GLUCOSE, ALPHA-AMINO NITROGEN, AND AMINO-ACID EXCHANGE ACROSS THE HINDLIMB IN YOUNG DOUBLE-MUSCLED TYPE BULLS MAINTAINED AT 2 GROWTH-RATES

The effect of growth rate and protein supplementation on muscle metabo lism of eight bulls from the Belgian Blue breed, double-muscled type, was investigated by the arterio-venous difference technique. A low gro wth (LG) group was maintained at a low growth rate over 36 d, and a ra pid growth (RG) group for 28 d before receiving a fattening diet allow ing for a rapid growth. At the end of the RG period the RG bulls recei ved a supplement of protected soybean meal. Animals were fitted with a n aortic ultrasonic blood flow probe and with catheters in the aorta a nd the vena cava. The blood flow in the hindlimbs of bulls varied grea tly by time of the day but was higher in the RG group. The RG group ha d a higher arterio-venous difference (AVD) and uptake of alpha-amino n itrogen while AVD in essential amino acids was four times higher and u ptake eight times higher. Significant higher AVD or uptake was observe d in individual amino acids such as leucine, isoleucine and lysine. Th e supplementation with protected soybean meal had significant negative effect on the uptake of several amino acids. It was concluded that ca ution should be exercised when measuring punctually blood flow in musc le tissue, for example by dilution techniques. At high growth rate, th e requirements for amino acids are larger than for glucose. Excess pro tein provides no additional benefit.