152 Maine Agricultural Experiment Station. 1920. 



The mean coefficient of correlation for these ovulation records is"- 

 -(-0.446. This mean coefficient of correlation is consequently, 

 slightly below that for butter-fat percentage (0.5215) the differ- 

 ence being 0.0755. This difference, on the face of it, would seem- 

 to indicate a greater dependence may be placed in the record of 

 the butter- fat percentage of a known lactation as to the future 

 butter-fat percentage in a given cow's milk than can be placed in 

 a knowledge of a month's egg production to determine the future 

 production of the hen. The difference is not great, however, and 

 may not be statistically significant. 



Correlation Between the Mean Butter-Fat Percentage of 



the First Five Lactations and the Mean Butter-Fat 



Percentage of these Individual Lactations. 



Of perhaps even more interest physiologically and practically 

 is the correlations of the butter-fat percentage of one lactation 

 with the butter-fat percentage as determined for a number of lac- 

 tations. For this purpose certain of the records on which the cor- 

 relations of Table 1 were based, were chosen for this purpose. 

 These records included the first five lactations for the cow's life. 

 The correlations and other constants for these are given in Table 



3- 



Table 3 shows that the standard deviation of the butter-fat 

 percentage for the mean of the five lactations in these 88 cows 

 is lower than the standard deviation of these cows for any lac- 

 tation. The coefficient of variation for the five lactation average 

 butter- fat percentage is consequently lower than the coefficient 

 of variation for the individual lactations. The mean coefficient 

 of variation for the individual lactations is 9.03. This mean 

 value is 1.38 greater than is the coefficient of variation for the 

 five lactation butter-fat percentage. This difference appears to 

 be slightly significant indicating a less variability for the butter- 

 fat percentage over long periods than over a period so short as 

 one lactation. 



The correlation coefficients for the relation of the individual 

 lactations butter-fat percentage for the five lactations are all 

 high correlations as the run of correlations for this kind of data 

 go. Compared with the similar data on milk production the 

 average correlations for milk production are ±0.818 and for 



