Dr Rebecca Stutz1, Dr Lucy Watt2, Mr Tony Swan1, Dr Lindsay Bell2
1CSIRO, Agriculture & Food, Canberra, Australia,
2CSIRO, Agriculture & Food, Toowoomba, Australia
Forage brassicas are a high value feed for livestock with a high nutritive value compared to grass and cereal forages at the same growth stage. However, forage brassicas contain antinutritional compounds that can negatively impact livestock health and production. In intensive grazing systems, grazing of forage brassicas is tightly managed to mitigate risks but this is not practical in less intensively managed systems that are typical of Australia’s mixed farming zone. Better grazing management guidelines require a greater understanding of the drivers of grazing behaviour and animal performance, and options to mitigate health risks. In particular, greater understanding of environmental, management and genotype influences on the expression of antinutritional compounds such a nitrates and glucosinolates. We analysed samples collected from a range of forage brassica genotypes grown in diverse production environments and found nearly two-thirds had nitrate concentrations > 9000 ppm, which is considered ‘risky’ or ‘deadly’ to livestock. Farmers in southern NSW have also reported photosensitisation in livestock, and samples collected from these farms revealed high glucosinolate concentrations. We have found that N-fertiliser management is a critical driver of nitrate concentrations irrespective of genotype, and N-fertiliser and crop S supply have an interactive effect on glucosinolate concentrations. Our research has improved our understanding of factors driving the expression of these compounds that will help to develop better management guidelines, and identify potential varietal improvements which together may help farmers manage the risks of grazing forage brassicas and remove barriers to their adoption in the mixed farming zone.