Effect of wheat straw processed with ammonia on chemical composition, digestibility, gas production parameters, and performance of fattening calves

Introduction: The shortage of feed, caused by the limitation and reduction of water resources, is the biggest challenge for the country's livestock industry. Every year, more than 20 million tons of by-products from the main agricultural production remain in the country, which are mainly used as animal feed. Agricultural by-products, which exceed the production of forage crops many times over, are valuable resources that can replace conventional feeds in animal nutrition. Due to their low protein content and low digestibility, they need to be processed. For almost a century, different processing methods have been used in many countries depending on the conditions and facilities, but unfortunately, the majority of these materials are still used raw and unprocessed as animal feed in the country, which is a waste of resources. Straw processing is carried out by various physical, chemical, and biological methods or a combination of these methods, with ammoniation being the most important chemical method. The use of ammonia gas for this purpose can facilitate and accelerate processing, especially with large quantities of by-products. This research was carried out to study the efficacy and economics of the method of ammonization of straw with ammonia gas and the use of the ammonia product in the diet of fattening calves. Materials and methods: Ammoniated wheat straw was prepared with ammonia gas at three weight percent of the dry matter of straw at 30% moisture by stacking method, and the chemical composition, digestibility, and gas production of the ammonia-containing product were determined. In the second phase, 30 Simmental crossbred fattening calves with an initial weight of 249.5±8.9 were divided into two control and experimental groups and for each group, considering three replicates of five calves for each group. Normal straw was used in the control group, and it was replaced by ammoniated straw in the experimental group. The duration of the trial was eight months, during which the weight gain of the calves was determined every 30 days, and the dry matter was consumed daily. Dry matter consumption, daily weight gain, feed conversion ratio, and the cost of weight gain of calves were determined and compared between the two groups. Results and discussion: The ammonia treatment of straw increased crude protein content in the ammoniated straw from 4.78% to 12.65%, and the amount of NDF and hemicellulose also decreased in ammoniated straw (from 71.33 to 66.80%, and from 30.75 to 26.25%, respectively), while the amount of ADF increased (from 38.7 to 41.20%). The ammonia treatment of straw increased the gas production per 24 hours from 25.71 mL to 38.06 mL and the estimated metabolizable energy from 5.69 to 6.8 MJ per kilogram of dry matter. The ammonia treatment improved the digestibility of dry matter (from 45.0 to 78.75%) and organic matter of straw (from 42.35 to 80.27%). Substituting normal straw for ammoniated straw in the diet of fattening calves increased daily dry matter consumption from 8.66 kg to 8.99 kg (P<0.01), daily weight gains from 1.33 kg to 1.48 kg, and average weight at the end of the fattening period from 423.98 kg to 440.67 kg (P<0.01), and improved feed conversion ratio from 6.43 to 6.01 (P<0.01). In addition, the use of ammoniated straw reduced the price of ration from 71230 Rials to 69210 Rials and the cost of feed for each kilogram of animal weight gain from 458008.9 Rials to 415952.1 Rials. Conclusions: Ammoniation of straw with ammonia gas increased the metabolizable energy, crude protein, and digestibility of straw. The use of ammonia gas for this purpose increased the speed, ease, and efficiency of processing, making it suitable for processing large quantities of straw. The profitability of this method depends on the cost of the ammonia product, in particular the price of ammonia gas and its transportation costs. At the national level and from a macroeconomic perspective, this method increased the digestible nutrients of agricultural residues (metabolizable energy and crude protein), it is, in a sense, a type of food production by increasing productivity and without the consumption of water and other agricultural inputs. It provides more nutrients for livestock, which reduces dependence on traditional feed, reduces competition between humans and livestock for food, protects the environment, and makes production more sustainable.