170 EXPERIMENT STATION EECORD. [Vol.37 



" The prevailing belief that all animals which receive leafy forage as a con- 

 siderable part of the ration consume and digest an abundance of mineral nutri- 

 ment is shown not to be true in relation to cows during ordinarily liberal milk 

 production. With rations of common practical foods, especially chosen to 

 provide maximum supplies of the mineral nutrients, all calcium, magnesium, and 

 phosphorus balances were negative, as in the previous year's work. With large 

 increases in the calcium, magnesium, and phosphorus contents of these rations, 

 through increased amounts of food consumed and through the addition to the 

 rations of large amounts of calcium carbonate and bone flour, all calcium bal- 

 ances and all but one magnesium balance remained negative, but the phosphorus 

 balances became positive. This work presents satisfactory evidence that in the 

 selective improvement of milch cows we encounter limited capacities to digest 

 calcium magnesium, and phosphorus, and inability to maintain their body 

 stores of these elements before any such limitations are apparent in their 

 ability to digest and to utilize the organic nutrients. . . . 



" Doubling the usual sodium clilorid allowance did not improve the reten- 

 tion of calcium, magnesium, and phosphorus. Twenty-eight gm. (1 oz. ) of 

 salt per head and day, with a ration of common foods, provides enough sodium 

 for cows producing 45 lbs. of milk per day. An allowance of 1 to 2 oz. of 

 salt per head and day, in accord with the amount of milk produced, will cover 

 all sodium requirements. Rations containing enough sodium to meet the cow's 

 needs commonly contain a larger proportionate supply of chlorin. 



" Enough potassium seems to have been supplied by all the rations studied. 

 A deficiency of potassium in normal rations, therefore, seems unlikelj-. 



" The various circumstances which determine the path of outgo of absorbed 

 nutrients are commonly without corre.sjionding effect on the retention of these 

 elements in the brxly. In .some cases nearly all the sodium of the excreta was 

 In the urine, while in others it was nearly all in the feces. The same may be 

 said of chluriii. The elimination of .sodium and chlorin in the urine is increased 

 by high intake of these elements, by constipation, and by high water intake. 

 Potassium in cows is commonly excreteil in much larger prt>p()rtion in the 

 urine than in the feces, but in rations characterized by predominance of acid 

 minerals, potassium was elimlnatetl more largely in the feces. 



" Calcium is excreted by cows almost wholly in the feces, but a pretloralnance 

 of acid minerals in the ration may cau.se slight increa.se in urinary calcium. 

 Magnesium always exceeds calcium in the urine, but is contained in the 

 feces in amounts usually about four times as great as in the urine. 



" The excretion of phosphorus is characterized by much the same propor- 

 tionate distribution as the excretion of calcium, except that urinary phosphorus 

 may be much increased by general physiologic disturbance. Sulphur is nor- 

 mally excreted in the feces. In quantities three or four times as great as in 

 the urine, but with high sulphur intake the urinary sulphur may equal the 

 feces sulphur. 



" There were no noticeable effects of the foodstuffs or the mineral supple- 

 ments (sodium chlorid, calcium carbonate, or bone flour) on the amount or 

 composition of the milk. 



" Such variations in the balance of acid and basic mineral elements as occur 

 in nornuil cow rations do not affect the retention of the minfral elements in 

 unmistakable ways. Evidence was obtained showing that negative balances 

 of the mineral nutrients may signify either deficient intake of the same or 

 the throwing off of previously absorlied stores in the face of continued super- 

 abundant supplies. Either positive or negative balances may signify, under 

 certain circumstances, only comparatively unimportant fluctuations in extensive 

 reserves. 



