Page 157 - Calculating Agriculture Cover 20191124 STUDENT - A

CH 14] Calculating Agriculture 14-7

In a digestion trial, the percentage of each nutrient in the feedstuff is determined through
proximate analysis. A weighed amount of the feedstuff is then fed to the animal during the test period.
The feces are collected, weighed, and analyzed using proximate analysis (refer to Figure 14.1). The
amount of each nutrient digested is assumed to be the difference between the amount consumed and the
amount excreted. The proportion of each nutrient digested is the digestion coefficient for the nutrient in
that feedstuff.

Figure 14.3 Feedstuff composition — Average total composition

Total Average total composition Digestion Coefficient
Total Dig. Dig. Nutri-
Feeding stuff dry pro- nutria- tive Pro- N-free Mineral N-free
Matter tein ents ratio tein Fat Fiber extract matter Protein Fat Fiber extract
Dry Roughages Per ct. Per ct. Per ct. 1: Per ct. Per ct. Per ct. Per ct. Per ct. Per ct. Per ct. Per ct. Per ct.

Alfalfa Hay, all analyses . 90.5 10.9 50.7 3.7 15.3 1.9 28.6 36.7 8.0 71 30 45 70
Concentrates

Corn, dent, Grade No. 1 .. 87.0 6.9 81.9 10.9 8.9 4.0 2.0 70.8 1.3 77 90 57 93

Data is derived from Table 14.1

Example A Referring to Figure 14.3, how many pounds of TDN would 100 pounds of Corn, dent, Grade
No. 1 contribute to a feed ration?
Solution A
Digestion 14
Total % of nutrient x Coefficient = % digestible nutrient
In feed
Digestible Nutrient
(%) (lb)

Protein: 8.9% x 0.77 = 6.9 (protein) 6.9

Ether extract: 4.0% x 0.90 = 3.6(fat) 3.6
(fat)

Fiber: 2.0% x 0.57 = 1.1 (Fiber) 1.1

Nitrogen-free 70.8% x 0.93 = 65.8 (NFE) 65.8
extract (NFE)

To approximate the greater caloric value of fat, the percentage of digestible fat (the Ether extract) is
multiplied by 2.25. In the above example for corn, the TDN would be calculated as:

% %
Digestible protein ................................... 6.9 x 1 = 6.9
Digestible fat (Ether extract) .................. 3.6 x 2.25 = 8.1
Digestible fiber ...................................... 1.1 x 1 = 1.1
Digestible NFE ...................................... 65.8 x 1 = 65.8
81.9% TDN, or
81.9 lb TDN/100 lbs
Or as kg
(81.9 kg TDN/100kg)

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