PRODUCTION OF WORK, MILK AND WOOL 81 



Source of fat in milk.— For many years it was believed that the 

 cow could form the fat of milk only from the fat in her food. This 

 was disproved in an ingenious experiment at the New York (Geneva) 

 Station.^ For over 3 months a cow was fed on hay, cornmeal, and 

 oats, from which the fat had been extracted by naphtha, as is done in 

 one method of extracting the oil from flax seed. During this time 

 the cow received only 5.7 lbs. digestible fat in her feed, but yielded 

 62.9 lbs, of fat in her milk. She was fatter at the end of the trial 

 than at the beginning and so could not have converted her body fat 

 into milk fat. From the amount of digestible protein in her feed, it 

 was computed that not over 17 lbs. of the milk fat could possibly have 

 come from the food protein. Thus, the larger part of the fat must 

 have been formed from the carbohydrates of the feed. 



Nutrients required for milk production.— A study of the nutrients 

 the cow yields in her milk will aid in showing the kind and amount of 

 nutrients her ration should furnish. A dairy cow of no unusual 

 ability should yield annually 8,000 lbs. of milk of average quality. 

 Taking the composition shown in a previous table (Page 64), we find 

 that she will produce in her milk 272 lbs. of protein, 296 lbs. of fat, 

 392 lbs. of milk sugar, and 56 lbs. of mineral matter. This is 56 per 

 ct, more protein, 30 per ct. more non-nitrogenous nutrients (fat and 

 carbohydrates), and 19 per ct. more mineral matter than is contained 

 in the entire body of a fat 2-year-old steer weighing 1,200 lbs. 



Thus, each year the cow yields more protein and mineral matter 

 than has been built into the body of the steer during its life. At the 

 same time she may be storing considerable protein and mineral matter 

 in the developing body of her unborn calf. It is therefore evident 

 that, far different from the requirements of the mature horse at work 

 or of a mature fattening animal, the cow needs a liberal supply of 

 protein and mineral matter. Just as in the case of growing animals, 

 this must not only be ample in quantity, but also of the proper kind or 

 quality. Furthermore, the high-producing cow is working just as 

 truly as the horse pulling a load, and hence needs a liberal supply of 

 concentrates rich in net energy. Energy used up in the mastication, 

 digestion, and assimilation of such feeds as straw takes the form of 

 internal heat and is of no value for the formation of milk. 



Since most of the scientific studies of the factors influencing the 

 production of milk have been conducted with the dairy cow, the dis- 

 cussion of milk production by that animal is continued in Chapters 

 XX and XXI. The requirements of the mare, ewe, and sow for the 

 production of milk are also treated in the respective chapters of 

 Part III. 



1 Jordan and Jenter, N. Y. (Geneva) Bui. 132. 



