Effect of using processed pinto bean straw in the diet on the growth performance of Farahani fattening lambs

Introduction: Livestock nutrition represents a significant portion of the total costs in animal husbandry. To enhance efficiency, identifying inexpensive feed sources is a key strategy. The gap between the demand and supply of feed ingredients has notably widened in recent decades, and livestock producers are facing numerous challenges in obtaining feed resources due to drought and rising prices of conventional feedstuffs. Consequently, there is an increasing need to utilize affordable alternative feed materials in ruminant diets. Processing and effectively using agricultural by-products and residues as feed for ruminants is essential for improving livestock production. Legume straws, particularly bean straw, have gained attention both domestically and internationally as an important and economical source of roughage in ruminant nutrition. With superior nutrient composition compared to cereal straws, legume straws offer greater potential for widespread use in animal diets. In regions where beans are cultivated, the production of bean residues is significant and can fulfill part of the nutritional needs of livestock. Feeding bean straw to ruminants may offer benefits over certain cereal straws, likely due to its higher crude protein content and other valuable nutrients. From a nutritional standpoint, processed legume straws serve as sources of energy and protein in the diets of fattening livestock, helping to reduce feeding costs and improve animal performance. Therefore, this study aimed to evaluate the effects of incorporating processed and unprocessed bean straw into the diets of Farahani lambs on their growth performance and fattening characteristics.
Materials and methods: Bean straw was processed with urea by ensiling in plastic covers. For every 100 kg of bean residue, 50 kg of water (50%), 3 kg of chemical urea fertilizer (3%), 1 kg of calcium carbonate (1%), and 100 g of sulfur were added. One month after ensiling, dry matter, ether extract, ash, crude protein, and acid detergent fiber and neutral detergent fiber contents of the processed bean straw were determined. In vitro digestibility of samples was also assessed using the gas test method. Subsequently, at a sheep farm in Arak County, 45 lambs aged 4–5 months with similar average weights were randomly assigned to three experimental groups: 1) wheat straw (control), 2) bean straw, and 3) urea-treated bean straw. The experiment lasted 90 days, during which lambs’ weight gain was measured every 30 days and daily dry matter intake was recorded by collecting feed refusals before morning feeding. Weight gain, feed conversion ratio (FCR) were examined monthly and over the entire fattening period. Data were analyzed using mixed model procedures in SAS software (version 9.1), and treatment means were compared by Duncan’s multiple range test.
Results and discussion: The study found that treating bean straw with urea significantly increased its crude protein content by 25.51%, elevating it from 8% in untreated straw to 12.1% in urea-treated straw (P<0.05). Ammoniation effectively reduced both neutral detergent fiber and acid detergent fiber contents (P<0.05). Additionally, urea treatment markedly improved the dry matter and organic matter digestibility of the bean straw compared to untreated samples (P<0.05). Ammoniation also resulted in higher gas production (P<0.05) and enhanced organic matter digestibility by approximately 11%, boosting the metabolizable energy content from 7.29 to 9.1 MJ/kg DM in treated straw (P=0.01). The feeding trial indicated that incorporating bean straw increased daily feed intake compared to the control diet, with urea-treated bean straw further enhancing intake over untreated straw (P=0.03). Furthermore, lambs fed urea-treated bean straw exhibited significantly greater daily weight gain than those in the control and untreated straw groups (P=0.01), along with an improved feed conversion ratio (P=0.01). Economic analysis showed that adding bean straw and urea-treated bean straw to the lambs' diet reduced the feeding cost per kilogram of weight gain compared to the control group.
Conclusions: Ammoniating bean by-products with urea is a straightforward and effective method to enhance their nutritional value. This technique significantly increases crude protein content and digestibility, allowing these by-products to replace conventional feeds like alfalfa, corn silage, and various oilseed meals in ruminant diets. As a result, it reduces overall feed costs and lowers meat production expenses.