Vitamins and trace minerals are routinely added in almost every commercial feed for all animal species, making their manufacturing, distribution, marketing and sales a global industry worth billions. Although their cost is relatively small, most would argue it is less than 2 percent of total feed cost; it is not insignificant — especially in an industry that often records losses instead of profits. Thus, every prudent nutritionist would be wise to constantly evaluate the vitamins and trace minerals added, their most efficient form and, of course, their payback in terms of animal productivity and health.
Wasting nutrients is no longer trendy
Vitamins and trace minerals are naturally found in most feedstuffs in variable amounts. Nutritionists, however, have routinely ignored these contributions (as we were taught at graduate schools) and supplemented animal diets with these micronutrients using premixes. Quite often, and this was the norm rather than the exception, these supplemental levels were in gross excess of established requirements. This was done based on two assumptions: some vitamins were prone to destruction before reaching the animal, and it did not cost much to be over-generous. Today, it is not as simple, because these supplements are more expensive and we have a better knowledge not only of animal requirements, but also how sensitive vitamins can be protected.
Lack of official scientific data supports waste
The recent report of the National Research Council’s Subcommittee in Swine Nutrition (2012) repeats the findings of the previous version (1998) that there is still considerable lack of meaningful research concerning the actual vitamin and trace mineral requirements of pigs. The relevant publication for poultry dates from 1994, which makes it 20 years old now, and rather of academic interest only. On the other hand, poultry breeder recommendations are nothing more than educated guesses, based on their desire for their genetics to always perform at top speed. Therefore, more research is needed to fill this gap in our knowledge of vitamins and trace minerals, but funding is usually diverted to more trendy topics or additives.
More research is needed to fill this gap in our knowledge of vitamins and trace minerals, but funding is diverted usually to more trendy topics or additives.
Which vitamins and trace minerals should be added?
One of the (good) reasons for over-supplementation is of variable concentration, which can be resolved by a vigorous national testing scheme for major ingredients, and largely unknown bioavailability (here, again, more research is needed especially for common ingredients like cereals and soybeans). It should be noted, however, that we already depend on natural feedstuffs to cover requirements for a number of water-soluble vitamins and semi-essential trace minerals that are not usually included in most premixes (these include biotin, folate, chromium, vanadium, boron, etc.).
The most common trace minerals added to diets are iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), iodine (I) and selenium (Se). Although several other trace and ultra trace minerals (e.g., chromium, cobalt, boron, vanadium) have an established physiological role, their dietary essentiality cannot be easily proven because they are required at extremely low amounts. Interestingly, soybean meal and phosphates contain enough iron, copper and manganese to more than cover requirements for some animal classes without further supplementation, even in low-phosphorus diets without phytase. Furthermore, most common diets contain enough copper for most animals. The only real concern in trace mineral supply is with iodine and selenium, especially when animals consume feedstuffs grown in selenium-poor areas.
As far as vitamins are concerned, corn and soybean meal are good sources of pyridoxine, thiamin, choline, folacin and biotin. When wheat is used instead of corn, the vitamin premix profile should be re-examined (as is the case for biotin and niacin). Other water-soluble vitamins, such as riboflavin, pantothenic acid, niacin, vitamin B12 and all of the fat-soluble vitamins (A, D, E, and K) are routinely added to diets for monogastric animals. Several vitamins (e.g., biotin) might need to be supplemented with alternate ingredients, especially those that represent purified concentrates from the agro-industrial industry (such as starch-rich by-products, or protein concentrates), as these are virtually devoid of most vitamins.
Clearly, little thought has been given to body stores later in life as sources of micronutrients before slaughter. One such example is vitamin B12 that requires at least 5 years to be totally depleted — clearly finishing animals do not require B12 until their last days! Furthermore, the role of microbial synthesis and intestinal absorption of vitamins of microbial origin has been overly underestimated — a prime example is rabbits that can benefit from the recycling of their cecal contents. Other species also consume feces (however disgusting we might consider it), and clearly animals housed in galvanized cages have different requirements in zinc than those in pasture or traditional pens.
Admittedly, the relative low cost of micronutrient supplementation has historically justified routine supplementation of vitamins and trace minerals up to market age. But, when it matters, especially when feed intake is maximal, modern advances in nutrition and the ever-reduced profit revenue mandate a reevaluation of such practices.