COMPARISON OF IN SITU AND IN VITRO DRY MATTER RUMEN DEGRADABILTY OF THREE DISTINCT QUALITY HAYS IN SHEEP

Abstract

The objective of this work was to evaluate the dry matter rumen degradability of three distinct quality hays, using in situ and in vitro techniques. The animals used to incubate the bags in and as inoculum donors were six Santa Ines sheep, male, castrated, weighting 40±5.7 kg LW, all with rumen cannulas. Three forage hays were chosen for this experiment, based on their crude protein content. The studied hays were alfalfa (Medicago sativa) (ALF), signalgrass (Brachiaria decumbens) (SIG), and Tifton-85 (Cynodon sp.) (TIF). The in situ rumen degradability kinetics was determined using the nylon bag technique, and the in vitro degradability was accessed by the semi-automated gas production technique. There was difference between the three hays for CP (P < 0.01), ADIP (P < 0.01), DM, (P < 0.05) OM (P < 0.05), NDF (P < 0.05), hemicellulose (P < 0.05), and cellulose (P < 0.05) contents. Feeds SIG and TIF did not differ (P > 0.05) among them for ADF, ADL and silica contents, but both differed of feed ALF for the same constituents (P < 0.05). There were noticed differences between in situ and in vitro degradabilities, mainly for readily soluble fraction and degradation rates. The in situ and in vitro techniques to estimate the degradation kinetics were consistent, except for data on the initial solubility and lag time. The in vitro technique showed strong dependence of the quality of inoculum; the inoculum from animals better fed presented the best results. When the focus was to determine the lag time, the first-order exponential model underestimated the observed results. The fermentative kinetics (gas production) described in greater fidelity the feed degradation due to microbial action.