Influence of ruminal and postruminal carbohydrate infusion on visceral organ mass and adipose tissue accretion in growing beef steers

¹ Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546
² Bovine Functional Genomics Laboratory, ARS, USDA, Beltsville, MD 20705
³ Food Technology and Safety Laboratory, ARS, USDA, Beltsville, MD 20705

^* To whom correspondence should be addressed. E-mail: kmcleod{at}uky.edu.

	Abstract

Forty crossbred beef steers (243 ± 2 kg BW) with ruminal and abomasal infusion catheters were used to test 2 hypotheses: 1) visceral mass is responsive to energy input and site of carbohydrate (CHO) assimilation and 2) rate and site of adipose accretion is dependent on site of CHO assimilation and complexity. Treatments included a pelleted forage-based basal diet fed at 161 (LI) or 214 (HI) kcal ME/(kg BW^0.75·d), LI plus ruminal (R-SH) or abomasal (A-SH) infusion of a partial starch hydrolysate (SH) and LI plus abomasal infusion of glucose (A-G). Basal diet was fed in 12 equal portions daily at 2-h intervals with starch and glucose infused over a 22-h period at rates of 12.6 and 14.4 g/(kg BW^0.75·d). After 35 d of infusion, steers were slaughtered and visceral organ and adipose mass were determined and subcutaneous adipose thickness over the 5^th and 12^th rib and longissimus intramuscular fat concentration were determined. Total intake energy (IE) increased (P = 0.0001) with ME intake (MEI). Dietary IE was similar between LI and CHO infusion treatments, but total IE increased (P < 0.001) with CHO infusion. Greater dietary MEI and CHO infusion increased or tended (P 0.09) to increase final BW and HCW. As a percentage of empty BW (EBW), total stomach-complex, rumen, omasum, liver, pancreas, and kidney weights were greater (P 0.05) for HI vs LI. Stomach complex, rumen, pancreas, and kidney weights as a percentage of EBW were greater (P 0.05) for R-SH vs A-SH. Compared with A-SH, A-G increased (P 0.02) total and epithelial weights from the 10-cm sections of the ileum. Increases in rumen mass were associated with either no change or an increase in rumen total and epithelial DNA concentrations. Greater dietary ME tended (P = 0.06) to increase subcutaneous fat thickness at the 5^th rib but did not affect alimentary adipose accretion on an EBW basis. Omental and total alimentary adipose weights were increased (P 0.04) by A-G compared with A-SH. Although SH infusion did not alter adiposity, there was a consistent numerical pattern in both total alimentary and subcutaneous fat depots with CHO infusion (A-G > A-SH > R-SH). Our findings demonstrate that increasing ruminal CHO supply results in a disproportionate increase in rumen mass, whereas increasing small intestinal CHO supply does not alter gastrointestinal organ mass. Small intestinal energy in the form of glucose resulted in greater adipose accretion, particularly the omental depot.

Key Words: adipose, carbohydrate, energy, steers, visceral organs

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