640 VETERINARY PHYSIOLOGY 



protein in the diet increased the yield. Excess of carbo- 

 hydrate or fat tends to fat formation and deposit in the 

 animal's body. 



The food requirements for milk cows are given on 

 page 375. 



(4) Housing. — It was formerly a custom to restrict 

 ventilation for the purpose of maintaining heat in byres, 

 the idea being that in warm byres the milk flow was 

 increased. Spier and Hendrick have shown that cool byres 

 and free ventilation do not reduce milk production. The 

 following are results obtained at different temperatures : — 



Aver. temp. Milk lbs. Fat 



of byre. per cow. per cent. 



Cool byres, free ventilation 41-2° F. 29-0 3-51 



Warm byres, restricted 



ventilation . . . 61-7° F. 28-9 3-48 



The animals in the cool byres had better coats and were 

 in better condition at the end of the winter. 



It has been found however that a marked decrease in the 

 temperature reduces milk secretion, and that animals exposed 

 in winter eat more food than those comfortably housed. 



The temperature below which more food is required, or 

 at which the milk secretion begins to diminish, depends upon 

 the critical temperature (p. 2 7 1 ) of the animal. Unfortunately 

 comparatively little work has been done to determine the 

 critical temperature of dairy cows. Owing to the stimulus 

 to metabolism caused by the large amount of food eaten it is 

 probably comparatively low. From the evidence available it 

 would appear to be not higher than 7° to 8° C. To have 

 animals housed in an atmosphere above the critical 

 temperature should lead neither to a saving in food nor to 

 an increased production of milk. 



