Poultry is a major item in world food production. In fact, of all the livestock species, poultry consumes the highest proportion of manufactured feed.
Poultry is a major item in world food production. In fact, of all the livestock species, poultry consumes the highest proportion of manufactured feed. The dynamic growth and success of the poultry industry is based on a high degree of vertical integration, improved production efficiency standards (e.g., increased market weights, reduced days-to-market and improved feed conversion) and greatly automated processing, combined with successful marketing (e.g., low-fat, high-protein convenience products) and changed consumer habits (e.g., health considerations). The 13 required vitamins account for approximately 33% of the total number of feed ingredients in many complete poultry rations. However, vitamins represent only a minute fraction of poultry feeds, amounting to less than 0.1% by weight and about 1% to 2% of the cost of poultry rations, depending on the diet used and the level of supplementation required. Table 1-1 lists the vitamin requirements for chickens and turkeys as suggested by the 1994 NRC. The requirements for chickens are divided according to Leghorn-type and meat-type. For the Leghorn-type, sections are included for starting and growing pullets and for hens in egg production. For broilers, separate sections are presented for starting and growing market broilers, broiler breeder pullets and hens, and broiler breeder males. Requirements of starting and growing turkeys and turkey breeders are also given in Table 1-1.
Nutrient requirements (NRC, 1994) for geese, ducks, pheasants and quail are provided in Table 1-2. These data, however, are based on a relatively meager amount of literature. Although 13 vitamin requirements are listed for Japanese quail, only eight vitamins are listed for ducks and from four to six for pheasants, geese and bobwhite quail.
Vitamin nutrition is a dynamic input for the production and marketing of poultry meat and eggs. It must be updated regularly to accommodate improvements in production and marketing methods, changes in conditions on the farm and new vitamin nutrition knowledge. Continued improvement of genetic potential of poultry demands that we determine if increased vitamin levels may be needed to adequately meet these higher performance levels. The dynamics of vitamin nutrition for poultry are demonstrated by the changes in the NRC vitamin requirements of growing chickens (zero to eight weeks of age) that have been made during the past four decades. These changes were due primarily to advances in vitamin nutrition knowledge, improvements in vitamin product forms and extensive changes in commercial broiler production that have occurred during this period. Over the years, the number of vitamins recommended by NRC has increased and vitamin requirement values have been revised. The number of vitamins recommended by the NRC for growing chickens increased from nine in 1944 to 13 in 1994. A fourteenth and fifteenth vitamin (vitamin C and carnitine), should now be considered in overall vitamin supplementation programs. Vitamin C is synthesized by poultry and is, accordingly, not considered a required dietary nutrient.
However, there is evidence of a favorable response to vitamin C by birds under stress (Pardue, 1987; Nockels, 1988). Carnitine is also synthesized by poultry, but some studies have shown improved weight gain, feed efficiency, hatchability, egg quality and improved carcass traits with carnitine supplementation (Rabie et al., 1997; Rabie and Szilagyi, 1998; Kidd et al., 2005). The 1944 and 1950 requirement values included margins of safety to compensate for vitamin losses during feed processing and storage and for other factors influencing the vitamin needs of commercially produced chickens. As an example, the 1944 NRC allowed a general 20% safety margin for all vitamins. Later, however, it was recognized that the influencing factors varied considerably from farm to farm. Thus, in 1954, the margins of safety were excluded, and the NRC vitamin requirements were reduced to minimum values. Most nutritionists consider NRC requirements for vitamins to be close to minimum requirements sufficient to prevent clinical deficiency signs. These requirements may be adjusted upward according to experience within the industry in situations where a higher level of vitamins is needed. Although the NRC periodically publishes nutrient recommendations for poultry and other species, these are usually of limited value to commercial formulations since controlled studies often do not include the stresses encountered in a commercial environment. Stress (e.g., heat stress, feed processing, feed restriction in combination with vaccination, coccidiosis, E. coliinfection, mold and mycotoxins, peroxides, and overcrowding) can influence nutritional requirements, and the NRC does not include overages to account for stress-related requirements (Ward, 1993). Users of the NRC requirements should view the stated “requirements” as “working approximations.” The requirements for vitamins depend upon the measurements that define the need, as well as the source of the birds and the environmental conditions under which they are raised.
A. To compensate for the influencing factors occurring in commercial operations, the poultry industry has more closely attempted to recommend higher supplementation levels for poultry diets. The industry vitamin average allowances have increased significantly (30% to 500%) to keep pace with greater genetic potential, faster growth rates, better feed efficiency, poorer quality ingredients, larger poultry houses, and generally higher disease levels, all of which cause increased stress. A reasonable amount of logic would suggest that vitamin requirements determined decades ago may not apply to today’s poultry diets.
