July 9,1917 Rate of Passage of Food Residues through Steers 57 



II.— USE OF RUBBER MARKERS 



In order to determine more accurately the influence exerted on the 

 digestion coefficients by the rate of passage of the food residues, it was 

 necessary to develop a method by which we could determine with a 

 fair degree of accuracy the time required for the passage of the food 

 residues through the animal, a problem much more difficult in the case 

 of ruminants than in the case of animals with simple stomachs. So 

 far as. the' available literature shows, little study has been made on this 

 problem as applied to farm animals. Guernsey and Bv^''ard ^ have done 

 some work along 'this line with swine at the Iowa station. With swine 

 very good results can be obtained by the use of either bone black, car- 

 mine, finely ground charcoal, or of bismuth subnitrate or other bismuth 

 compounds, as indicators by feeding at a specified time and noting the 

 time of their first appearance in the feces as manifested by discoloration. 

 Indicators dependent on change of color in the feces can not be used on 

 ruminants, cattle in particular. In some manner they seem to "wash" 

 ahead of the feed and show an abnormally rapid passage. In order 

 to get a marker applicable to ruminants, we experimented with soft 

 rubber disks cut from heavy rubber tubing. One hundred of these were 

 fed at the beginning of a lo-day digestion trial and a count was made of 

 them as they appeared in the feces. By finding the number that appeared 

 during each 12-hour period we expected to obtain a fairly accurate 

 measure of the time required for the passage of the food residues. The 

 number of rubbers appearing up to 48 or 72 hours after feeding, for 

 example, should represent a measure of the feed fed at the same time as 

 the rubbers which had passed through. Some of the indicators appeared 

 within 12 hours, while others were recovered as late as 60 days following, 

 and still others never came out until the steers were slaughtered. 



The above-described plan of feeding markers with the ration was 

 followed out, using the same rations given in Table I. An attempt was 

 made to retard or hasten the passage of the food by feeding 60 or 120 

 gm. of calcium carbonate or magnesium sulphate so that the varia- 

 tions in time required for passage of the food residue might be more 

 marked even on the same ration. Naturally with the use of such small 

 amounts no great variations would occiir either in the time required for 

 passage or the moisture content of the feces. This was observed when 

 either of the two salts was fed. In order to determine what effects the 

 substances would have upon the digestion coefficients, comparisons were 

 made between the coefficients of each of the eight rations when fed with 

 120 and 60 gm. as against those obtained when none was fed. As well 

 as could be determined, there was very slight variation in the mois- 

 ture content of the feces; and, with the exception of a lowering of the 



> Guernsey, S. C, and Ewakd, J. M. the digestibiuty of maize consumed by swins. In 

 Biocbem. Bui., v. 3, no. ii/ia, p. 369-372. 1914. 



