Fat and fatty acid content and composition of forages: A meta-analysis

Abstract

Forages, through the amount and composition of their fatty acids (FA), and because they represent a major part of ruminant diets, can help improve the nutritional quality of milk and meat. However, no comprehensive dataset is available to estimate fat and FA content and composition of forages. This study used the available data on fat and FA content and composition of forages to (i) compute mean composition values for the main forages, and (ii) estimate the influence of forage conservation, cultivation and harvest conditions on fat and FA content and composition. We report mean values for the main forage species in the form of fresh forage, silage or hay. The main factor influencing fat and FA composition was vegetation stage of forage at harvest (estimated by the month of harvest or regrowth interval). Compared with fresh forage at harvest, wilting or drying forages (especially in bad drying conditions) altered their FA, whereas unwilted silage, the use of ensiling additives and N fertilization had only minor effects. The differences between grass (except corn) and legume species were lower than those induced by vegetation stage and wilting or drying. We gave equations to estimate the effects of these factors and thus refine the estimation of the FA content and composition of the forages. Total FA content and proportion of linolenic acid were positively related to crude protein, and negatively related to fiber content of the forages.