52 



Maine Agricultural Experiment Station. 1920. 



1713 have records for the butter-fat percent. The weighed 

 monthly averages of the bi-monthly test have been used to ob- 

 tain the weighed 8 months average for the 8 months lactation 

 period chosen for study. 



Variation of Jersey Milk Production with Age at Com- 

 mencement of Test. 



The tabulation of these records in complete eight months 

 records has been done by the author. The chief physical con- 

 stants of the distributions are presented in table 1 together with 

 their probable errors. 



TABLE 1. 



Constants of Variation of Milk Production for the Successive 



Ages at Test in Jersey Milk. (8 Months Lactation 



Period). 



Age at Test 



Mean 



Standard i Coefficient 

 Deviation of Variation 



Skewness 



2 years months 



3 years months 



4 years months 



5 years months 



6 years months 



7 years months 



8 years months 



9 years months 

 10 years u months 

 Total population 



to 3 years 

 to 4 years 

 to 5 years 

 to 6 years 

 to 7 years 

 to 8 years 

 to 9 years 

 to 10 years 

 and above 



months 

 months 

 months 

 months 

 months 

 months 

 months 

 months 



4032.9±31.7| 

 4686.5±46.S l 

 4992.9±46.3 

 5281.4±57.0, 

 5536.5±64.5 

 5314.7±64.9 

 5226.4±77.9 

 4938.2±95.3 

 4838.8+70.3 

 4887.6±20.2 



818.9+22.4 

 1101.5+33.1 

 1079.4+33.0 

 126-2.8+40.3 

 1325.3+45.6 

 1255.0±45.9 

 1302.0±55.1 

 1302.6+67.4 

 1077.3+49.7 

 1249.7+14.3 



20.304± .577 

 23.503± .712 

 21.619± .684 

 23.911+ .801 

 23.938± .865 

 23.613+ .907 

 24.912±1.111 

 26.377±1.453 

 22.264+1.028 

 25.569+ .310 



+0.2642±.0548 

 +0.3532±.0635 

 +0.3894+.0714 

 +0.2586±.0628 



+0.3141+.1173 



+0.3150+.0222 



The mean milk production for the eight months period, 

 for those cows which are between 2 and 3 years of age, is 4032.9 

 pounds. From this point the milk production rises rapidly 

 at first then more slowly to a maximum at about 7 years. From 

 this maximum the decline in milk production is less rapid toward 

 the higher ages. 



The difference between the production of 2 years and 6 

 months and the maximum is significant as the difference is about 

 20 times its probable error (1503. 6+71.9). The difference 

 between the maximum production and that for the 10 years and 

 above is also significant as the difference is more than 6 times 

 the probable error (697.7zh95.40). This rise and fall of milk 



