VITAMINS ▶▶▶


Factors affecting vitamin B synthesis in the rumen


BY SALAH H. ESMAIL, PHD B


vitamins are a class of water-soluble vitamins that contain chemically distinct compounds such as thi- amine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9) and


cobalamin (B12). These compounds play a vital role in cell metabolism, synthesis of red blood cells, and other biological functions. Ruminant animals are capable of synthesising these compounds through the microbial action taking place in the rumen (see Table 1). The rate of synthesis is influenced by several factors but with different responses, i.e. some B vi- tamins may respond positively to a given factor while nega- tive responses may be observed with others. It is therefore important to consider these factors when planning a feeding programme to meet the requirement for a specific vitamin and hence achieve the target performance.


Forage-to-concentrate ratio In one study, concentrations of folates in the rumen fluid were higher in steers fed a diet with a hay-to-concentrate ra- tio of 30:70 than than those fed a diet with a ration of 70:30. In other studies, thiamin, pantothenic acid, folic acid, niacin, and cobalamin were found in greater concentrations in the rumen fluid of steers fed all-concentrate rations, compared to those fed hay in their rations.


Effect of dietary nitrogen The addition of urea as a source of nitrogen increased the synthesis of riboflavin, nicotinic acid, biotin, and pantothenic acid in the bovine rumen when a readily available carbohy- drate was present. Pyridoxine and folic acid were not too closely correlated with ration composition.


Effect of dietary carbohydrates The addition of starch to the diet resulted in increased syn- thesis of B vitamins, particularly riboflavin. In one study, the starch was added at low, moderate, and high levels to diets of lactating cows, and the amounts of riboflavin synthesised in


▶ ALL ABOUT FEED | Volume 29, No. 2, 2021 31


Ruminants are capable of synthesizing B vitamins. The rate of synthesis is influenced by a variety of factors.


the rumen were 16.6, 17.0, and 24.4 microgram/g, respective- ly. Similar responses were noted with niacin and pantothenic acid, but to a lesser extent when graded levels of starch were added to the diet.


The physical form of the feed The riboflavin content was higher when the corn was ground than when it was fed in intact form. Similar responses were noted with ground alfalfa hay, where the amount of thiamine synthesised in the rumen increased by 2-3 fold compared to that synthesised with intact alfalfa hay. The increased values found when ground corn or alfalfa was fed were due to the greater concentration of carbohydrates and water-soluble material per gram of dry ingested feed, resulting in an in- crease in rumen bacterial growth.


Acidosis In rumen acidosis, there is an initial decrease in rumen pH, primarily due to an increase in organic acids. As the pH is _


The rate of Vita- min B synthesis is influenced by several factors. It is therefore important to consider these factors when planning a feed- ing programme.


PHOTO: SHUTTERSTOCK


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