MILK PRODUCTION 483 



It is still true, of course, that the energy for all muscular 

 exertion is ultimately supplied by the feed. In the instance 

 just mentioned the extra feed required for this purpose may 

 be approximately estimated, on the basis of the data contained in 

 Chapter XIV, at two-thirds of a pound of digestible matter per 

 day, equal to about eight- tenths of a pound of maize. The feed 

 cost of the exercise ordinarily taken by cows turned out in the 

 yard must be insignificant and be far outweighed by the tonic 

 effects of fresh air, sunshine and freedom on their health and 

 general condition, while in the case of heavily fed cows some 

 exercise may possibly be of advantage in diminishing the tend- 

 ency to fatten. The question of turning out dairy cows for 

 exercise, then, virtually reduces itself to the question whether 

 the cost of the labor involved is repaid by the effect upon 

 the health of the animals. 



Temperature. Shelter 



579. Air temperature. The general principles regarding 

 the relations between external temperature, heat production 

 and feed supply, already discussed in Chapters VII (350-356), 

 VIII (395-397) and XII (535-543), apply also to the dairy cow. 

 Like the beef steer, the well-fed dairy cow in full flow of milk is 

 consuming a large excess of feed above her maintenance ration 

 and is producing a correspondingly large amount of heat. 



For example, in an experiment reported by Jordan 1 the computed 

 heat production of two cows (disregarding slight changes in weight) 

 and the estimated amount of heat which would have been produced 

 on a maintenance ration were as follows : 



TABLE 127. ESTIMATED HEAT PRODUCTION OF Cows 



Cow No. 10 Cow No. 12 



Weight 775 Lb. 1200 Lb. 



Computed heat production . . 18.67 Therms 21.10 Therms 

 Estimated heat production on 



maintenance ration . . . . 10.10 Therms 13.70 Therms 



The heat production was greater in one case by 85 per cent and 

 in the other by 54 per cent than the estimated amount on maintenance, 

 which is a considerably greater excess than that computed (537) for 

 Kellner's fattening steers. 



1 The Feeding of Animals, The Macmillan Co., New York, 1908, p. 310. 



