4 PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 



synthesize protein in the paunch from urea and other simple nitrogenous 

 compounds/ has been rendered largely unintelligible through lack of an 

 accurate knowledge of protein requirements. 



One of the most practical contributions of the science of nutrition to 

 the feeding of farm animals is the formulation of feeding standards 

 applying to different classes of animals and to a variety of conditions. 

 How practical these standards have proved to be and how greatly they 

 have modified feeding practices cannot be told. Whether or not their 

 value in increasing the financial profits of feeding operations is con- 

 siderable, undoubtedly knowledge of feeding standards and their limita- 

 tions will aid materially in the intelligent appreciation of the live stock 

 business, particularly in the ability to cope successfully with changing 

 conditions of feed supply and to avoid exploitation by manufacturers of 

 commercial feeds and other products for live stock. 



Feeding standards should promote maximal production with a mini- 

 mum of overfeeding. They should include a factor of safety, so that a 

 normal variation in the composition and nutritive value of feeds and in 

 the functional capacities of animals will rarely if ever result in under- 

 feeding. But obviously, a factor of safety cannot be scientifically 

 included in a feeding standard until the actual minimum requirements 

 of animals for the different nutrients have been determined. For the 

 same reason an engineer cannot intelligently impose a factor of safety in 

 the construction of a bridge unless a satisfactory estimate of the maxi- 

 mum load that the bridge will have to bear can be made. Hence, feeding 

 standards for farm animals must ultimately be based upon satisfactory 

 determinations of minimum animal requirements. 



It may never be necessary or advisable to feed a farm animal in exact 

 accord with its protein requirements, but when an animal is non- 

 producing at certain seasons of the year, or when protein concentrates 

 become relatively high in price, it may become expedient to approximate 

 these requirements. In such cases it is clear that an exact knowledge of 

 protein requirements, as well as of the protein values of farm feeds, 

 becomes of immediate practical significance. 



For these reasons, a study of the protein requirements of farm animals 

 is well worth while. In a recent report of the Subcommittee on Animal 

 Nutrition (^) a method of measuring such requirements was proposed, 

 differing in all essentials from methods commonly used in previous 



^In most of these experiments, the question of the nutritive value of the urea 

 addition depends for its answer upon the question whether the digestible crude 

 protein of the basal ration is adequate in itself to cover the protein requirements 

 of the animal. 



