Comparison of perennial ryegrass varieties for differences in grazing efficiency

Abstract

The aim of this study was to determine differences in grazing efficiency between varieties of perennial ryegrass (Lolium perenne L.) and to determine varietal traits influencing grazing efficiency. Grazing efficiency refers to the proportion of leaf tissue that is removed, relative to the amount presented to the animals prior to grazing. Low post-grazing sward heights are desirable as they condition the sward to increase leaf production and thus reduce the proportion of stem in the sward in subsequent rotations. Thirty varieties of perennial ryegrass from the Irish Recommended List were studied. The plots were grazed on nineteen occasions over two years, 2017 and 2018. Pre-grazing sward height, post-grazing sward height, herbage production, nutritive quality and morphology were measured throughout the trial. Varieties differed in their level of grazing efficiency (P<0.001) with post-grazing sward heights ranging from 3.54 to 4.60 cm. Residual Grazed Height (RGH) was derived as a measure of grazing efficiency calculated as the difference between achieved post-grazing height and predicted post-grazing height from a mixed model. Nutritive quality analysis was shown to have a significant effect on grazing efficiency. Organic matter digestibility (OMD) was shown to have a significant negative effect on postgrazing sward height (R2=0.63). Tetraploids had greater OMD than diploids (787 g kg‑1 DM vs 776 g kg‑1 DM respectively)