SECTIONAL TRANSACTIONS.— M. 635 



Monday, September 10. 



Dr. J. F. TocHEE.— ^ Milk Survey : Recent Results of a Study of the 

 Variations in the Compositiojt of Milk. 



For the past fifteen years a systematic study has been made of the composition 

 of cows' milk from many thousands of cows. Variations in composition have been 

 determined for different breeds of dairy cows, different ages of cows, and different 

 durations of lactation period, seasons and areas. The proportions of butter fat and 

 solids not fat vary widely during a lactation period and decrease steadily with age 

 of cow. A positive correlation exists between butter-fat and solids-not-fat percentages 

 in samples of milk from individual cows taken on the same day. Thus a good butter- 

 fat producer is, on an average, a good soUds-not-fat producer. On the other hand a 

 negative correlation has been found to exist between butter-fat and soUds-not f at per- 

 centages in the daily samples of bulked milk from the same herd. This is duo to the 

 tendency of a herd to give day after day a constant proportion of total soUds (i.e. 

 butter fat plus solids not fat). Daily samples of bulked milk from a fairly large herd 

 show greater variations in constituents than have hitherto been supposed. As expected, 

 the smaller the herd the greater were the daily variations in the constituents. Friesians 

 show the highest proportion of sugar and the highest yield of butter fat for a lactation 

 period, both owing to their higher yields. Ayrshires show the highest proportions of 

 protein and butter fat. The system of milk recording which has been in existence in 

 Scotland for twenty-five years has had a very material effect in improving the quality 

 of milk among the herds of members of the Scottish Milk Records Association. Yield 

 of milk has been found to be largely a function of age as well as a function of breed, 

 duration of lactation period, and other factors. It is to be noted that the data obtained 

 from the Scottish Milk Records Association are data of cows which are more or less 

 selected. It might thus be held that yield was a function of age because of this 

 selection. It has, however, been established that yield is a function of age both for 

 selected and unselected groups of cows. A selected group differs markedly from an 

 unselected group in showing increased yield with age from seven years onwards. 

 The effect of the elimination of poor milkers at the younger ages is clearly evident in 

 the increased yield among the older cows in JJhe selected herds when compared with 

 the corresponding yields of older cows in unselected herds. An important fact must 

 however be specially noted, namely, that the variabihties of yield for various ages 

 increase steadily with age. Selection is, therefore, not stringent. The least variable 

 over a period of years in average weekly yield of good cows should be selected for milk 

 production for succeeding lactation periods. 



The following figures are abstracted from a table in a memoir about to be published 

 showing the average yield of butter fat in pounds for a given age of cow and a given 

 length of lactation period. This table should prove of practical value to milk 

 producers. 



Weeks in Age of Cow. 



Milk 23456789 10 II 



26 132 147 160 171 180 186 190 192 191 189 pounds 

 38 210 227 241 253 263 271 276 279 280 279 

 50 276 294 309 323 334 343 349 354 356 355 



Mr. A. E. Magee. — Milk Selling Agency. 



Prof. R. A. Berry and Mr. A. Macneilage. — Utilisation of Surplus Milk 

 and Milk Residues. 



Afternoon. 



Mr. H. R. Davidson. — Reproductive Disturbances caused by Feeding 

 Protein-deficient and Calcium-deficient Rations to Breeding Pigs. 



The number of foetuses which undergo atrophy in the uterus of the sow is known 

 to be large, and according to the investigations of Marshall and Hammond this 

 degeneration is due neither to bacterial infection nor to overcrowding. A genetic 

 lethal factor has been suggested, but as atrophy takes place at all stages of development 



