Abstracts. 287 



the absolute maximum of production is reached. After the 

 time of maximum productivity, the absolute production per 

 unit of time decreases with advancing age at a continually in- 

 creasing rate. 



The mean fat percentage of the milk was found to decline 

 with advancing age until the tenth year of the cow's life is 

 reached. From that point on, the fat percentage remains about 

 constant through the remainder of the milking life of the cow. 



STUDIES IN MILK SECRETION. V. ON THE VARIA- 

 TIONS AND CORRELATIONS OF MILK SECRE- 

 TION WITH AGE IN JERSEY CATTLE.* 



The purpose of this paper is to present quantitative data, 

 along with the biometrical analysis of the same, on the normal 

 variations and correlations of milk production during the cow's 

 life. The necessity of such data and analyses is, now, well rec- 

 ognized in physiological and genetic investigations on a quan- 

 titative subject. The economic value of milk makes this inves- 

 tigation have a significant relation to improvement in yield and 

 in the selection of cows to remain within the herd. The materi- 

 als used for this' study are peculiarly suited to the ends in view. 

 They are a strictly homogeneous group of milk records of normal 

 pure bred Jersey cows maintained under the conditions of a 

 large farm, managed by a well trained man thoroughly versed 

 in his business. While the conclusions derived from this study 

 are stated in general form, it is not presumed that the conclu- 

 sions are of more generality than the data on which they are 

 based. It is altogether probable however that the conclusions 

 drawn do apply to most of the other dairy breeds of cattle. 



The conclusions of most moment may be summarily stated 

 as in the following paragraphs. Unless otherwise stated, the 

 conclusions apply to the pure bred Jersey herd the data for 

 which are given in this paper. 



The frequency polygons for milk production are only 

 slightly unsymmetrical. The range of variation is large, one 

 cow producing less than 1500 pounds in her eight months' lac- 



*This is an abstract from a paper by John W. Gowen having the 

 same title and published in the Genetics, Vol. 5, No. 2. 



