Effects of different levels of urea supplementation on nutrient intake and growth performance in growing camels fed roughage based complete pellet diets

摘要

Abstract The utilization of urea in camels has beneficial and negative effects. The aims of this study were to investigate the effects of different levels of urea supplementation on nutrients intake, digestibility, growth performance, feed efficiency and economics in growing camels fed roughage based complete pellet diets. In the present study, eighteen growing camels with an average live body weight of 306.17?±?2.05?kg were randomly assigned in three treatments: T1?=?roughage complete pellet diet without urea, T2?=?T1 plus 1% urea, and T3?=?T1 plus 2% urea. The results showed that the urea supplementation significantly affected average daily feed and nutrient intake of dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) ( P ?0.05). Similarly, digestion coefficient of DM, CP, ether extract (EE), crude fiber (CF) and ADF was influenced by increasing urea level ( P ?0.05). The intake of digestive nutrients was similar among all treatment groups. Total body live weight gain and average daily gain were significantly higher in urea supplemented groups ( P Keywords Urea ; Nutrient intake ; Growth performance ; Complete pellet diet ; Feed conversion ratio prs.rt("abs_end"); 1. Introduction Potential production of the cereals in tropic areas is very important ( Zhang et?al., 2012 ). Thus, most ruminants are fed low-quality roughages, agricultural crop-residues and industrial byproducts ( Wanapat et?al., 2013 ). However, roughages are low in nutritive value, protein level, high content of ligno-cellulose and low digestibility ( Freeman et?al., 1992 and Mawuenyegah et?al., 1997 ), thus resulting in low voluntary feed intake ( Wanapat et?al., 2012 ). The improvement of low quality roughages can be fulfilled by supplementation of true protein sources ( McCollum and Horn, 1990 ) and non-protein nitrogen (NPN) like urea ( McAllen, 1991 and Huntington and Archibéque, 1999 ). In addition, the efficiency of protein utilization should always consider economical as well as environmental aspects ( Yin et al., 2010 ). Urea in rumen is converted to ammonia by urease and the ammonia released from urea has the capacity to weaken the lignified outer walls, allowing better penetration by rumen microorganisms to produce more effective fermentation and liberation of nutrients ( Chenost, 1995 ). However, the addition of urea to animal diet should be done under limitations to avoid the risk of hyper ammonia. The hydrolysis of urea to NH₃ in the rumen by microbial enzymes is rapid and occurs at a faster rate than NH₃ utilization by the rumen bacteria ( Highstreet et?al., 2010 ). This results in the accumulation of NH₃ in the rumen and the transformation of this product in urea by liver cells ( Golombeski et?al., 2006 ). In normal conditions, ammonia is detoxified in the hepatocytes through urea cycle ( Visek, 1968 ). But when its concentration is elevated in the rumen, blood, cerebrospinal fluid and other tissues, it is resulting in ammonia poisoning by overwhelm hepatocytes capacity of detoxification through inhibiting the Krebs cycle ( Davidovich et?al., 1977 ). An effort to improve the low quality of straws and to slow down the ammonia release from urea has been initiated by making roughage based complete pellet diets. Therefore, a study was needed to generate reliable information of feeding complete pellet diet with supplemental nitrogen from urea in camels. This study was designed to measure the optimum level of urea that could be incorporated in the diets of growing camels. 2. Material and methods 2.1. Animals and experimental diets Three complete pellet diets with different levels of urea were prepared for eighteen growing camels. Animals were distributed equally in three groups (6 camels in each group, 3 males and 3 females), fed a complete pellet diet containing 0 (T1), 1 (T2) and 2% (T3) of urea, respectively. Composition analysis of the diets can be found in Table?1 . The complete pellet diets were produced as following: crop residues (groundnut and wheat straws) were chaffed to 1 to 5?cm and concentrate ingredients (bajra grains and mustard cake) were coarsely ground separately. Urea was dissolved in hot water at 1?L to 1?kg urea and the solution of urea was then mixed with 5% molasses. The whole mass of urea-molasses and remaining ingredients were transferred into a vertical mixer in order to obtain homogenized total mixed ration. Care was taken for the mixture of ingredients to be uniform. Finally, the desired quantity of total mixed ration was pulled in a plate dye roughage based complete pellet making machine for densification of the ingredients.