Effect of pasture allowance and species diversity on rumen degradability and short-term grazing intake

Abstract

Pasture allowance and rumen degradation rates have been shown to affect herbage intake and nutrient supply of lactating dairy cows, which ultimately influence milk production. The objective of this study was to compare the effect of allowance and pasture type on dry matter intake (DMI) during the first grazing session (GS) and subsequent impacts on rumen fermentation. Holstein Fresian X Jersey cows in late lactation were assigned to two perennial ryegrass dominant pasture with two pasture allowances. Pasture types were simple and diverse and were offered at high (HA, 17 kg DM cow⁻¹ d⁻¹) and low (LA, 15 kg DM cow⁻¹d⁻¹) herbage allowances. Herbage intake during the first 4hr GS was greater on simple compared to diverse pasture (10.5 and 7.9 kg DM cow⁻¹, respectively, P<0.05). Increasing allowance affected 4hr DMI, with greater DMI at HA compared to LA (9.9 vs 8.5 kg DM cow⁻¹, respectively, P≤0.05). Daily DMI (14.31 kg DM cow⁻¹) was not affected by treatments. In sacco DM disappearance was affected by pasture type, with diverse pasture having greater potential disappearance than simple (84.2% of DM vs 78.3% of DM, respectively, P<0.05). Rumen degradation rate (mean 11.5% hr⁻¹) was not significantly affected by treatment. Altering pasture diversity and pasture allowance will influence short-term DMI. Results show the benefits of increasing pasture species diversity on improving degradability and nutrient availability to the animal.