The effect of gastrointestinal nematode infection level on grazing distance from dung

Understanding Animal-Plant-Parasite Interactions to Improve the Management of Gastrointestinal Nematodes in Grazing Ruminants

Grazing systems have great potential to promote animal welfare by allowing animals to express natural behaviours, but they also present risks to the animals. Diseases caused by gastrointestinal nematodes are some of the most important causes of poor ruminant health and welfare in grazing systems and cause important economic losses. Reduced growth, health, reproduction and fitness, and negative affective states that indicate suffering are some of the negative effects on welfare in animals infected by gastrointestinal nematode parasitism. Conventional forms of control are based on anthelmintics, but their growing inefficiency due to resistance to many drugs, their potential for contamination of soil and products, and negative public opinion indicate an urgency to seek alternatives. We can learn to deal with these challenges by observing biological aspects of the parasite and the host’s behaviour to develop managements that have a multidimensional view that vary in time and space. Improving animal welfare in the context of the parasitic challenge in grazing systems should be seen as a priority to ensure the sustainability of livestock production. Among the measures to control gastrointestinal nematodes and increase animal welfare in grazing systems are the management and decontamination of pastures, offering multispecies pastures, and grazing strategies such as co-grazing with other species that have different grazing behaviours, rotational grazing with short grazing periods, and improved nutrition. Genetic selection to improve herd or flock parasite resistance to gastrointestinal nematode infection may also be incorporated into a holistic control plan, aiming at a substantial reduction in the use of anthelmintics and endectocides to make grazing systems more sustainable.

Relationships between sheep nematode infection, nutrition, and grazing behavior on improved and semi-natural pastures

Gastrointestinal nematodes (GINs) are key parasites of grazing sheep worldwide. To understand the factors influencing GIN infections, we examined the relationships among infection and nutrition, foraging behavior, and animal performance. Further, the parasitism and nutrition of sheep between improved and semi-natural pastures in Japan were compared. Sheep were grazed for 1 month each, first on an improved and then on a semi-natural pasture. Afterward, vegetation surveys, forage analyses, and (plant) nematode larval counts were conducted in both pastures, and fecal egg counts, biochemical analyses, and bite counts were completed for each sheep. The semi-natural pasture had diverse plant species, though it contained less crude protein, and nematode larvae were rarely observed on bamboo. Consequently, fecal egg per gram decreased after grazing on the semi-natural pasture. White blood counts, hematocrit, and glucose also decreased and body weight increased after grazing on this pasture. Principal component and correlation analyses revealed a significant relationship between GIN infection and behavior, but not between nutrition and either behavior or infection. As parasitized animals may become more aggressive feeders to compensate for their reduced nutritional uptake, grazing sheep on semi-natural pastures may facilitate more stable performance due to the lower risk of nematode infection from wild plants.

The role of IgA in gastrointestinal helminthiasis: A systematic review

Immunoglobulin-A (IgA) is an important mediator of immunity and has been associated with protection against several pathogens, although its role in gastrointestinal infections remains unclear. Then, the aim of this systematic review was to synthesize qualitative evidence in respect of IgA as mediator of protective immunity against gastrointestinal helminths. Following recommended guidelines, we searched for articles published between January 1990 and October 2019 that evaluated IgA levels and their association with gastrointestinal helminth infections. Twenty-five articles were included after screening 1,546 titles and abstracts, as well as reading in full 52 selected articles. Consistent associations between higher IgA levels and lower parasitological parameters were only found in mice, rats, and sheep. However, the role of IgA in other host species remains uncertain, making it difficult to create a consensus. Therefore, it is too soon to claim that IgA is an effective protective factor against gastrointestinal helminths, and further studies are still needed.

How mammals stay healthy in nature: the evolution of behaviours to avoid parasites and pathogens

Mammals live and thrive in environments presenting ongoing threats from parasites in the form of biting flies, ticks and intestinal worms and from pathogens as wound contaminants and agents of infectious disease. Several strategies have evolved that enable animals to deal with parasites and pathogens, including eliminating away from the sleeping-resting areas, use of an array of grooming techniques, use of saliva in licking, and consuming medicinal plant-based compounds. These strategies all are species-specific and reflect the particular environment that the animal inhabits.This article is part of the Theo Murphy meeting issue 'Evolution of pathogen and parasite avoidance behaviours'.