292 Maine Agricultural Experiment Station. 1919. 



tained under the conditions of a large farm, managed by a well 

 trained man thoroughly versed in his business. While stated in 

 general form the conclusions are not presumed to be more gen- 

 eral than the data on which they are based. Certain compari- 

 sons with other data contained in the body of the paper make 

 it seem altogether probable that to a large degree the conclusions 

 are of general application to most of the other dairy breeds of 

 cattle. The well recognized need for such data and analysis in 

 physiological and genetic research and the significant relation 

 such data have to the improvement in yield and in the selection 

 of cows to remain within the herd have made it seem desirable 

 to present as complete numerical data as possible. 



The following paragraphs briefly state the conclusions 

 which are considered of most importance. Unless stated to the 

 contrary, these conclusions apply to the pure bred Jersey herd 

 the data for which are given in this paper. 



This investigation deals with 1713 records for the butter- 

 fat percentage of the first eight months lactation, each cow 

 milking at least nine months. The frequency polygons for 

 butter-fat percentage are nearly symmetrical. One only, at the 

 ages nine to ten years, diverges noticeably from this form. The 

 range of variation extends from 3.65 to 6.95 percentage of but- 

 ter-fat. The height of the modal ordinate and the shape of the 

 polygons do not change markly with age as was the case for 

 milk production. Only one mode is evident in any of the his- 

 tograms. 



Comparatively studied the butter-fat in the milk secreted 

 by twenty-eight breeds of cows shows that the means of these 

 breeds form a distribution distinctly bimodal in characters. The 

 mode of the first curve coming at about 3.7 and of the second 

 at about 5.0 per cent of butter-fat. 



Study of the standard deviation of typical members of the 

 above groups shows a greater scatter in the butter-fat percent- 

 ages in the group where the butter-fat concentration is high 

 than in the group where the butter- fat concentration is low. 



The analytical constants show that the butter-fat percentage 

 histograms of the eight months milk production are Pearson's 

 type I, III, IV and V, and normal curves. The skewness of 

 these curves, where they are skew, is plus four times and minus 

 twice. The skewness for each curve is small in amount. This 



