Comparative Performance of Three Hen Genotypes for Dual-Purpose Egg and Meat Production in Free-Range Systems

Abstract

Breed selection is a key factor for small- and medium-scale poultry producers, particularly regarding the adaptability of birds to local conditions, their productive performance, and product quality. In this study, we evaluated the laying performance and egg quality among hens of three genetic origins (Canarian, Lohmann Dual, and Novogen BT), as well as post-laying carcass and meat characteristics. In addition, consumer panels were employed to undertake sensory evaluations of eggs and meat. Sixty hens fed a commercial diet were reared under traditional free-range conditions. The production of eggs was monitored from 20 to 74 weeks of age, after which, the hens were slaughtered for carcass and meat analyses. Growth trajectories of hens were assessed using the Gompertz equation, which revealed distinct patterns among the three genotypes. The Canarian breed was characterized by a later age at inflection (9.5 weeks) and reached a higher asymptotic weight (2.2 kg) than the Lohmann Dual (7.3 weeks; 1.5 kg) and Novogen BT (7.9 weeks; 1.7 kg) breeds. With respect to egg production, efficiency was lower in Canarian hens (feed conversion ratio > 8.2) than that in Lohmann Dual and Novogen BT hens (feed conversion ratio = 2.9–3.9), which is assumed to be associated with the brooding behavior of Canarian hens. Compared with the other assessed breeds, Canarian eggs were characterized by distinctive quality traits, including tinted shell coloration and higher redness (a*) and yellowness (b*) values. Similarly, the meat and skin of Canarian hens had higher yellowness (b*) values, indicating specific quality attributes. Sensory evaluation revealed comparable acceptability among the three breeds, although Canarian hens received higher scores for specific sensory attributes of meat, particularly aroma, juiciness, and greasiness. These findings highlight the potential of local breeds for dual-purpose production and their valorization in free-range systems at the end of the laying cycle.

Introduction

Over recent decades, poultry products have become the most widely consumed livestock commodity worldwide, and it is anticipated that this growth in consumption will continue to increase over the next 10 years[1]. This surge is being driven by a range of factors, foremost amongst which is rising demand reflecting consumer desire for more affordable and high-quality sources of protein[2]. The meat and eggs of poultry serve as important sources of nutrients such as essential amino acids, lipoproteins, lipids, and a wide variety of minerals, vitamins, and other bioactive compounds[3,4]. These attributes, along with the relatively low and competitive pricing of chicken products compared with other sources of animal protein, and the absence of any cultural or religious obstacles, have contributed to this global expansion of the poultry industry[5,6].

In addition to these trends, technological advances associated with innovations in genetics, feed, automation, and disease control have, since the middle of the last century, transformed the rearing of poultry from a predominantly rural farming practice into a fully developed industry[7]. For example, almost all the meat and eggs currently produced by the poultry industry are provided by specialized lines/strains of birds characterized by high productive performance and feed efficiency[8,9]. However, this high degree of specialization within the poultry industry has led to substantial reductions in the farming of local breeds, which although often characterized by superior quality traits, have considerably lower production outputs. Moreover, this increasing homogeneity of breeds is contributing to a marked loss of genetic variability[10]. Indeed, several authors have highlighted the need to conserve poultry genetic resources in order to confront the challenges of climate change and the potential emergence of new avian diseases, as well as the sustainability of all natural and farmed ecosystems[11,12].

The current complex requirements with respect food hygiene standards and stringent specifications governing the homogeneity of product characteristics have limited the potential for small-scale poultry breeders to commercialize their products[10]. Nevertheless, worldwide there have been growing consumer concerns regarding the sustainability and animal welfare of poultry production, particularly in Europe[13], thereby stimulating the demand for eggs and meat produced through alternative and less intensive farming practices[14]. One such example in this regard is the production of dual-purpose poultry, which can be conducted using less specialized genotypes or local breeds that are generally reared under free-range conditions[15], with males being reared for fattening and females for laying[16].

Regardless of the production system adopted, it is important to note that in many developed countries, when laying hens reach the end of their productive lives (approx. 60–72 weeks of age) they are considered by-products[17,18]. Given the lack of demand among consumers, market prices for the carcasses and meat of old laying hens are essentially negligible and, as such, these products are typically utilized for the production of canned produce as well as for pet food[19,20]. Nevertheless, the consumption of this type of meat could represent a biologically efficient means of recycling nutrients as well as a profitable approach for small- and medium-sized farms, thus contributing to a scale-up of the variety of foods offered on the market[6,18].

