Feed lipids and fats in animal nutrition

Abstract

Lipids in roughages and concentrates are less known than carbohydrate, protein and mineral fractions. The fat content of feeds is usually estimated by ether extraction, sometimes with previous hydrolysis with boiling HCl when this is necessary to ensure a complete extraction. The content of ether extract in roughages varies from 2 to 12 %. The percentage of linolenic acid in the total fatty acids is very high and generally exceeds 50 %. As roughage plants move from young shoots to maturity stages, the percentages of palmitic, stearic and oleic acids rise while the linolenic acid percentage decreases.

Twenty concentrate feeds were selected among those which are the most used in the nutrition of monogastric animals and ruminants. Their ether extract contents and fatty acid compositions have been reported from four databases: AFZ, CVB, MAFF, and SOUCI. For vegetable oils, the comprehensive literature review of Givens was considered.

The ether extract content of cereals and legume grains is generally low (1.2-2.2 %), with the exception of maize and several cereal by-products. There are also low quantities of saturated fatty acids, with palmitic acid giving the highest values. The fatty acid composition of oil seeds varies according to the species. The fatty acid composition of fish oils and fish meals is characterised by a large amount of polyunsaturated fatty acids having more than 18 carbon atoms. The lipid composition of land animal fats and meals is rich in saturated acids and low in polyunsaturated acids.

A good relationship can be observed between the AFZ and CVB data for cereals and oil seeds, and between the AFZ, SOUCI and Givens data for vegetable oils and animal fats. However, several discrepancies were noted between the MAFF database and the AFZ and CVB databases. Databases such as the ones studied here make objective knowledge about lipids in feeds more available, but much progress remains to be done regarding the causes of variation of ether extract contents and fatty acid compositions, and, particularly, regarding the values of minor fatty acids and isomer acids of n-6 and n-3 families.