XIV.] 



VARIATIONS OF FAT IN MILK 



275 



which the butter fat in the milk of Jerseys rises to 6 or 

 7, and even lo, per cent. 



Table XXVI.— Percentage of Fat in Milk of 

 Different Breeds. 



3. Food. — It is commonly supposed that the per- 

 centage of fat in the milk of a given herd can be raised 

 by feeding concentrated foods rich in fat. Experiments, 

 however, show that the difference which can be brought 

 about in this way is very small ; the proportion of fat 

 contained in the milk yielded by a given cow being a 

 physiological function of the cow itself, it is compara- 

 tively unaffected by the food. If the amount of food 

 given be insufficient for the average requirements of the 

 cow, the animal will begin to lose weight, and will draw 

 the material from its own tissues in order to keep the 

 yield of milk and the proportion of butter fat up to its 

 normal percentage; only when the cow has lost an 

 appreciable amount of weight will both the yield and 

 the richness of the milk begin to fall off more markedly. 

 On the other hand, an excess of rich food will cause the 

 cow to put on fat, and as the cow gets very fat the milk 

 will again begin to fall off both in quality and quantity. 

 A high proportion of fat in the food does not make the 

 milk any richer in fat. The chief effect of a liberal but 

 not excessive diet appears to be to maintain the milk 

 yield somewhat longer during the period of lactation 



