Comparative Use by Lambs of Nitrogen from Soybean, Urea and Extruded Grain-Urea Products

Abstract

Nutrient digestibility and nitrogen balance were used as response criteria to evaluate extruded grain-urea products, soybean meal, or urea as nitrogen supplements in high roughage lamb diets. In the first experiment, soybean meal was compared with three grains (sorghum grain, corn, and wheat) extruded with urea at two levels of gelatinization, low cook and high cook. Dry matter, organic matter, and gross energy digestibilities were similar among treatments. Lambs receiving the high cook sorghum grain-urea product had lower nitrogen free extractives and non-protein organic matter digestibilities. Ether extractive digestibilties tended to be increased in highly gelatinized products. Nitrogen retention was affected by gelatinization level in sorghum grain-urea products but not those made with corn or wheat. With proper gelatinization, the extruded grain-urea products appear to be similar to soybean meal as protein supplements in high roughage lamb diets. In the second experiment, urea was compared to four extruded sorghum grain-urea products of varying gelatinized starch:urea ratios (44, 56, 70 and 84% protein equivalents). Nitrogen-free extractives digestibilities were greater in extruded products than for urea. Other nutrient digestibility differences appeared to reflect differences in product quality rather than starch:urea ratio. Nitrogen retentions tended to be lower in 44 and 70% protein equivalent products. Trans. Kans. Acad. Sci., Vol. 78 (1-2), 1975. Introduction Urea has been reported to cause lower nitrogen retention by animals than natural protein supplements (Gallup, Whitehair and Bell, 1954; Graingeret al., 1960; Oltjen and Putnam, 1966). Lower nitrogen retention is caused by rapid hydrolysis of urea to carbon dioxide and ammonia (Pearson and Smith, 194 3) with subsequent absorption of ammonia into the blood stream (Coombe, Tribe and Morrison, 1960; Hogan, 1961) and loss of nitrogen through the urine. However, if sufficient carbon skeletons arising primarily from dietary carbohydrates are available (McNaught, 195 1), the liberated ammonia can be used to synthesize bacterial protein and increase nitrogen retention. Urea as a protein supplment in low quality, high roughage diets is limited by lack of readily available carbohydrates (Williams, Whiteman and Tillman, 1969). Deyoe et al. (1968) developed a product called Starea (expansion product of starch and urea) that has improved use of urea nitrogen. These extruded products were nearly equal to soybean meal for lactating dairy cows (Helmer et al., 1970), steers (Thompson et al., 1972) and lambs (Shiehzadeh 'Contribution No. 447, Department of Animal Science and Industry. Kansas Agricultural Experimnent Station. 2Present address: Department of Biochemistry, School of Medicine, Pahlavi University. Shiraz. Iran.