The Nutritive Value Of Forage And Weed Species Grazed By Beef Cattle In Australia And The Effect On Livestock Selectivity

The majority of Australian paddocks are heterogeneous (non-uniform) and hence vary in pasture biomass and quality widely at a variety of scales. Cattle are selective graziers, spending time in some areas whilst avoiding others. However, despite this, many grazing studies fail to examine the underlying pasture quality and potential influence these pasture variables have on livestock selection. Therefore, the aim of this study was to investigate beef cattle selectivity (time spent at a site) due to the underlying quality of pasture that had recently been sown, and non-sown pasture species along with a number of weeds. Prior to cattle grazing, a range of pasture attributes were measured including pasture biomass and  Normalised Difference Vegetation Index (NDVI) along with individual plant species to determine forage quality. These were later analysed for protein, minerals, organic acids, alcohols, fibre and non-fibre carbohydrates. Paddock variables (elevation and distance to shelter, boundary fence and water) were also determined. Eleven Angus heifers were fitted with a Global Navigation Satellite System (GNSS) collar and tracked for 58 days. Statistical analysis included pasture quality differences between species and random forest modelling to determine the main variables driving where livestock spend time. There were significant differences across species for all pasture biomass and quality variables, except for Cu, Se and Starch. Preliminary results suggest that pasture quality variables are the major drivers of livestock selection emphasising the importance of the underlying role that pasture quality has on livestock behaviour. A repository of data for a range of pasture species including non-sown and weed species which are rarely sampled, for numerous pasture quality variables (protein, non-fibre carbohydrates, minerals etc.) is needed for improvements to be made for livestock production. By understanding the pasture quality drivers of livestock selection, producers are able to improve management practices including paddock utilisation, manipulation of pasture species and strategic rotation of paddocks.