Biochemistry of plant secondary metabolites and their effects in animals.

Plant secondary metabolites, which include a wide variety of phytochemicals, have always been constituents of the diets of man and other animals. Although a high proportion of these phytochemicals have been considered to be of little value in plants (although this view is changing), they have frequently been shown to have adverse effects on animals when ingested. The effects depend to a great extent on the chemistry of the compounds, their concentration in the diet and the amount consumed, and are further dependent on the health status of the animals. Traditionally, most studies of the effects of these compounds on animals have focused on their adverse effects and how to alleviate them. However, recent public concern about the use of synthetic compounds in animal diets to enhance performance and health and welfare issues, coupled with changes in regulations on the use of synthetic medicaments, has stimulated interest and research in the use and effects of phytochemicals in the diets of farmed animals. Phytochemicals vary in their chemistry but can be divided into hydrophilic and hydrophobic compounds, of which a wide variety of polyphenolic and terpenoid compounds, as well as alkaloids, carbohydrates and non-protein amino acids, invoke special interest. The chemistry, biochemistry and mechanisms of action of these compounds in plants and their effects in animals when ingested will be explored.