Abstract
Several scientists called for a new paradigm in animal nutrition by implementing feed diversity in otherwise homogeneously fed livestock production systems as former was shown to have a notable impact on animal productivity and health and the ecological footprint thereby decrease concerns regarding global food security from a societal perspective. However, there are no specific definitions and no threshold values available, so far, for desired grazed grassland feed diversity levels on pastures that enable envisaged sustainable ruminant livestock production and possibly the production of animal products with particular human health-values. Therefore, we conceptualize grazed grassland feed diversity in multiple layers for the very first time in this review to define its relevance from an animal perspective and implications for human health. The data reviewed reveals a close relationship between grazed grassland feed diversity with regard to plant secondary metabolites and animal characteristics that include animal health, welfare, and behavior as well as product quality with possible human health value. Nevertheless, it remains an open question whether plant species diversity per se or increasing occurrence of plant metabolites are responsible for feed diversity effects at grazing. Further, we demonstrate that solely the information about the level of feed diversity present on a field is not sufficient for deducing possible effects on animal related parameters and product quality as other interacting effects such as production level, pedo-climatic effects, and animal breed, have a relevant impact on the actual feed diversity consumed by the animal. Therefore, further research is required to shed light in the dark to understand the interaction between botanical compositions, pasture feed diversity and animal related factors for obtaining benefits for animal health, product quality and its human health value.