Submitted to: European Association of Animal Production Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2000
Publication Date: N/A
Interpretive Summary: It is generally recognized that the conversion of dietary starch energy to tissue energy is greater if assimilation occurs via intestinal glucose absorption rather than rumen fermentation and subsequent volatile fatty acid absorption. However, there is limited scientific data which directly quantifies the divergence in energetic efficiency associated with site of starch digestion. The results of the present experiment in steers show that shifting site of starch digestion from the rumen to the small intestine decreases energy losses associated with methane and body heat and increases energy retention in body tissue. Our estimates of the partial efficiency of converting metabolizable energy to tissue energy are 0.482 and 0.594 for ruminally and abomasally supplied starch, respectively. Based on total energetic efficiency (i.e., conversion of starch energy to body tissue energy), our data demonstrate that ruminally fermented starch (32%) is only 74% as efficient as starch digested in the small intestine (43%).
Technical Abstract: Influence of site of carbohydrate digestion on whole body energy balance was studied in growing steers. Eight beef steers with ruminal and abomasal infusion catheters were assigned to replicated 4 4 latin squares with 21-d periods. Treatments included a pelleted forage-based basal diet (89% orchard grass hay) fed at 0.68 (LE) or 0.90 MJ ME # (kg BW.75)-1 #d-1 and LE plus ruminal or abomasal infusion of partially hydrolyzed maize starch. Starch was infused at a rate of 12.8 g # (kg BW.75)-1 #d-1, approximately 20% of total metabolizable energy (ME) intake, and total volume (5 kg # site-1 #d-1) of infusate was equalized across treatments and infusion sites by infusion of water. Energy balance was determined the final 7 d of each by total collection of excreta and measurements of respiratory exchange. Ruminal and abomasal starch infusion increased (P < 0.01) digestible energy, ME, and retained tissue energy (TE) and nitrogen (RN) relative to LE. Digestible energy, ME, and RN were unaffected by site of starch infusion. However, shifting site of starch infusion from the rumen to the abomasum decreased energy losses from methane (P < 0.01) and body heat production(P < 0.15) and increased (P < 0.10) TE. Partial efficiency of converting ME from ruminally and abomasally infused starch to TE were .482 and .594, respectively. These results indicate that energetic efficiency of ruminally fermented starch is 74% of that of starch digested in the small intestine.