Effects of dietary fat type and xylanase supplementation in rye containingdiets on energy metabolism in male broilers

An experiment was carried out to examine the effects of dietary fat type (1 0% of either soya oil, S, or beef tallow, T) and xylanase supplementation ( -, without; +, with) in rye-based diets (56%) on energy metabolism in male broilers. Measurements of energy metabolism and subsequent regression analy sis were based on C- and N-balance technique using a respiration facility. It was found that xylanase supplementation resulted in an increase in metab olizability of energy (ratio between AME and gross energy) from 0.643 to 0. 706 in S- and S+ fed birds, respectively, and from 0.606 to 0.656 in T- and T+ fed birds. Similarly, the energetic efficiency (ratio between net energ y and AME) was improved from 0.421 to 0.449 and from 0.426 to 0.462, respec tively. It was concluded that soya oil is more efficiently metabolized than tallow but the latter was found to be more effective in energy retention. Changes in energetic efficiency were attributed mainly to changes in fat en ergy retention. Partial utilization of ME for energy retention (k(pf)) was obtained by regressing ME-intake on energy retention. This was increased af ter enzyme supplementation whereas the maintenance energy requirement (ME,) was enhanced at the same time. The respective values for k(pf) and MEm wer e 0.665, 0.729, 0.662, 0.886, and 468, 521, 482, 720 kJ/day/W-0.75 in S-, S +, T- and T+ groups, respectively. Similar relationships were found using a multiple regression approach. According to these estimates, partial expend iture of ME for protein energy retention (1/k(p)) and partial expenditure f or fat energy retention (1/k(f)) were decreased after enzyme supplementatio n. The respective values for S-, S+,T- and T+ groups were as follows: 1/k(p ) (kJ/kJ), 1.63, 1.32, 1.41 and 1.11, respectively, 1/k(f) (kJ/kJ), 1.05, 1 .08, 1.3 and 1.09, respectively, and MEm (kJ/day/W-0.75), 539, 624, 572 and 741, respectively.