Effect of ammonia or urea treatment of straw on chewing behaviour and ruminal digestion processes in non-lactating dairy cows

Abstract

Three non-lactating Holstein-Friesian cows (575 kg average body weight) fitted with ruminal and duodenal cannulas were used to examine fermentation products and extent of digestion in the rumen in relation to chewing behaviour. They were fed isonitrogenous diets composed of chopped 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 be slightly greater with the treated straws. Total nitrogen reaching the intestine also was greater with treated-straw diets, resulting from an increase of bacterial protein synthesis. Bacterial nitrogen flow was 104 g day −1 with ATS and UTS, but only 81 g day −1 with US. The cows devoted more time and jaw movements to eating untreated straw than to eating treated straws. The figures for duration (min) and number of jaw movements devoted to eating, expressed per kg of dry matter intake, were 52.4 and 2610 for ATS, and 60.4 and 3150 for UTS, compared with 74.5 and 3400 for US. Consequently, the cows spent more time ruminating each kilogram of US compared with ATS and UTS. Frequency of jaw movements 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 addition to the expected increase of cell wall digestion, leading to a substantially increased nitrogen value for the forage.