Low voluntary intake and animal performance with perennial ryegrass has been attributed to its high leaf strength. Perennial ryegrass populations were selected for high or low shear strength and individual plants of low (LS) and high (HS) selections grown in a controlled environment. Shear strength of LS leaves (290 g) was half that of HS leaves. LS leaves were shorter, narrower and lighter. However, shear strength of LS remained significantly lower after adjustment for differences in leaf width. Shear strength in both selections declined from leaf base to leaf tip. LS leaves contained less sclerenchyma but had similar vascular tissue content. Sclerenchyma was significantly correlated with shear strength (r=0.82). Chopped leaves (5 cm) from both selections, placed in polyester bags were subjected to rumen microbial digestion. The higher shear strength of HS selected plants was maintained for at least 24 h rumen digestion. It is concluded that lower shear strength was a result of decreased sclerenchyma content and that potential improvements arising from easier breakdown would be maintained during rumen digestion in vivo.
Proceedings of the New Zealand Society of Animal Production, Volume 49, , 183-190, 1989
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