Short communication: Rate of propionate infusion within meals does not influence feeding behavior

Propionate has been shown to depress the feed intake of ruminants, but whether the rate of propionate infusion influences this response is unknown. To test this possibility, the rate of propionate infused within meals was altered while the total amount of propionate infused was held constant. Eight multiparous Holstein cows (51 +/- 19 d in milk, 44.0 +/- 4.8 kg/d of milk; mean +/- SD) were randomly assigned to the treatment sequence in a crossover experiment with a 10-d diet adaptation period, 24-h treatment periods, and 3 d between treatments. Treatments were intraruminal infusion of 1.26 mol of Na propionate (2.33 +/- 0.06 L, 0.54 M, pH 6.0) over the course of either 5 min (fast) or 15 min (slow) at each spontaneous meal. The experimental diet included high-moisture corn and was formulated for 27% neutral detergent fiber, 36% starch, and 17.5% crude protein. Feeding behavior was monitored by a computerized data acquisition system that triggered infusion pumps at the initiation of meals, and consecutive infusions began at least 15 min apart under both treatment protocols. Feeding behavior data were analyzed to quantify the number, size, length, and time between all meals. Compared with pretreatment intake, propionate infusions depressed feed intake by 20 and 23%, respectively, for the slow and fast treatments. However, the rate of propionate infusion did not significantly alter dry matter intake, meals/day, meal size, meal length, or intermeal interval. We found no evidence that the rate of infusion, within the range of typical meal lengths, determines the extent of hypophagia from propionate.