CHAPTER V 
DETERMINATION OF THE NUTRITIVE VALUE OF 
FEEDING STUFFS 
THE nutritive walue of different feeding stuffs may be determined 
by two different methods: First, by chemical analysis and digestion 
trials with farm animals; second, by trials with animals in a respira- 
tion apparatus or respiration calorimeter. The first method shows 
the proportions of the feeds that are dissolved in the digestive 
processes, while the second method furnishes direct information as 
to the nutritive effect of the feeds or rations and shows the uses 
which an animal makes of the feed eaten. 
Digestion Trials—The digestibility of feeding stuffs is deter- 
mined in so-called digestion trials with animals. Numerous such 
trials have been conducted with ruminants during the past half- 
century in this country and abroad, and a number of trials have 
also been conducted with horses, pigs, and poultry. In these trials 
the animals experimented with are fed the feeding stuff whose 
digestibility is to be determined, for a period of about a week, and 
the solid excrements voided by the animal are then collected for 
another week. Samples of both the feed eaten and of the feces are 
taken for chemical analysis, and by a comparison of the total 
amounts of feed components in each the proportion of each com- 
ponent retained or digested by the animal may be determined and 
calculated on a basis of percentage digestibility. An example will 
readily explain the method of calculation. 
In an experiment by the author, in which the digestibility of 
corn silage was to be determined, a cow was fed, on the average, 
55.0 pounds of silage per day; a small amount, 0.71 pound, was re- 
fused. She voided 58.8 pounds of dung daily during the trial. 
Chemical analyses were made of both the silage fed and that refused, 
as well as of the dung voided. The digestion coefficients for the 
silage were then calculated as shown below: 
Digestion Trial with Corn Silage 
Dry ' |Nitrogen- 
Protein, Fat, iber, f ; 
Sends pounds pounds gown decrack, sas 
: pounds 
In 54.3 pounds of silage. .| 20.55 ‘| 1.52 67 4.25 | 13.23 88 
In 58.8 pounds of dung. .| 7.62 .68 12 2.29 3.73 72 
Digested...... biciethaetaaNs 12.93 84 55 1.96 9.50 .16 
Digested in per cent.....| 62.9 55.3 82.1 45.4 71.8 18.2 
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