Intestinal nitrogen digestibility of heat-moisture treated rapeseed meals as assessed by the mobile-bag method in cows

Abstract

An experiment was designed to study the effects of commercial heat-moisture (HM) treatment (Öpex®) and a rapeseed ( Brassica campestris) cultivar on intestinal N and amino acid (AA) digestion values of rapeseed meal (RSM) estimated by the mobile-bag method. Experimental feeds were either untreated or HM-treated rapeseed meals (RSM1, RSM2, RSM3 and RSM4), and soya bean meal (SBM) as a control. RSM1 (untreated) and RSM2 (HM treated) originated from black-seeded single and double zero varieties, respectively, and RSM3 (untreated) and RSM4 (HM treated) from yellowish-seeded double zero varieties. The effect of pepsin-acid incubation of experimental feeds on intestinal digestion values obtained by the mobile-bag method was also investigated. Four ruminally cannulated bulls were used to study N degradability of experimental feeds in the rumen by nylon-bag technique, and four duodenally cannulated non-lactating cows to study post-ruminal digestion values of nitrogenous compounds by the mobile-bag method. HM treatment effectively increased the proportion of rumen-undegradable N in RSM without adverse effects on the subsequent disappearance of N from mobile bags within the intestine. Generally, HM treatment had a similar effect on the disappearance of individual AAs from bags in the intestine as on that of total N. However, the disappearance of amino acid N or individual AAs of RSMs from the mobile bags was clearly greater than that of total N. Rapeseed variety had only a minor impact on the intestinal digestion values of nitrogenous compounds. The digestion values for N were clearly lower for RSMs than for SBM, probably owing to the greater proportion of totally unavailable feed N in RSMs. Pepsin-acid incubation prior to the mobile-bag measurement did not affect the intestinal N digestion values obtained for the rumen-undegradable feeds. Thus pepsin-acid treatment is not necessary in mobile-bag procedure which includes pre-incubation of feeds in the rumen.