Effect of grazing system, stocking rate and season of use on diet quality and herbage availability of alfalfa-grass pastures

Abstract

A 3-yr field experiment was conducted (1991–1993) near Brandon, MB to determine the effects of continuous and rotational stocking, both at heavy (2.2 steers ha−1) and light (1.1 steers ha−1) stocking rates, and of season of use on nutritive value and sward characteristics of an alfalfa-grass pasture [approximately 70% alfalfa (Medicago sativa L.), 25% meadow bromegrass (Bromus biebersteinii Roem & Schult.) and 5% Russian wildrye (Psathyrostachys juncea (Fisch.) Nevski)]. Grazed herbage quality and herbage mass were determined concurrently on continuous and rotational stocking treatments several times each year, as animals entered and exited the 5th of 10 rotationally stocked paddocks. Grazing system and stocking rate did not affect (P > 0.05) dietary CP and IVDOM, except once (P < 0.05) for IVDOM in 1993. Both ADF and NDF were sometimes greater (P < 0.05) on heavy compared to light stocking rate treatments, but did not differ (P > 0.05) between grazing systems. As the 1991 season advanced, there was a decline (P < 0.05) in CP, but IVDOM, ADF and NDF remained unchanged (P > 0.05). In 1992, seasonal declines (P < 0.05) in CP and IVDOM and increases (P < 0.05) ADF and NDF were observed for all treatments. In 1993, in vitro digestible organic matter and CP decreased (P < 0.05) on most treatments, while ADF and NDF increased (P < 0.05). Herbage mass tended (P < 0.10) to be lower when heavy stocking rates were used in all years, but was not affected (P > 0.05) by grazing system. Significant relationships (P < 0.001) among IVDOM, ADF and NDF were found. Neither grazing system nor stocking rate appeared to affect the quality of herbage ingested by cattle grazing alfalfa-grass pastures. Key words: Alfalfa, pasture, grazing system, stocking rate