A Method to Include Animal Fibre in Dietary Fibre Analysis

Animal fibre consists of the nitrogen-rich molecules in the non-digestible fraction of body tissues of prey animals, for example, in fur and bones. Animal fibre has a health effect on carnivores and; therefore, its quantification is important for nutrition research in carnivores as well as in omnivores. Traditional fibre analyses were developed to quantify the carbohydrate-based molecules of plant fibre and currently no method exists to quantify animal fibre. This study adapted the filter bag technique of the amylase-treated neutral detergent fibre method by adding a protease step to remove digestible protein from the residue to measure animal fibre. Sodium sulphite was omitted, similar to the neutral detergent residue (NDR) method, as it removes keratinaceous residues of animal origin. The amylase-treated neutral detergent residue including animal fibre (aNDRa) values were compared to the total dietary fibre (TDF) method. Test materials were lignocellulose, beet pulp, pea, barley, beef, horse meat with skin and coat, day-old chicks, rat, hair, cat faeces, faeces from bears fed a fruit-based diet and faeces from bears fed a rabbit-based diet. Several experiments preceded the validation of aNDRa with results as follows: pre-extraction of fat was sufficient when F57 bags, each containing 0.5 g of sample, were placed in a Soxhlet extractor for 1 h; grinding samples over a 2.0 instead of 1.0 mm screen in a centrifugal mill resulted in less sample loss in the F57 bags; pre-extraction of protein was sufficient when refluxed for 90 min with 5 mg protease per 0.5 g sample. The TDF concentration in beef and prey samples showed highly variable results with the TDF concentration in beef being too high showing that the TDF analysis is inaccurate to quantify animal fibre. In contrast, the aNDRa method was capable of quantifying animal fibre and plant fibre in a diverse range of samples.