Introduction

Mexico’s poultry industry currently produces more than 5 million tons of products (e.g. eggs, chicken and turkey) annually to meet national demand¹. This represents 63.8 % of the country’s total annual livestock production, eggs alone accounting for 29 %. Projected egg production for 2018 is 2.806 million tons. Feed costs are 60 to 70 % of the input costs in poultry production¹.

Eggs are an excellent food due to their high biological value, ease of handling, various preparation options, especially in combination with other foods, and their accessible cost. Consumers expect egg yolks to have a certain color. In intensive production systems laying hens are not exposed to natural pigments through their feed, meaning these must be added for egg yolks to have the expected color. This represents a substantial increase in input costs and affects final product price^2,3. Natural source yellow and red pigments, including carotenoids, are added to feed for laying hens^2,3. Research is ongoing into new sources of natural pigments that provide carotenoids, are easy to use, and have minimal impact on production costs.

Tithonia diversifolia, known as tree marigold among many other common names, is native to Central America and Mexico. Its almost 15,000 species can be found worldwide in tropical and subtropical areas⁴. It grows quickly, even in unfavorable conditions such as roadsides, and multiplies easily. In soils this plant is known to improve nutrient recycling, prevent erosion, reduce the effects of animal trampling and produce high biomass productivity without agrochemical inputs^5,6. It is a multipurpose plant that can be used as a living fence, green manure, grazing forage in silvopastoral livestock systems, and cut forage in poultry and ruminant systems. Tithonia diversifolia has reported values of 23.0 g/100 g dry matter, 14.8-28.7 g/100 g crude protein, 21.4 g/100 g ash, and 78.6 g/100 g organic matter⁷. Of note is its high carotenoid content, suggesting its use as a pigment source in egg production systems; indeed its inclusion in feed for laying hens at 15% results in good egg yolk color⁸. The present study objective was to evaluate the effect of different inclusion levels of Tithonia diversifolia meal in diets for first-cycle laying hens on yolk color and egg quality.

Material and methods

Results

Pigment quantification of the TDM showed the majority component to be lutein (50.67 %), followed by zeaxanthin (0.65 %) and total carotenoids (0.92 %) (Table 3). Neither egg weight nor feed conversion were affected (P>0.05) by TDM inclusion levels during the six-week (42-d) experimental period (Table 4). Laying percentage was lower in the 15% TDM treatment (89.8 %) versus the Control and the other inclusion levels. Feed intake/d decreased by an average of 5 g in the 15% TDM treatment versus the other treatments (P<0.05). Egg mass was lowest (P<0.05) in the 15% TDM treatment (52.5 g), higher in the 10% TDM treatment (55.1 g), and did not differ between the 1.77% TDM (55.9 g) and 5% TDM treatments (56.3 g) and the Control (56 g).

Yolk color based on DSM values, with no added red pigment (Figure 1A), was lowest in the 1.77% TDM treatment (DSM= 8) and highest in the 10 and 15% TDM treatments (DSM= 10). When red pigment was added to the diet the values followed a similar pattern to when no red pigment was added, with the lowest value (DSM= 8) in the 1.77% TDM treatment (value 8) and higher values in the other treatments and the Control (DSM= 11) (P<0.05) (Figure 1B).

Total carotenoids content was lowest in the 1.77% TDM treatment (142 μg/100 g) and then increased from the Control (235 μg) to the 5% TDM treatment (269 μg), the 10% (367 μg) and the 15% (440 μg). Lutein values were also lowest in the 1.77% TDM treatment (87 μg/100 g) and highest (P<0.05) in the 15% TDM treatment (291 μg). No differences between treatments were observed for zeaxanthin and capsanthin contents.

A= without added red pigment; B= added red pigment.

