Changes in chemical composition of different grass species and -mixtures in equine pasture during grazing season

Abstract

This study was conducted to characterise changes in chemical composition during the grazing season in Finland (14 May to 24 September) of timothy (T; Phleum pratense), meadow fescue (MF; Festuca pratensis L.) and tall fescue (TF; F. arundinacea Schreb.) and T-MF, T-TF and TF -Kentucky bluegrass (KB; Poa pratensis L.) mixtures. Ten Finnhorse mares were rotated in three paddocks, each containing 24 plots (six treatments in four blocks), during ten grazing periods of 10-14 days. Grass samples were taken from each plot before grazing to determine chemical composition and in vitro organic matter digestibility (OMD) with an enzymatic pepsin-cellulase method. Crude protein (CP) content decreased from 195 g/kg dry matter (DM) being at its lowest on July 2nd 130 g/kg DM and rising again to 216 g CP/kg DM on September 10th. Crude fibre, neutral detergent fibre and acid detergent fibre increased linearly until beginning of July, from then on the content was more stable. The change in OMD reflected the changes in chemical composition. The value decreased in average from 856 g/kg to 701 g/kg until beginning of July. As the grazing season progressed, OMD averaged around 750 g/kg. TF-KB had high and constant CP content (187 g/kg DM; sd. 18.4), lowest average fibre content (510 g NDF/kg DM) and highest average OMD value (785 g/kg sd. 39.8). Different grass species and time point of grazing season had a marked effect on the chemical composition of equine pasture.