Evaluation of three rape seed commodities in the rumen of steers 2. Degradation of fibre fractions and disappearance of macrominerals <i>in situ</i>

Abstract

Rate and extent of ruminal degradation of detergent fibre fractions and disappearance of macrominerals (Ca, P, Mg, Na) of rape seed and of untreated and formaldehyde-treated rapeseed meals containing less than 8 ,umol glucosinolates per gram of dry matter were investigated. Feeds were incubated in polyester bags in the rumen of three fistulated steers for 0, 2, 4, 8, 16, 24 and 48 h.Degradation characteristics of fibre fractions indicated that rapeseed fibre can be more degradable than previously assumed. The rape seed had the most degradable neutral and acid detergent fibre fractions. Fibre fractions of the formaldehyde-treated rapeseed meal were more degradable than those of the untreated meal. The effective degradabilities of neutral detergent fibre at assumed ruminal passage rates of 2, 5 and 8%/h ranged from 62 to 53% for the rape seed, 52 to 38% for the untreated meal and 65 to 49% for the formaldehyde-treated meal. The three rape seed commodities were a good source of macrominerals for ruminants, as indicated by macromineral concentrations in the feeds and by pattern and extent of ruminal disappearance of the minerals. The rape seed had a faster rate of disappearance of most macrominerals than the two meals. In contrast to fibre, macrominerals tended to disappear at a faster rate from the untreated meal than from the formaldehyde-treated meal.