BULLETIN 290 



THE VARIATION OF BUTTER-FAT PERCENTAGE 

 WITH AGE IN JERSEY CATTLE.* 



By John W. Gowen. 

 SUMMARY 



This paper deals with the variation of butter-fat percentage 

 for a pure bred herd of Jersey cattle. The mean butter-fat per- 

 centage for this herd is 5.2260 ±.0073. The comparison of the 

 butter-fat percentage of the milk of 28 different breeds of cattle 

 shows this mean butter-fat percentage as high as that for any 

 breed. The range of variation of these means for the different 

 breeds is between 3.05 to 5.12. The frequency distribution for 

 this range is bimodal one mode occurring at about 3.7 per cent 

 and the other at about 5.0 per cent. 



When the variability of the butter-fat percentage is com- 

 pared with that of the other milk constituents it is found that 

 the variation of the butter-fat percentage from cow to cow is 

 about twice as much as is the variation of the solids-not-fat 

 percentage. 



Comparing the variation of the percentages of the different 

 parts of the egg with the variation of the butter-fat percentage 

 it is found that the percentage of yolk and of shell vary to the 

 same degree as the butter-fat percentage but that the percentage 

 of albumin has only half the variation of the butter-fat per- 

 centage. 



There is a slight negative correlation ( — 0.1126±.0161) 

 between the age of the cow and the butter-fat percentage which 

 the cow will produce. Described in word this correlation states 

 that for each increment added to the age of a cow there is a 



*This paper is an abstract of a longer paper on "Studies in Milk 

 Secretion VI. On the Variations and Correlations of Butter-Fat Per- 

 centage with Age in Jersey Cattle," published by the same author in 

 Genetics, May 1920. All literature citations should be made to this com- 

 plete paper. 



