Milk Yield of Jersey Cattle. 



129 



Correlation of One Lactation Record With the Milk 

 Yield for the First Five Lactations. 



From a practical view point perhaps nothing is more impor- 

 tant than a knowledge of the degree of accuracy with which the 

 record of one lactation expresses what the milk yield over a 

 number of lactations will be. 



For this purpose a series of data including records of five 

 lactations was chosen. Each of the cows whose records were 

 selected began milking in the second year. The five lactations 

 were consecutive and approximately a year apart depending on 

 how long the previous lactations were continued. The lactation 

 records for the five successive lactations were correlated with the 

 total milk production for the five lactations. The correlation 

 coefficients and other constants for these are given in table 4. 



TABLE 4. 



Age when lactation Mean Milk Produe- 

 commenced tion 



2 years to 3 years 



3 years to 4 years 



4 years to 5 years 



5 years to 6 years 



6 years to 7 years | 

 Total of five lac- 

 tations 



4159.1± 57.8 

 4840.9± 86.1 

 5380.7± 78.8 

 5568.2± 87.1 

 5681.8± 91.4 



25613.6+335.9 



Standard Deviation Coefficient of Varia- 

 for the Milk Pro- tion for the Milk 

 duction Production 



803.2± 40.8 

 1197.9± 60.9 

 1096.2± 55.7 

 1211.2+ 61.6 

 1270.7+ 64.6 



4672.0+237.5 



19.31±1.00 

 24.74±1.35 

 20.37±1.06 

 21.75±1.17 

 22.36±1.17 



18.24+ .94 



ICorrelation of Indi- Correlation Ratio of 

 Age when lactation vidual lactation rec- Individual lactation 

 commenced ords and five laeta- records and five lac- 



tion total Production tation total Produc- 

 tion 



Regression Equations. 



8 months lactation 



and five lactations 



total Production 



years to 



years to 



years to 



years to 



years to 



years 

 years 

 years 

 years 

 years 



+0.7416±.0323 

 .8418±.0209 

 .8613±.0186 

 .8250±.0230 

 .8205+.0234 



+0.7517±.0312 

 .8856+.0155 

 .8796±.0162 

 .8561±.0192 

 .8466+.0203 



Total of five lac- 

 tations 



YT=7671.9+4.3139y3 

 YT=9719.5+3.2833y 3 

 YT=5861.4+3.6710y4 

 YT=7893.5+3.1824ys 

 YT=8471.9+3.0l70y 8 



The high correlation between the record of one lactation and 

 the total production (first five lactation periods) is manifest. 

 The correlations are so high as to lead to the conclusion that the 

 record of one lactation in a cow's life serves to determine the 

 records for the total production in the cow's life. 



