Heavy stocking and early-season deferment of grazing on Mediterranean-type grassland.

Abstract

An experiment with beef cows grazing Mediterranean-type grassland was conducted to study the effect of grazing deferment at the beginning of the growing season on pasture productivity and animal performance under intensive herd management conditions. The grazing trial was composed of 4 treatments (deferred grazing at stocking rates of 0.83 and 0.67 cows per ha and continuous grazing at 0.67 and 0.5 cows per ha) replicated in 2 blocks and continued for 5 consecutive years. The herds were given low-energy supplemental feed during deferment and during the dry summer. At the intermediate stocking rate, at which both deferred and continuous grazing were compared, herbage production was significantly reduced by grazing during the 'deferment period' and calf weaning weights without deferment were significantly lower than in the deferred grazing treatments. Weaned live weight per cow was significantly lowest in the continuous intermediate treatment. Weaned weight per hectare was greatest at the highest stocking rate (with deferment). Utilization of supplementary feed per unit weaned live weight was significantly greater in the deferred treatments. Only about a third of the herbage production was grazed, even at the heavy stocking rates. Herbage production varied more between years than between treatments. It is concluded that in the system studied, deferment with supplementary feeding becomes important for both animal and vegetation production as stocking rate approaches and exceeds 0.67 cows ha-1. With deferment, herbage production during the main growing season can be maintained even under heavy grazing pressure. This result can be explained with a simple dynamic growth and grazing model.