A continuous digestibility trial, lasting 50 days with subperiods of 5 days eacb, was made witb the spring regrowth of Eragrostis curvula grown in tiie semi-arid region of Argentina. Five sheep were used to measure tbe digestibility of DM, organicmatter, cell-waU contents and N. DM yield was estimated simultaneously. Tbe fall iu digestibility of all fractions examined was described by quadratic equations. Cell-wall digestibility explained 91% of tbe variation in organic-matter digestibility. Tbe rate of decrease in crude-protein digestibility increased witb time and was particularly noticeable after about 40 days of growtb. Digestible DM yield increased at a decreasing rate as maturity advanced, but digestible crudeprotein content decreased linearly tbrougbout tbe trial. It is concluded tbat tbe optimum stage of maturity for weeping lov^rass utilization depends upon tbe performance required from tbe animak that are to utilize it.

Faecal samples from a continuous digestibility trial with Eragrostis curvula were analyzed for cell-wall contents, acid-detergent fibre, lignin, asb and N. DM digestibility was regressed on all these fractions and organic-matter digestibility was also regressed on faecal organic-matter N. The best predictions of digestibility were obtained by the use of faecal lignin as a percentage of acid-detergent fibre, and by cell-wall contents. N was a comparatively poor predictor and it is shown that its relationship with organic-matter digestibility varies with the level of N in the diet. It is concluded that both lignin and cell-wall contents could serve as useful internal indicators since their use is unlikely to be biassed by metabolic and microbial contamination.

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