MILK PRODUCTION 485 



of breeding or of continuous shelter and warm quarters, and is 

 to that extent a poorer protection against loss of heat. 



For all these reasons, it is clear that the loss of heat from the 

 dairy cow may well be more rapid than that from the steer of 

 like weight under the same external conditions and that con- 

 sequently the minimum limit of external temperature below 

 which additional katabolism is caused may be higher for the 

 former than for the latter. 



582. The direction of production. Another important 

 consideration in connection with the question of temperature 

 and shelter for dairy cows is that of their possible influence 

 upon the direction of production. Stress was laid at the outset 

 of this discussion of the factors of milk production (558) upon 

 the essential difference between beef production and milk pro- 

 duction due to the fact that in the latter it is simply the secre- 

 tion of a single gland and not a general increase of the whole 

 body which is desired. The activity of the milk gland, how- 

 ever, is much more sensitive to external influences than, for 

 example, that of adipose tissue. It is quite conceivable, there- 

 fore, that a degree of cold or exposure which, from the standpoint 

 of heat production merely, might not require any additional 

 katabolism to maintain the body temperature, might neverthe- 

 less check the formation of milk, especially if the cow were sub- 

 jected to it suddenly. In such a case it would be anticipated, 

 either that feed previously used for milk production would be 

 stored up as body fat or else, if the cow continued to eat the 

 same amount, would lead to a stimulation of the general body 

 katabolism and so to an unnecessary increase in heat production. 



In other words, exposure to cold might conceivably neither 

 increase the feed consumption nor diminish the total utilization 

 of surplus feed but might, nevertheless, be a disadvantage be- 

 cause it diverted the current of productive activities from the 

 formation of milk to other and undesired forms of production. 



583. Results in practice. Only meager experimental evi- 

 dence is available regarding the practicable or desirable limits 

 of temperature for dairy cows. 



Plumb r compared the feed consumption and milk yield of two 

 lots of purchased cows, one of which was turned out into the yard 

 about one hour per day on sunny days while the other was turned 

 1 Ind. Expt. Sta., Bui. 47 (1893), pp. 89-96. 



