Grazing selectivity of Lolium perenne L. cultivars by dairy cows

Abstract

The objective of this study was to determine the effect of herbage mass, metabolizable energy content, tiller density and dimensions on grazing selectivity, measured by grazing time and estimated herbage intake, on the ryegrass ingestive behaviour of lacting dairy cows. This study was conducted with ten L. perenne cultivars: Bronsyn SE, Bronsyn AR1, Impact, Impact AR1, Aries, LP 296, Arrow, Meridian, Matrix and Nui. During the establishment period, 35 kg of N, 228 kg of P₂O₅ and 123 kg of K₂O were applied per ha and 30 additional kg of N were applied after each grazing event. When any L. perenne cultivar reached an average undisturbed sward surface height of 20 cm, all plots were harvested and then grazed, with no more than 60 days between harvests. After each grazing event, the trial was cut to a 4 cm stubble height. The undisturbed sward surface height and the herbage mass preand post-grazing, the estimated herbage intake, metabolizable energy content, tiller density, leaf length, leaf width, sheet weight and leaf weight were evaluated. Grazing behavior variables included only grazing time. The experimental design was a randomized block with 10 treatments (10 L. perenne cultivars) and 3 blocks. The results were analysed through ANOVA and the Waller - Duncan test was used to compare means. The cows did not discriminate among cultivars during the entire experiment, with no significant differences in grazing time and estimated herbage intake between cultivars. In general, there were no significant differences among cultivars in terms of: herbage mass, undisturbed sward surface height, metabolizable energy content, tiller density and dimensions, and any significant differences in these variables for some grazing events were not large enough to influence grazing selectivity.