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Ruminant Nutrition and Forage Utilization
Asian-Australasian Journal of Animal Sciences 2005;18(7): 957-965.
DOI: https://doi.org/10.5713/ajas.2005.957    Published online November 26, 2005.
Influence of Urea Treatment and Soybean Meal (Urease) Addition on the Utilization of Wheat Straw by Sheep
M. S. Kraidees
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 3횞2 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<0.001) as compared to NT straw. The degree of urea hydrolysis, either with or without SBM addition, was nearly similar. Lambs fed either UT or US straw based diets had significantly (p<0.01) and numerically (p>0.05) higher straw DM intake (g d-1 kg-1 BW0.75), 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<0.001) and 7.8% (p<0.07); this corresponds to 35 (p<0.001) and 51% (p<0.001) in N digestibility and approximately 78 (p<0.017) and 105% (p<0.002) in N retention, for UT and US diets, respectively, as compared to NT diet. However, the UT diet had higher (p<0.01) fiber digestibility over the US diet. Addition of SBM tended to improve (p = 0.09) straw DM and digestible OM intakes, while significantly increasing (p<0.001) total and digestible CP intakes across all diets. Lambs fed on US diet had higher ruminal ammonia N than those fed on UT (p<0.05) or NT (p<0.001) diets. However, ruminal pH and molar proportion of the volatile fatty acids did not differ (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.
Keywords: Urea; Soybean Meal Urease; Wheat Straw; Digestibility; Lambs


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