Influence of age on the apparent metabolisable energy and total tract apparent fat digestibility of different fat sources for broiler chickens

The influence of age of broilers on the apparent metabolisable energy (AME) and total tract digestibility of fat in five fat sources (tallow, soybean oil, poultry fat, palm oil and a 50:50 blend of tallow and soybean oil) was investigated. The assay diets were developed by substituting the different fats for 40 g/kg (w/w) of a maize-soy basal diet and the measurements were made during weeks 1, 2, 3 and 5 posthatch. The AME of fats was influenced (P<0.001) by the age of broilers. The AME was markedly lower (P<0.05) during week 1, but improved during week 2. There were no further improvements (P>0.05) in the AME after week 2. There was no interaction (P>0.05) between fat source and age of broilers for the AME, indicating that the effect of age on the AME was similar for all fat sources. The effect of age on the apparent total tract digestibility of fat generally followed the same trend as that on the AME. The AME of palm oil, soybean oil and poultry fat were determined to be similar (P>0.05), but higher (P<0.05) than that of tallow. The AME of the 50:50 blend of tallow and soybean oil was determined to be 9% higher than the arithmetic averages of tallow and soybean oil, suggesting a synergistic effect. Overall, the present data highlight the physiological limitation in newly hatched chicks to effectively digest and utilise fats.