Response of cattle to algae in the diet

In Australia, cattle graze pastures with low crude protein (CP) content and digestibility during the dry season, resulting in low liveweight (LW) gain, or loss. This poor performance is linked to an inadequate supply of N to the microbial population in the rumen, resulting in low efficiency of microbial protein production (MCP). True protein supplements can be provided to increase LW gain but current prices make this uneconomical. Single cell protein sources, more specifically micro-algae, may be an alternate source to traditionally used supplements. Algae may become available as a ruminant feed source, either as a byproduct of other industries or as an on-farm produced protein source. A few algae species were tested at the University of Queensland from which Spirulina platensis and Chlorella pyrenoidosa had the highest protein content (675 and 580 g/kg DM, respectively). Supplementation of steers with the latter algae species increased total dry matter (DM) intake (21.2 and 18.2 g DM/kg LW.day, respectively), and the efficiency of MCP [90.7 and 105.9 g MCP/kg digested organic matter intake (DOMI), respectively] compared to unsupplemented steers fed a low CP forage (24 g CP/kg DM, total DM intake = 12.6 g DM/kg W.d, efficiency of MCP = 52.1 g MCP/kg DOMI). Some of the beneficial effects of algae supplementation have been studied here and suggest that there is potential to increase LW gain of cattle grazing low CP tropical forages. The cost of algae will determine whether it is a valuable new source of protein to ruminant animals.