Besoins protéiques et maîtrise des rejets azotés du bovin producteur de viande

Protein requirements and control of nitrogen excretion by beef cattle

What are the protein requirements of beef cattle (suckling cows with their calves, animals for rearing and animals for fattening), and, at the same time, what amount of nitrogen are they excreting into the outside environment ? The synthesis of data supplied by animal physiology, feeding, and more global approaches gives interesting answers to these questions.
Thanks to the knowledge of the physiology of nitrogen utilization by the animals, it has been possible to build a model for the process of protein storage by cattle for rearing and cattle for fattening, from feed intake to fixation in the various animal tissues. The French PDI system (i.e. calculation of Protein Digestible in the small Intestine) makes it possible to determine rationally each animal's requirements according to its characteristics and to assess the nitrogen excreted according to the diets fed ; the cases of excess nitrogen in the nutrition or of nitrogen saving (nitrogen re-cycled by the animal) can be accounted for. Lastly, more global balances can be used for the estimation, at the level of the production cycle, of the amount of nitrogen ingested, fixed, or excreted. With beef production, nitrogen derives mainly from the forages, and that portion that is imported to the farm becomes significant only in the most intensive systems.