346 FEEDS AND FEEDING 



make twice as much cheese as one testing 3 per ct. Therefore, milk 

 should be paid for at cheese factories, not on the basis of the fat con- 

 tent alone, but by som^ method which gives credit for both fat and casein. 



Not only does the composition of milk depend on the breed but it is 

 also influenced by the several factors discussed in the following para- 

 graphs. 



It is well known that the fat in milk is in the form of minute globules 

 or droplets, which are distributed thruout the milk in the form of an 

 emulsion. The fat globules of Jersey and Guernsey milk are considera- 

 bly larger than those in Holstein and Ayrshire milk, while the size of 

 the globules in Shorthorn milk ranges between. The fat will rise to 

 the surface most rapidly in milk containing large fat globules. 



So minute in size are the fat globules that the number secreted by a 

 cow in a day is beyond comprehension. It has been estimated that an 

 average cow in full flow of milk secretes at least 138,210,000 fat globules 

 each second thruout the day of 24 hours. Babcock 14 has computed that a 

 quart of average milk contains not less than 2,000,000,000,000 fat glob- 

 ules. These figures will illustrate the marvelous processes which are 

 constantly going on in life. 



552. Influence of individuality. Cows of the same breed differ one 

 from another, both in the amount of milk they produce and in its com- 

 position, especially the percentage of fat. Indeed, cows of the same 

 breed may yield milk differing as much in fat percentage as the average 

 differences between the several breeds. The milk from an individual 

 cow may also vary considerably in fat percentage from day to day, due 

 to changes in health, change of milkers, excitement, variations in weath- 

 er, and, in small degree, to changes in feed. 15 



The cow that gives the richest milk does not necessarily produce the 

 largest total yield of fat. Eckles states that as a rule the highest annual 

 productions of butter fat are generally secured with milk carrying the 

 average percentage of fat for the breed or even less. 16 



To determine the variation in the percentage of fat in single milk- 

 ings of individual cows, Anderson 17 studied 200 seven-day records made 

 under ordinary herd conditions where regular feeding and milking were 

 practiced, and 2,000 seven-day records of official Advanced Registry tests. 

 From these data he draws the following conclusions: 



One may expect that during 7 consecutive days about 30 per ct. of a 

 herd of cows will show a range in the percentage of fat in the milk at dif- 

 ferent milkings of 1 per ct. or less ; 50 per ct. of 1.1 to 2.0 per ct. ; 14 per 

 ct. of 2.1 to 3.0 per ct. ; and the remaining 6 per ct. of the herd even a 

 greater variation. In other words, 6 per ct. of the cows might yield 

 milk testing 3 per ct. of fat at one milking during the week and at some 



"Wis. Bui. 18. 



"Eckles and Shaw, U. S. D. A., Bur. Anim. Indus., Bui. 157. 



"Dairy Cattle and Milk Production, pp. 133-4. 



"Mich. Spec. Bui. 71. 



