372 VETERINARY PHYSIOLOGY 



mental results obtained bv Bull and Emraett show how the 

 protein requirement relative to weight decreases with age. 



The milk of the mother contains the material necessary 

 for growth in the requisite proportions. Bunge has shown 

 that the proportion of protein and ash in milk varies with 

 the rapidity of growth. 



The accessory factors (p. 281) are of importance in 

 growing animals in confinement after the sucking is stopped, 

 especially when the food is cooked. It is probable that 

 certain diseases to which young pigs are liable are really 

 nutritional disorders caused by the absence of these. 



A deficiency of calcium and phosphorus limits bone 

 formation. In pigs it is usual to allow free access to a 

 mineral mixture containing these. 



(2) Energy. — The available energy of the food must be 

 sufficient (1) to meet the maintenance requirement, i.e. the 

 amount liberated as heat, and (2) to supply an amount of 

 energy equal to that contained in the new tissue formed. 



The maintenance requirement can be determined by the 

 calorimeter (p. 259). It is greater per unit of surface in 

 the growing than in the full-grown animal. It is certain 

 that energy is expended in the structural organisation of 

 growing tissue, but to what extent is not known. 



The energy content of the new tissue is determined by 

 slaughter tests (p. 869). It is found to vary with age, being 

 less in very young animals, where the increase is chiefly in 

 protein tissue, which contains about 75 per cent, of water, 

 and greater as the animal approaches maturity, when a 

 higher projDortion of the increase is fat. 



