Vitamins are micronutrients that participate in numerous organic metabolic processes and are therefore indispensable for excellent animal health and productive performance.When compared to other nutrients, there are very few studies carried out in the last years to estimate the optimum levels of vitamins for broilers, and there is a huge variation in the levels used commercially. Most levels recommended by the NRC (1994) were based on old studies, performed under controlled conditions and using the minimum levels to avoid signs of deficiency, not evaluating the best performance under the challenge conditions found in the field. Moreover, the modern breeds have higher growth and production rate, and have higher nutritional requirements to express their genetic potential. Besides production rates, other parameters are also presently evaluated to determine the vitamin requirements, as immunity, animal welfare, carcass characteristics, microbiological analysis, etc. Supplementation with higher levels than the minimum recommendations result in higher production performance, better health, welfare and carcass quality.

In this sense, vitamins are micronutrients that take part in almost all organic metabolic processes and are vitally important for achieving good performance and health. Deficiency of one or more vitamins can lead to multiple metabolic disorders, resulting in decreased productivity, delayed growth, reproductive problems and/or decreased immunity.

Vitamins are divided into two groups based on their solubility in lipids (liposoluble) or water (hydrosoluble). The liposoluble include vitamins A, D, E and K, and the complex B vitamins (B1, B2, B6, B12, folic acid, nicotinic acid, pantothenic acid) and vitamin C are classified as hydrosoluble. In general, liposoluble vitamins have specific functions in the development and maintenance of tissue structures, while the hydrosoluble vitamins participate in catalytic functions or act as control mechanisms of the metabolism, as coenzymes (AWT, 2002).

The literature shows a large variation in vitamin levels used in commercial supplements for broilers (Rutz et al., 1999; Barroeta et al. 2002; Leeson, 2007). Therefore, there is a great interest in new studies to determine the levels that provide the best economic return, without interfering with the production performance of birds.

Vitamin Recommendations

When the nutritionist is considering the need for vitamin supplements, several factors have to be taken into consideration, as they can demand changes in the birds’ requirements. These factors include breed, sex, management practices, development status of the bird, stress and diseases (Moreira, 2002). But there are also factors related to the feed as ingredients, energy level, processing, storage and vitamin sources. Studies are being performed on the use of higher levels of certain vitamins to improve the nutritional value and meat quality for the consumer.

The vitamin recommendations suggested by international research bodies as the National Research Council (NRC), Agriculture and Food Research Council (AFRC) and Institut National de Recherche Agronomique (INRA), and the Brazilian recommendations, as the Brazilian Tables for Poultry and Swine, are important foundations to estimate the levels that should be used in different production stages. However, they only present the minimum requirements, which are usually not sufficient under field conditions and have low correlation with the levels that presently used by the industry. Most studies to determine the vitamin requirement of broilers were performed under controlled experimental conditions using purified or semi-purified diets. These diets are highly digestible, their nutrients have high bioavailability, and include ingredients that not usual in feeding broilers, as isolated soy protein or casein (protein sources), and dextrose, starch or sucrose (energy sources), which also demonstrates the low correlation with the field situation (Leeson, 2007). Moreover, few trials have been performed in the last 30 years to estimate the vitamin requirement of broilers with higher genetic potential for growth, with more than 20% improvement in feed conversion (higher weight gain in a short period) (Pérez-Vendrell et al., 2002) and a 87%increase in daily weight gain (from 26.8g/day in 1970 to 50g/day in 2000) (Barroeta et al., 2002).

Besides deficiency signs and/or weight gain and feed conversion, new parameters are being presently evaluated to determine the vitamin requirements of broilers, as immune response, animal welfare and quality of the final product (meat and eggs). The goal is to improve the aspect and nutritional value of the product and lengthen its shelf life. Higher vitamin levels have been used in the diet of broilers to compensate for variations in intake, bioavailability of the vitamins in the diet, antinutritional factors of the feedstuffs, stress (temperature, stocking density, management practices, diseases, etc). These are some of the other factors that can prevent the minimum requirements of the birds from being met.

Evaluating two levels of vitamin supplementation for broilers, Castaing et al. (2003) concluded that the highest level (approximately two times the standard dose used by the industry) resulted in higher weight at 38 days (1,919 g) than with the lower level (1,878 g). Moreover, the deposition of vitamin E in the carcass was also higher (5.4 mg/kg in the group supplemented with 20-25mg vitamin E and 12.5mg/kg in the group supplemented with 240mg).

Pérez-Vendrell et al. (2002) obtained similar results when they studied two supplementation levels, under controlled conditions (12.7 birds/m²) or under stress (16.4 birds/m²). The best outcomes (weight gain, feed intake, breast yield, vitamin deposition in the meat) were obtained with the higher supplementation level in both stocking densities.

