Faecal output and estimated voluntary dry-matter intake of grazing beef cows, relative to their live weight and to the digestibility of the pasture

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Abstract
Two experiments were carried out with 12 non-pregnant, non-lactating beef cows (Simmental x Hereford cross), six in each experiment. In experiment 1, the cows were grazing stubble pasture and each cow was hand fed 750 g/day soya-bean meal. In experiment 2, the cows were grazing green pasture at the pre-blossom stage. Paraffin-coated magnesium ferrite (MF) was used as an external marker. A capsule containing 5 g marker was administered to each cow twice daily at about 08.00 and 14.00 h. At the same time the cows were also weighed and faecal grab samples (GS) were taken. Each experimental period lasted 18 days: a 10-day period for attaining steady state of the marker, followed by an 8-day period during which faecal GS were taken.Average live weight (LW, kg) and daily faecal output (DFO, kg dry matter (DM) per day) were, respectively 364·2 and 3·39 for cows in experiment 1, and 484·4 and 4·62 in experiment 2. DFO (g): LW (kg) ratios were 9·31: 1 and 9·53: 1 in experiments 1 and 2, respectively.In-vitro digestibilities were used for calculating the voluntary intake (kg DM per day), which was found to be 6·8 and 13·6 for cows grazing stubble and pre-blossom pastures, respectively. The relationships between LW of grazing cattle and their DFO and voluntary food intake are discussed.