MEATS AS TEOUT FOOD 137 



MILK PRODUCTS 



We have used only two examples of dried milks in our experi- 

 ments — a dry skim milk and a dry buttermilk. The formei- is a 

 fine powder, which is readily soluble in water, while the latter is 

 insoluble and can be obtained in the form of meals of varying 

 degrees of coarseness. Some of the meals are ground very fine, 

 ! while the coarser grades may contain particles up to one-eighth of 

 Ian inch in diameter. 



McCay and his coworkers (McKay, Bing, and Dilley, 1927; 

 I McKay, Dilley, and Crowell, 1929) have obtained excellent results 

 I with dry skim milk and conclude that a mixture of skim milk and 

 beef liver is superior to beef liver alone. They were even able 

 to keep brook-trout fingerlings for 15 weeks on a diet of skim milk 

 and cod-liver oil with a 500 per cent increase in weight. At the 

 end of this time, however, the fish ceased to grow and began to 

 die rapidly. 



In our own experiments dry buttermilk has given better results 

 than skim milk, although the differential in favor of the former was 

 not great. Probably the superiority of buttermilk is due largely 

 to its insolubility. It is very difficult to feed dry skim milk with- 

 out a considerable percentage going into solution in the water before 

 the fish can get it. There is no evidence that the comparatively 

 high acidity of buttermilk has any deleterious effect on the fish. 



In order to determine the comparative value of clam meal, dry 

 buttermilk, and dry skim milk, three lots of brook fingerling during 

 the summer of 1929 were fed a ration composed of To per cent beef 

 liver, supplemented with either 25 per cent dry clam meal or the 

 same percentage of dry skim milk or dry buttermilk. (Fig. 3.) At 

 the end of the season the average individual weight of fish fed on 

 beef liver and clam meal was 5.i7 grams; of those fed on beef liver 

 and buttermilk, 3.72 grams; and of those fed beef liver and skim 

 milk, 3.50 grams. The differences in the mortality of the three lots 

 Avere not significant. 



Another lot of fish was kept on a ration made up of 40 per cent 



beef liver and 60 per cent " consolidated buttermilk." Although 



the fish in this lot made practically the same growth as those receiving 



beef liver and dry skim milk (Fig. 10) the results are believed to 



be of little value. The " consolidated buttermilk " has much the 



same consistency as clabbered milk, and consequently large amounts 



J are lost in feeding. In fact, so much of the buttermilk was lost that 



lit was necessary to feed much larger amounts of the mixture than in 



'the case of beef liver and dried milk. Consequently, the fish were 



actually receiving a much larger quantity of liver than is indicatecl 



by the composition of the ration, and it is probable that their rapid 



growth was largely due to this fact. 



Owing to the excessive waste in feeding " consolidated buttermilk " 

 and similar products they are a much less economical food for trout 

 than dry buttermilk. Aside from their food value, however, these 

 products appear to have a tonic effect; and where they can be ob- 

 tained at a low cost their inclusion in the diet may be advisable from 

 this standpoint. Trout appear to be very fond of all milk products, 

 either moist or dry, and their presence in a ration no doubt often 

 makes it more palatable. 



