INTERACTIONS BETWEEN DIETARY-FAT TYPE AND XYLANASE SUPPLEMENTATION WHEN RYE-BASED DIETS ARE FED TO BROILER-CHICKENS - 2 - PERFORMANCE, NUTRIENT DIGESTIBILITY AND THE FAT-SOLUBLE VITAMIN STATUS OF LIVERS

1. The interactions between dietary fat type and xylanase supplementat ion of rye-based diets were investigated using a 2 X 2 factorial desig n in which a rye-based diet (610 g rye/kg) was combined with 100 g/kg of soya oil or beef tallow, with or without xylanase supplementation a t 3000 IU/kg, and fed to 1-d-old male broilers for 35 d. Growth, nutri ent digestibility and AMEN values were determined and the vitamin stat us of livers assessed at various ages. 2. There were significant inter actions between crude fat and xylanase supplementation on the faecal d igestibility of crude fat and crude protein. Fat digestibility was imp roved by xylanase in both fat type groups but to a greater extent for the tallow diets. However, the effects were found to be significant on ly for oleic, linoleic and linolenic acids. Similarly, protein digesti bility and AME(N) values were significantly improved by xylanase, but only for the tallow diet. 3. Ileal digestibility of nitrogen and amino acids also were affected by enzyme for both fat type diets, the effec t generally being more pronounced for the tallow diet. 4. The depositi on of the fat soluble vitamins A and E in livers was significantly inc reased by xylanase supplementation and was also better for soya oil th an for tallow. 5. Xylanase supplementation increased the digestibility of insoluble pentosans whereas for the soluble pentosans the opposite effect was noted. 6. Without xylanase supplementation the tallow-base d diet caused high mortality. Liveweight gain and the efficiency of fo od utilisation were greatest in the soya oil-based, xylanase-supplemen ted diet, followed by the unsupplemented soya oil-, supplemented tallo w-and unsupplemented tallow-based diets.