GENERAL PROBLEMS IN DAIRY HUSBANDRY 361 



The good results secured with such mixtures may possibly be due in large 

 part to a better mixture of proteins furnished by such a variety of feeds. 

 However, as is pointed out later, it is not necessary for good results to 

 use a complicated concentrate mixture made up of a large number of 

 feeds, if good roughages are fed, such as silage and legume hay. (650) 



574. Mineral requirements. The mineral requirements for milk produc- 

 tion have been discussed in considerable detail in Chapter VI. (149) It 

 has there been pointed out that the demand for calcium and phosphorus 

 is so large with high-producing cows in full flow of milk that they may 

 be unable to assimilate enough of these mineral constituents from their 

 feed to prevent loss from their bodies, even when fed plenty of legume 

 hay and protein-rich feeds, these making a ration quite high in both 

 calcium and phosphorus. 



Our knowledge concerning the cause of this surprising condition is as 

 yet fragmentary. As has been pointed out earlier (149), possibly the 

 inilk-producing capacity of our dairy cows has been so increased by 

 selective breeding that it exceeds the ability of high-yielding cows to 

 assimilate sufficient mineral nutrients from their feed to meet the heavy 

 demand brought about by the large milk flow during the first part of 

 the lactation period. Forbes 56 has recently shown that later on in 

 lactation, or when they are dry, they are able to build up again the stores 

 of these mineral constituents in their bodies. 



The losses of calcium which may occur when a cow is fed a ration 

 deficient in this mineral nutrient are shown in a trial by Hart, McCollum, 

 and Humphrey at the Wisconsin Station. 57 A cow producing about 30 

 Ibs. of milk daily was fed a ration which was liberal, except that it lacked 

 lime. It was found that there went into the milk daily about 20 grams 

 of lime (CaO) and into the solid excrement and urine, principally the 

 former, about 30 grams, the latter loss being due to the normal changes 

 (metabolism) taking place in the body. In all, about 50 grams, or nearly 

 2 ounces, of lime disappeared daily from the body of this cow, only one- 

 half of which could have been furnished by the lime in the food. Dur- 

 ing the trial, which lasted 110 days, this cow maintained a good flow 

 of milk and continued to put the normal amount of lime into it. It 

 was calculated that during the trial she gave off in milk and excrement 

 5.5 Ibs. more lime than she received in her food. It was estimated that 

 her skeleton contained about 24.2 Ibs. of lime at the start, and this be- 

 ing true, this cow gave up in 110 days about 25 per ct. of all the lime in 

 her skeleton ! Here is a striking illustration of the overpowering force 

 of maternity. 



In recent experiments at the Wisconsin Station 58 Hart and Steen-. 

 bock have found that dairy cows and milk goats are able to assimilate 

 calcium more completely from fresh green forage than from dried forage, 

 such as hay. They have suggested that such green forage may contain 



6s Am. Soc. Anim. Production, Proceedings, 1921, pp. 70-79. "Wis. Res. Bui. 5. 

 "Wis. Bui. 323, p. 17; Res. Bui. 49, p. 18; information to the authors. 



