Butter-Fat Percentage in Jersey Cattle. 



137 



TABLE 1. 



Constants of Variation of Butter-Fat Percent for the Succes- 

 sive Ages at Test in Jersey Milk. (8 Months Lactation 



Period.) 



Age at test 



Mean 



Standard 

 Deviation 



Coefficient 

 of Variation 



Skewness 



2 yrs. 



3 yrs. 



4 yrs. 



5 yrs. 

 6- yrs. 



7 yrs. 



8 yrs. 



9 yrs. 

 10 yrs. 

 Total 



mo. to 

 mo. to 

 mo. to 

 mo. 

 mo. 

 mo. 

 mo. 

 mo. 



to 

 to 

 to 



to _ 

 \i iuw. to 10 yrs. 

 mo. to above 

 Population 



3 yrs. 



4 yrs. 



5 yrs. 



6 yrs. 



7 yrs. 



8 yrs. 



9 yrs. 



mo. 

 mo. 

 mo. 

 mo. 

 mo. 

 mo. 

 mo. 

 mo. 



5.2635±.0183 

 5.2777±.0204 

 5.2759+.0196 

 5.2345±.0187 

 5.1875±.0216 

 5.1697±.0223 

 5.1553±.0249 

 5.1668±.0353 

 5.1339±.0288 

 5.2260±.0073 



0.4662±. 

 0.4749±. 

 0.4415+ . 

 0.4132±, 

 0.4445+, 

 0.4322±. 

 0.4156±, 

 0.4818+ . 

 0.4419+. 

 0.4492±. 



0129 

 0145 

 0139 

 0132 

 0153 

 0158 

 0176 

 0249 

 0204 

 0052 



8.8581±.3473 

 8.9976±.3909 

 8.3680±.3744 

 7.8938±.3644 

 8.5686+.4191 

 8.3599±.4359 

 8.0619±.4359 

 9.3259±.6875 

 8.6073±.5647 

 8.5950±.0995 



+ 0.1333+.0490 

 +0.2635±.0556 

 +0.2744+.0583 



+0.1047±.0732 

 — 0.1357+.0718 

 — 0.5656+.2963 



+67ld03±.0209 



The mean butter-fat percentage is the highest in the early 

 ages at which the Jersey cow's mammary gland is functioning. 

 From this high point the percentage of this butter-fat declines 

 irregularly toward the older years of the cow's life. The low- 

 est percentage is reached when the cow is over ten years of age. 

 The difference between the highest mean value of the percentage 

 of butter- fat occurring at three years old and the lowest mean 

 value at ten years and older (5.2777=^.0204 and 5-i339±.0288) 

 is 0.1 438=!=. 0354 or the difference is 4.05 times the probable 

 error. Such a difference while only mediocre, is likely to be 

 significant. The point will be discussed later in connection with 

 other data. The mean percentage of butter-fat of these Jersey 

 cows (5. 2260 ±.0073) agrees fairly well with that on other Jer- 

 sey data (5.12) published by the author in table 2 of a previous 

 bulletin. As the data on which the 5.12 percentage was based, 

 included a wide variety of conditions, climate, management, etc. 

 it would appear reasonable to suppose that this figure represents 

 a fair average for the Jersey breed. If such is in fact the case 

 the average production of the Jerseys included in the herd 

 studied are above those of the breed as a whole in butter-fat 

 percentage contained in their milk. The difference is slight in 

 absolute amount, however. 



If we examine the butter-fat concentration of the milk of 

 the various breeds summarized in the table referred to above, 

 we see that the Jersey stands at the top of the list of these. 



