58 



Journal of Agricultural Research 



Vol. X, No. 2 



apparent digestibility of ash, which was observed when calcium carbonate 

 was fed, the variation in the digestion coefficients was not greater than 

 could be accounted for on the basis of the dry-matter content of the feces. 

 After careful and extensive feeding trials, it was found necessary to 

 abandon the use of rubber markers for determining the time for passage, 

 since the method had proved unreliable in each of the experiments. On 

 some of the rations the rubbers apparently passed through with the 

 feeds, while on other rations they either passed through ahead of the 

 food mass or were retained in the alimentary tract during an abnormally 

 long period. When the particles of the feed resembled the rubbers in 

 size, the markers would pass through with the feeds, but when there 

 were no coarse particles of feed in the ration, as in the case of rations 

 made up of cottonseed meal and starch, the rubber markers were passed 

 in some instances, while in others they were not. Furthermore, on the 

 same rations the extent to which the markers passed through seemed 

 partially dependent on the moisture content of the feces. 



in. ^SLAUGHTER TESTS 



A third method was used, based upon a digestion trial followed by a 

 slaughter test. A measure of the time required for the passage of the 

 residue of the feed was obtained by dividing the food and fecal dry- 

 matter content of the alimentary tract by half the sum of the dry matter 

 ingested and excreted per given unit of time. The inaccuracies of the 

 method, arising from certain metabolic processes, are recognized; but 

 their influence would be no greater on these results than on the diges- 

 tion coefficients, if as much. The data obtained from the digestion 

 trials are summarized in Tables 11, III, IV, and V. 



Table II. — Results of the digestion trials 



