BULLETIN 284 



ABSTRACTS OF PAPERS PUBLISHED BY THE 

 STATION IN 1919 BUT NOT INCLUDED IN THE 

 BULLETINS. 



A complete list of all the publications issued by and from 

 the Station in 1919 is given on pages x to xii of the introduc- 

 tion to this Report. The following pages contain abstracts of 

 the papers issued during the year that are not included in the 

 Bulletins or Official Inspections for the year. 



VARIATION OF AYRSHIRE COWS IN THE QUANTI- 

 TY AND FAT CONTENT OF THEIR MILK.* 



This paper presents the results of a biometrical analysis of 

 variation in the quantity per unit of time, and the quality, as 

 indicated by fat percentage, of the milk of Ayrshire cows. Its. 

 purpose is to establish normal constants for interindividual vari- 

 ation in these characters, to serve as a base of reference in fu- 

 ture genetic studies on milk production. 



The chief results of this first part of the investigation may 

 be summarized as follows : 



The mean weekly yield and fat percentage of the milk 

 change in a considerable degree and definite manner with in- 

 creasing age of the cow. 



The weighted mean standard deviation and coefficient of 

 variability for mean weekly yield of cows of any given age are 

 2.806 gallons and 17.081 per cent respectively. Reasons are 

 given tending to show that these may be taken as very close 

 approximations to true normal values. For cows of all ages 

 lumped together the corresponding values are 3.329 gallons and 

 20.816 per cent. 



For fat percentage the weighted mean values for cows of 

 any given age are as follows : Mean— 3.738, standard deviation. 

 =0.330, and coefficient of variation=8.827. 



*This is an abstract from a paper by Raymond Pearl and John Rice 1 

 Miner having the same title and published in the Jour. Agr. Research,. 

 Vol. XVII, No. 6, pp. 285-323. 



