EFFECT OF AMMONIA OR UREA TREATMENT OF STRAW ON CHEWING BEHAVIOR AND RUMINAL DIGESTION PROCESSES IN NONLACTATING DAIRY-COWS

Three non-lactating Holstein-Friesian cows (575 kg average body weight ) fitted with ruminal and duodenal cannulas were used to examine ferme ntation products and extent of digestion in the rumen in relation to c hewing behaviour. They were fed isonitrogenous diets composed of chopp ed straw (70%) and concentrate (30%). The straw was either untreated ( US) and supplemented with urea or treated with ammonia (ATS) or urea ( UTS). Apparent organic matter (OM) digestibility in the rumen did not differ among the three diets whereas true OM digestibility tended to b e slightly greater with the treated straws. Total nitrogen reaching th e intestine also was greater with treated-straw diets, resulting from an increase of bacterial protein synthesis. Bacterial nitrogen flow wa s 104 g day(-1) with ATS and UTS, but only 81 g day(-1) with US. The c ows devoted more time and jaw movements to eating untreated straw than to eating treated straws. The figures for duration (min) and number o f jaw movements devoted to eating, expressed per kg of dry matter inta ke, were 52.4 and 2610 for ATS, and 60.4 and 3150 for UTS, compared wi th 74.5 and 3400 for US. Consequently, the cows spent more time rumina ting each kilogram of US compared with ATS and UTS. Frequency of jaw m ovements was also increased markedly after treatment of the straw. The results are interpreted to suggest that ammonia or urea treatment of wheat straw increased bacterial protein synthesis in the rumen in addi tion to the expected increase of cell wall digestion, leading to a sub stantially increased nitrogen value for the forage.