INFLUENCE OF TIME BETWEEN RUMINAL GLUCOSE CHALLENGES ON RUMEN FUNCTION

Ruminal lactic acidosis is one of the most important metabolic problems in feedlot cattle. Gradually transitioning cattle to finishing-feedlot diets may reduce the risk for ruminal acidosis by providing sufficient time for adaptation. This adaptation of feedlot cattle to high-concentrate diets may causes marked changes in the ruminal environment, and time is required to establish stable ruminal conditions. However, few studies have evaluated the ruminal adaptation in steers. A metabolism trial was conducted to evaluate the effects of two consecutive glucose challenges on rumen function in steers fed a high-energy finishing diet. Four Holstein steers (320 kg LW) with cannula in the rumen were used in a 4 x 4 Latin square design. Four treatments were used and consisted of the time elapsed between both challenges of glucose (2, 4, 6 or 8 d). Ruminal fluid samples were taken at 0700 h (just prior the first glucose challenge), and from the second challenge (d 2, 4, 6, or 8) at 1 h before and 2, 4, 6, 8, 28, 52, 124, 196 and 268 h. As the time between fluctuation of energy intake increased, ruminal fluid pH (P 0.10). During the first 6 h following the second glucose challenge ruminal fluid pH decreased. No effects of treatments on ruminal pH were observed (P >0.10) among treatments from 3 days after the second challenge. Ruminal fluid osmotic pressure increased (P <0.10) after dosed glucose with all treatments. Ruminal osmolality increased (P <0.10) as the time between challenges were 2 or 4 days. After dosed glucose, total volatile fatty acids increased, except by treatment 1 after second challenge. Total volatile fatty acid and pH were related positively (R 2 =0.69). As the time increased, a tendency on increment of concentrations of protozoa was observed. Ruminal glucose concentration decreased linearly (P <0.10) 2 h after the second fluctuation of energy intake. We conclude that ruminal alterations are magnified as the time between glucose challenge decreases.