A simple isocratic h.p.1.c. technique was developed for the simultaneous quantitative analysis of lactic, formic, acetic, propionic, isobutyric, n-butyric and isovaleric acids in aqueous acid extracts of silage. An Aminex HPX-87H strong cation exchange resin column at 41"C, 0.0025~ H2S04 mobile phase and ultraviolet detector at 210 nm were utilised. Estimated recoveries of acids added to silage ranged from 98.2 to 103.5%.

was introduced into New Zealand in 1949 for soil protection purposes (Watson, 1982) because of its favorable A precise prediction of quality of legumes in the field would enable characteristics and is considered a suitable forage plant harvests to be conducted at appropriate nutritive composition levels. Our objective was to predict the nutritive value of sulla (Hedysarum in New Zealand and Australia (Stienezen et al., 1996). coronarium L.) with the codified morphological stage and weather Sulla is a high-yielding crop, up to 14 Mg ha Ϫ1 DM per parameters at two Mediterranean sites (Ancona and Sassari, Italy) season (Stringi et al.produces forage mainly during early spring and autumn morphological stages, from vegetative stage to seed setting. Mean and is useful for grazing, haying, and ensiling (Sulas et stage by weight (MSW), dry matter yield (DMY), leaf/stem ratio al., 1995; Valente et al., 1999). It is a good source of (L/S), crude protein concentration (CP), neutral detergent fiber protein for livestock and has a moderate extractable (NDF), gross energy (GE), and organic matter digestibility (OMD) condensed tannin concentration that ranges from 25 to were determined. Forage characteristics were regressed on growing 40 g kg Ϫ1 DM (Terrill et al., 1992; Douglas et al., 1999; degree days (GDD) and MSW. The DMY ranged from 2 to more Piluzza et al., 2000). than 10 Mg ha Ϫ1 from vegetative to seed set while L/S decreased from almost 5.6 to 0.2 and the CP from a maximum of 295 to a minimum A better knowledge of the developmental morpholof 107 g kg Ϫ1 dry matter (DM). The NDF ranged from 200 to 616 g ogy and quality changes of sulla in different environkg Ϫ1 DM and was best predicted by L/S and MSW. The GE was ments is necessary to optimize its potential for livestock relatively constant across growth stages with a mean value of 18.0 production. The variation in nutritive value of the herb-MJ kg Ϫ1 DM. The OMD ranged from 398 to 846 g kg Ϫ1 organic age is related to the environmental and physiological matter (OM) and declined linearly with increasing MSW. The OMD history of the crop (Marten et al., 1988; Nelson and decreased 32.6 g kg Ϫ1 OM per stage unit and followed similar trends Moser, 1994). It is well known that forage maturity at for the two sites, with a lower level at the warmer site (Sassari). The the time of harvest is the primary factor influencing MSW was a better predictor of sulla OMD than GDD, with a higher nutritive value within a species. Additionally, nutritive R 2 (0.70 vs. 0.54) and a lower root mean square error.

quality during the spring growth cycle would allow targeting of harvests or grazing to desired levels of nutritive A precise prediction of changes in digestibility of grasses during composition to meet specific animal requirements. It is the growth cycle would allow targeting of harvests to desired levels also necessary for optimization of ration composition of nutritive composition to meet specific animal requirements. In this study, regression analysis was used to formulate and test prediction with respect to maximal production, minimal excretion equations for organic matter digestibility (OMD) of standing crops of undigested material, and minimal cost (Hvelplund et of Italian ryegrass (Lolium multiflorum Lam.) with codified morphoal., 1995). logical stage, canopy age, growing degree days (GDD), and N fertiliza-Although intake is more important than digestibility tion as independent variables. The field study was conducted for 7 yr in assessing forage quality, extensive research has been with six Italian ryegrass cultivars, diversified for ploidy and earliness, devoted to measuring digestibility and relating it to feed grown in the western Po Valley (Italy). Nitrogen fertilizer was applied characteristics because digestibility can be accurately at various rates as top dressing. Sequential harvesting from early measured with relative ease compared to intake (Mervegetative to full flowering provided herbage samples (n ϭ 153) varytens, 1994). ing in age and stage of development. The 0-400 classification systemIn temperate grasses, digestibility depends mainly on that was used to evaluate the morphological stage included four primary stages: vegetative, elongation, inflorescence emergence, and the growth stage, the growth cycle, and the species (Van flowering. The OMD decreased from 928 to 576 g kg Ϫ1 OM, as the Soest, 1994). Digestibility generally decreases with adherbage aged. All cultivars responded in the same way during the vancing age, especially during the first growth cycle. whole growth cycle. Morphological stage was a better predictor of This decline results from the interaction of factors such OMD than GDD or age in days, with a higher r 2 (0.88) and a lower as increased fiber concentration in plant tissues (Wilson root mean square error (28.0 g kg Ϫ1 OM). Nitrogen fertilization slightly et al., 1991), increased lignification during plant develdecreased digestibility. The developed equation tested on an indepenopment (Morrison, 1980), and the different leaf/stem dent set of farm scale data (n ϭ 34) showed that this codified morphoratio (Hides et al., 1983). Terry and Tilley (1964) relogical stage system can provide a rapid and easy estimate of Italian ported that at early stages of growth, all parts of the ryegrass digestibility in the field.

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