A Critical Study of Energy Determination in Fresh and Dried Cow Feces

An accurate method of determining energy in fresh feces is described in detail.The energy content of eight samples of cow feces was deternfined in freeze-dried, oven-dried, and fresh feces.5{oisture was determined by freeze drying, by the toluene distillation method, and by oven drying at 80 ° C. The three methods are compared and discussed.The results of the duplicate energy determinations in the feces dried by two different methods, and the triplicate deternfinations in the fresh feces calculated on a comparable basis by means of the three different moisture determinations, are compared and evaluated and their errors discussed.The difference between the energy content of freezedried, oven-dried, and fresh feces calculated to a comparable basis by means of the most reliable water determination used in this study (freeze drying) was less than 2%.Two papers (2, 6) have been published recently dealing with the determination of energy in fresh cow feces employing a combustion primer.These investigators used ethanol to promote combustion and found energy values averaging 13.8% (range--4.1-20.9%)and 3.3 +_ 3.1% higher than when the same material was oven-dried and then burned in the usual way.The lower values in the ovendried material were attributed to fermentation and loss of ammonia and other volatile substances during the drying process.The first investigators (2) worked with feces having a dry matter content of 20-25%.The average dry nmtter content of cow feces collected in recent digestion trials at this station has been approximately 12% (range 10-14%).Complete combustion of such wet feces was found to be impossible when ] inl. of ethanol was added to a 2-g.sample.The senior author of this paper developed a new technique in 1956 to overcome this difficulty and has nmde a thorough, detailed study of the factors which affect the determination. EXPERIMENTAL PROCEDUREThe first step was an attempt to secure complete combustion by mixing ethanol with feces, using a short piece of glass rod (3 cm.long by 0.35 cm.diameter), the rod being left in the combustion cup during the determination.Control tests with benzoic acid showed no change in energy value due to inclusion of the glass rod.Complete combustion was attained by this procedure, but it at once posed another problem.The mixing process resulted in volatilization of a considerable amount of ethanol, which gave lower results and also made it very difficult to obtain triplicate determinations within an acceptable range of variation.The error was further compounded by the high ratio of the energy in the added ethanol to the energy in the sample of fresh feces (approxinmtely 5 or 6 : 1).l~or these reasons the use of ethanol as a primer was abandoned.