Abstract
The effect of ammoniation with urea and with soybean meal (SBM) as a source of urease on the nutritive value of wheat straw was evaluated in sheep. Twenty-four male Najdi lambs were used in a 3x2 factorial design, in which the animals were allocated to three straw treatments: 0% urea-treated (NT), 6% urea-treated (UT) and 2.2% urea-supplemented (US) straws. Each straw treatment was either supplemented or non-supplemented with 70 g SBM kg - 1 straw during the treatment time with urea, giving a total of six straw treatments. Each of these treatments was individually fed ad libitum to 4 lambs, together with 300 g of barley grain/head/day. Total N content of UT and US straws increased significantly (p 0.05) higher straw DM intake (g d - 1 kg - 1 BW 0 . 7 5 ), compared to those fed NT straw based diet. Apparent DM or OM digestibilities increased significantly (p = 0.014) in lambs fed UT diet, and numerically (p>0.05) in lambs fed US diet as compared to those fed NT diet. Fiber (CF, NDF, ADF, cellulose and hemicellulose) digestibility increased to a similar magnitude, averaging 20.2 (p 0.05) among the treatment diets. This study suggests that US and UT treatments, particularly the latter, improved straw intake, digestibility and N utilization by lambs compared to NT treatment. On the other hand, addition of SBM as a source of urease had a negligible effect on urea hydrolysis.
Highlights
In the kingdom of Saudi Arabia, water represents a major limiting factor for crop and forage production
The experiment was conducted in the Animal manually before feeding to the lambs
Straw was divided into six stacks and allocated to three weight (BW) were used in a 3×2 factorial arrangement of straw treatments of two stacks each: 0% urea-treated [NT], treatments
Summary
In the kingdom of Saudi Arabia, water represents a major limiting factor for crop and forage production. Wheat straw is one of the widely available sources of roughages in Saudi Arabia, with an estimated annual production of 3 million tons (Anon, 2002), and is fed heavily to sheep. The use of straw as an animal feed is limited by its low digestibility and inadequate nitrogen (N) content, which in turn has a negative effect on its voluntary intake. Cereal straws contain more than 80% carbohydrate, mainly cell wall polysaccharides. The rumen microorganisms do not utilize much of this cell wall, due to covalent bonding between the polysaccharide and lignin (Hartley and Jones, 1978). It is commonly accepted that chemical treatments of crop residues by alkalis improve their nutritive value, and make them more utilizable by animals.
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