Butter-Fat Percentage in Jersey Cattle. 



153 



butter-fat percentage ±0.827. The value of the correlation co- 

 efficients are so high in each case that the average milk produc- 

 tion or butter-fat percentage over a number of lactations can 

 quite accurately be predicted from the productions obtained for 

 any lactation. 



TABLE 3. 



Correlations and Constants for Butter-Fat Percentage over a 



Number of Lactations and the Butter-Fat Percentage for 



the Individual Lactations. 







Standard Deviation 



Coefficient of Varia- 



Age when lactation Mean Butter-Fat Per- 



for butter-fat Per- 



tion of the butter- 



commenced 



centage 



centage 



fat percentage 



2 years to 3 years 



5.245-K035 



0.491-K025 



9.35+.46 



S years to 4 years 



5.227+.035 



.485+.025 



9.29+.46 



4 years to 5 years 



5.291+.036 



.532+.026 



9.48+.46 



5 years to 6 years 



5.225+. 033 



.462+. 023 



8.83+.46 



6 years to 7 years 



5.177+.031 



.425+.022 



8.20+.41 



Five lactation but- 









ter-fat percentage 



5.216±.029 



.399+.020 



7.65±.39 



I Correlation of indi- 1 Correlation Ratios Regression Equations 

 I vidual lactation rec- for individual records' for the five lactation- 

 Age when lactation 1 ords and the record and the record of the; butter-fat percentage- 



commenced 



for the five lacta- 

 tions 



five lactations 



as calculated from 



any of the given 



lactations 



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 

 Five lactation but- 

 ter-fat percentage 



+0.797±.026 

 .836±.022 

 .862±.018 

 .857+.019 

 .784+.028 



0.827±.023 

 .855±.019 

 .876±.017 

 .873±.017 

 .815+.024 



BT=1.819+.648b 2 

 BT=1.621 + .688b3 

 BT=1.591 + .685bt 

 BT=1.349+.740bs 

 BT=1.406+.736ba 



If it is admitted that there is a regulatory mechanism con- 

 trolling the amount of milk produced by a cow in any lactation 

 as it seems that it must be admitted from the evidence of a par- 

 ticular gland for its secretion, etc; then the large size of the cor- 

 relations indicate clearly that this mechanism is quite accurately 

 working in governing the relative amount of milk a cow will 

 produce from lactation to lactation. 



The precision of action of this mechanism for the secretion 

 of butter-fat in a given cow's milk is greater than is the preci- 

 sion of action of the ovary of a hen in secretion of eggs as may 

 be seen from the data of Harris and Blakeslee. For the White 



