174 Essay on the Interpretation of Milk Records. 



an approximate indication of the yield for the normal lactation 

 in gallons. A lower figure, say eighteen or nineteen, has to be 

 used for cows calving in spring or summer." 



The data given in the consideration of influence of season 

 of calving gave the following figures : — 



Average R.M. 

 Cows calving September — May 14-4 

 ,, ,. June — August 12'5 



This quite confirms Professor Wilson's figures, which he gives 

 approximately as twenty and eighteen or nineteen. 



Summary. 



{a) It seems necessary both for practical breeding on a 

 large scale and for scientific enquiry on the inheritance of 

 milk yield and allied questions, to be able to describe the 

 milking capability of a cow by a single unqualified figure. 



(6) In view of the large number of exterior influences that 

 afi'ect total yields over long periods (which are generally used in 

 milk records) it is advisable to adopt some additional descriptive 

 figure. 



(c) The maximum daj'-yield three times reached or exceeded 

 (" revised maximum ") is a useful figure for such a purpose. 

 It bears a close relationship to the total yield of a normal 

 lactation, and shows rather less variation than that total. It is 

 outside two of the most active external influences, namely 

 length of lactation and time of service, and it is suggested that 

 general environment has a minimum effect on it. Further, a 

 cow can usually be judged wdthin a few weeks of calving, since 

 normal lactation totals can be estimated from the R.M. with 

 considerable accuracy. 



{d) By making a few rough corrections to the R.M. (easily 

 embodied in a table) for age of cow and season of calving, the 

 most frequent range of variation found from year to year in 

 the same cow can be reduced from seven quarts to three and a 

 half quarts. It has not yet been found possible to bring it 

 below this figure. 



In conclusion, the author must thank Mr. A. V. Hill and 

 Mr. G. Udny Yule for their valuable criticisms and suggestions. 

 He also wishes to express his thanks to Lord Rayleigh and Mr. 

 E. G. Strutt, firstly for appointing him to this study and 

 secondly for their consideration and advice throughout the 

 two years during which the work has been in progress. 



Any useful results that may be obtained by the investigation 

 of their records is of course entirely owing to them, but for any 

 deficiencies in method, or treatment of the material, the author 

 is alone responsible. 



