High production dairy-beef cattle grazing systems: a review of research in the Manawatu

Abstract

During a span of 20 years, eight farmlet-scale experiments conducted in the Manawatu used a simple system of grazing management to maximise pasture growth and utilisation. Farmlets of 1.6 ha were stocked annually with 12 Friesian bulls (7.4 wintered/ ha) from early November at 3 months-of-age (70-80 kg liveweight (LW)) until slaughter during December - March at 16 - 19 months (350 - 420 kg LW). The grazing management system involved seasonal adjustment in pasture spelling intervals, and an increase in grazing pressure in spring by addition of 3-month-old weaner bulls followed by the progressive removal of 'finished' animals during summer. With this control over feed supply and demand and the inherent capacity of growing bulls to cope with changes in feed availability, old permanent pasture producing approximately 13 t dry matter/ha/yr was conver ted to approximately 1000 kg/ha/yr of net carcass weight gain. Using loafing pads in winter to reduce treading damage on wet soils and increase pasture utilisation and growth, increased annual LW gain (LWG)/ha by 2%. Controlling the intensity of defoliation in summer through timely removal of bulls for slaughter increased average daily gain (ADG) during autumn and winter, but annual LWG/ha by only 1%. Pastures renewed with improved cultivars and species produced more forage in summer (red clover), autumn (prairie grass) and winter, identified as per iods of feed deficit for old permanent pastures. Strategic inputs of nitrogen (N) fertiliser (100 kg N/ha/yr) in autumn or in spring on old permanent pasture, in conjunction with irrigation (approximately 250 mm/ season) during November - March, and in combination with cool season active grasses, all increased annual meat output by up to 12% above that possible from old permanent pasture, by extending the duration of stocking in summer, increasing ADG, or a combination of both. While these gains are important, the studies highlighted the very high levels of output sustained from year-round all-grass grazing systems based on principles for maximising pasture growth and utilisation. Those high yields remain a benchmark in terms of the biological efficiency of growing and converting pasture to animal product, although the economic optimum was at a lower stocking rate and level of output. Keywords: dairy beef, grazing systems, liveweight gain, pasture utilisation