The Effect of Adding Different Levels of Wheat Straw to Paulownia (Paulownia sp.) Leaf Silage on the Chemical Composition and in vitro Fermentation Indices

Introduction: The lack of water resources and the high water requirements of common forage plants have created significant limitations in the production of good quality forage in the country. Therefore, it is very important to identify and properly use new forage sources for inclusion in ruminant nutrition. A new fodder source must not only be fast-growing and resistant to hot and drought conditions, but also have acceptable nutritional value. Plants of the Paulowniaceae family in China and East Asia are a notable source of fodder in this regard. Several types of Paulownia are known in the world. These plants are known for their high growth rate and intense photosynthesis, which are specific to C4 plants, and with wide leaves with a diameter of about 90 cm. The commercial production of Paulownia wood produces a large mass of leaves, which are usually used as natural fertilizers. At the age of about 6 to 8 years, the leaf production of each Paulownia tree reaches about 100 kg. When the leaves have a favorable nutritional value, they can be used as fodder in feeding ruminants. In Iran, about 20 million tons of wheat straw (WS) are produced annually, a large part of which is used as the main source of animal feed. However, the nutritional value of these by-products is very low. Wheat straw is deficient in crude protein (CP), mineral elements, and digestible energy, and has low palatability. Considering the large amount of WS produced in the country, and in order to optimize the dry matter (DM) content of silage and prevent wastes from it, it seems that silage with appropriate characteristics and nutritional value can be produced using a mixture of fresh Paulownia leaves (PL) and WS. Therefore, the purpose of the present study was to determine the nutritional value of PL and then to investigate the effects of adding different levels of WS to PL silage on chemical composition, gas production parameters, digestibility and fermentation parameters in vitro.Material and Methods: Paulownia leaves (Tebjoo hybrid variety) and wheat straw (WS) were first collected and analyzed for their chemical composition using standard methods. Subsequently, both forages were chopped into 2–4 cm pieces using a hand chopper to prepare them for silage. Experimental treatments included adding WS at levels 0 (PL silage only), 6, 12, 18, and 24% to PL on DM basis. The materials were compacted in the plastic containers and the silage period lasted two months. Determination of chemical composition of fresh fodders and the nutritional value of experimental silages including chemical composition, in vitro gas production and fermentation parameters, digestibility and enzyme activity were carried out.Results and Discussion: Results showed that DM, organic matter (OM), CP, neutral detergent fiber (NDF), acid detergent fiber (ADF), ether extract (EE), lignin and non-fibrer carbohydrates (NFC) content of fresh PL were 266, 911, 173, 402, 201, 35.5, 75.5 and 301 g/kg DM, respectively. The mentioned chemical composition in PL silage were 273, 896, 168, 394, 191, 36.8, 74.6 and 297 g/kg DM, respectively. With increasing the level of WS in PL silage content of DM, NDF, ADF, lignin and pH increased linearly (P<0.05), although CP and NFC content and ammonia-N concentration of silage decreased linearly (P<0.05). The OM and ether extract content of the experimental silages were not affected (P<0.05). With increasing the level of WS in PL silage, gas production at all investigated times, gas production potential (coefficient b), short-chain volatile fatty acids, DM and OM digestibility, estimated metabolizable energy, ammonia-N and microbial protein synthesis decreased linearly (P<0.05), but the gas production rate (coefficient c) was not affected (P<0.05). With increasing WS to PL silage, the activities of carboxymethyl cellulase, filter paper degradation activity, alpha-amylase and protease activity the culture medium decreased linearly (P<0.05), although microcrystalline cellulase enzymes activity was not affected (P<0.05).Conclusion: The current study indicated that fresh or ensiled Paulownia leaves (Tebjoo hybrid variety) has a significant nutritional value as a new forage source for use in ruminant nutrition. Moreover, adding different levels of wheat straw to paulownia leaf silage is recommended as a method of enrichment and improving the palatability and nutritional value of wheat straw.