In this context, a number of authors have reported the strong influence of genotype on the quality of poultry meat and eggs[13,15]. Consequently, the choice of breed is seen as a key factor for alternative producers[21], who are seeking birds adapted to local environmental conditions, that have a good production performance, and require minimal care for efficient growth and development[22]. Although in this regard, the production and quality of the eggs of many native breeds raised under alternative systems have been well studied, there has been comparatively little research focusing on the dual-purpose potential of free-range hens. In this context, one such example is the Canarian chicken, an indigenous breed traditionally associated with small-scale poultry systems in the Canary Islands. In addition to its agricultural and cultural value, this local breed constitutes an important genetic resource potentially adapted to local environmental conditions, making its productive characterization relevant for the sustainable use and conservation of poultry biodiversity[12].

In this study, with a view toward providing benchmarks for breeds of chicken that are widely reared on small- and medium-sized farms in the Canary Islands, we sought to evaluate the productive performance and egg quality parameters of hens of three different genetic origins, and to determine the attributes of their carcasses and meat after the laying period. In addition to maximizing benefits at the farm level, this could also represent a sustainable approach to meet consumer expectations, as well as providing a competitive niche for the production of eggs and meat from free-range hens.

Materials and Methods

Animals, rearing system, and diets

In this study, conducted at the farm of the Canary Islands Institute for Agricultural Research (Tenerife, Spain), we assessed the performances of the hens of three chicken breeds that are typically reared on small- and medium-sized farms in the Canary Islands: (1) Canarian, an autochthonous breed originating in the islands, (2) Lohmann Dual, a crossbreed of broiler and layer genetic backgrounds (Lohmann Tierzucht GmbH, Germany), and (3) Novogen BT, a modern dual-purpose breed (Novogen S.A.S, France). Hatching eggs from Canarian and Lohmann Dual hens were obtained from the Asociación La Campera (Tenerife, Spain), and Ibertec S.A.U (Valladolid, Spain), respectively. These eggs were incubated together for 21 days in our facilities (Incubator Mod.25-I; HLC Masalles, Barcelona, Spain). Coinciding with the time at which these eggs hatched, we purchased 1-day-old Novogen BT chicks from Incubadoras San Lorenzo (Gran Canaria, Spain). All chicks were separated based on genotype, sexed, and marked using leg tags.

For the first 4 weeks of life, the birds were maintained in three 15-m² indoor pens, the floors of which were covered with wood shavings as litter. At this age, any sexing errors were rectified, and the number of birds in each pen was adjusted to give equivalent group sizes of 20 pullets per pen. Thereafter, the birds had access to a grass paddock (24 m² per pen), in which were provided two circular plastic drinkers (25 L capacity), two circular metal feeders (25 kg capacity), two wooden perches (each of 1.5 m) on two levels, and four nest boxes installed at a height of 60 cm above ground level. The pens had an earthen floor, natural ventilation, and natural lighting. During the course of rearing, all chicks were initially fed a starter feed (1–8 weeks), which was in turn replaced with a standard growth feed (9–19 weeks), and thereafter a layer feed (20–74 weeks), the main constituents of which were soybean meal, corn, wheat, soybean oil, barley, and calcium carbonate (Graneros de Tenerife SL, Santa Cruz de Tenerife, Spain). The compositions of these feeds are shown in Table 1. From week 1 until week 36, the birds were weighed individually once weekly using a BIT PS 3.0 portable poultry scale (Bröring Technology GmbH, Oldenburg, Germany).

Table 1.  Composition of the experimental diets

	Starter (weeks 1–8)	Growth (weeks 9–19)	Layer (weeks 20–74)
Crude protein (%)	16.0	15.2	14.5
Crude fat (%)	2.5	3.4	2.5
Crude fiber (%)	5.5	6.5	3.7
Methionine (%)	0.4	0.3	0.3
Lysine (%)	0.8	0.7	0.7
Calcium (%)	1.0	1.0	3.8
Phosphorus (%)	0.5	0.5	0.4
Metabolizable energy (MJ/kg)	11.6	11.4	11.4

Egg measurements and quality analysis

From 20 to 74 week of age, the eggs produced by hens were collected daily and weighed. Feed intake was recorded once weekly at the pen level by weighing the total amount of feed offered and that remaining unconsumed at the end of each week. Using these daily and weekly records, we calculated feed intake, laying rate, egg mass, and the feed conversion ratio (FCR), the values of which for each genotype were expressed as the mean performance per hen over the experimental period. Percentage egg laying was calculated by dividing the number of eggs laid by the number of hens and multiplying by 100; egg mass was determined by multiplying the laying percentage by the average weight of eggs and dividing by 100; and FCR was calculated by dividing the weight (kg) of feed consumed by that of eggs produced.

