FEEDING AND CARE OF DAIRY COWS 253 



Influence of individuality. — Cows of the same breed differ one from 

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

 tion, 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 

 weather, and, in small degree, to changes in feed. 



First and last drawn milk. — The first milk drawn from the udder 

 is very poor in fat, each succeeding portion increasing in richness. 

 In a trial at the New York (Geneva) Station ° the first portion of milk 

 drawn from a Guernsey cow contained but 0.76 per ct. fat ; the second, 

 2.60 per ct. ; the third, 5.35 per ct. ; and the last 9.80 per ct. The 

 percentages of casein and albumin vary but little, decreasing slightly 

 as the milk becomes richer in fat. 



Effect of period between milkings. — When the intervals of time 

 between milkings are unequal, cows generally yield a smaller amount 

 of milk after the shorter period, but this milk is slightly richer in fat 

 and total solids. For this reason the evening milk is usually richer 

 than that drawn in the morning. Where the intervals are equal there 

 is no regular difference in quality with cows milked twice a day. 

 When they are milked 3 times daily the mid-day milking is usually 

 the richest. 



Effect of age. — The richness of milk yielded by cows remains prac- 

 tically constant until after the third lactation period, after which 

 there is a slow, gradual decline in fat percentage. The total yield 

 of milk and fat by a heifer normally increases until she is 5 years old. 

 A 2-year-old may be expected to give about 70 per ct. as much milk 

 and fat as when mature, a 3-year-old about 80 per ct., and a 4-year- 

 old about 90 per ct. A cow may make her best record when 10 or 11 

 years old, altho she usually does her best somewhat earlier. Cows 

 that breed regularly, usually show no marked decline in yield until 

 at least 12 years old. 7 



Effect of advancing lactation. — For a few weeks after freshening 

 cows usually give somewhat richer milk than during the following 

 month or two. The fat percentage then remains fairly constant until 

 toward the close of the lactation period, when it gradually increases. 

 The most marked effect of advancing lactation is upon the yield of 

 milk. In well-managed herds the normal monthly shrinkage in milk 

 flow is about as follows : From the second to the seventh month the 

 shrinkage varies irregularly, ranging from 4 to 9 per ct. per month, 



e Van Slyke, Jour. Am. Chem. Soc, 30, p. 1173. 



7 Eckles, Dairy Cattle and Milk Production, p. 153. 



