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Comparison of internal and external markers in digestibility studies involving the Australian freshwater crayfish, Cherax destructor Clark (Decapoda, Parastacidae)
journal contributionposted on 1998-07-01, 00:00 authored by Paul Jones, S S De Silva
Apparent dry matter and protein digestibility coefficients (DMD and PD, respectively) were determined using several different marker compounds [Cr 2 O 3 , ash, crude fibre (CF), hydrolysis resistant ash (HRA) and hydrolysis resistant organic matter (HROM)] for nine different pelleted diets fed to adult Australian freshwater crayfish, Cherax destructor Clark. For a soybean-meal-based diet (Soy-60), HRA resulted in the highest DMD and PD coefficients (98.6 and 99.6%, respectively), while the lowest values were obtained by using CF (DMD, 74.3%; PD, 91.6%). For the series of diets tested, digestibility coefficients determined using Cr 2 O 3 were significantly higher than those obtained using ash or CF, and lower than those obtained using HRA and HROM. Using ash as the marker resulted in a mean reduction in DMD and PD of 12.4% and 5.5%, respectively, compared to Cr 2 O 3 . On average, coefficients obtained using CF were 11.8% and 4.2% lower, respectively, than the values obtained using Cr 2 O 3 . Despite an overall reduction in the digestibility coefficients estimated using ash, the ash-ratio technique provided a reasonable estimate of nutrient digestibility for some diets. Based on the ease and speed of determination, it is proposed that dietary ash is suitable for use as a digestibility marker in field situations.