At 60, 64, 68 and 72 weeks of age, 40 eggs were randomly collected from the hens of each genotype (a total of 160 eggs per genotype) to enable the measurement of egg traits within the 48-h period post-oviposition. The eggs were weighed individually using a Kern PCB 1000-2 digital scale (Kern & Sohn, Balingen, Germany), and the lengths and widths were measured using digital calipers (Workzone, Shandong, China), the values of which were used to calculate values of the egg shape index (width/length × 100), according to Gervais et al.[23]. Measurements of eggshell strength were obtained from intact eggs using a TA-HD-Plus texture analyzer equipped with a 5-mm stainless steel cylindrical probe (Stable Microsystems, Surrey, UK), as described by Sigut et al.[22]. Having broken the shells of eggs, the yolk, albumen, and eggshell were separated and weighed to assess their respective proportions. Color parameters (L*, a*, b*) of the eggshell and yolk were measured using a Minolta CR-400 colorimeter (Minolta Camera Co. Ltd, Osaka, Japan). In addition, at each sampling age (60, 64, 68, and 72 weeks), we randomly collected five eggs (a total of 20 eggs per genotype) for determination of fat percentage and fatty acid profiles. The yolks were initially separated and stored frozen at -20°C until used for analysis performed commercially by Trouw Nutrition Masterlab (Madrid, Spain) suitable for agro-food product analyses[24].

For analyses of carotenoid contents, a further six egg yolks were obtained from eggs collected at 62 and 66 weeks (a total of 12 egg yolks per genotype), and were frozen at -20°C. The frozen egg yolks were subsequently lyophilized for 5 days using a Lyomicron freeze dryer (Coolvacuum Technologies, Barcelona, Spain) at a final condenser temperature of -55°C and maximum vacuum of 0.030 mbar. Thereafter, the samples were homogenized, with subsequent extraction performed using the method described by Domínguez et al.[25] with slight modifications. Approximately 0.8 g freeze-dried egg yolk powder was extracted twice (10 mL each) in the dark for 10 min using a ternary solvent mixture (hexane: acetone: petroleum ether, 1:1:1, v/v/v) in a cool bath with magnetic stirring. The extract thus obtained was thereafter placed in an ultrasonic water bath (Ultrasons-H; Selecta, Barcelona, Spain) for 10 min. After phase separation, the entire organic phase (hexane) was collected, and the absorbance was determined at 450 nm using a UV-visible spectrophotometer (UV-160A, Shimadzu, Kyoto, Japan). Results were expressed as the weight (mg) of carotenoid equivalents per 100 g of dried yolk.

For the sensory evaluation of eggs, we selected 61 untrained panelists from among researchers, staff, and students at the Canary Islands Institute for Agricultural Research. Eggs were collected at 73 weeks of age and stored at 4°C for 7 days prior to evaluation. Having randomly coded the eggs, these were presented to all tasters under the same conditions. Panelists were instructed to provide external assessments of whole eggs (eggshell color, shape, and size), internal assessments of raw eggs (color and size of yolk and appearance of the egg white) and overall palatability of hard-boiled eggs on a 9-point hedonic scale[26]. The boiling process consisted of placing the eggs in boiling water for 8 min, cooling to an external temperature of approximately 40°C, peeling, halving lengthwise, and serving immediately to the panelists. Each panelist evaluated one half egg from each genotype (three samples per session) and to clear the palate between each sample, the evaluators were instructed to eat unsalted crackers, drink room temperature water, and pause for 20 s, as described by Williams and Damron[27].

Meat measurements and quality analysis

At 74 weeks of age, the hens were weighed and feed was withdrawn at 24 and 12 h prior to slaughter, respectively. The birds were electrically stunned, killed by manual exsanguination, plucked, and eviscerated, as required by the Council of the European Union[28]. Carcasses were refrigerated for 24 h at 4°C for determinations of carcass weight and dressing percentage. Breast and legs (drumstick + thigh) were removed and weighed, and using the values thus obtained, we determined the respective percentages relative to the total carcass weight. The left portion of each breast was used to measure pH, color parameters, cooking loss, and shear force, determined at 24 h post-mortem, whereas the right portion was vacuum packed and maintained at -20°C until used for the determination of fat percentage and fatty acid profile, performed commercially by Trouw Nutrition Masterlab (Madrid, Spain) suitable for agro-food product tests[24].

The pH of the meat was determined by inserting the penetration electrode of a GLP 21 pH meter (Crison Instruments SA, Barcelona, Spain) into samples, with measurement being carried out in triplicate. Color parameters (L*, a*, b*) of breast skin and meat were measured using a Minolta CR-400 colorimeter, with measurements from meat being performed immediately after removal of the skin. For each sample, three measurements were performed at the same anatomical location. Cooking loss was measured using the procedures described by Díaz et al.[29]. Shear force was measured using a TA-HD-Plus texture analyzer equipped with a Kramer Shear Cell (Stable Microsystems, Surrey, UK), with the assessment of cooked meat being performed in triplicate by cutting cores (1 cm² in cross-section and 3 cm in length) parallel to the muscle fibers.

