Predetermining factors for grazing efficiency differences in perennial ryegrass varieties

Abstract

Perennial ryegrass (Lolium perenne L.; PRG) is the principal forage species sown in Ireland for ruminant production. This forage is predominantly fed as grazed grass and has been shown to be the most efficient feed for Irish ruminant production systems. Anecdotal evidence exists from farmers claiming that grazing livestock show preference for certain perennial ryegrass varieties. The aim of this study was to determine what varietal traits in perennial ryegrass influence grazing efficiency by examining differences in grazing intensity between varieties. Grazing efficiency was defined as the proportion of leaf tissue grazed, relative to that presented. Fifty-five PRG varieties were assessed. The plots were rotationally grazed by dairy cows for four grazing seasons from 2015 to 2018 inclusive. Varieties were shown to differ in their level of grazing utilisation (P<0.001). The average difference across the four years between the most and least grazed variety was 0.85 cm (3.72 and 4.54 cm respectively). Tetraploid varieties as a group were shown to have a greater utilisation performance than the diploid group (P<0.001) with mean Residual Grazed Surface Heights (ResGSH) of -0.15 and +0.11 respectively. Increased digestibility and a more open sward structure were associated with varieties found to have greater graze-out potential