SBW is shrunk body weight;

N is number of animals; and

DOP is days on pasture.

SUPPLY OF NUTRIENTS

Amounts are computed from actual dry matter intake when available or from predicted intake equation. Risk of use increases when predicted intakes are used versus actual DMI.

Level One

ENERGY

Ration energy values are computed by summing the energy contribution of each feed to arrive at a total energy content of the ration, using tabular energy values. Tabular energy values used include % TDN, ME (Mcal/kg), NEma (Mcal/kg), and NEga (Mcal/kg).

PROTEIN

Supply of metabolizable protein (MP) is the sum of digested ruminally undegraded feed protein and digested microbial protein. Feed composition parameters used include percentage CP, percentage UIP, and percentage DIP.

Undegraded available feed protein is assumed to be 80 percent digestible. Hence,

The contribution of microbial protein to the MP supply is estimated from the microbial crude protein yield.

where

MCP is microbial crude protein, g/d;

eNDFadj is 1.0 if the effective NDF (eNDF) of the ration is >20%;

eNDFadj is 1.0-((20-eNDF) * 0.025) when eNDF =20%;

TDN is total digestible nutrients, g/d;

MCP is assumed to be 80% true protein and 80% digestible, hence,

Level Two

Level 2 computes amino acid requirements and predicts energy and protein supply from feed physical and chemical properties. All energy and protein requirements are the same as level 1.)

AMINO ACID REQUIREMENTS FOR MAINTENANCE

where

MPmaint is metabolizable protein required for maintenance, g/d;

MPAAi is metabolizable requirement for the ith absorbed amino acid, g/day;

AATISSi is amino acid composition of tissue, Table 10–5.

AMINO ACID REQUIREMENTS FOR GROWTH

where

PB is protein content of empty body gain, g/100g;

EBG is empty body gain, g/d;

RPN is net protein required for growth, g/d;

RPAAi=growth requirement for the ith absorbed amino acid, g/d.

AATISSi is amino acid composition of tissue (Table 10–5);

EAAGi is efficiency of use of the ith amino acid for growth (Table 10–6), g/g, and

AMINO ACID REQUIREMENTS FOR LACTATION

where

AALACTi is the ith amino acid content of milk true protein, g/100g (Table 10–6);

Table 10–5 Amino Acid Composition of Tissue and Milk Protein (g/100 g of protein)

Amino acid

Tissuea

Milkb

Methionine

2.0

2.71

Lysine

6.4

7.62

Histidine

2.5

2.74

Phenylalanine

3.5

4.75

Tryptophan

0.6

1.51

Threonine

3.9

3.72

Leucine

6.7

9.18

Isoleucine

2.8

5.79

Valine

4.0

5.89

Arginine

3.3

3.40

aAverage of three studies summarized by whole empty body values of Ainslie et al., 1993.

bWaghorn and Baldwin, 1984.

cBased on hindlimb uptake studies (Robinson et al., 1995).

 



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