T. Panjaitan, S. P. Quigley, S. R. McLennan and D. P. Poppi
Spirulina, a freshwater microalgae, has previously been shown to increase the efficiency of microbial protein production in cattle fed hay with a low crude protein content. The present study was carried out to determine the effect of increasing the concentration of Spirulina in the drinking water on the intake of water and the amount of water containing Spirulina bypassing the rumen of cattle. Five rumen-cannulated steers were given a fixed amount of pangola grass hay (14 g DM/kg W.day1) and water containing 0, 1, 2, 2.7 and 3.5% (w/w) Spirulina in an incomplete Latin squaredesign. Water intake by the control steers (0% Spirulina) was 29.7 and 49.3 g/kgWfor the first drinking event after it was made available and over 24 h, respectively. For steers receiving the algae, intake of water plus Spirulina increased linearly(P < 0.01) from 42.7 to 60.2 g/kgWduring the first drinking event, as the concentration of Spirulina in the drinking water increased, but over 24 h was not affected by Spirulina concentration and averaged 74.4 g/kg W. The bypass of water through the rumen, as determined using chromium-EDTA as a marker, averaged 20.5 1.2% and was not affected by the concentration of Spirulina in the drinking water. Increasing inclusion of spirulina was associated with a decrease in rumen pH, an increase in urea concentration in blood serum, and an increase in ammonia-N concentration, propionate and branchedchain fatty acids, and a decrease in butyrate proportions in rumen fluid. Spirulina inclusion in the drinking water increased water intake and may provide a potential safe and inexpensive alternative to urea for extensively grazed ruminants.