EFFECTS OF LEAF SHEAR BREAKING LOAD ON THE FEEDING VALUE OF PERENNIALRYEGRASS (LOLIUM-PERENNE) FOR SHEEP .1. EFFECTS ON FEED-INTAKE, PARTICLE BREAKDOWN, RUMEN DIGESTA OUTFLOW AND ANIMAL PERFORMANCE

A series of experiments was conducted at Palmerston North, New Zealand , during 1988-91 to compare the efficiency of chewing during eating an d rumination, rumen fractional outflow rate (FOR), voluntary organic m atter intake, liveweight gain and wool production in sheep fed either low (LS) or high (HS) leaf shear breaking load perennial ryegrass (PRG ). The LS ryegrass had a 13% lower mean leaf shear breaking load and i ngestion rates tended to be higher than for HS PRG, but no consistent significant treatment differences were observed in rate of particle br eakdown, rumen FOR, voluntary intake or animal performance. It was con cluded that selection for reduced leaf shear breaking load per se did not improve feeding value. The total shear load required to reduce a u nit dry weight of PRG leaf to < 1 mm particles (index of masticatory l oad; IML) differed by only 3% between LS and HS PRG in this study, due to higher leaf length: dry weight ratios for LS PRG. It is therefore suggested that IML, which takes into account both leaf shear breaking load and associated changes in leaf morphology may be a better criteri on for selection than leaf shear breaking load alone in breeding progr ammes to improve the feeding value of perennial ryegrass.