Oklahoma State University
Stillwater, OK

Oklahoma Alfalfa
Oklahoma Cooperative Extension Service
Oklahoma Agricultural Experiment Station

 

FORAGE QUALITY TESTING (RFV)
  
Forage testing provides alfalfa producers with quantitative measures of forage quality. The results from forage testing are used to calculate ration formulations, estimate feeding value, and establish market prices for various lots of hay.   

The OSU Soil, Water, & Forage Analytical Laboratory (SWFAL) measures three principal forage quality values: crude protein, acid detergent fiber (ADF), and neutral detergent fiber (NDF). These three values are then used to calculate the other quality parameters listed on the forage test report such as digestible protein, total digestible nutrients, and net energies for maintenance, lactation, and gain.   

Another quality parameter gaining interest among Oklahoma alfalfa producers is the relative feed value (RFV). Relative feed value is calculated using both ADF and NDF in the formula. The greater the RFV, the higher the quality of the forage in terms of animal intake and digestibility. The RFV of a forage has no specific nutritional meaning, however it can be used as a marketing tool for comparing feeding quality among various lots of hay. Remember, the protein level of forage must be evaluated independently, since crude protein is not included in the calculation of RFV.   

If you know the NDF and ADF values for a hay sample and want to  know the RFV of your alfalfa, use the following table listing RFV's for selected values of ADF and NDF to estimate it, or use the equation at the bottom of the table to calculate it directly. 
 

Calculated relative feed values (RFV) 
 
Selected values of acid detergent fiber (ADF) and neutral detergent fiber (NDF).* 
 
NEUTRAL DETERGENT FIBER (NDF)  
 ADF
30 32 34 36 38 40 42 44 46 48 50 52 54 56
227 213 201 189 179 171 162 155 148 142 136 131 126 122 20
225 211 198 187 178 169 161 153 147 141 135 130 125 121 21
223 209 196 185 176 167 159 152 145 139 134 128 124 119 22
220 206 194 183 174 165 157 150 144 138 132 127 122 118 23
218 204 192 181 172 163 155 148 142 136 131 126 121 117 24
215 202 190 179 170 161 154 147 140 135 129 124 120 115 25
213 200 188 177 168 160 152 145 139 133 128 123 118 114 26
197 186 175 166 158 150 143 137 132 126 121 117 113 27
195 184 173 164 156 149 142 136 130 125 120 116 111 28
181 171 162 154 147 140 134 129 123 119 114 110 29
179 169 160 152 145 139 133 127 122 117 113 109 30
167 159 151 143 137 131 125 120 116 112 108 31
165 157 149 142 135 129 124 119 114 110 106 32
155 147 140 134 128 122 118 113 109 105 33
153 145 138 132 126 121 116 112 108 104 34
143 137 130 125 119 115 110 106 102 35
142 135 129 123 118 113 109 105 101 36
133 127 121 116 112 107 103 100 37
131 125 120 115 110 106 102 99 38
124 118 113 109 105 101 97 39
122 117 112 107 103 99 96 40
115 110 106 102 98 95 41
114 109 105 101 97 93 42
107 103 99 95 92 43
106 102 98 94 91 44
100 96 93 89 45
99 95 91 88 46
94 90 87 47
92 89 86 48
87 84 49
  
*RFV calculated using the following equation: RFV = [88.9 - (0.779 x ADF)] x (120/NDF) x 0.775   

For additional information:  
Forage Quality Interpretations. OSU Extension Facts F-2117   

Hay Judging. OSU Extension Facts F-2588   

Collecting Forage Samples for Analysis. OSU Extension Facts F-2589 

Minimizing Losses in Hay Storage and Feeding

Understanding Forage Quality

 
Earl Allen, Former Soil Extension Specialist 
Department of Plant and Soil Sciences 
Oklahoma State University

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