Aside from its function of contraction, the muscle is also a pool of mobilisable protein which may be released or stored according to the needs of the animal. An approach of this aspect can be theorically studied by measure of arterio-venous differences of plasma metabolites from blood in the muscle mass. The aim of this experiment was to study uptake of α amino-nitrogen, glucose and urea across the hind-limb of bulls from a breed with large muscle development.

Three bulls from the Belgian Blue breed-double muscled type-were used. They weighed about 300 kg when an ultrasonic flow probe (Transonic Systems, Inc.,Ithaca, NY) was implanted around the abdominal aorta, back to the renal vessels, in order to measure the blood flow in the hind-leg (Eisemann et al., 1987). After an one month recovery period, circumflex iliac artery and vein were implanted with catheters. During the periods of surgery, the bulls were offered hay only at a rate of three kg daily. Ten days after the second surgery, increasing amounts of concentrate were given with the hay so that the animals received one kg concentrate on day 1 (level 1), three kg concentrate on day 3 (level 3), five kg concentrate on day 5 (level 5).