A comparison of gas production during incubation with rumen contents in vitro and nylon bag degradability as predictors of the apparent digestibility in vivo and the voluntary intake of hays

Abstract

Ten hays harvested at three stages (early bloom MB, mid bloom MB or in seed) made from lucerne (Medicago sativaj, sweet clover (Melilotus segetalis), Persian clover (Trifolium resupinatum) and pre-bloom (PB) Italian ryegrass (Lolium multiflorum var.), were offered ad libitum to four Merino male sheep and daily intake (g dry matter (DM) per kg M0·75) and DM apparent digestibility (DMD) were measured. In sacco DM degradation (g per 100 g DM), gas production (ml per 200 mg DM), in vitro digestibility and fibre composition (g/kg DM) of the hays were also studied. Gas production or DM degradation were calculated at 6, 12, 24, 48, 72 or 96 h and their kinetics were described using the equation p = a + b(1 - e-ct). Intake and in vivo DMD of the hays were variable (P < 0·01). Lucerne EB and Persian clover (all stages) had the highest nutritive value, whereas sweet clover (all stages) had the lowest. Apart from neutral-detergent fibre, which was only related to intake (r = -0·68; P < 0·05), chemical components and in vitro digestibility were poorly (P > 0·05) related to animal performance. Between 12 and 96 h incubation, intake and in vivo DMD were better related to DM degradation (r = 0·79 to 0·83; r = 0·61 to 0·77) than to gas production (r = 0·73 to 0·80; r = 0·58 to 0·78). Prediction of intake and in vivo DMD from the (a + b) values did not provide a great advantage over using some of the static values of gas production or DM degradation.Multiple regression using separated kinetics of degradation resulted in highest accuracy for predicting intake and apparent digestibility from gas production (R2 = 0·63; R2 = 0·78) and nylon bag degradability (R2 = 0·77; R2 = 0·89). It was concluded that the gas test has good potentiality as it was capable of predicting not only apparent digestibility, but also intake to a level close to that of the nylon bag technique.

A note on the effect of diet and type of fat on cellulose degradability in the rumen of sheep

“…The ability to predict animal performance on diets containing different quality of roughages by using simple, reliable and cheap techniques is becoming important in animal nutrition (Khazaal et al, 1993). In our experiments to determine effective degradability of cellulose in sheep we used the in sacco method, which is more suitable than in vitro methods because rumen micro-organisms need time to adapt to new conditions, and in vitro methods therefore tend to underestimate microbial degradation at short incubation times (Stensig et al, 1994;Noziere and Michalet-Doreau, 1996).…”

Estimating the extent of degradation of ruminant feeds from a description of their gas production profiles observedin vitro: comparison of models

“…The popularity of in vitro gas production stems mainly from (1) the ability to exercise experimental control, (2) the capacity to screen a large number of substrates, (3) the kinetic information which may be derived which, although possible, is a limitation of the end-point techniques such as in vitro digestibility (Tilley & Terry, 1963) and (4) the fact that no assumptions need be made on the degradability of the soluble fraction of the substrate, as is required for the in sacco technique (Ørskov & McDonald, 1979). Potential use of gas production to approximate in vivo kinetics is a major expectation and some studies have been published (Blümmel & Ørskov, 1993;Khazaal et al 1993Khazaal et al , 1994Sileshi et al 1996;Lopez et al 1998), where it has been compared with the in situ polyester bag method. The models discussed in the present paper should help to interpret gas production profiles and provide estimates of kinetic parameters and other biological quantities, including the extent of degradation.…”

In vitro determination of ruminal dry matter and cell wall degradation, and production of fermentation end-products of various by-products

“…The prediction of the extent of degradability using an in situ method has advantages and is now widely used and reported [16,38]. This technique proposed by Ørskov et al [26] can be used for the prediction of dry matter intake, digestible dry matter intake and animal performance.…”