No abstract

Metabolism of muscle growth in the hindquarter was investigated by the arterio-venous difference (AVD) technique in Belgian Blue double-muscled type bulls at maintenance or at fattening. The bulls were fitted with an aortic ultrasonic blood flow probe and with catheters in the aorta and vena cava. They were offered a diet allowing for maintenance (MP) during a period of 15 d, at the end of which measurements were made over 3 d. Bulls were then given a fattening diet (FP) and the measurements were repeated. Arterial blood flow was approximately 1 L/min greater when the bulls were standing than when lying. Blood flow was 2 L/min higher during FP than during MP. The AVD and uptake of glucose were maximal at 1400 and 1600. Uptake of alpha-amino nitrogen decreased immediately after a meal. The increase in glucose from MP to FP fitted very well with the calculated energy needs for muscle growth. The AVD and uptake of alpha-amino nitrogen, total amino acids, and total nonessential amino acids were negative during MP and positive and significantly higher during FP. There was also a significant increase in AVD and uptake of essential and branched-chain amino acids when the bulls were changed from MP to FP. When changing from maintenance to fattening, the incremental glucose and amino acid hindquarter uptake provided energy and supply for muscle protein accretion, respectively. The level of alanine transamination was also sharply reduced.

As far as consumers are concerned, the major quality characteristics of beef meat are an attracting color and tenderness (Smulders et al., 1991). The chemical composition - protein, fat and fatty acids contents mainly - is of importance for the dietitian. These parameters are influenced to a large extent by the management - diet and environment - of the fattening animals. The aim of the present paper is to relate some parameters of meat quality and meat composition with animal performance in growing fattening bulls.

Since CAP reform and environmental problems, there is, in agriculture, a tendency to reduce the production. Reduction of nitrogen fertilizer was suggested to decrease intensification. Nowadays, high quality milk has to be produced for the dairy industry, in order to be processed as cheese, butter,... Another aspect in milk production is the payment based on the composition (Beguin, 1994). The aim of this experiment was to study the effects of a reduction in nitrogen fertilizer on milk yield, butterfat, protein, urea and cells contents. The trial was repeated over four years consecutively.

As far as consumers are concerned, the major quality characteristics of beef meat are an attracting color and tenderness (Smulders et al., 1991). The chemical composition - protein, fat and fatty acids contents mainly - is of importance for the dietitian. These parameters are influenced to a large extent by the management - diet and environment - of the fattening animals. The aim of the present paper is to relate some parameters of meat quality and meat composition with animal performance in growing fattening bulls.