238 



Bulletin 397 



STUDIES OF JERSEY RECORDS! COWS IN UNIFORM STAGE OF LACTATION 



Enough Jersey records were available to permit of a little corrobo- 

 rai:ive work with this breed. The study was made in a similar way to 

 the study of Holsteins in which the records of production for a twenty- 

 weeks period began one month after calving. Only cows that freshened 

 between August 15 and December 15 were used. 



Individual variation. 



The records were first sorted into groups of equal individual pro- 

 duction and the variation of individuals was thus determined. The 

 results of this study are shown in table 15: 



TABLE 15. Individual Variation 



Individual production, two- weeks period 

 (pounds) 



150-199. 



200-249 . 

 250-299. 

 300-349 . 



350-399 • 

 400-449. 

 450-499 . 



Number of 

 individuals 



Total. . . 

 Average . 



7 

 17 



23 

 32 

 18 



9 

 6 



112 



Coefficient of 



variability 



7 

 12 



15 

 II 



9 

 13 



4 



02 

 13 



33 



±1.27 

 ±1.40 



±1-52 



42 ±0.96 



13 ± 1-03 

 18 ± 2. 10 

 70 d= 0.92 



11.47 ±0.53 



The coefficient of individual variation for Jerseys, as shown by the 

 average value listed in table 15, is nearly identical with the corresponding 

 figtu^e for Holsteins as shown in table i. 



Group variation 



In the study of group variation the individuals were chosen at random, 

 the only consideration being to have the group production fall within 

 the limits prescribed. The results are shown in table 16: 



TABLE 16. Variation in Groups 



Group production, two- weeks period 

 (pounds) 



1,900-1,999 



Number 

 of groups 



Number 



of cows 



per group 



Coefficient of 

 variability 



4.25 ± 0.48 



.^4«^ 



