Sward Height in Grazing Management: Vertical Profiles in Forage Quality

Vertical and temporal trends in herbage yield and quality were assessed in a study sown in 1989 near Elora, Ontario. In a replicated field trial with 0.1 ha paddocks, Hereford heifers rotationally grazed 2 swards to each of 2 residual grazing heights, namely, SO and 100 mm, with a requisite 200-2S0 mm entry height. Profiles in yield and in in vitro organic mailer digestibility (IVOMD) were developed from 6, 1500 cm2 quadrats per paddock, which were subjected to vertically stratified clipping, using sheep shears with a vacuum attachment. In 1990, obliging entry. at 200-2S0 mm stabilised herbage organic matter on offer, but IVOMD nonetheless declined seasonally, in all sward strata, by a weighted average of 10 percentage points, The vertical distribution of OM was sharply skewed In both swards, with yield in each stratum significantly greater than that above it, while IVOMD differed only among the three lowest strata. Sward height has revealed promising insights into the vertical array of herbage quantity and quality, which should prove directly useful to Ontario graziers.