optimal time for sampling, both in terms of season and time of day, is also crucial. This project aims to address these questions.
The starting point is a flock of 40 young sheep, half of which are mountain sheep and half Jura sheep. The animals originate from several different breeding farms to ensure maximum genetic diversity. Upon arrival in Gumpenstein, the animals are quarantined for two weeks. During this time, each animal's individual daily feed intake is recorded. They are fed free-choice hay plus concentrate, amounting to 1% of their body weight. During these two weeks, the animals are weighed twice weekly, and at the end of this period, a body condition score (BCS, body measurements) is assessed. During the grazing season, the animals are weighed only once a week and assessed once a month.
After the individual feed intake is recorded, the young sheep are moved to pasture. Throughout the grazing season, parasite load is assessed by regularly examining feces for eggs. The animals are sampled once a week, once in the morning and once in the evening. Egg excretion is assessed using the McMaster method. Since egg counting does not yet provide information about the type of parasites, a total of four fecal samples are incubated per grazing season, and the worms are differentiated based on the larvae. In parallel, the parasite load is checked using the FAMACHE method.
In autumn 2020, the young sheep are bred for the first time with purebred rams. The female offspring suitable for breeding (from mothers with low parasite loads) are raised and also undergo parasite control during the 2021 grazing season, following the same procedure as their mothers in the 2020 season. The ewes and their offspring are subjected to regular fecal examinations during the 2021 to 2023 seasons.
Should any animals show an excessively high parasite load, targeted deworming is carried out, with fecal samples taken before and 14 days after deworming for larval differentiation and to verify the effectiveness of the deworming treatment.
All experimental animals are genotyped using a high-throughput method for approximately 50,000 genetic markers (single nucleotide polymorphisms, SNPs). For this purpose, DNA is extracted from blood at the Wels branch, a portion of this DNA is sent to an SNP chip service provider, and an aliquot is retained for potential future analyses. The genotypes are associated with the results of the parasite control. The sample size is very small for a genetic association analysis; therefore, ways are being explored to collaborate with experimental stations in the Alpine region (Switzerland, Germany, Italy, France) for the genetic analysis. Should results for candidate genes for parasite resistance be published during the experimental period (see Kathiravan et al., 2014), it will be possible to control for these variants in the SNP chip or through targeted genotyping from the retained DNA.