Figure 1 Egg yolks from treatments with increasing amounts of Tithonia diversifolia meal 

Discussion

Studies of how inclusion of natural ingredients in livestock forages affects animal productive behavior and product quality traits have been done largely in ruminants, particularly in agrosilvopastoral systems. Very little research of this type has been done in monogastric species such as chickens since this type of digestive system does not degrade high fiber diets, although fiber can be used in poultry diets¹³. There is therefore only a very limited literature on the use of T. diversifolia in poultry systems and even less comparing it to ruminant systems.

In the present results laying percentage, feed intake and egg mass were better in the 5% TDM treatment, which did not differ from the control. Feed conversion was better in the 10% TDM treatment. These data generally coincide with those in a study of the effects of T. diversifolia foliage meal inclusion (5, 10, 15 and 20% TDM, and a commercial feed control) in laying hens in which egg production did not differ between treatments, feed intake was lowest in the 20% TDM (96.3 g/bird/d) compared to the control (107 g/bird/d), and feed conversion was best in the 15% TDM⁸. This response may have been due to the negative effects of high fiber content and the presence of antinutritional factors in the 20% TDM treatment, which could compromise absorption of nutrients, mainly of amino acids^14,15. Tannins are a common antinutritional factor which can undermine feed palatability by imparting bitter flavors, but can also form complexes with proteins, starches and digestive enzymes, consequently reducing feed nutritional value, and negatively influencing animal growth, feed digestibility and protein and amino acids availability. Lower T. diversifolia inclusion levels do not seem to negatively affect productive performance in poultry; for example, 2 % inclusion of T. diversifolia leaf meal in laying hen diets is reported to improve egg mass and feed conversion¹⁶.

Poultry do not synthesize pigments that will add color to skin or egg yolk, which therefore need to be added to diets. The present data on the pigment contents of the studied TDM can function as a standard for its use as a source of xanthophylls for improving egg yolk color. Other natural sources of carotene pigments include alfalfa leaf meal (396 mg/kg), yellow corn (22 mg/kg), dehydrated Ladino clover meal (490 mg/kg), chili meal (187 mg/kg) and Tagetes erecta (Mexican marigold flower) (8,000 to 10,000 mg/kg), which has the highest xanthophylls content (80 to 90 % lutein). When ingested by laying hens xanthophylls enter the blood stream and are deposited in the skin, fatty tissue, the liver and egg yolks; carotenes are incorporated in smaller quantities and are transformed into vitamin A¹⁷. In a study of laying hens fed diets including 5, 10, 15 and 20% TDM, the T. diversifolia was found to be the only source of yellow pigments (lutein and zeaxanthin) in egg yolks⁸. Some variation is to be expected between different studies due to study conditions such as the age and element of the plant used as pigment source, animal assay conditions, climate, temperature, etc.

Relative to the treatments without red pigment (Trial 1), addition of red pigment to the feed formulation (Trial 2) in the present study notably increased yolk red hue in the Control, 5, 10 and 15% TDM treatments, although not in the 1.77% TDM treatment. This behavior may have been due to the combination of yellow and red colors in the treatments, which resulted in an orange color. Diet yellow pigment content increased as TDM inclusion level increased. Because red pigment was added in comparable amounts to the yellow pigments yolk color differed minimally between treatments, which is why the 1.77% TDM treatment had the least orange color of the red pigment treatments. The two 1.77% TDM treatments (no red pigment, red pigment) had the lowest color values since they were formulated based on an adjusted total carotenoids content of 15 ppm, the same proportion as in the Control, considering total carotenoids as the pigment. The egg yolk pigment content results were therefore directly proportional to TDM inclusion level, with increases in lutein corresponding to approximately 50 % of total carotenoids. In the egg yolk colorimetry values the yellow hue (b*) was higher in the Control and 15% TDM treatments, confirming the majority presence of lutein in the TDM.

Conclusions and implications

The leaves and petioles of Tithonia diversifolia constitute a valid source of natural pigments. They can be included in laying hen diets at up to 10% to improve egg yolk color, without negatively affecting productive parameters. Combination of a natural red pigment (canthaxanthin) with the yellow pigments in the Tithonia diversifolia meal produced egg yolks with a stronger orange color.