herd. This small difference in herd life of only 0.12 of 1 year or about 

 1^2 months is not significant.- ^ Therefore, it was concluded that for the 

 last owner purchased cows have as long a productive herd life as raised 

 cows. As purchased cows were older than raised cows at disposal, it was 

 also concluded that the total productive life of purchased cows (assuming 

 comparable ages at first freshening for both raised and purchased cows) 

 was significantly longer than for raised cows. 



The average herd life of 3.43 years for purchased cows represented 

 only the years in the herd that reported the cow as being removed. The 

 reported herd life as a purchased cow did not include the time the pur- 

 chased cow spent in the original herd in which she was classed as a raised 

 cow. Therefore, the total productive herd life of the sample of purchased 

 cows was estimated to be 4.87 years. This compares with a total herd life 

 of 3.55 years for raised cows. Some of the difference of 1.32 years addi- 

 tional herd life of purchased cows is related to life expectancy. 



Table 11 shows the reported average life expectancy of samples of cows 

 of various ages in New Hampshire, Indiana, Iowa, Kansas, and Florida. 

 The life expectancies are similar in the several states, except for young 

 cows in Iowa. The Iowa records were taken in 1927-28 and 1930-36. Records 

 for the other states were taken in 1949-54. Changes in technology between 

 the two periods may explain the lower figure for Iowa. 



Life expectancy declines more slowly as cows grow older. In the New 

 Hampshire sample, a cow exactly 2 years old had an average future life- 

 time of 4.1 years, or a total life of 6.1 years. But when she reached the 

 age of 6 years, she had not just 0.1 years to live but an average future 



Table 11. Life Expectancy of Cows of Various Ages in Samples of Herds 

 in New Hampshire, Kansas, Indiana, Iowa, and Florida^ 



1 The erratic differences in life expectancy at older ages is due to the small number of cases studied. 

 Theoretically, with large numbers of cases the results would be less discrete. 



2 Removal records for 2,135 cows in New Hampshire Dairy Herd Improvement Associations for 1952-54. 

 ^ Removal records for 8,691 cows in 1950-54. The original data for both New Hampshire and Kansas 



excluded cows that were removed for dairy purposes and therefore did not fully represent the cow universe. 



■• The Indiana and Iowa statistics were developed from age distribution relationships. In terms of 

 cow-removal records, the Indiana data covers 7,196 cows in 1952. The Iowa sample covers 27,091 cow 

 removals in 1927-28 and 1930-36. 



^ Computed by R. B. Becker, P. T. Dix Arnold, and A. H. Spurlock, Productive Life-Span of Dairy- 

 Cattle, Fla. Agr. Expt. Sta. Bui. 540, 1954. 



21 Statistical measurements of the age distributions and years in the herd were 

 made using the Chi-square and t tests. 



27 



