AMINO ACID SUPPLY

Essential amino acid composition of the undegradable protein of each feedstuff is used to calculate supply of amino acids from the feeds. Microbial composition of essential amino acids are used to calculate the supply of amino acids from bacteria.

Bacterial Amino Acid Supply to the Duodenum

where

AABCWi is the ith amino acid content of rumen bacteria cell wall protein, g/100g (Table 10–7);

AABNCWi is the ith amino acid content of rumen bacteria non-cell wall protein, g/100g (Table 10–7);

REBCWj is the bacterial cell wall protein appearing at the duodenum as a result of fermentation of the jth feedstuff, g/day;

REBTPj is the bacterial non-cell wall protein appearing at the duodenum as a result of fermentation of the jth feedstuff, g/day, and

REBAAi is the amount of the ith bacterial amino acid appearing at the duodenum, g/day.

Bacterial Amino Acid Digestion

where

DIGBAAi is the amount of the ith absorbed bacterial amino acid, g/day;

Table 10–7 Amino Acid Composition of Rumen Microbial Cell Wall and Noncell Wall Protein (g/100 g of protein)

Amino acid

Cell wall

Noncell wall

Ruminal Bacteriaa

Mean

SD

Methionine

2.40

2.68

2.60

0.7

Lysine

5.60

8.20

7.90

0.9

Histidine

1.74

2.69

2.00

0.4

Phenylalanine

4.20

5.16

5.10

0.3

Tryptophan

1.63b

1.63

Threonine

3.30

5.59

5.80

0.5

Leucine

5.90

7.51

8.10

0.8

Isoleucine

4.00

5.88

5.70

0.4

Valine

4.70

6.16

6.20

0.6

Arginine

3.82

6.96

5.10

0.7

aAverage composition and SD of 441 bacterial samples from animals fed 61 dietary treatments in 35 experiments (Clark et al., 1992). Included for comparison to the cell wall and noncell wall values used in this model.

bData were not available, therefore, content of cell wall protein was assumed to be same as noncell wall protein (O’Connor et al., 1993).

 

Feed Amino Acid Supply

where

AAINSPij is the ith amino acid content of the insoluble protein for the jth feedstuff, g/100g;

REPB1j is the rumen escaped B1 protein from the jth feedstuff, g/day;

REPB2j is the rumen escaped B2 protein from the jth feedstuff, g/day;

REPB3j is the rumen escaped B3 protein from the jth feedstuff, g/day;

REPCj is the rumen escaped C protein from the jth feedstuff, g/day, and

REFAAi is the amount of ith dietary amino acid appearing at the duodenum, g/day.

Total Duodenal Amino Acid Supply

where

REAAi is the total amount of the ith amino acid appearing at the duodenum, g/day.

Feed Amino Acid Digestion

where

DIGFAAi is the amount of the ith absorbed amino acid from dietary protein escaping rumen degradation, g/day.

Total Metabolizable Amino Acid Supply

where

AAAsi is the total amount of the ith absorbed amino acid supplied by dietary and bacterial sources, g/day.

FEED COMPOSITION VALUES FOR USE IN THE NRC MODELS

A feed library developed for use with the computer models (Appendix Table 1) contains feed composition values that are needed to predict the supply of nutrients



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