Influence of Urea Treatment and Soybean Meal (Urease) Addition on the Utilization of Wheat Straw by Sheep

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 3×2 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 BW 0.75 ), 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.

The impact of hydrolyzing and oxidizing agents on chemical composition and digestibility of various high‐fibre forages

“…As expected, total forage N content was increased significantly in all experiments by urea application as noted in previous studies (Aregawi et al., ; Hanafi, el Khadrawy, Ahmed, & Zaabal, ; Kraidees, ; Mehra et al., ; Milad et al., ; Souza & dos Santos, ; Vieira Pires, Giordano Pinto De Carvalho, & Oliveira Ribeiro, ). All HFF treatments with urea alone or combined with other chemical agent resulted in final CP values above 60–80 g/kg DM.…”

“…Higher ADF values also were observed by Dias-Da-silva and Sundstøl (1986), Mehra, Dass, Verma, and Sahu (2001) and Kraidees (2005) who studied the effect of urea ammoniation on the nutritive value of different straws. Although it is not clear how the urea treatment could result in an increase in ADF values in this study, it may have to do with swelling of the fibre as indicated by Kumar, Kamra, Agarwal, and Chaudhary (2009).…”

“…Overall, digestibility is negatively correlated with the concentration of fibre (Hanafi et al., ; Raffrenato et al., ), and particularly lignin (Hatfield & Fukushima, ). The treatments containing a urea solution do not show an impact of nutritional significance on cell wall concentration or ADL in any of the experiments, but IVDMD was improved, presumably due to an increase in cell wall porosity or fragility associated with cleavage of lignocellulosic linkages (Kraidees, ) and alteration of cellulose crystallinity (Mittal et al., ). Such changes make structural polysaccharides more susceptible to the enzymes produced by ruminal microbes (Hanafi et al., ; Vieira Pires et al., ).…”

“…Increases in ruminal digestion of straws after treatment with urea alone or in combination with other treatments have been reported. This effect was attributed to both cleavage of cell wall linkages and reduction in fibre content (Crestini et al., ; Grabber, Panciera, & Hatfield, ; Kraidees, ; Mehra et al., ; Vieira Pires et al., ) as well as to N binding (Hanafi et al., ). Such changes in forage chemical composition should lead to increases in DM intake (Kayastha, Dutta, Kayastha, & Deka, ; Wanapat et al., ) that also can lead to an increased animal performance.…”

“…Other research also reported variable results after urea or ammoniation treatments applied to diverse HFF. Kraidees (2005) and Bravo et al (2008) reported no significant changes in NDF, ADF and ADL from urea treatment of wheat straw; in contrast, Milad, Rymer, and Radley (2010) and Aregawi, Animut, Kebede, and Kassa (2013) detected a significant decrease in these fractions.…”