The objective of this study was to compare the grazing efficiency of 30 perennial ryegrass varieties, differing in ploidy and heading date. Plots were grazed by lactating dairy cows and managed under a rotational grazing system with 19 grazing events occurring over two years. Pre‐grazing and post‐grazing compressed sward heights were measured with a rising plate meter. A mixed model was used to predict the post‐grazing sward height of each variety based on year, grazing event, block and pre‐grazing sward height. Residual grazed height (RGH) was derived as the difference between the actual and predicted post‐grazing sward height and was used as the measure of grazing efficiency. Negative RGH values indicated that the actual herbage removed was greater than that predicted and so indicated a superior grazing efficiency. Varieties differed in their level of grazing efficiency (p < .001), with RGH values ranging from −0.38 to +0.34 cm. Tetraploid varieties exhibited significantly greater grazing efficiency performance than diploids (p < .001), with average RGH values of −0.13 and +0.13 cm respectively. A significant difference in grazing efficiency was found among recommended perennial ryegrass varieties that are not being recorded by mechanically harvested simulated grazing protocols. A variety reappraisal that included grazing efficiency could identify varieties capable of improving on‐farm livestock productivity from grass.

中文翻译：

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多年生黑麦草品种放牧效率的调查

这项研究的目的是比较30个多年生黑麦草品种的放牧效率，它们的倍性和抽穗期不同。通过泌乳的奶牛放牧地块，并在轮牧系统下进行管理，在两年内发生了19次放牧事件。放牧前和放牧后的压缩草皮高度用立式平板计测量。使用混合模型根据年份，放牧事件，块和放牧前的草地高度来预测每个品种的放牧后草地高度。实际放牧后草皮高度与预测放牧后草皮高度之间的差可得出残余放牧高度（RGH），并将其用作放牧效率的度量。RGH负值表示实际去除的牧草量大于预期值，因此表示较高的放牧效率。p <  .001），RGH值介于-0.38至+0.34 cm之间。四倍体品种的放牧效率显着高于二倍体（p <  .001），平均RGH值分别为-0.13和+0.13 cm。在推荐的多年生黑麦草品种之间发现了放牧效率的显着差异，但没有通过机械收获的模拟放牧方案进行记录。包括放牧效率在内的品种重新评估可以确定能够提高草场牲畜生产率的品种。