Rate and Extent of Cell Wall Digestion of Total Forage and Morphological Components of Oats and Barley1

Abstract

Rate of cell wall (CW) digestion in forages has been proposed an indicator of intake potential by ruminant animals. Extent of CW digestion determines the nutritive value potential of the nonsoluhle (fibrous) part of forage dry matter. The objectives of this study were to compare the rate and extent of CW digestion of the total forage and the morphological components of oats (Avena sativa L.) and barley (Hordeum vulgare L.) and to ascertain the effect of maturity on CW digestion. Oats (cv. ‘Lyon’) and barley (cv. ‘Manker’) were grown at each of two locations and harvested at each of six maturity stages. Rates of CW digestion in barley total forage (10.34 to 7.35%/hour) were significantly greater than those of oats (7.88 to 3.88%/hour) all maturity stages. Extent of CW digestion was also significantly greater for barley (72.4 to 49.3%) than for oats (69.2 to 41.2%). The decline in both rate and extent of CW digestion with increasing maturity was statlsticaHy linear. Rate of CW digestion was most highly correlated with in vitro digestible dry matter (r = 0.83, P<0.01). Extent of digestion was most highly correlated with acid detergent lignin (ADL; r = −0.92; P<0.01) and ADL/cell wall constituents (r = −0.93, P<0.01). Of the morphological components, the leaf blade had the fastest rate of CW digestion (10.67%/hour), whereas rates of CW digestion for stem (7.53%/hour) and leaf sheath (7.91%/hour) were similar. We conclude that forage quality assessment in grasses involving leaf/ stem ratios does not necessarl]y require the tedious task of separation of sheaths from stems in that the best leaf/stem ratio relationship to forage quality of barley and oats occurred when the stem and sheath were grouped as one morphological entity. Because rate of CW digestion declined slowly with maturation until stage 3 and then declined sharply as grain filling initiated (between stages 3 and 4), we conclude that oats and barley should be harvested by stage 3 in animal feeding systems that require high intake (high rate of digestion) such as systems for milk production or rapid animal growth. These results substantiate our earlier report that if the cultivars of barley and oats used in this and previous studies are representative of adapted cultivars generally, barley provides a superior quality forage.