June 17, 1918 Physical Changes in Feed Residues in Cattle 643 



COMMINUTION 



In but very few instances have efforts been made to measure the 

 extent, efficiency, and results of the comminution of coarse feeds during 

 the process of digestion. It has been recognized at all times that the 

 comminution of feeds was important in order to obtain the most com- 

 plete digestion. For example, old horses and cattle fail to fatten or 

 secure the fullest benefits from coarse feeds consumed when their teeth 

 become worn out or unsound, mastication being the most important 

 step in the comminution of feed, as shown by our results. The extent 

 of disintegration of coarse feeds is dependent on several factors, but 

 from our figures it is evident that the comminution of silage is over 90 

 per cent efficient, with 2 mm. as the dividing line. The silage as fed 

 was 100 per cent over 2 mm., while the residue of the feces over 2 mm. 

 was in every case less than 20 per cent. Since the dry matter of the 

 feces did not amount to 50 per cent of the dry matter of the feeds, it is 

 quite apparent that over 90 per cent of the silage consumed was reduced 

 from above 2 mm. to below 2 mm. 



The data showing the amounts of the contents of the organs above 

 and below 2 mm. furnish an indication of the extent of comminution 

 taking place in the various organs. The extent of comminution is 

 determined by difference, a method which possesses certain inaccuracies, 

 but which is probably the best method applicable to our figures. 



COMMINUTION IN MOUTH, RUMEN, AND RETICULUM 



A small amount of comminution may take place during prehension. 

 Most of it takes place, however, as a result of mastication, which may 

 be of one or two kinds: The preliminary, to prepare the bolus for deglu- 

 tition, or the final, which takes place much more slowly and completely 

 when the animal ruminates.* In this study we can secure a measure 

 of the total extent of comminution accomplished by mastication and 

 rumination by knowing the condition of the food as it is fed the animal 

 and by measuring the physical condition of the contents of the rumen, 

 reticulum, and other organs. 



A study of the data given in Tables IV and V shows that in the first 

 two rations, which were made up of silage alone, the extent of com- 

 minution taking place before the food leaves the rumen and reticulum 

 amounted to 65.8 per cent in the smaller ration and to 58.5 per cent in 

 the larger ration. This is in accord with previous results,^ when it was 

 found that a smaller quantity of silage was comminuted to a greater 

 extent than a larger quantity. When to these two rations were added 

 the 60 and 40 per cent of cottonseed meal, an increase resulted in the 

 extent of comminution of 5.1 and 10.5 per cent. 



1 Smith, Frederick, mantjai, op veterinary physiology. Ed. 4, p. 157. London, 1912. 



2 EwiNG, P. v.. Wells, C. a., and Smith, F. H. Op. cit. 



