STUDIES ON IN-SITU DEGRADATION OF FEEDS IN THE RUMEN .1. EFFECT OF SPECIES, BAG MOBILITY AND INCUBATION SEQUENCE ON DRY-MATTER DISAPPEARANCE

Implicit to the newer more complex predictive models for estimating nu trient requirements for ruminants is a need for an accurate determinat ion of feed degradation kinetics. The rumen in situ technique has been adopted as the standard method. However, recent ring tests and review s have highlighted the need for improved standardisation of the in sit u procedure. The aim of this experiment was to investigate differences between host species and to determine the effect of anchor weight and incubation sequence on dry matter (DM) disappearance of hay, soyabean meal (SBM) and fish meal (FM) in situ. Three mature rumen cannulated non-lactating cows and wether sheep fed a grass silage, barley diet (8 0:20, DM basis) were used. The experimental design was based on a lati n square model with nine experimental periods, two major treatments an d three levels of each treatment. Sheep and cow designs were run in pa rallel. Duplicate bags of each substrate were incubated (complete exch ange) for 0, 2, 4, 8, 16, 24, 48 and 66 h and were allocated to treatm ent according to the latin square design. Treatment levels were: half normal, normal and twice the normal anchor weight for each species (0. 5, 1 and 2 kg for cows and 75, 150 and 300 g for sheep) and three incu bation sequences (i) 8, 16, 2, 4, 66, 48, 24 h; (ii) 8, 24, 66, 4, 2, 16, 48 h; (iii) 24, 4, 2, 66, 8, 48, 16 h. No species differences were observed (P > 0.05) with overall mean losses of 55.8 and 55.6% for sh eep and cows respectively. The degradation profiles of hay, SBM and FM were found to be different (P < 0.001). Anchor weight and incubation sequence did not significantly effect (P > 0.05) effective degradabili ty values. Mean effective degradability (0.08 h(-1) outflow) measureme nts for incubation sequence (i, ii and iii) were 52.9, 53.1 and 53.3% and for anchor weight (0.5 x, 1 x and 2 x normal) were 52.9, 53.2 and 53.2%. It was concluded that mature ruminant species degrade hay, SBM and FM DM similarly and that anchor weight and the sequence of incubat ion has no effect on the degradability profiles of these feeds.