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

Introduction: Livestock nutrition constitutes a significant portion of the total costs in animal husbandry. To improve efficiency, identifying inexpensive feed sources is a fundamental strategy. Considering that the gap between the demand and supply of feed ingredients has substantially increased over recent decades, and that livestock producers face numerous challenges in acquiring feed resources due to drought and rising prices of conventional feedstuffs, there is a growing necessity to utilize cheap alternative feed materials in ruminant diets. Therefore, processing and proper utilization of agricultural by-products and residues as feed for ruminants is indispensable for enhancing livestock production. Legume straws, particularly bean straw, have attracted attention domestically and internationally as an important and economical roughage source in ruminant nutrition. Due to their superior nutrient composition compared to cereal straws, these materials have greater potential for extensive use in animal diets. The production of bean residues in regions where this crop is cultivated is considerable and can supply a portion of the nutritional requirements of livestock. Feeding bean straw to ruminants may offer advantages over certain cereal straws, potentially due to its higher crude protein content and other valuable nutrients. From a nutritional perspective, processed legume straws serve as a source of energy and protein in the diets of fattening livestock, helping to reduce feeding costs and improve animal productive performance. Accordingly, this study was carried out to evaluate the effects of incorporating processed and unprocessed bean straw into diets on growth performance and fattening traits of Farahani lambs.
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, 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 results showed that urea treatment increased the crude protein content of bean straw by 25.51%, raising it from 8% in untreated straw to 12.1% in urea-treated straw (P < 0.001). Ammoniation significantly decreased neutral detergent fiber and acid detergent fiber contents (P < 0.001). Urea treatment also significantly enhanced dry matter and organic matter digestibility of the treated bean straw compared to untreated samples (P < 0.001). Additionally, ammoniation led to greater gas production (P < 0.001) and increased organic matter digestibility by about 11%, which subsequently raised the metabolizable energy content from 7.29 to 9.1 MJ/kg DM in treated straw (P = 0.008). The feeding trial revealed that inclusion of bean straw increased daily feed intake compared to the control diet, and urea-treated bean straw further improved intake compared to untreated bean straw (P = 0.028). Moreover, daily weight gain in lambs fed urea-treated bean straw was significantly higher than that of control and untreated bean straw groups (P = 0.001), with a correspondingly improved feed conversion ratio (P = 0.001). The calculation of economic indicators and their comparison among the experimental and control groups demonstrated that the inclusion of bean straw and urea-treated bean straw in the lambs’ diet resulted in a reduction in feeding cost per kilogram of weight gain compared to the control group.
Conclusion: In summary, ammoniation of bean by-products with urea constitutes a simple and effective method to process and enhance the nutritional value of these residues. This processing technique significantly improves crude protein content and digestibility, enabling greater substitution of these by-products for conventional feeds such as alfalfa, corn silage, and various oilseed meals in ruminant diets. Consequently, it reduces overall feed costs and lowers meat production expenses.