Abstract: The invention relates to the use of alkaloid lolines to reduce parasitic infection in livestock and especially in ruminants, particularly sheep. The loline alkaloids are produced by and found in, grasses infected by endophytes. These grasses can be sown in areas where ruminants graze. Consumption of the grass supports the accumulation of loline alkaloids in the rumen of the animals and leads to a lower rate of infection by internal parasites and hence healthier livestock. The loline alkaloids may be produced by a number of endophytes present in a range of suitable grasses. The invention also provides a range of grasses which are suitable for the treatment of internal infection by parasites in livestock, especially ruminants and more especially sheep.