PSXIV-21 Metabolic and hormonal response to abomasal and ruminal propionate infusion.

Abstract Volatile fatty acids (VFA) are the primary source of metabolizable energy in ruminants, with propionate serving as the major precursor for hepatic glucose synthesis. Although the rumen is the primary site of VFA absorption, a portion of propionate can escape the rumen and some likely reaches the abomasum. However, limited research has evaluated the impact of propionate in the abomasum. Therefore, the objective of this experiment was to determine the effect of abomasally and ruminally infusing propionate in beef cattle. Two experiments were conducted using four ruminally cannulated steers in a crossover design. In both experiments, the rumen was evacuated and washed with saline at 1700 h, and a bicarbonate buffer was placed in the rumen overnight. The buffer was replaced at 0500 the following morning. In experiment one, an abomasal infusion line was placed, and steers received either a saline or propionate buffer (0.40 g propionate/kg BW). In experiment two, the omasal orifice was blocked with a Foley catheter, and steers received saline or a propionate buffer (0.40 g propionate/kg BW) in the rumen. Blood samples were collected via a jugular catheter before and after infusion. After a seven-day washout period, the collections were repeated with steers switching treatments. Data were analyzed using a mixed model in SAS 9.4 (SAS Inst. Inc.) with the fixed effects of treatment, time, treatment × time, and period, and animal was included as a random variable. In experiment one, abomasal propionate infusion increased both plasma insulin (P = 0.002) and glucose (P = 0.001), while decreasing NEFA (P = 0.006) and active ghrelin (P < 0.001). In experiment two, ruminal propionate infusion increased insulin (P < 0.001) and glucose (P = 0.011), and decreased NEFA (P < 0.001). While there was a treatment × time interaction for active ghrelin (P = 0.041), the means for each treatment never differed from each other. These experiments indicate that propionate supplied ruminally and post-ruminally induces metabolic and hormonal responses. While the project did not allow direct comparison of ruminal to abomasal infusion, the insulin, glucose, and NEFA responses were greater when propionate was infused ruminally. In contrast, the ghrelin response was more rapid and greater with abomasal propionate infusion. These data indicate that propionate flowing from the rumen and escaping omasal absorption could have physiological effects that contribute to propionate’s effects on appetite regulation.