[ 478 J 



XXXVI. 



THE INFLUENCE OF FEEDING ON MILK FAT. 



By E. J. SHEEHY, F.E.O.Sc.L, B.Sc, M.E.LA. 

 [Bio-Chemical Laboratory, D.A.T.I.] 



[Read February 28. Published April 13, 1922.] 



Each individual species of mammal produces milk of composition peculiar to 

 its own group, but among domesticated animals the proportion of some of 

 the constituents, especially that of fat, to the total milk yield varies con- 

 siderably in the different varieties of each species, in the different strains 

 inside a variety, and, further, even in the individuals of any single strain. 

 The variation in the percentage of fat in the milk of cows and goats, for 

 instance, is practically due to the selection exercised by man ; indeed it has 

 long been recognised that selection is the principal method available to 

 the stock-breeder for raising milk fat percentage. 



The influence of feeding on milk fat has been the subject of frequent 

 investigation, but very little precise information on the subject is available. 

 Speir [1894, 6 and 7] compared a large number of rations, all liberal in 

 quantity, with one another for the purpose of milk and butter fat production 

 in the dairy cow, and came to the general conclusion that the criterion of 

 efficiency in a ration is its total dry matter. But he was of opinion that 

 some foods tend to increase the milk yield, while others tend to increase the 

 milk fat principally. Fresh grass and brewers' grains, he states, tend to 

 increase the milk yield at the expense of the percentage of butter fat ; on 

 the other hand, vetches and decorticated cotton cake tend to increase the 

 percentage of fat at the expense of milk yield. It is significant that both of 

 these foods contain a high proportion of protein ; in fact, Speir concludes 

 that rations with a very high albuminoid ratio seem to have a depressing 

 effect on the milk yield. On the other hand, Crowther [1906], reviewing 

 the work done in Great Britain for some years previously, makes the following 

 statement : " Such changes as may possibly be effected in the quantitative 

 composition of milk by change of food are only very slight, provided, of 

 course, the rations prior and subsequent to the change are suitable in nature 

 and in quantity." Wing and Foord [1904] record an attempt to increase 

 the fat in milk by means of liberal feeding, and state that in a herd of poorly 



