MILK PRODUCTION 519 



above 0.4 to 0.5 pound per 1000 pounds live weight, although a 

 gain may result with individual cows. 



613. The minimum of feed fat. On the other hand, the 

 extensive investigations by Morgen and his associates on sheep 

 and goats, already referred to (599) , have shown that with these 

 animals an increase of the fat content of rations exceptionally 

 deficient in this ingredient results in most cases in an increased 

 yield of milk solids and especially in a specific increase of the 

 fat content of the milk. 



The rations consisted of a basis of roughage poor in fat J to which 

 various commercially pure nutrients were added. Fat in various 

 forms was added to scant basal rations and likewise substituted for 

 carbohydrates or protein in heavier rations. Experiments of the latter 

 sort, in which the energy content of the rations was kept substantially 

 unchanged, are especially convincing. An increase of the fat content 

 of the fat-poor rations, either by direct addition or by substitution, 

 up to 0.5 to i.o Ib. per 1000 Ib. live weight not only resulted in a 

 distinct increase in the yield of milk and of milk solids but likewise 

 in an increased percentage of fat in the fresh milk and in the milk 

 solids. This specific influence of fat as compared with protein is 

 illustrated in Table 140, which shows that while a substitution of 

 protein for fat or for carbohydrates increased the yield of solids, 

 -the yield of fat was decreased in the former case. Fingerling 2 has 

 likewise shown that increasing the fat content of a ration by substi- 

 tuting a feed rich in fat for one rich in carbohydrates (rice meal in 

 place of barley meal) likewise increases the fat yield. 



This specific effect of feed fat on the production of milk fat 

 appears to be more marked in the case of sheep and goats than 

 in the case of cows. It was observed up to a limit of approxi- 

 mately i.o pound per 1000 pounds live weight, but above that 

 the results were if anything negative, while with cows, as al- 

 ready shown, an increase of the digestible fat above 0.4 pound 

 per 1000 pounds live weight generally produces little or no 

 effect. Morgen ascribes the difference to the greater relative 

 production of fat per unit of weight by the smaller animals. 



In ordinary dairy rations fat will not often fall below the 

 apparent limit of 0.4 to 0.5 pound. Only when feeds unusually 

 poor in fat are used, such as straw or inferior grades of hay or 



1 In part artificially extracted. 2 Landw. Vers. Stat., 64 (1906), 299. 



