Comparison of total feces collection methods and internal markers in determining the digestibility of wheat straw with pomegranate pomace or chicken manure in camel

The total fecal collection (TFC) method is a reliable method for determining the digestibility of diets by animals. In this method, the animals are kept in a metabolic cage to collect all the feces and hence it is the most accurate method to measure the digestibility of the feed. Despite the high accuracy of this method, TFC is labor intensive and time consuming when evaluating a wide range of feed samples and requires many animals. Also, considering that being surrounded by camels is accepted for a short period of time and for camels that are fed with rations containing high amounts of energy, the animals should be confined in the stall. Another disadvantage of keeping a trapped animal is the possible effect on the animal's metabolism. These problems led to separation from the animal's natural behavior. Accurate measurement of feed intake and stool collection are difficult. Digestibility coefficients can be also measured indirectly by markers. There arevarious indigestible markers including polyethylene, chromium oxide (Cr2O3), acid detergent lignin (ADL) and acid insoluble ash (AIA) to determine the digestibility of nutrients in different parts of the digestive tract. At the end of the 19th century, lignin was used as a potential internal marker to estimate digestibility. Given that there are no specific enzymes for lignin degradation in mammals or anaerobic bacteria, different results have been reported by researchers when using ADL to estimate digestibility. Digestibility was underestimated when using AIA as a natural marker. However, it is difficult to use the AIA method for grazing animals. One of the advantages of AIA compared to other indicators is the simplicity of its analysis and does not require special equipment. This study was aimed to evaluate the apparent digestibility of nutrients in camels using AIA, ADL and TFC methods.

To measure the apparent digestibility of nutrients using AIA, ADL and TFC methods, four male camels (age= 1 year, weight = 116.3 ± 9.35 kg) were used.  This experiment was carried out based on a completely in a fully randomized design. The experimental period was 42 days (2 periods of 21 days) with 14 days of adaptation to the experimental diets and 7 days of data collection. Camels had free access to water and feeding was done once a day at 8 AM. In order to determine the apparent digestibility of feed nutrients, feces and feed samples were collected at the end of the 7 days of the experiment. The fecal samples weighed at 8:00 AM before feeding. The camels were kept in the stall for 5 days for adaptation. Then each camel was placed in an individual cage. In this experiment, three types of agricultural waste were used, including wheat straw, pomegranate pomace and chicken manure.

The results showed a significant difference in the digestibility coefficients of dry matter, organic matter, crude fat, neutral detergent fiber and acid detergent fiber between the two methods of AIA and TFC in diets containing wheat straw or pomegranate pomace (P<0.05). There was no significant difference in the digestibility coefficients of nutrients of wheat straw diet with chicken manure between the two methods of AIA and TFC. The recovery percentage of AIA marker in diet containing 75% wheat straw + 25% poultry manure was 105.14±17.08.

In general, it seems that due to the weak correlation between the three methods of measuring digestibility and considering the existing limitations, including the cost and many facilities, especially in large livestock, in determining digestibility with the method TFC and ADL, the AIA method can be used to determine digestibility in camels.