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Net Absorption and Oxygen Consumption by Holstein Steers Fed Alfalfa or Orchardgrass Silage at Two Equalized Intakes

U.S. Department of Agriculture^,3, Beltsville, MD 20705

Abstract

The objective of this experiment was to compare net nutrient absorption and oxygen consumption by portal-drained viscera (PDV) of catheterized Holstein steers (333 kg) when fed alfalfa or orchardgrass silage at two equalized intakes. The design was a 4 x 4 Latin square with a 2 x 2 factorial arrangement of alfalfa or orchardgrass fed at 65 or 90 g dry matter/kg·⁷⁵ live weight daily. Blood flow through PDV (dilution of p-aminohippurate), net nutrient absorption and oxygen consumption (venoarterial concentration differences times blood flow) were measured hourly for 12 h, followed by measurement of N and energy balance over 7 d. Compared with orchardgrass, steers when fed alfalfa absorbed more NH₃-N (P < .05), branched-chain volatile fatty acids (P < .10) and n-valerate (P < .05). Silage type did not affect (P > .10) blood flow to or O₂ consumption by PDV or net absorption of glucose, L-lactate, acetate, propionate, urea-N, -amino N or most amino acids. Oxygen consumption by PDV as a percentage of whole-animal O₂ consumption was not different (P > .10) for steers when fed orchardgrass (27.2) or when fed alfalfa (23.6). Interrelationships between N and energy metabolism were responsible for the increased (P < .05) metabolizable energy/ kilogram silage dry matter and increased (P = .10) N retention by steers when fed alfalfa compared with orchardgrass. The PDV accounted for a substantial portion of whole-animal O₂ consumption.

¹ Rumin. Nutr. Lab., Anim. Sci. Inst., Beltsville, MD.

² Pennsylvania State Univ., University Park, PA.

³ Agric. Res. Serv.

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