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Published online by Cambridge University Press: 21 November 2017
Urease enzymes occur naturally in straw and may hydrolyze added urea to form a mixture of ammonia, carbon dioxide, and “ammonium carbonate”.We have previously found the digestible intake of barley straw by sheep to be lower when it is treated with urea than when treated with an isonitrogenous amount of ammonia (Sherwood and Owen, 1986). At ad libitum feeding levels, urea was considerably less effective than ammonia for improving voluntary straw intake, and the improvement in digestibility by urea treatment appeared to be temperature dependent. However, as level of intake is known to influence digestibility (Kiangi et al., 1981), differences in digestibility may have been confounded by differences in level of intake. There was therefore a need to compare the digestibilities of untreated, ammonia-treated and urea-treated straws where levels of intake were identical across treatments.