Research note: Comparison of total tract endogenous fat losses and fat digestibility determined by fat-free diet and regression methods in broiler chickens and laying hens

This study aimed to compare endogenous fat losses (EFL) and fat digestibility determined using fat-free diet (FFD) and regression methods in broiler chickens and laying hens. Two metabolism trials were conducted with 28 broiler chickens (21 d of age, 0.96 ± 0.04 kg BW) and 28 laying hens (72 wk of age, 2.01 ± 0.05 kg BW). Birds within each strain were randomly allotted to 4 dietary treatments: FFD and the supplementation of 2, 4, or 6 % corn oil to the FFD. Results indicated that increasing supplementation of corn oil increased (linear, P < 0.001) apparent total tract digestibility (ATTD) of fat for both broiler chickens and laying hens. The basal EFL estimated using the FFD method was similar between broiler chickens (1.75 g/kg DM intake) and laying hens (1.62 g/kg DM intake). Supplemental levels of corn oil did not influence standardized total tract digestibility (STTD) of fat for both strains. The ATTD and STTD of fat at each level of corn oil supplementation did not differ between strains. Regression analysis indicated that total EFL and true total tract digestibility (TTTD) of fat were 2.024 g/kg DM intake and 97.4 % for broiler chickens, and 1.686 g/kg DM intake and 97.1 % for laying hens, respectively. However, no differences in total EFL and TTTD of fat were observed between strains based on their 95 % confidence intervals. Furthermore, comparisons between FFD and regression methods revealed no differences between basal and total EFL in both strains. Moreover, values for the STTD of fat did not differ from those for the TTTD of fat in both strains. In conclusion, the comparable values for the STTD and TTTD of fat suggested that the STTD of fat can serve as a reliable and practical measure of dietary fat utilization in poultry. For highly digestible fat sources (i.e., corn oil), fat digestibility appeared to be similar between broiler chickens and laying hens.