Pigments: use of additives in poultry diets

Additives are used to ensure that nutrients in the diet are ingested, digested, protected from destruction, absorbed and transported into the cell. In turn, they can alter the metabolism of birds to promote growth and/or improve the final product.

Additives are considered to account for 0.5% of the diet and 5% of the total ration cost.

Some of the most commonly used additives are: pigments, antioxidants, flavorings, growth promoters, mycotoxin sequestrants, exogenous enzymes, etc.

This first article,aims to delve on additives used for improving yolk color and chicken skin color. Such additives are known as pigments.

Pigments

Pigments are used in birds for  the improvement of the final product according to consumer preferences, without altering the normal metabolism of animals.

Birds are able to store pigments in: yolk, fat deposits, skin and in their legs. It has been proven that  color is associated with palatability amongst consumers. Therefore, alterations in color can be associated with better taste, or may cause rejection.

Pigment incorporation in bird diets seeks to achieve a degree of pigmentation that satisfies consumers:

– For egg yolks, a yellow to orange color is sought. Which is equivalent to: 10 – 13 on the Roche scale. These preferences vary according to location and region.

– An intense yellow is usually sought for the color of chicken skin.

Besides the importance of the achieved color, a uniform pigmentation is also sought. In this sense, it is important to highlight the fact that certain products such as coccidiostat nicarbazine can interfere with color uniformity.

Pigment sources  [register]

The color present in egg yolks, skin and fat of birds is due to pigment consumption, and mainly xanthophylls. Birds do not synthesize any kind of pigment. That is why the absence of pigments in the diet will result in a lack of coloration in egg yolks and the skin. The visual appearance can be altered by changing both the concentration of a pigment and the type of pigment.

Pigments can be natural or synthetic 

Carotenoids are natural pigments that can be found mainly in nature, with different shades of yellow, orange and red. The availability of dietary carotenoids ranges from 58 to 77%.

There are to large groups included within carotenoids:

• Alpha and Beta carotenes are precursors of vitamin A and also have antioxidant function.

• Xanthophylls, within this group are Lutein, Zeaxanthin, Capsantin.

Xanthophylls are the natural pigments with the highest availability. There are a large number of raw materials used in poultry feed that contain xanthophylls.  Amongst these, those which contribute the most are: corn (zeaxanthin) and its derivatives and the green leaves of certain plants, such as alfalfa (lutein). (See table 1).

Natural pigments in raw materials can be lost due to oxidation over prolonged storage times. Reaching losses of up to 50% at high temperatures. In addition, they are sensitive to ultraviolet light and moisture. On the other hand, if the fats present in the food have some degree of rancidity, this generates the oxidation of carotenoids reducing their pigmenting capacity.

Beta carotene, lutein and zeaxanthin give a yellow to orange coloration, while capsanthin has a more intense red color. Lutein has a greater affinity for egg yolk than for skin, while zeaxanthin has greater affinity for the skin and legs.  Capsanthin on the other hand has no deposits on skin and legs, so it is only useful for laying hens.

Within the synthetic pigments, we can find apocarotenoic esters and Cantaxanthin. The latter provides a reddish color and is deposited considerably on the skin of birds.

If only canthaxanthin were used, a red/orange colouring would occur, which would be unacceptable amongst consumers. A mixture of 4:1 (xanthophyll:canthaxanthin) is desirable. Synthetic pigments facilitate mixing within the diet and are more stable.  Making them less succeptible to oxidation compared to natural pigments.

Table 1. Pigment content in certain raw materials

Yolk pigmentation

To achieve optimal pigmentation, xantophyll concentration in the diet of laying hens should be 25-30 mg/kg (see Figure 1.) . Color preservation is obtained by high levels of vitamins and by the presence of antioxidants in the egg.

Figure 1. Relationship between xanthophyll levels in food (mg/kg) and yolk pigmentation measured on the Roche color scale

(Rutz, 2016)

To measure the degree of yolk pigmentation, at least 20 eggs per batch should be chosen. They must be evaluated against a black or white background in order to eliminate possible interference with contiguous colors.

The Roche scale’s range is used, placing it directly above the yolk. The use of natural light is recommended, as artificial lights can cause appreciation errors. In turn, it is recommended that the evaluation is always done by the same person to avoid interpretation differences.

Skin pigmentation

For broilers, a xanthophyll concentration of 50-60 mg/kg is recommended. Chicken life span is becoming shorter and shorter which leads to the need of increasing pigment inclusion wihin the ration in order to achieve desired pigmentation in less time. Maintaining bird skin appearance is more complicated than that of eggs due to several factors.

• On one hand, pigments that are deposited in the epidermis are not stable and can rapidly deteriorate. In turn, the carcass surface is irregular and the deposition of melanin is not uniform.

• On the other hand, processing and packaging of the cases, as well a how they are exhibited, influence the product’s appearance when it is chosen by the consumer.

Factors that interfere with pigment deposition

Scheme 1. Absorption, transport and deposition of pigments in the organism of birds

There are several factors that can interfere with the different links that lead to pigment deposition in birds:

• Food. Composition, preservation, presence of antioxidants, mycotoxins and form in which it is administered, all influence pigment contribution. The presence of unsaturated fats facilitates carotenoid transport.

• Excess nutrients. Vitamin A levels greater than 25000 IU/kg and calcium intakes above 4% in laying hens, decrease pigment deposits in yolk.

• Health. Stress and diseases such as coccidiosis or bacterial diarrhea that cause intestinal malabsorption will alter normal pigment absorption.

• Genetics. Some genetic lines have greater predisposition to pigment deposition than others.

• Type of housing. In the case of layers, free range birds have greater competition regarding water and feed consumption compared to hens housed in cages. This competition generates great variability in yolk pigmentation levels.

Pale bird syndrome

Pale bird syndrome occurs when there is a deficiency in the bird’s skin pigmentation. Its cause may be due to:

• Malabsorption
• Poor transport
• Poor deposition
• Increased excretion

The presence of mycotoxins in feed can lead to pale bird syndrome. Aflatoxins reduce the presence of lutein by interfering with its absorption and tissue deposition.

Ochratoxin is a mycotoxin that inhibits pigmentation more potently than aflatoxins. Ochratoxin reduces the absorption of carotenoids through the intestinal mucosa and in turn alters the transport of carotenoids in plasma.

At a concentration of 4 ųg/g, ochratoxin reduces the concentration of carotenoids in the liver by 75%.

Other benefits of pigments

• Pigments and reproductive efficiency 
  Canthaxanthin supplementation improves hatchability in heavy breeders. This effect has been attributed to the antioxidant capacity of this pigment.

• Lutein and zeaxanthin for humans
  These pigments are concentrated in the macular area of the eye and prevent macular degeneration which along with cataracts are the leading causes of blindness in humans

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