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<p><strong>B-vitamins are a group of 8 water soluble vitamins that play important roles in cell metabolism. They can not be produced by the body itself, but can be produced by bacteria, fungi and plants. In the horse, microorganisms in the gut (mainly the hind gut) is capable of synthesizing B-vitamins and nutrient requirements have only been established for thiamin (B<sub>1</sub>) and riboflavin (B<sub>2</sub>). In this article we will look at the function, dietary sources and requirements for riboflavin (vitamin B<sub>2</sub>).</strong></p>
<p><img style="vertical-align: middle;" src="images-joomla/stories/seasons/riboflavinformel.png" alt="riboflavinformel" width="250" height="250" /><img style="vertical-align: middle;" src="images-joomla/stories/seasons/grazingnight.jpg" alt="grazingnight" />&nbsp;</p>
<p><strong>Function</strong><br />Riboflavin is a precursor to the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). Both are involved in oxidation-reduction reactions used in energy metabolism (ATP synthesis), lipid metabolism and antioxidant defense mecanisms.</p>
<p><br /><strong>Dietary sources</strong><br />Riboflavin is found in relatively high concentrations in legumes like lucerne and clover and slightly less in grass hays (see table).</p>
<table style="border-collapse: collapse;" border="1" cellspacing="0" cellpadding="0">
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<td style="width: 91.9pt; border: 1pt solid windowtext; padding: 0cm 5.4pt;" valign="top" width="92">Legumes</td>
<td style="width: 4cm; border-width: 1pt 1pt 1pt medium; border-style: solid solid solid none; border-color: windowtext windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="113">13-17 mg/kg DM</td>
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<td style="width: 91.9pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="92">Grass hays</td>
<td style="width: 4cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="113">7-10 mg/kg DM</td>
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<td style="width: 91.9pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="92">Cereal grains</td>
<td style="width: 4cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="113">1.4-1.7 mg/kg DM</td>
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<p style="line-height: normal;">These concentrations of riboflavin in feeds will be reduced to about 70% during 1 year storage.</p>
<p>Riboflavin is included in most concentrate mixtures for horses (5 – 15 mg/kg) and in vitamin supplements.</p>
<p><strong>Requirements<br /></strong>Riboflavin is absorbed with decreasing efficiency with increasing amounts ingested. Excess is rapidly excreted in the urine, and there is little storage in the body.</p>
<p>The NRC 2007 gives requirements for riboflavin for horses (see table).</p>
<table style="border-collapse: collapse;" border="1" cellspacing="0" cellpadding="0">
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<td style="width: 106.1pt; border: 1pt solid windowtext; padding: 0cm 5.4pt;" valign="top" width="106">Maintenance</td>
<td style="width: 5cm; border-width: 1pt 1pt 1pt medium; border-style: solid solid solid none; border-color: windowtext windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="142">0.04 mg/kg body weight</td>
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<td style="width: 106.1pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="106">Light exercise</td>
<td style="width: 5cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="142">0.04 mg/kg body weight</td>
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<td style="width: 106.1pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="106">Moderate exercise</td>
<td style="width: 5cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="142">0.04 mg/kg body weight</td>
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<td style="width: 106.1pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="106">Heavy exercise</td>
<td style="width: 5cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="142">0.05 mg/kg body weight</td>
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<td style="width: 106.1pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="106">Very heavy exercise</td>
<td style="width: 5cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="142">0.05 mg/kg body weight</td>
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<td style="width: 106.1pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="106">Pregnant mares</td>
<td style="width: 5cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="142">0.04 mg/kg body weight</td>
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<td style="width: 106.1pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="106">Lactating mares</td>
<td style="width: 5cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="142">0.05 mg/kg body weight</td>
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<td style="width: 106.1pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="106">Growing horses</td>
<td style="width: 5cm; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="142">0.05 mg/kg body weight</td>
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<p><strong>Deficiency<br /></strong>Riboflavin is produced by microorganisms in the intestine of the horse and deficiency has not been described.</p>
<p><strong>Toxicity<br /></strong>As riboflavin is a water-soluble vitamin, excess intake will be excreted in the urine. Riboflavin toxicity in horses has never been reported.</p>
<p><strong>PC-Horse<br /></strong>PC-Horse calculates requirements for riboflavin individually for each horse according to the NRC recommendations. It has also included values for riboflavin (vitamin B<sub>2</sub> ) in all feed tables. When composing rations for your horse using PC-Horse, you will always be able to control that your horse’s riboflavin intake is in accordance with its requirements.</p>
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<p style="margin-top: 0.1pt; margin-right: 0cm; margin-bottom: 0.1pt;"><em>This article was originally written by Dr. Day Austbø.</em><br /> <em>Copyright: PC-Horse International - Norway 2015</em><br /> <em>Feel free to use and publish the material. Please indicate the source and author.</em></p>