Pastures and forages for deer growth

Abstract

Pasture is the primary feed source for NZ deer production with the greatest proportion grazed in situ. The quantity and quality of the pastures available to grazing deer varies markedly as a result of environmental factors and feed planning decisions by deer farmers. The grazing behaviour of deer responds to changes in pasture height and mass and the effect of pasture variables (height, pre -and post-grazing pasture mass and pasture allowance) on deer productivity are presented. These show that maximum levels of deer production from pasture will be achieved at a pasture height of around 8 cm (continuously stocked or post-grazing) although there is some evidence that for large genotypes, higher pasture availability is required. The relationship of liveweight gain of young deer with pasture availability shows marked seasonal effects. At the same level of pasture availability liveweight gain in spring is about twice that in winter, with autumn and summer intermediate. Increasing pasture availability cannot compensate for seasonal differences in liveweight gain. Furthermore, liveweight gain increases at a greater rate in spring than winter to increasing pasture availability, thus it is more important that appropriate pasture allowances are provided in spring than in winter. There is more variability in liveweight gain at a similar pasture availability in summer than in other seasons because of the greater variation in pasture quality in summer with the potential accumulation of seedheads and dead material. Alternative forage species are used in deer production for times of the year when quantity and quality of perennial ryegrass-based pastures limit productivity. Relative to weaner red deer grazed on perennial ryegrass/ white clover pasture, grazing on pure swards of red clover or chicory increased growth during autumn by 26-47% and during spring by 10-14%. The proportion of stags attaining target slaughter liveweight at 12 months of age increased from 75 to 94%. Pre-weaning growth during lactation was increased by approximately 20%. Red clover and chicory produce a greater proportion of their total DM during late summer and autumn than does perennial ryegrass/white clover pasture, and are therefore better aligned with deer feed requirements, particularly those of lactating hinds. Grazing on sulla in autumn and spring increased the growth of weaner deer by 33 and 10%, relative to pasture fed deer. Indoor studies showed that relative to perennial ryegrass, chicory was of higher organic matter digestibility, disintegrated more rapidly in the rumen with a low rumination time and had shorter mean retention time of material in the rumen. This explains differences in voluntary feed intake which were 56, 26 and 15% higher for deer grazing chicory than perennial ryegrass/white clover pastures during summer, autumn and spring respectively. Similar r esults have been found for the digestion of red clover versus perennial ryegrass by red deer. Plant density in stands of both chicory and red clover declines with time, with their lifetime under deer grazing being approximately 4 years. A mixture of both plants offers a food option as specialist forage for increasing deer growth and also fixing nitrogen. To ensure good persistence such forages should not be grazed in periods of prolonged wet weather. Best persistence is obtained when these are managed as specialist forages for increasing deer growth on a small area of the farm, (10- 20% total area), rather than being sown as a mixture with grasses over large areas of the farm. There is no specific comparison of deer production under different stocking systems and both continuous grazing and rotational grazing are used. Based on evidence and practices with other species, choice of stocking system has more to do with pasture/forage species, feed budgeting, pasture management and animal behaviour than with productivity. At high stocking densities (150 deer/ha), the grazing time of subordinate animals is reduced. Where possible, without inducing undue stress (e.g. at weaning), young deer should be grouped for grazing by liveweight. Deer production systems have a seasonal pattern of energy demand that does not match that of pasture growth in most NZ environments. This calls for manipulation of the feed demand by integration of livestock systems and/ or modification of the feed supply through conservation and supplementation. The most commonly used supplements are pasture and lucerne silage/baleage and grain. The quality (ME/kg DM) has a significant impact on the resulting liveweight gain.