670 EXPERIMENT STATION RECORD. 



cent ; eighth, 3.G9 per cent ; ninth. S-GO per cent ; tenth, .?.07 per cent ; and over 

 10 years, 3.75 per cent ; general average of 799 lactations, 3.69 per cent. 



(3) Variations according to the month Of the year : Normal fat content in 

 April, strong depression in May, June (minimum, 3.45 per cent), and July; 

 again average in August and rapid increase in September, with maximum (3.9G 

 per cent) in October; and slightly varying fat contents dliring the winter 

 months. 



(4) Variations according to the place of the month of calving in the calendar 

 year : Increased average fat contents in periods beginning in JMarch, August, and 

 September, and decrease in periods beginning in May and October. This varia- 

 tion is a direct residt of the preceding one. 



(5) The different power of cows for larger oF smaller production : Cows yield- 

 ing abnormally little milk have higher fat contents, and an abnormally high niilk 

 yield is accompanied by a lower fat content, while a« milk yield falling within 

 the natural variations of a family shows a normal fat content. 



(G) Changes in the normal milk production depending upon clianges in the 

 system of feeding : The milk yield stands in an inverse ratio to the fat content. 

 The variation refers to an entire year and months, as well as to short periods. 

 The variations in the fat content are, however, much smaller than that of milk 

 production. 



The curve for the average monthly fat content of the milk for the calendar 

 months April to October was found to correspond in a striking manner to the 

 corresponding part of the curve for cows calving in March to April, and the 

 author traces the cause on the hypothesis that March and April is the natural 

 calving time for cows, and that they, therefore, continue to change the fat con- 

 tent of the milk throughout the summer months in such a way as is best for the 

 calf when dropped at normal calving time. It is also shown that the difference 

 in the production of milk and fat during an entire lactation period caused by 

 the time of calving are very marked, amounting in the case of cows calving in 

 March and in August to about 18 per cent. In general, the milking periods com- 

 mencing during the winter months give larger yields than those that commence 

 during the summer. 



The influence of the individual variations was studied by the statistical 

 method, as was that of the normal variations. In this case, however, no such 

 large material was available. The largest series that was obtained consisted 

 of 7G daughters, but most of these, as well as their dams, were tested for more 

 than a year. In all, 584 determinations of the yearly fat production were made 

 in the case of the progeny of, or dams mated to, the four bulls included in the 

 investigation. Briefly stated, the conclusions drawn from this study are as 

 follows : The lower the fat content of the dam's milk, the more that of the 

 daughters is increased by the sire. If the fat contents of both parents appre- 

 ciably exceeds that of the average for the family, their united influence is not 

 able to increase the fat content of the daughters to the average of that of the 

 parents, against the influence of the family, but it will remain below that of the 

 parents. The fat content of the daughters is never the average of that of the 

 parents, but comes near to the average of the family. While the variations 

 studied in these investigations can not be taken to apply in all details to other 

 hei'ds and breeds of cattle, they may safely, in the author's opinion, be con- 

 sidered of general value, with the distinct limitation that their extent and their 

 development in certain directions may vary in different families and breeds. — 



F. w. WOI.L. 



Cow testing associations, with some notes on the sampling and testing 

 of milk, J. A. RuDDicK and C. F. V.'hitley (Canada Dept. Agr., Dairy Codii: 



