Measuring the Apparent Nutrient Digestibility of Wheat Straw and Wheat Straw Mixed with Rice Hull by using Three Methods of Acid-Insoluble Ash, Acid-Insoluble Lignin and Collecting Total Feces in Camels

Various methods have been used to evaluate the digestibility coefficients of nutrients. The total fecal collection (TFC) method is a reliable approach for determining the digestibility of rations in live animals. In this method, animal are kept in a metabolic cage in to collect all the feces, making it the most accurate method for measuring feed digestibility. Total fecal collection (TCF) is one of the most accurate direct procedures to determine apparent digestibility. Despite its accuracy, TFC is labor-intensive and time-consuming when evaluating a wide range of feed samples and requiring a large number of animals. Moreover, animals should be confined in stalls, considering that being surrounded will be accepted by camels for a short period and training is necessary for camels fed with ration containing high amounts of energy. Other disadvantage of keeping the animal trapped includes the potential impact on animal metabolism. These problems led to separation from the animal's normal behavior. Accurate measurement of food intake and fecal collection is a tough work. Digestibility coefficients can be measured indirectly by markers. Various indigestible markers include polyethylene Various indigestible markers include polyethylene, chromium oxide (Cr2O3), acid detergent lignin (ADL) and acid-insoluble ash (AIA) have been used to determine the digestibility of nutrients in different parts of gastrointestinal tract. By the end of 19th century, lignin was considered as a potential internal marker for the estimation of digestibility. Because no specific enzymes exist for degradation of lignin in mammals or in anaerobic bacteria, different results have been re-ported by researchers when using ADL for the estimation of digestibility. Digestibility was reported to be underestimated when using AIA as a natural marker. However, it is difficult to apply this method to grazing animals. AIA is one of the most common internal indicators for determining apparent digestion coefficients. One of the advantages AIA compared to other markers is simplicity of analysis and it does not need special equipment. This study aims to evaluate the nutrient apparent digestibility of different diets in camels using AIA, ADL and TFC.

The field phase of the research was conducted at Asrar Sabzevar Agricultural Research Station, and the laboratory phase was conducted at the Animal and Poultry Nutrition Laboratory of Gorgan University of Agricultural Sciences and Natural Resources. Four male camels (age=1 year, BW= 116.3±9.35 kg) were used in a completely random design to measure the apparent digestibility of nutrients in wheat straw and wheat straw with rice hull using AIA, ADL, and TFC. The experimental period was 42 days (2 periods of 21 days) with 14 days of adaptation to experimental diets and 7 days of data collection. Camels had free access to water, and feeding was done once a day at 8 A.M.

The results showed no significant difference between TFC and AIA for measuring the digestibility of dry matter, organic matter, crude fat, crude protein, neutral detergent insoluble fibers, and acid detergent insoluble fibers in wheat straw and wheat straw with rice hull (P>0.05). However, digestibility was significantly higher in TFC than in ADL (P<0.05).

The recovery percentage of AIA marker was 92.8±92.38 in the diet of 75% wheat straw with 25% rice hull. Based on the study's results, AIA can be used as a suitable internal indicator to measure digestibility in camels if the recovery percentage is more than 90%. The amount of digestibility measured using AIA was close to the amount of digestibility measured using TFC.