Abstract
Life expectancy of the dairy cattle in our district was studied for the purpose of knowing the economical life span of the dairy cattles in various feeding circumstances.
Referring to the register of livestock insurance issued in September 1988 and that in September 1989, a life table was prepared based on the number of individuals replaced in one year. The life expectancy calculated from this table was 3.9 years with those one year of age, 3.4 years with those two years of age, 2.1 years with those five years of age, and 1.4 years with those ten years of age. It seemed advisable to use the life expectancy not of those one year old, that is the age in the raising term, but of those two years old, that is the age of primipara, when the life expectancy is used as an index for feeding circumstances of the dairy cattles.
The animals were divided into groups by districts, sizes of livestock keeping in numbers, renewal percentages, and systems of grazing, and the respective life table was prepared. As the result, in comparison of the life expectancies obtained from the two year old animals, it was noted shorter as the number of feeding animals was larger. It was also shorter as the renewal percentage was higher, showing no difference between the open yard feeding and the drylot feeding.
