<< A2. Adjusted Crude Protein

Appendix B - Predicting Minerals by NIR >>

A3. Estimates of Energy Availability

Scope:
The following equations are applicable for the estimation of energy in forages for ruminants. Prediction of energy availability from laboratory analyses usually requires specific equations for each type of feed. The accuracy of energy predictions is a function of the accuracy of laboratory analyses and the accuracy of the animal experimentation used to develop the prediction equation. Digestibility and energy value can be measured under a variety of conditions that influence the values that are obtained. Compared to cattle, sheep will obtain different digestibilities for the same feed. In addition, the level of feed intake of the animal has a significant effect on the digestibility of the feed and the utilization of its energy. For dairy cows, each level of intake above maintenance (the amount of feed needed to maintain a nonproducing animal's weight) reduces digestibility by about 4%. The dairy NRC assumes that lactating cows eat at 3X maintenance and reduces digestibility to 92% of that measured at maintenance.

Another major variable affecting the measurement of digestibility is the amount of selection allowed by the animal. Given a choice, most animals will eat the high protein, low fiber part of the feed (leaves) and leave the high fiber part (stems). Methods used to measure digestibility vary. Some scientists restrict the amount offered to the animal thereby encouraging the animal to consume it all. In this case a core sample of the feed represents what the animal consumed. However, most scientists measure ad libitum intake and digestibility in the same trial by offering the animals 5 to 15% more than they consume. Because they selectively consume the feed, a core sample may not represent the feed actually consumed and regression equations from these trials will be biased. Unfortunately it is difficult to uncover the exact techniques used to develop many of the equations for predicting energy value.

Basic Principle:
Available energy and digestibility cannot be measured in the laboratory and is estimated from chemical composition. Most energy values are predicted from fiber analyses because fiber is negatively related to the animal's ability to digest and use nutrients in the feed. Various groups have developed equations for predicting energy value and several are provided in the following tables for your consideration. Comparisons of the predictions of the various equations are given in tables 6 and 7. National Research Council (NRC) values are given for comparison, but it should be recognized that the source and accuracy of NRC values are also unknown.

Total digestible nutrients (TDN) is the sum of digestible protein, digestible carbohydrates and digestible fat (fat is multiplied by 2.25 to adjust for its higher energy content). In general TDN is highly correlated with digestible dry matter (DDM) and digestible energy (DE). Estimated net energy (ENE) is a term formerly used to estimate net energy for production (weight gain or milk). Net energy of lactation (NEL) is the current term used by NRC for assessing the energy requirements and feed values for lactating cows. All equations express ADF, NDF, TDN and DDM as percentages (1 to 100) and ENE and NEL are expressed as Mcal/lb.

Table 1. Prediction Equations from Midwest   

Legume and Grass Forages
%DDM = 88.9 - (0.779 x ADF)a

Corn Silage
%TDN = 87.84 - (.70 x ADF)b

Shelled Corn
%TDN = 92.22 - (1.535 x ADF)c
NEL (Mcal/lb) = 0.905 - (0.0026 x ADF)c

Ear Corn
%TDN = 99.72 - (1.927 x ADF)c
NEL (Mcal/lb) = 1.036 - (0.0203 x ADF)c

TDN conversion to NEL
NEL (Mcal/lb) = (TDN x .01114) - 0.054d
______________________________________________________________
a Source: Rohweder, Barnes and Jorgensen, J. Anim. Sci. 68:403
b Source: Schmidt et al., Agron. J. 68:403
c Source: Pennsylvania State
d Source: NRC, Dairy Update, 1989


Table 2. Prediction equations from Pennsylvania Statea
Legumes
%TDN = 4.898 + (89.796 x NEL)
ENE (Mcal/100 lb) = NEL x 82.6
NEL (Mcal/lb) = 1.044 - (0.0119 x ADF)

Mixed Forages
%TDN = 4.898 + (89.796 x NEL)
ENE (Mcal/100 lb) = NEL x 82.6
NEL (Mcal/lb) = 1.0876 - (0.0127 x ADF)

Grasses
%TDN = 4.898 + (89.796 x NEL)
ENE (Mcal/100 lb) = NEL x 82.6
NEL (Mcal/lb) = 1.0876 - (0.0127 x ADF)

Corn Silage
%TDN = 31.4 + (53.1 x NEL)
ENE (Mcal/100 lb) = NEL x 82.6
NEL (Mcal/lb) = 1.044 - (0.0124 x ADF)

Sorghum, Small Grain Forages
%TDN = 4.898 + (89.796 x NEL)
ENE (Mcal/100 lb) = NEL x 82.6
NEL (Mcal/lb) = 0.7936 - (0.00344 x ADF)



Complete Rations
%TDN = 93.53 - (1.03 x ADF)
ENE (Mcal/100 lb)= 82.04 - (0.76 x ADF)
NEL (Mcal/lb) = (TDN x 0.0234) - 0.5448

Grain Mixtures (CF = crude fiber)
%CF = ADF x .80
%TDN = 81.41 - (0.60 x CF)
ENE (Mcal/100 lb) = 90.02 - (1.0532 x CF)
NEL (Mcal/lb) = (TDN x 0.0234) - 0.5448

Ear Corn
%TDN = 99.72 - (1.927 x ADF)
ENE (Mcal/100 lb) = TDN x 1.025
NEL (Mcal/lb) = 1.036 - (0.0203 x ADF)

Shelled Corn
%TDN = 92.22 - (1.535 x ADF)
ENE (Mcal/100 lb) = TDN x 1.053
NEL (Mcal/lb) = 0.950 - (0.0026 x ADF)

Small Grains
%TDN = 4.898 + (89.796 x NEL)
ENE (Mcal/100 lb) = 96.0548 - (0.8929 x ADF)
NEL (Mcal/lb) = 0.9265 - (0.00793 x ADF)
_________________________________________________
a Source: Proceedings 41st Semiannual Meeting,
1981. Am. Feed Manufacturers Association.
Lexington, Ky. p16-17.



