Use of binders in feed pelleting : technological and nutritional aspects

Abstract

Binders (or pelleting aids) are additives which are incorporated to a feed in low concentrations (0.5 to 2.5 %) in order to increase the durability and the hardness of pellets and the efficiency of pelleting. These substances could be of organic or mineral origin. Among the organic substances used, lignosulfonates are provided as by-products by the paper industry. Mineral substances are mainly from the clay family. Other substances, such as polysaccharides could be used in marine animal feed.

Laboratory tests may provide information on the binding and/or the lubricating properties of the pelleting aids according to their moisture level and type of raw material. Pilot tests for the addition of lignosulfonates have generally shown a positive influence on the mechanical properties of pellets and a tendancy to decrease the energy consumption mainly with starch-rich feeds or materials. The effect of mineral substances is quite variable and depends on the pelleting conditions. At industrial scale small differences can be buffered by hazardous variations.

Generally, binders have no nutritive value per se. Lignosulfonates and other organic compounds are exceptions as they have a low sugar content. Usually, mineral binders are considered to be diluting components of the diet. An indirect effect on the feed conversion ratio could be related to the fact that the pellets are harder. Attention has to be paid to a possible tanning effect of the protein of the feed with lignosulfonates. The physical structure and behaviour of clays (bentonite, sepiolite) could explain some of the effects on the digestibility of energy in non-ruminant animals through their modification of the water retention and the transit time within the gut of the animal, and also on nitrogen utilization by ruminant animals.