24 
BULLETIN 1352, TJ. S. DEPARTMENT OF AGRICULTTJBE 
single-letter class. Furthermore, no information is given to indicate 
what proportion of the cows were milked more than twice daily. 
The increase in production from an initial record to a reentry 
record is owing partly to increased age and partly to the develop- 
ment which the animal undergoes during the progress of her initial 
official test. This latter, which has been called the factor of develop- 
ment, averages 11.0 per cent of the reentry record for Jerseys and 
12.2 per cent for Guernseys. 
The average initial records of cows retested are somewhat above 
the average for all cows having initial records. 
In the case of the Jersey records studied, carrying a calf for 155 
days of the test period has no noticeable effect on the average produc- 
tion of heifers up to the age of 3 years, but the average production 
of cows 3 years old and upward which met this requirement was less 
than that of the cows which failed to qualify. 
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