In this context, the supplementation can be based on the Optimum Vitamin Nutrition (OVN) concept, which is presented by DSM (2006) as the most adequate level (optimum level) of both hydrosoluble and liposoluble vitamins. The objective is to optimize the health status, welfare and productivity of the animals, assuring efficiency in the production of quality food. Using this concept it is possible to determine four vitamin supplementation levels related to the degree of animal response. They are depicted in Figure 1 and described below:

Figure 1. Relationship between vitamin consumption and animal response

Figure translation:

Animal response / Vitamins in the diet

(1) Deficient / (2) Sub-optimum / (3) Optimum / (4) Special applications

1 – Deficient: vitamin supplementation below the required level, and the animal is under risk of developing clinical signs of deficiency as a result.

2 – Sub-optimum: vitamin supplementation in amounts that are appropriate to prevent deficiencies as long as the animals are under adequate health, environmental and physiological conditions (low challenge). However, when the animals undergo any type of stress, the level of vitamin supplementation is not sufficient to prevent reduced performance or reproduction rates.

3 – Optimum: contributes for the maximum expression of the productive potential of modern breeds under field conditions.

4 – Special applications: besides their contribution to the maximum performance of the animal, these vitamin supplementation levels improve certain attributes as the quality pf the final product (meat and eggs) and immunity.

As for most nutrients, the vitamin requirements for broilers have probably undergone very few modifications in the last 30-40 years, as the nutrient levels required for maintenance are practically fixed and the composition of muscles / tissues are resistant to changes. There has been, however, an increase in the vitamin requirements for specific metabolic processes, as the immune responses related to performance expectations of broilers under high stocking densities imposed by today’s commercial rearing conditions. As an example, there has been a linear decrease in vitamin E intake in the last 20 years, of 0.8%/year/kg weight gain, considering 20 IU vitamin E/kg feed and a feed conversion of 1.0 in 1987 and 1.7 today (Leeson, 2007).

Change in the parameters of vitamin levels determination

Much emphasis is given presently to nutrients with nutraceutical functions, mainly the vitamins, as they play an important role in promoting health, well-being and immunity.

The classical dose-response curve evaluation, often used to estimate the requirements of other nutrients, does not seem to be the most adequate for vitamins. Older studies evaluated the minimum requirement of vitamins needed to prevent the animal from presenting deficiency signs or they evaluated basic performance variables as weight gain, feed conversion and mortality. As most of these trials were performed under controlled environmental conditions (low challenge), the levels that were obtained are very little representative in practice. To find the optimum levels for broilers reared under industrial conditions, other factors beside performance should be evaluated, as carcass characteristics, breast yield, microbiological quality and immune response.

Vitamin levels used in Brazil

Table 1 shows the relationship between average levels found in the vitamin supplements used by the major Brazilian broiler companies in 2008, the levels based on the Optimum Vitamin Nutrition (OVN) concept for broilers and also the levels used in Brazil in 2005 (Nascimento et al., 2005). It can be seen that there was an increase in the vitamin levels used by the Brazilian industry during the growth period when 2008 and 2005 figures are compared. It can be concluded that the companies are aware of the need for a higher vitamin supplementation to follow the birds genetic development, although the levels being used are still bellow those put forward by the broiler breeding companies and the OVN levels recommended by DSM (2006).

_{¹ Average levels used by the Brazilian broiler companies in 2008. ² Coefficient of variation found between the various companies. ³ Percentage of the recommended value (OVN - Optimum Vitamin Nutrition) that is met. ⁴ Average levels used by the Brazilian broiler companies in 2005 (Nascimento, et al., 2005). ⁵ It is very difficult to determine the level of choline used by industry, as in most companies choline hydrochloride is added by itself, making it hard to determine the levels that are effectively used.}

Cost of the vitamin supplementation

The physical and chemical characteristics of vitamins are important aspects and should be taken into consideration not only by the premix producer but also by the final consumer, the buyer of the vitamin premix. Both should demand that high quality raw materials are used in the production of the premix. The increase in the vitamin levels represents only a 0.5% increase in the total cost of the feed (Figure 2). However, if the quality of the vitamin premix is not assured, the supplementation of marginal vitamin levels can cause serious losses in the animals performance.

Figure 2. Participation (%) of each ingredient in the final cost of a grower feed (2008)

According to the authors, changes in the research parameters and methods are necessary to obtain more accurate results, applicable to practical conditions. As to the vitamin requirements of today’s broiler breeds. They are related to optimum performance, final quality of the product and financial return. Besides the production rates within this context, there are also important variables to be analyzed as immunology, interaction between vitamins and other nutrients, composition, meat quality and food safety, performance under stress conditions, effect of supplementation of the breeder’s diet on chick quality. New trials involving the vitamin requirements of modern broiler breeds reared under industrial conditions are needed. These trials should include some form of stress to the birds in order to be more similar to the industry’ real situation. They should also take into account variables such as vitamin levels in the final product (meat and eggs), shelf life and organoleptic characteristics.

March 2010