A comparison of pelleting and expander treatment on nutritional value of a broiler diet containing two different fat sources.

A study was conducted to assess the interaction between different source of fat application through the process of pelleting and expander treatment followed by pelleting, and its influences on nutritional value of the feed and performances of broiler chicken. Soy oil and a fat containing a high level of palmitic acid (Akofeed) were added in a feed mixture at two different inclusion levels (2.5 and 5%) before being processed. Pellet durability decreased as fat addition increased, but the reduction in pellet quality was much higher for soy oil than for Akofeed. Expander treatment improved pellet durability compared to pelleting only. Expander treatment tended to give poorer weight gain, and feed/gain was significantly poorer with expansion compared with pelleting only. Expander treatment increased starch gelatinisation, but this did not have an effect on faecal starch digestibility. However, both expansion and fat source had an effect on jejunal starch content, indicating that degradation rate may be affected by both processing and fat source used. Introduction Pelleting is the dominating process used for broiler feed production. However, a recent development is the use of the expander for a more severe thermal treatment of the feed prior to pelleting. The advantage of this process is a better sterilization of the feed and an improved pellet quality. However, the high temperature may induce other changes in the feed that may be disadvantageous for the nutritional value of the feed. One such negative effect may be the formation of complexes between fat and starch in the feed. Other negative effects include reduced protein digestibility and loss of heat labile components such as vitamins and enzymes. The purpose of the current experiment was to compare the effect of pelleting and expander treatment, and to study the interaction between processing method and fat type used. Materials and Methods Diets A broiler diet containing 34 % ground wheat, 34 % ground barley and 22 % soybean meal was composed in accordance with requirements. The diet contained titanium oxide added as a marker, and also contained fibre-degrading enzymes. The experiment was organized as a three factorial design with two fat sources, two inclusion levels of fat and two processing method. Soy oil and akofeed were included at levels of 2.5 and 5% and all mixtures were either pelleted or expanded and pelleted. Akofeed consists of 94 % free fatty acids, of which palmitic acid dominates with 65 % of the fat. Feed production was performed at the Centre for Feed Technology, Ås, Norway. Soy oil was sprayed on the feed mixture during mixing, while akofeed was added in a solid form. Pelleted feeds were conditioned at 75°C and pressed through 3mm pellet die, while expanded feeds were processed on 110°C with cone pressure of 20 bars before pelleting. Chicken experiment Eleven day-old male broiler chickens (Ross 208) were selected at random and moved to single-bird cages (50 cm x 35 cm x 20 cm) in a room with constant temperature (21oC) and with 16 hours light. Each of the 8 diets was given ad libitum to 14 birds. In the morning of the 25th day of age, the food was removed and weighed. After 6 hours starvation, each bird was