B. Commercial supplementation levels of most vitamins for poultry often reflect stresses encountered under production practices. Over 90% of the broilers, turkeys and laying hens were included in two broad surveys of vitamin supplementation rates (Ward, 1993; 2005). In the survey, levels for most vitamins were substantially higher than NRC recommendations.
C. There has been little research on poultry vitamin requirements during the last 40 years and unfortunately new NRC poultry requirements still rely on these older established requirements (Leeson, 2007). As an example, vitamin requirements for egg production, as suggested by the NRC (1994), have changed little over the last 30 to 50 years. However, during this time period, layer feed conversion rates have dramatically improved by approximately 40% based on higher egg mass production (approximately 30%) and lower feed consumption (approximately 10%) (Pérez-Vendrell et al., 2003b). Likewise NRC requirements for broilers have changed little in recent years. However, for the last 30 years broiler feed conversion rates have improved dramatically, more than 20%, due to a much higher weight gain in a shorter production period. Additionally, modern broiler production systems often place animals under high stress conditions, so an optimum level of vitamins in feed is essential for birds to achieve their full potential and maintain good health.
D. It is of interest to note that in 1925 it took 112 days for a broiler chicken to be ready for market. The average market weight was 1.14 kg (2.5 lb) and it took 2.14kg (4.7 lb) of feed for the bird to put on a kg (lb) of gain. Bird mortality was high in 1925, averaging 18%. Today, it only takes 48 days to get a bird to the market weight of 2.5 kg (5.5 lb), and it only requires0.89 kg (1.95 lb) of feed per kg (lb) of gain, with mortality rate of 4%. Note: Ask Nelson to change this paragraph.
E. Some studies have shown that profitability for poultry grown under common stress conditions is greatly improved by increased vitamin supplementation. Vitamin supplementation as high as 25% above the 1994 National Research Council recommendations has resulted in this higher profitability (Ward, 1993).
The requirements suggested for the newest NRC for poultry, unlike previous revisions, utilizes only information from refereed research. Many good studies have reported vitamin requirements under “farm conditions” and often these are published in proceedings and popular articles.
F. Another concern with the NRC recommendations is that the older research studies involved purified diets (Leeson, 2008). These diets often contained purified ingredients that were highly digestible and were not encumbered with facets of variable nutrient availability. Also, in recent years, assessment criteria for nutrients have changed. In 1994, virtually all nutrient needs for broilers were assessed by NRC in terms of growth rate and feed utilization; and for layers, egg production and egg weight (Leeson, 2008). Now, the needs for broilers also include breast meat yield and carcass quality; and for layers, egg production with a nutrient composition that is favorable to human health. Designer eggs (specialty eggs or value-added eggs) are available with low cholesterol, a favorable fatty acid profile, increased trace minerals, and improved vitamin content (Duddley-Cash, 2009).
Under intensive production systems poultry species are particularly susceptible to vitamin deficiency (Scott et al., 1982). Reasons for this susceptibility include: (1) they derive little or no benefit from microbial synthesis of vitamins in the gastrointestinal tract (2) they have high vitamin requirements and (3) the high-density nature of modern poultry operations places stresses on the birds that may increase their vitamin requirements. Broiler, turkey and the respective breeder diets typically are supplemented with all vitamins, except vitamin C (Ward, 1993). Some layer diets may be void of supplemental thiamin, pyridoxine, folic acid and biotin (Ward, 1993). More attention is now being given to circumstances where these vitamins may be necessary.
Vitamins D3 and B12 are almost completely absent from diets based on corn and soybean meal. Vitamin K is generally added to poultry diets more than to other species’ diets. Birds have less intestinal synthesis of vitamin K because of a shorter intestinal tract and faster rate of feed passage. Caged birds have less access to feces (coprophagy) and therefore need higher levels of many supplemental vitamins.
The dynamics of vitamin allowances (amounts fed) have paralleled the dynamics of vitamin requirements (minimum amounts needed). An allowance today may become a requirement tomorrow. The dynamics of vitamin fortification—the best assurance for arriving at optimum vitamin allowances for poultry—coincide with the dynamics of vitamin allowances. To assure that poultry are fed the amounts of vitamins needed to prevent deficiencies and allow optimum performance, the vitamin fortification levels in poultry diets should be reviewed and adjusted periodically. This should be done in accordance with the latest meat and egg production requirements, marketing methods, farm conditions and vitamin nutrition knowledge. A balanced vitamin fortification program which meets requirements under a wide range of feeds and different production systems will more than offset the cost of adding vitamins.
