Rumen digestion, intake, milk production and nitrogen partitioning of dairy cows grazing simple vs diverse pasture swards at high and low pasture allowance: A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science (hons) at Lincoln University

Abstract

A field grazing experiment was conducted in New Zealand during autumn (March/April 2012), offering grazing dairy cows in late lactation simple vs diverse pasture swards at high and low (17 vs 14 kg DM cow⁻¹ d⁻¹ respectively) pasture allowances. Objectives of the research were to compare the effect of pasture allowance and pasture mix on DMI and rate of DMI and subsequent impacts on rumen fermentation and milk production, and to quantify effects of pasture allowance and pasture mix on N partitioning and NUE in dairy cows. Herbage intake during the first 4hr GS was greater on the HS pasture compared to HSD pasture (10.5 and 7.9 kg DM cow⁻¹ respectively, p < 0.05). Increasing PA affected 4hr DM intake, with greater intakes at HA compared to LA (9.89 vs 8.52 kg DM cow⁻¹, respectively, p<0.05). Total mean daily DM intake (14.31 kg DM cow⁻¹ ) was not affected by treatments. Rate of herbage disappearance was not significantly affected by treatments. In sacco DM disappearance was affected by pasture type, with diverse swards having greater disappearance than simple swards (84.2% of DM vs 78.3% of DM respectively, p <0.05). Rumen degradation rate (mean 7.3% hr⁻¹ ) was not significantly affected by treatment. Diverse pasture mixes incorporating herbs were found to have similar ability in reducing urinary nitrogen losses than swards containing higher proportions of WSC: CP from high sugar grasses. Diverse pasture swards may therefore have the potential means to reduce environmental footprints of dairy farms. Altering pasture diversity and pasture allowance will influence short-term DM intake. Results confirm the benefits of increasing pasture species diversity and animal selectivity in pasture systems on improving degradability and nutrient availability to the animal.