More feed for New Zealand dairy systems

Abstract

An upper limit to productivity of perennial ryegrass-white clover pastures in New Zealand at about 15 t DM/ha per year has been identified as a constraint to future increases in productivity. With potential yields of 26.6 t DM/ha per year from temperate grasses and 45 t DM/ha per year from maize at mid-latitudes, the challenge for New Zealand dairy farming systems is to achieve greater than 15 t DM/ha per year without imposing additional production or environmental costs. Given these constraints a major switch to crops is not feasible because those that produce more than pasture, e.g., maize, have insufficient crude protein to support lactation. Theoretically, a farm area allocation to 78% perennial ryegrass-white clover and 22% maize-winter oats could provide 23.3 t DM/ha per year at a crude protein content of 16%. This is greater than the 20 t DM/ha per year upper limit of irrigated perennial ryegrass-white clover. Incremental yield improvements of grasses and clovers by traditional plant breeding are low (1.5% per year), and difficult to capture. Future plant breeding gains are more likely to come from increased plant stress tolerance. Improved pasture monitoring to allow timely removal of constraints, will enable potential yields to be achieved. Biotechnology offers the possibility of improving the potential yield of net photosynthesis by 20% either through the transfer of genes from a C4 plant (e.g., maize) or a C3 plant (e.g., perennial ryegrass), or use of the major photosynthetic enzymes, rubisco, from a thermophilic alga. Biotechnology is also providing new knowledge about the control of plant development and response to stresses. The application of this knowledge may allow dairy farmers to achieve another 5 t DM/ha per year from perennial ryegrass-white clover pastures. Keywords: biotechnology, dairy, perennial ryegrass, photosynthesis, white clover, yield limitation