The infestation with gastrointestinal nematodes (GIN) represents a considerable health risk to small ruminants, and therefore a significantly limiting factor to the husbandry of such species.
As the GIN issue is of great importance in Switzerland as well, the project Ram Pasture (Projekt Widderweide) was initiated a few years ago by the Advisory and Health Service for Small Ruminants, in order to select GIN-resistant milk sheep rams for breeding. In contrast to methods abroad, the rams are not kept on a station (the likes of which do not exist in Switzerland), but rather together on a pasture with induced GIN contamination during grazing season. Accordingly, all animals are equally exposed and should be able to mobilise the immunological resources available to them against GIN. The selection of rams suited for breeding happens on the basis of GIN egg secretion.
For several decades, GIN have been controlled almost entirely on the use of anthelmintics. The thus far most commonly used group (Bezimidazole) has been rendered most limited in practical use due to a strong resistance problem. Certain farming practices (dairy farms) currently have an urgent need for action, taking in account animal-protection aspects, which is linked to substantial economic loss through the use of anthelmintics with a long withdrawal period. Due to the aforementioned resistance problem, the research of alternative and/or complementary control of GIN has been intensified in recent years.
In this context, notably Australia and New Zealand have seen extensive studies on selection with sheep in order to determine animals with an increased genetic resistance for GIN. The selection of resistant sheep happens because of the lacking of an appropriate genetic marker via phenotypic parametres, which correlate with the worm burden. The frequency of GIN egg excretion in the host’s faeces is the most commonly used selection criterion.
GIN resistant sheep are already being successfully employed in a multitude of sheep farms in the aforementioned countries. Countries such as France, England or South Africa have also been making use of the selection of GIN resistant sheep for a number of years now. In most cases, the male line (ram) is being selected. This happens on so-called ram stations where the animals are infected with GIN in a controlled manner.
In contrast to methods abroad, the rams are not kept on a station (the likes of which do not exist in Switzerland), but rather together on a pasture with a given GIN contamination during grazing season. Accordingly, all animals are equally exposed and should be able to mobilise the immunological resources available to them against GIS. The selection of rams suited for breeding happens on the basis of GIS egg secretion.
The young rams are being pastured together during the first half of the grazing season, and thusly being exposed to GIN. In the second half of their first grazing season, the entirety of animals are being drenched and then once infected with a defined number of infectious GIN larvae in a controlled manner (animal housing follows). The evaluation and selection of the rams is ultimately undertaken by means of repeated quantitative measurements between early patency and day 49 post-infection.