Introduction: In ruminants, protein sources that provide amino acids and nitrogen requirements of ruminants, are among the most expensive parts of the diet (Hashem and Tayeb, 2023). Plant protein sources (such as soybean meal, rapeseed meal, etc.), animal protein sources (such as meat meal and seafood), and non-protein nitrogen are used to provide the protein requirements of ruminants. However, the shortage of protein sources has become a global problem and the global price of soybean meal, as an important standard protein source, remains high, which has led to increase in production costs. Therefore, finding alternative sources of soybean meal to provide crude protein in diets seems to be essential. NPN sources are a group of compounds that are not proteins but contain nitrogen in their structure and include urea, ammonium salts, nitrates, alkaloids, asparagine, purine, choline, uric acid, amines, amides, amino acids and nucleic acids. Urea is considered a practical NPN source due to its lower cost and contains 46% nitrogen, which is equivalent to 287.5% crude protein. However, rapid breakdown of urea in the rumen and high release of ammonia will increase the amount of nitrogen excreted in the urine and reduce livestock performance. One of the less studied sources of slow-release urea is biuret. Biuret (carbamyl urea or alphanamides) with the chemical formula NH2CONHCONH2 is produced by the condensation of two urea molecules at high temperatures in the Bosh-Meiser process, and can be used as a slow-release NPN source in ruminant nutrition. Biuret contains about 41% nitrogen (256% crude protein) and is degraded by ruminal microorganisms at a slower rate than urea. Most studies conducted on the use of NPN sources in ruminant nutrition has focused on animal health and performance, and very few studies have been conducted on the effects of these sources on the carcass quality of fattening lambs. Therefore, the aim of the present study was to investigate the effects of replacing different levels of biuret at the expense of urea on growth performance, rumen microbial protein synthesis and meat quality characteristics in Afshari fattening male lambs.
Material and Methods: The experiment was conducted in a completely randomized design with 4 experimental treatments and 7 lambs in each experimental group (total 28 Afshari male lambs). The average age of the animals was 135±15 days and their average live weight was 34±1.13 kg. The lambs were kept and raised in individual pens from the first day of experiment. The animals were fed with experimental diets for 84 days, the first 14 days considered as adaptation period to the experimental diets and individual pens, and the remaining 70 days as the main period of the experiment. The experimental diets contained biuret at levels 0 (control treatment), 0.54, 1.08 and 1.61% on dry matter (DM) basis. Biuret production from urea was carried out by converting one urea molecule into equimolar amounts of ammonia and cyanic acid at a temperature above the melting point of urea (145°C). The cyanic acid produced from urea then reacts with other urea to form biuret. In general, two urea molecules are converted into one biuret molecule and one ammonia molecule. In this study, the process of producing biuret from urea was carried out at a temperature of 145°C for 3 hours without using catalyst.
Results and Discussion: The results showed that with increasing biuret level in the diet total weight gain, average daily weight gain and micro protein production increased linearly (P<0.05), although the average final weight and DM intake were not affected by the experimental diets (P>0.05). With increasing biuret level in the diet, meat crude protein percentage tended to increase linearly (P=0.07), although the moisture, crude fat, and crude ash contents of meat were not affected (P>0.05). With increasing dietary biuret level, meat pH tended to increase (P=0.08). Water holding capacity, tendency to redness (a*) and brightness (L*) of meat increased linearly with increasing dietary biuret levels (P<0.05), but meat shear force decreased linearly (P<0.05). Cooking weight loss was not affected by the experimental diets (P>0.05). With increasing level of biuret color score and overall acceptance of raw and cooked meat increased linearly (P<0.05). Concentrations of major essential amino acids in meat increased linearly with increasing the level of biuret in the diet (P<0.05), while glutamine concentration decreased linearly (P<0.05).
Conclusion: The current study indicated that using biuret instead of urea up to 1.61% of the dietary DM improved growth performance, microbial protein production and meat quality and sensory properties in fattening lambs. |
