Effects of supplementation on the ingestive behaviour of grazing steers*

Abstract

AbstractHerbage intake is usually depressed when beef cattle grazing abundant pastures are supplemented with energy‐rich feedstuffs but relatively little is known about the effects of supplementation on the components of ingestive behaviour. An experiment was conducted to establish the effect of ground corn (Zea mays L.) on the ingestive behaviour of yearling Angus and Angus × Hereford steers (Bos taurus) (mean live weight (LW) of 323 kg) grazing autumn stockpiled Boone cocksfoot (Dactylis glomerata L.) using a tethered grazing system in which the experimental unit was the tethered steer and its grazing area (45 m2) for one grazing session. Herbage dry matter (DM) mass was 1662 kg ha−1 and herbage DM allowance was 7–5 kg steer−1 for each grazing session. Herbage DM intake was measured as the difference between herbage DM mass offered and refused. Grazing took place during two daily sessions each of about 2 h duration commencing at 08.00 and 14.00 h for 9 days. Ground corn (0, 1·5, 3·0 and 4·5 kg steer−1) was fed each day at 12.00 h and had no significant (P < 0·05) effect on rate of DM intake, rate of biting or DM intake per bite. Mean DM intake was 6 2 kg steer−1 d−1 (87 mg (kg LW)−1 min−1). Steers averaged 4832 bites per grazing session, with a mean DM intake per bite of 644 mg (2·0 mg (kg LW)−1) and a mean rate of 44 bites min−1. Data obtained at the beginning and end of each grazing period on ingestive behaviour of one group of four steers (mean LW of 306 kg) fitted with oesophageal fistulae supported data for the two groups of normal steers and showed no response to supplementation. Mean values for rate of DM intake, DM intake per bite and rate of biting established for the fistulated cattle were 73 mg (kg LW)−1 min−1, 521 mg bite−1 (1·7 mg (kg LW)−1) and 39 bites min−1, respectively.