CALCIUM AND PHOSPHORUS IN THE FEED OF DAIRY COWS. 3 



the test cows were better bred, but a part also is due to the larger 

 quantity of feed they consumed. How much of the increased milk 

 yield to attribute to each of these factors is a question of great prac- 

 tical interest. 



STANDARD RATIONS INSUFFICIENT FOR OPTIMUM MILK YIELD. 



The cycle of lactation consists of two phases which may be called 

 the preparatory and the active phases. Considerable changes go 

 on in the udder of a cow for some time before her calf is born, and 

 usually make themselves manifest by an increase in size and con- 

 gestion of that organ. There is no doubt that the amount of the 

 subsequent milk yield largely depends on these changes, and it is 

 highly probable that the changes themselves depend on the state of 

 nutrition in which the animal happens to be for the few weeks 

 before her calf is born. 



JAN. 

 1919 



3 4 5 6 7 



HUNDRED POUNDS OF MILK 



10 



Fig. 1. — Influence of the length of the dry period on the subsequent milk yield in the case 

 of cow 17. The columns represent the pounds of milk given in the first clear calendar 

 month after calving in the y.ears indicated. Before calving in the years 1914 to 1917, 

 inclusive, this cow was fed the routine ration for dry cows at Beltsville ; her dry periods 

 averaged 44 days. Before calving, in December, 1918, she was given a dry period of 122 

 days and fed approximately as in her previous dry periods. 



It is well known that animals are capable of storing up large 

 quantities of nutritive material in times of plenty and using these 

 stores in times of stress. The effect of the feed on milk secretion, 

 therefore, often may be long delayed and rather complicated. It is 

 not at all impossible that the effects of a deficient ration supplied 

 in one lactation period may not show themselves until the subsequent 

 period or even later. 



Figures 1 and 2 give graphically the histories of two cows which 

 were brought to the Beltsville farm some years ago and fed and 

 treated according to the usual routine. The milk yields fell off very 