Table 3.  Equations from Western Regiona             

Alfalfa    
%TDN = 82.38 - (0.7515 x ADF)
NEL (Mcal/lb) = 0.8611 - (0.00835 x ADF)
____________________________________________
aBath, Donald L. and Vern L. Marble. 1989. Testing Alfalfa for Its Feeding Value. Univ of CA.
Cooperative Extension. Leaflet 21457. (WREP 109).


Table 5. Prediction equations from D.R. Mertens (personal communication)                

Legumes
%TDNm = 86.2 - (0.513 x NDF)
NEL (Mcal/lb) = 1.054 - (0.0098 x NDF)

%TDNm = 84.2 - (0.598 x ADF)
NEL (Mcal/lb) = 1.011 - (0.0113 x ADF)

Grasses
%TDNm = 105.2 - (0.667 x NDF)
NEL (Mcal/lb) = 1.297 - (0.119 x NDF)

%TDNm = 97.6 - (0.974 x ADF)
NEL (Mcal/lb) = 1.120 - (0.0159 x ADF)
______________________________________________


Table 4.  Prediction Equations from New York State
Grasses
%TDN = 34.9 + (53.1 x NEL)
ENE (Mcal/lb) = NEL x 0.826
NEL (Mcal/lb) = 1.085 - (0.0150 x ADF)

Legumes
%TDN = 29.8 + (53.1 x NEL)
ENE (Mcal/lb) = NEL x 0.826
NEL (Mcal/lb) = 1.044 - (0.0123 x ADF)

Mixed Forages
%TDN = 32.4 + (53.1 x NEL)
ENE (Mcal/lb) = NEL x 0.826
NEL (Mcal/lb) = 1.044 - (0.0131 x ADF)

Complete Feed
%TDN = 95.88 - 0.911 x ADF
ENE (Mcal/lb) = 1.0123 - (0.01432 x ADF)
NEL (Mcal/lb) = 0.866 - (0.007 x ADF)


Grain mix
%TDN = 81.41 - (0.48 x ADF)
ENE (Mcal/lb) = 0.9002 - (0.0084 x ADF)
NEL (Mcal/lb) = [(TDN x 0.0245) - 0.12] x 0.454

Ear Corn
%TDN = 99.72 - (1.927 x ADF)
ENE (Mcal/lb) = TDN x 1.025
NEL (Mcal/lb) = 0.94 - (0.008 x ADF)

Shell Corn
%TDN = 92.22 - (1.535 x ADF)
ENE (Mcal/lb) = TDN x 0.01053
NEL (Mcal/lb) = 0.94 - (0.008 x ADF)

Corn Silage
%TDN = 31.4 + (53.1 x NEL)
ENE (Mcal/lb) = NEL x 0.826
NEL (Mcal/lb) = 0.94 - (0.008 x ADF)
__________________________________________________________________________   


Table 6.  Comparison of TDN prediction equation for alfalfa and legumes.                  

       Table 3	Table 1	Table 2	Table 4	Table 5	
        NRC	Western	Midwest	Penn St	NY	Mertens	Mertens
        Alfalfa	Alfalfa	Gr.&Leg	Legume	Legume	Legume	Legume
ADF	%TDN	%TDN	%TDN	%TDN	%TDN	%TDNm	%TDN3X
__________________________________________________________________________

27	68	62.1	67.9	69.8	67.6	68.1	62.6
29	63	60.6	66.3	67.7	66.3	66.9	61.5
31	60	59.1	64.8	65.5	65.0	65.7	60.4
33		57.6	63.2	63.4	63.7	64.5	59.3
35	58	56.1	61.6	61.2	62.4	63.3	58.2
37	55	54.6	60.1	59.1	61.1	62.1	57.1
39		53.1	58.5	57.0	59.8	60.9	56.0
41		51.6	57.0	54.8	58.5	59.7	54.9
43		50.1	55.4	52.7	57.2	58.5	53.8
___________________________________________________________________________



  
Table 7.  Comparison of TDN prediction equations for grasses.                 

	Table 1	Table 2	Table 4	Table 5	
	NRC	Midwest	Penn St	NY	Mertens	Mertens
	Grass	Gr.&Leg	Grass	Grass	Grass	Grass
ADF	%TDNa	%TDN	%TDN	%TDN	%TDNm	%TDN3X
________________________________________________________________

27		67.9	71.8	71.0	71.3	65.6
29	74	66.3	69.5	69.4	69.4	63.8
31	71	64.8	67.2	67.8	67.4	62.0
33	69	63.2	64.9	66.2	65.5	60.2
35	67	61.6	62.6	64.6	63.5	58.4
37	64	60.1	60.4	63.0	61.6	56.6
39	62	58.5	58.1	61.5	59.6	54.8
41	60	57.0	55.8	59.9	57.7	53.1
43	57	55.4	53.5	58.3	55.7	51.3
________________________________________________________________
a NRC Grass is an average of bromegrass, orchardgrass and ryegrass.
  NRC timothy was 7 to 8 %-units lower in TDN at each level of ADF.
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