348 FEEDS AND FEEDING 



continues to breed, she usually shows no marked decline until at least 12 

 years old. Occasionally a cow continues to breed until she is 16 or 18 

 years old." Eckles and Palmer 22 report that the milk from a cow that 

 was 19 years old and in her thirteenth lactation period was pronounced 

 to be of excellent quality. 



The age of the cow has but little effect upon the percentage of fat in 

 her milk. 23 From studies of the advanced registry records of cows of 

 the Ayrshire, Jersey, Guernsey, and Holstein breeds, including a total 

 of 19,002 yearly records, White and Judkins of the Connecticut (Storrs) 

 Station 24 conclude that on the average the fat test is highest for the 

 first lactation and gradually and very slowly declines until maturity is 

 reached, but nearly half of the cows whose records were studied proved 

 exceptions to this general rule. Often the richness of the milk is lower 

 in the first or second lactation period than in the following ones. After 

 maturity, other factors are more important than age in determining the 

 percentage of fat, and an animal may test even higher when old than 

 when immature. 



556. 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 usually remains fairly constant 

 until toward the close of the lactation period, when it gradually in- 

 creases. 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, 

 based on the yield of the given cow for the previous month. The 

 average monthly decrease during this period is about 6 to 7 per ct. 

 After this the decrease becomes more rapid, being 9 to 11 per ct. for 

 the eighth month, 12 to 18 per ct. for the ninth month, and 12 to 23 

 per ct. for the tenth month, after which the cows are generally dried off. 25 



The further advanced a cow is in lactation the more food she usually 

 requires for a given quantity of milk, especially towards the end of the 

 lactation period, when her production is low. For the first few weeks 

 after calving a good dairy cow usually draws on her own body substance 

 for some of the nutrients she uses in milk production, therefore apparent- 

 ly producing milk with surprising efficiency. On the other hand, late in 

 the lactation period, when her production is low, most of her feed goes to 

 maintain her body and to nurture the unborn calf. 



^Jour. Agr. Res. 11, 1917, pp. 645-57. 



M Gowen, Me. Buls. 279, 284, 290, 293. 



24 Bul. 94. 



*Carlyle and Woll, Wis. Bui. 102; Woll, Wis. Bui. 116; Wis. Res. Bui. 26; 

 Beach, Conn. (Storrs) Bui. 29; Linfield, Utah Bui. 68. 



Pearl has published (Maine Station, Report of Progress on Animal Husbandry 

 Investigations in 1915, pp. 3-8.) a table giving the theoretical percentage yield 

 of cows of various ages and during the different months of the lactation period, 

 taking as 100 per ct. the maximum monthly yield when mature. 



