Lesser known indigenous vegetables as potential natural egg colourant in laying chickens

The experiment was carried out at the Teaching and Research farm, Faculty of Agriculture, University of Ilorin. Two hundred and Fifty (250) twenty-week old Black Harco layers were used for the experiment that lasted six weeks. The laying hens were housed in a 2-tiers battery cage system. Diet was formulated to meet NRC [10] requirements for energy and protein of laying birds. Each natural plant colorants (Red Pepper, Baobab Leaf and Waterleaf) and a commercial yolk colorant (Canthaxanthin) were incorporated into the diet at separate rates of 40 g/kg and 50 mg/kg of feed, respectively. Other routine management practices such as vaccination, medication and proper hygiene recommended by animal science regulations in Nigeria were complied with.

The leaves of Adansonia digitata (Baobab) (BL), Capsicum annuum (Red pepper)(RP) and Talinium triangulare (Water leaf) (WL) were collected, destalked and washed. The leaves were air dried for four days to reduce the moisture content and achieve a constant dry weight while retaining their colours. After drying, the leaves were pulverized into fine powder using an electric blender (Moulinex Philips). A known commercial egg yolk colorant (Canthaxanthin, CTX) was procured from a commercial feedmill in Ilorin, Nigeria. Experimental Birds were randomly assigned to five treatments using the Completely Randomized design (CRD) comprising fifty (50) birds per treatments. Each treatment was replicated in five units of ten [10]. The treatments were allocated as such; Diet A containing Capsicum annuum as colorant at 40 g/kg of feed, Diet B containing Talinium triangulare as colorant at 40 g/kg of feed, Diet C containing Adansonia digitata as colorant at 40 g/kg of feed, Diet D containing Canthaxanthin at 50 mg/kg of feed, and Diet E (Control) diet with no yolk colorant (Table 1).

Data were collected for performance and egg quality assessment. Average Feed Intake (AFI) was recorded daily, while Body weight gain (BWG) was recorded weekly as follows:

F₁ = left over feed at the end of the day (g)

F₀ = feed offered in the morning (g)

W₁ = weight change at the end of the week

W₀ = weight at the beginning of the week

Hen-Day Production (HDP) was calculated using the formula:

At the end of each week, fifty eggs per treatment were selected for analysis. Parameters measured include; Egg Weight (EW), Egg Length (EL), Egg Breadth (EB), Yolk Height (YH), Yolk Width (YW), Albumen Height (AH), Shell Thickness (ST), Yolk Colour (YC), Yolk Index (YI)and Haugh Unit (HU).

EW was collected by cleaning the eggs to remove impurities and weighing them using a sensitive electronic scale (Metler). ST was determined using a pair of micrometer screw gauge calibrated in millimetres. The accuracy of ST was ensured by measuring shell sample as one egg at the broad end, middle portion, and the narrow end all referred to as the thin, medium and thick, respectively. The average of these three parts measured was taken as the ST. YI was determined by relating the ratio of YH in millimetres to the YW measured in millimetres. The YH and YW were measured using a Spherometer and Venier calliper, respectively. YW was also taken as the maximum cross sectional diameter of the yolk which is the width at maximum point, usually across the centre of the yolk. The YC of collected eggs were determined using DSM yolk colour fan.

Albumen was separated from the yolk and carefully placed on a flat surface. The AH was measured using a Spherometer calibrated in millimetres. HU was measured relating the albumen height and the egg weight from the formula:

H.U = Haugh unit

H = Observed albumen height.

W = Observed weight of egg in grams.

Data obtained from the experiment were subjected to analysis of variance for completely randomized experimental design using the SPSS package, according to [11]. Significant means were separated using the Duncan’s Multiple Range Test [12].

Birds differed significantly (P < 0.05) in AFI across the various treatments (Table 2). Diet supplemented with BL recorded a significantly lower (P < 0.05) mean intake value (94.07 g) when compared with other treatments. This could be due to the anti-nutritional agent present in baobab leaf. It has been reported [13] that high tannin content of BL prevent its use as a potential feed ingredient in poultry diets. However, BL has been used as a source of pigments in diets for laying birds where yolk colour was observed to have increased at 1% or 2% BL, with no adverse effects on feed intake, egg production and quality. Canthaxanthin has been reported to have no influence on AFI [6].

HDP increased comparatively over the period of experiment. Laying hens fed with the control diet had the highest mean value (58.60%) while the diet supplemented with BL had the lowest value (48.8%). RP supplemented diet did not influence (P > 0.05) the performance parameters measured viz: Body weight gain, feed intake, Hen-day production. The observation on HDP disagreed with the report of [6] that CTX increased egg production. CTX has been reported to have no effects on HDP [14].

There was no dietary effect of treatment (P > 0.05) on egg external quality traits (Table 3). Canthaxanthin and other dietary supplements had no significant effects on egg external quality traits such as; EW, EB, EL, EI and ST; this is consistent with the previous findings [15]. This study showed a shell thickness range of 0.27 mm-0.29 mm which is within normal range for poultry. The Egg ST is an important trait for hatchability and handling [16].

The various dietary treatments had no significant effect (P > 0.05) on egg internal qualities such as: AH, YH, YI and HU. This is also consistent with earlier reports [10].

There was however, a significant effect (P < 0.05) of dietary treatment on YC (Table 4). Laying hens fed Red pepper supplemented diet had significantly higher (P < 0.05) YC (colour index of 7.50) compared with the other treatments. However, diets supplemented with WL, BL (Adansonia digitata) and CTX had similar (P > 0.05) values for YC. CTX was reported (6) to enhance egg yolk pigmentation. The observed low YC score for CTX in this study may be related to reduced potency owing to post-importation storage. The control diet had significantly lowest YC score which further buttress the fact that yolk pigmentation is influenced mostly by diets given to the birds [17]. In this study, RP is the best natural source of potential egg colourant, this is consistent with the report of [18]. That canthaxanthin had similar score with other lesser known indigenous vegetables shows that these vegetables can be harnessed into layer diets for egg yolk colour pigmentation. BL and WL are potential good sources of xanthophylls, known to enhance yolk pigmentation. Natural xanthophylls are well absorbed by hen intestinal cells [19] and it is transferred into the yolk after being released into the circulatory system [20].