G. The actual minimum nutritional requirement for vitamins is difficult to assess as it is most often determined under favorable experimental conditions. In 1994, the NRC reported the most recent vitamin requirements for chickens. These were determined under optimal rearing conditions, thereby implying that these levels should be increased under “field conditions” (Castain et al., 2003). In this regard it is suspected that virtually all data used in the compilation of NRC (1994) requirement values were derived from studies where birds were in optimum health and not under immunological stress (Leeson, 2007). This would not be the case for many commercial operations. Supplementation allowances need to reflect different management systems, and be high enough to allow for fluctuation in environmental temperatures, energy content of feed or other factors that influence feed consumption. Optimum concentrations of vitamins in poultry diets allow poultry today to perform to their genetic potential. Vitamin requirements established decades ago do not take into account the modern genetically superior birds with increased growth, egg production and improved feed efficiency. Vitamin intake per unit of output is continually declining. The yearly decline for layers is around 1% per egg produced, while for broilers it has been 0.6%-0.8 % for body gain (Leeson, 2007). Also, vitamin allowances today need to take into account modern management procedures that increase bird densities and stress conditions. Vitamins are important for maintaining optimum immune response. Higher levels of vitamins (e.g., vitamins A, carotenoids, E and C) have been shown to increase overall health by improving disease resistance as a result of improved immunity. Thus, under commercial production conditions, vitamin allowances higher than NRC requirements may be needed to allow optimum performance. Generally, the optimum supplementation level is the vitamin concentration that achieves the best growth rate, feed utilization and health (including immune competency) and provides adequate body reserves. Barroeta et al. (2003) defines optimum vitamin nutrition (OVN) as “Vitamin levels above minimum requirements to optimize genetic potential and improve immune status in the bird, leading to an improvement in production and egg quality.”
Poultry meat and eggs constitute a large proportion of the high quality protein foods consumed today. These protein sources are a good source of vitamins. Not only does OVN improve poultry production and health, it impacts the nutrition of those consuming the products. An egg can provide anywhere from 100% of the human requirement for vitamin K to only 0.3% of requirements for niacin (Leeson, 2007). However niacin can be synthesized from the high levels of tryptophan in eggs. Higher levels of vitamins E, thiamin and pantothenic acid are found in broiler meat from birds receiving OVN (Hernandez et al., 2002). In addition to poultry meat with higher vitamin content, OVN can even more dramatically increase vitamin content of eggs. The recent OVN studies with laying hens resulted in significantly higher concentrations of vitamin A, E, thiamin, riboflavin, pantothenic acid, biotin, folic acid and vitamin B12 in eggs. Sheehy et al. (1991) showed a linear relationship between dietary alpha-tocopherol levels and its accumulation in muscle. It is important to realize that vitamin content of eggs today is lower than it was in 1995. When fed at the same level, Pérez-Vendrell et al. (2003b) reported vitamin A, vitamin E and vitamin B12 found in eggs decreased by 25.1, 37.5 and 33.0 percent, respectively, compared to the concentrations in 1995. The reason for lower vitamin content in recent years is likely due to improvements in layer feed conversion due to better poultry genetics and management. Obviously a lower total feed intake will make less quantities of vitamins available to be transferred to eggs. This applies to production of poultry meat as well. Greater feed efficiency limits the amount of vitamins transferred to meat. Therefore, poultry diets now need higher levels of dietary vitamins to have the same nutritional value as in the past.
Supplemental vitamins and trace minerals added to poultry diets have generally been provided in separate premixes. It is now becoming more common to include both vitamins and trace minerals together in a single premix (Leeson, 2007). Traditionally, vitamins and trace minerals were added as separate premixes since the mineral oxides can lead to the destruction of some vitamins (McDowell, 2000). With today’s more stable vitamins and where premixes are not stored for more than four to six weeks, a combined premix is possible and obviously more convenient during feed manufacture. Actually, more important than storage of less than four to six weeks, is the moisture level of the premix. As moisture levels increase during storage, the chemical reactions of mineral-destroying vitamins is greatly enhanced. Choline should not be combined with vitamin premixes as it is added in relatively large quantities and is very hygroscopic and thus very destructive to vitamins.
A summary of the importance of providing optimum vitamin nutrition is as follows:
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