Selected ruminal variables and purine urinary excretion rate of steers subjected to feeding, fasting, and re-feeding conditions

The effects of feeding, fasting, and re-feeding on the ruminal profile of growing cattle were studied. Ruminal fluid and urine samples were obtained from 12 crossbred steers weighing approximately 300 kg during the following periods: 11 h of normal feeding (postprandial period), 48 consecutive hours of fasting, and followed by 48 h of re-feeding. Fasting promotes changes in the ruminal profile, such as an increase in ruminal pH, reduction in the number of rumen protozoa and bacteria, and decrease in the urinary excretion of allantoin; however, it does not change the urinary uric acid excretion rate. The overall mean ruminal pH was higher during fasting (7.53±0.27) in comparison to those at normal feeding (6.72±0.25) and re-feeding (6.62±0.31) (p⟨0.05). During re-feeding, the ruminal profile returned to normal, except for the protozoa count, which despite a slight increase only after 48 h of re-feeding, did not recover to baseline values.