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XLII. 



POSSIBLE CAUSES OF VARIATION IN THE QUANTITY AND 

 QUALITY OF COWS' MILK. 



By E. J. SHEEHY, F.R.C.Sc.L, 

 Demonstrator in Zoology, Royal College of Science, Dublin. 



[COMMUNICATED BY PROFESSOR J. WILSON, M.A., B.SC.] 

 [Read December 17, 1918 ; published May 26, 1919.] 



The cow normally produces milk which is inconstant in quantity and quality. 

 When milking is performed at equal intervals, twice daily, the percentage of fat 

 is very slightly higher after the day interval than after the night one. 1 When 

 the intervals are unequal the quantities of milk are, more or less, in the direct 

 ratio, and the percentages of fat in the indirect ratio of the times after which 

 milking takes place. The total fat yield after the short interval is, however, 

 practically equal to that given after the long one. 2 In successive-day yields 

 the quantities of milk and of butter-fat vary considerably. The variation in 

 total milk is accompanied by more or less similar variation in solids -not-fat 

 and water, but the total fat seems to vary in a fashion peculiar to itself. 3 



Some of these peculiarities may be explained as the effect of external 

 influences. 4 Thus the conditions obtaining during the day seem to have a 

 slightly different effect on a cow's milk-yielding capacity from those which 

 prevail at night; violent weather changes seriously affect the condition of 

 some cows, and the maimer of treatment undoubtedly so influences the 

 nervous condition that there is a probable effect on the milk yield. None 

 of these things explains all the phenomena of variation outlined above. It 

 is necessary to refer to the " individuality " of the cow, and to explore the 

 complex mechanism and co-ordinated activities of the milk-producing organs 

 for the basis of an explanation. 



1 '•'Variation in the Composition of Cows' Milk," Crowther, Journal of Agricultural 

 Science, vol. i, p. 153. 



2 Ibid. 



3 Sheehy : Scientific Proceedings of the Royal Dublin Society, vol. xv, No. xl. 



4 "Variation in the Composition of Cows' Milk," Crowther, Journal of Agricultural 

 Science, vol. i, p. 152. 



SCIENT. PROC. R.D.S., VOL. XV., NO. XLII. 4 Z 



