194 Maine Agricultural Experiment Station. 1920. 



TABLE 4. 



Mean 365 Day Butter-Fat Percentage of Hoist ein-Friesian 

 Cows at Different Ages. 















Mean Butter- 



















Mean Butter- 







Age at Test 







Fat Percent- 









Agf 



al 



Test 







Pat Percent- 















age 



















age 



1 yr. 



6 



mo. 



to 1 yr. 



11 



mo. 



3.489 



8 



yr. 







mo. 



to 



8 yr. 



5 



mo. 



3.399 



2 yr. 







mo. 



to 2 yr. 



5 



mo. 



3.432 



8 



yr. 



6 



mo. 



to 



8 yr. 



11 



mo. 



3.416 



2 yr. 



6 



mo. 



to 2 yr. 



11 



mo. 



3.483 



9 



yr. 







mo. 



to 



9 yr. 



5 



mo. 



3.376 



3 yr. 







mo. 



to 3 yr. 



5 



mo. 



3.442 



9 



yr. 



6 



mo. 



to 



9 yr. 



11 



mo. 



3.342 



S yr. 



6 



mo. 



to 3 yr. 



11 



mo. 



3.398 



10 



yr. 







mo. 



to 



10 yr. 



5 



mo. 



3.388 



4 yr. 







mo. 



to 4 yr. 



5 



mo. 



3.449 



10 



yr. 



6 



mo. 



to 



10 yr. 



11 



mo. 



3.442 



4 yr. 



6 



mo. 



to 4 yr. 



11 



mo. 



3.409 



11 



yr. 







mo. 



to 



11 yr. 



5 



mo. 



3.300 



6 yr. 







mo. 



to 5 yr. 



5 



mo. 



3.417 



11 



yr. 



6 



mo. 



to 



11 yr. 



11 



mo. 



3.533 



6 yr. 



6 



mo. 



to 5 yr. 



11 



mo. 



3.410 



12 



yr. 







mo. 



to 



12 yr. 



5 



mo. 



3.200 



6 yr. 







mo. 



to 6 yr. 



5 



mo. 



3.443 



12 



yr. 



6 



mo. 



to 



12 yr. 



11 



mo. 



3.350 



6 yr. 



6 



mo. 



to 6 yr. 



11 



mo. 



3.414 



13 



yr. 







mo. 



to 



13 yr. 



5 



mo. 



3.600 



7 yr. 







mo. 



to 7 yr. 



5 



mo. 



3.366 



13 



yr. 



6 



mo. 



to 



13 yr. 



11 



mo. 





7 yr. 



6 



mo. 



to 7 yr. 



11 



mo. 



3.415 



15 



yr. 







mo. 



to 



15 yr. 



5 



mo. 



3.000 



These observational means are shown as the small circles in 

 figure 32. The ordinates are the percentages of butter-fat and 

 the abscissas are the ages. These observations on butter-fat 

 percentage clearly are linear in their relation to age when the 

 test was made. Such being the case the ordinary regression 

 formula may be used to fit this curve. The equation to this 

 curve is 



Butter-Fat Percentage = 3.470 — .009 age 



There is consequently a slight decrease in the butter-fat 

 percentage which a Holstein-Friesian cow is capable of giving 

 as the age of that cow increases. That this increase is slight 

 may be seen from the fact that the decrease in butter-fat per- 

 centage from the age of one year and nine months is only 0.130 

 per cent as shown by the fitted curve of the above figure. 



These conclusions concerning the milk yield and the butter- 

 fat percentage make it possible to answer a number of practical 

 questions which are today occupying prominent places in our 

 dairy husbandry. Perhaps one of the most interesting concerns 

 the admission of cows into the advanced registry. In the ad- 

 vanced registry work the linear nature of the butter-fat require- 

 ment has already been mentioned. In view of the fact that milk 

 yield in Holstein-Friesian cows is a logarithmic function of age 

 instead of a linear one and that butter-fat percentage has only 

 a slight relation to age it follows that butter-fat is a logarithmic 



