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ARS Home » Research » Publications at this Location » Publication #174898
Title: INFLUENCE OF ABOMASAL CARBOHYRDATES ON SUBCUTANEOUS, OMENTAL, AND MESENTERIC ADIPOSE LIPOGENIC AND LYPOLYTIC RATES IN GROWING BEEF STEERS.

Author
item Baldwin, Ransom - Randy
item Baumann, Richard
item MCLEOD, K - UNIVERSITY OF KENTUCKY

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2006
Publication Date: 8/15/2007
Citation: Baldwin, R.L., Baumann, R.G., Mcleod, K.R. 2007. Influence of abomasal carbohyrdates on subcutaneous, omental, and mesenteric adipose lipogenic and lypolytic rates in growing beef steers. Journal of Animal Science. 85:2271-2282.

Interpretive Summary: Fat synthesis by adipose tissue from three distinct sites within the steer including the mesenteric, omental and subcutaneous depots were compared. Treatments were designed to simulate alterations in site of starch delivery from the rumen to the small intestine as current feeding practices in beef production result in as much as 25% of feed starch arrives at the small intestine. In a randomized design, forty crossbred beef steers (242 ± 2.5 kg BW) were fed at 1.5 times maintenance energy intake requirements (1.5M) or 2.0 ME intake(2M) or they were fed the 1.5 M diet and infused for 35 d into the rumen (R) or abomasum (A) with starch hydrolysate (S) or into the abomasum with glucose (G). Steers were slaughtered, adipose tissue samples were obtained, and uniform slices were prepared and incubated for 2 h in either media to support fat synthesis or fat breakdown. Rates of fat synthesis by subcutaneous adipose tissue were generally higher than the rates attained by mesenteric and omental adipose depots. Acetate is used to a greater extent by all of the adipose depots tested than glucose as a precursor for fat synthesis. Glucose use as a precursor for fatty acid synthesis by all depots was enhanced by post-ruminal delivery of starch and glucose. Increased energy delivery, either from dietary or infusion of starch or glucose, resulted in increases in fat synthesis. Abomasal delivery of starch and glucose resulted in increased synthetic and breakdown rates for all adipose depots tested. These results support the concept that alterations in tissue nutrient specificity and enzyme expression result from changes in diet composition that result in a shift in the site of delivery of starch from the rumen to the small intestine. Current feedlot finishing rations are formulated to deliver large amounts of starch post-ruminally based on the premise that increased energetic efficiency will be realized. However, while feed energy efficiency is enhanced by dietary alterations, this efficiency does not always result in increased average daily gains. This may be due in part to a metabolic shift from muscle tissue deposition towards adipose deposition. However, time to market may be decreased by altering the time on feed required to achieve desired carcass quality measurements.

Technical Abstract: The in vitro rates of lipogenesis and lipolysis by adipose from mesenteric, omental and subcutaneous depots were compared across treatments designed to simulate alterations in site of starch delivery. In a randomized complete block design, forty crossbred beef steers (242 ± 2.5 kg BW) were fed 0.163 Mcal ME/(kg BW0.75'd) (1.5M) or 0.215 Mcal ME/(kg BW0.75'd) (2M) or they were fed 0.163 Mcal ME/(kg BW0.75'd) and infused for 35 d into the rumen (R) or abomasum (A) with starch hydrolysate (S) or into the abomasum with glucose (G). Steers were slaughtered, adipose tissue samples were obtained, and uniform slices (100 mg) were prepared and incubated for 2 h in either lipogenic or lipolytic media. Rates of lipogensis by subcutaneous adipose tissue were generally higher than the rates attained by tissue from mesenteric and omental adipose depots. Acetate is used to a greater extent by all of the adipose depots tested than glucose as a lipogenic substrate. Glucose use as a precursor for fatty acid synthesis by the all depots was enhanced by post-ruminal delivery of starch and glucose. Increased energy delivery, either from dietary or infusion of starch or glucose, resulted in increases in lipogenic activity. Abomasal delivery of starch and glucose resulted in increased lipogenic and lipolytic rates for all adipose depots tested. These results support the concept that alterations in tissue nutrient specificity and enzyme expression result from alterations in diet that result in a shifting of the site of delivery of starch from the ruminal to post-ruminal. Increases in lipogenic and lipolytic activity with increased energy and altered site of glucose delivery are consistent with the observed changes in adiposity of these steers. Increased efficiency of nutrient use observed by steers fed diets with higher energy densities can be partially explained by alterations in viseceral tissue metabolism of energy substrates and the subsequent alterations in adipose depot lipogenic rates.