The effect of reduced leaf shear strength on the nutritive value of perennial ryegrass

Abstract

S U M M A R YProgeny of perennial ryegrass (PRG) plants selected for low and high leaf shear strength were sown in a spaced-plant field experiment and were shown to differ in leaf strength in the same direction, confirming this to be a heritable trait. Selection for low leaf shear strength also reduced weight per leaf length, but had no effect on dry-matter (D.M.) percentage, growth score, rust score or tendency towards aftermath heading.Rates of D.M. consumption (g D.M./min) and ruminal degradation of D.M. using the polyester bag technique, were then determined with small quantities of the two PRG selection lines, and also white clover, using sheep fed a basal diet of fresh ryegrass/white clover pasture. Selecting PRG for low leaf shear strength slightly reduced concentrations of cellulose and hemicellulose, slightly increased total N concentration and increased rate of D.M. consumption by sheep (17%) but had no effect on rates of ruminal D.M. degradation. The selection thus moved the nutritional characteristics of PRG in the direction of white clover.The first nutritional response to the selection appears to be a faster rate of D.M. consumption, and it is considered that leaf shear strength has potential for selecting PRG with increased rates of voluntary intake by ruminants.Sinclair (1982) deduced that slow degradation and I N T R O D U C T I O N outflow rates were the principal factors causing long Feeding value defined as the live-weight gain of young rumen retention time and reduced voluntary intake in sheep grazing New Zealand (NZ) temperate forage s h e e P f e d perennial ryegrass. and expressed in relative units, is higher for white Although breeders of temperate forage plants have clover (Trifolium repens: 100) than for perennial selected to improve apparent digestibility (Cooper ryegrass (Lolium perenne: 52), with annual ryegrasses et al. 1962;Dennis & Frandsen, 1986), there has been and other legumes being intermediate (Waghorn & no selection for improving feeding value once maxi- Barry, 1987). Both voluntary intake measured in field mum apparent digestibility has been attained. When studies (Ulyatt, 1971) and rate of D.M. consumption maintained in the vegetative state, most forage measured under controlled indoor conditions (Ulyatt cultivars used in New Zealand would be close to et al. 1986) are much lower for sheep fed fresh maximum digestibility (75-80%). We wished to test perennial ryegrass than fresh legumes, and there is the hypothesis that selecting perennial ryegrass for thus a need to improve the voluntary intake and reduced leaf toughness, using leaf shearing strength as hence feeding value of perennial ryegrass for rumi-the testing criterion, would increase the rates of D.M. nants. consumption and rumen degradation by sheep. The Long retention time of digesta in the rumen experiments reported examine this hypothesis: Expt 1 of forage-fed animals reduces voluntary intake examines whether leaf-shear strength is an heritable (Thornton & Minson, 1973) and hence feeding value, characteristic t...

Prospects for improving the nutritive value of temperate, perennial pasture grasses

“…Rupture of herbage in chewing is a function of both tensile and shear strength; both are highly heritable traits (Wilson 1965;MacKinnon et al 1988).…”

“…Shear strength varies with physiological age of leaves so that, for good sampling accuracy, leaves need to be selected for uniform age. Reduced shear strength of ryegrass leaves from plants selected for high and low shear strength is associated with a faster rate of eating but not with fermentation characteristics in situ (MacKinnon et al 1988;Kennedy & Doyle 1993). Thus leaf shear strength has potential for use in selecting perennial ryegrass with increased rates of voluntary intake by ruminants (Henry et al 1993).…”

Nutritive value and physical characteristics of Xaraes palisadegrass as affected by grazing strategy

“…Studies to better characterize the quality of forages by their physical properties have considered techniques such as the resistance to grinding (Minson & Cowper, 1974) and to shearing (Mackinnon et al, 1988). Evidence exists that shearing resistance is related to chemical composition, especially to the cell wall and its components (Wilson, 1997;Hughes et al, 2000;Nave et al, 2009).…”

Shearing force of alfalfa stems: effects of cultivar and shearing site

“…Higher leaf tensile or shearing force was related to higher concentrations of cellulose (Wilson 1965;Mackinnon et al 1988) and hemicellulose (Mackinnon et al 1988) in perennial ryegrass plants. However, Nguyen et al (1982) and Iwaasa et al (1996a) reported difficulty in establishing a consistent relationships between CW chemical constituents and tensile or shearing force.…”

“…Weston and Davis (1991) reported shear or comminution energy as the best characteristic of forages to predict constraint to forage intake, and in turn voluntary intake. Differences between forages in their resistance to chewing and removal from the rumen were reflected in shearing force differences in perennial ryegrass leaves (Lolium perenne L.) (Mackinnon et al 1988;Inoue et al 1989). …”