Similar to the sensory analysis performed for eggs, we recruited 47 untrained panelists from the Canary Islands Institute for Agricultural Research to undertake a sensory evaluation of meat. Legs (right and left) were initially deboned, and the muscles were homogenized in a domestic blender. Samples of the homogenates thus obtained (35 g) were molded and stored at -20°C until used for sensory analysis. The frozen burgers were thawed at 4°C for approximately 24 h and then cooked without the addition of salt or spices at 200°C on a double-plate grill until the internal temperature had reached 70°C. The samples were randomly coded and presented under the same conditions to the panelists, who were instructed to assess the attributes of aroma, taste, juiciness, greasiness, and overall palatability on a 9-point hedonic scale[26].

Statistical analysis

For each hen, growth curve parameters were estimated using a Gompertz equation[30] as follows:

  

$f\left(x\right)=W_f{e}^{\left(1-e^{-bx}\right)\ln \left(\frac{W_f}{W_0}\right)}$

where f(x) is the body weight (BW) at age x, W₀ and W_f are the zero- and infinite-time values of BW, respectively, and b (per week) is a positive constant[31]. Values obtained for BW and age are presented in terms of grams and weeks, respectively. To assess genotype-level growth patterns, for each genotype, we subsequently determined the mean parameter values, Calculations were carried out using the non-linear regression option in SPSS 15.0 software (SPSS Inc., Chicago, USA) based on the Levenberg-Marquart estimation method. Having determined values for these parameters, we subsequently calculated values for the time of inflection (timeI), BW at inflection (BWI), and the growth rate per day at inflection (GRI), using the procedure described by Porter et al.[31]. Genotypic effects for the productive and quality parameters evaluated in this study were assessed using an analysis of variance followed by a post hoc Tukey test. Prior to analysis, the normal distribution of the data and homogeneity of variances were verified based on assessment using the Kolmogorov–Smirnov and Levene tests, respectively. The sensory attributes of eggs and meat were analyzed using a Kruskal–Wallis test followed by the Dunn test with Bonferroni correction. Statistical significance was set at a P-value of <0.05.

Results

Growth performance

Growth curves for the three assessed chicken breeds and their functional parameters, as determined using the Gompertz equation, are presented in Figure 1 and Table 2, respectively. With respect to the parameter describing the mature BW (W_f) of hens, we detected significant differences among the three breeds, with the Canarian and Lohmann Dual birds being characterized by the highest (2.2 kg) and lowest (1.5 kg) values, respectively. Furthermore, compared with that obtained for the other two genotypes, the value of exponent b in the Gompertz equation, which determines the sigmoidal shape, was lower for Canarian hens (P < 0.05). Notably, however, whereas Lohmann Dual and Novogen BT hens reached the inflection point during weeks 7 to 8, the Canarian hens reached this point almost 2 weeks later, and had a significantly higher weight at inflection (BWI) (P < 0.05). Similarly, the Canarian hens were found to show the highest growth speed (ca. 20 g/d) during inflection (GRI.day), followed by Novogen BT (ca. 17 g/d) and Lohmann Dual (ca. 15 g/d) hens (P < 0.01). Finally, for the fitted Gompertz curves, we obtained coefficient of determination (R²) values of 0.898, 0.984, and 0.999 for the Canarian, Lohmann Dual, and Novogen BT genotypes, respectively, indicating that the model provided a good fit to the observed growth data.

Fig. 1.

Growth curves for hens of the three genotypes¹.

¹The lines indicate fitted values based on the Gompertz equation.

Table 2.  Calculated growth parameters corresponding to the Gompertz equations for three hen genotypes^1,2

	Canarian	Lohmann Dual	Novogen BT	SEM	P-value
Wf (g)	2244.89c	1508.03a	1743.79b	55.402	0.001
b (weeks-1)	0.17a	0.19b	0.19b	0.003	0.006
timeI (weeks)	9.54b	7.31a	7.94a	0.187	0.001
BWI (g)	826.12c	554.96a	641.71b	20.388	0.001
GRI.day (g/d)	19.65c	14.96a	17.31b	0.443	0.001
R2	0.898	0.984	0.999

^a–cMeans within the same row denoted by different superscript letters are significantly different at the P < 0.05 level.

¹W_f is the infinite-time values of body weight (BW), b is a constant, timeI is the time of inflection, BWI is BW at the time of inflection, and GRI.day is the growth rate per day at the time of inflection.

²Twenty hens per genotype were individually fitted to the Gompertz model, and the reported parameters correspond to the mean values of individual estimates.

Laying performance

Curves showing the cumulative number of egg produced and values obtained for productive laying parameters are presented in Figure 2 and Table 3, respectively. Over the 54-week period during which they were reared under free-range conditions, Canarian, Lohmann Dual, and Novogen BT hens produced 131, 187, and 263 eggs, respectively. With respect to egg production throughout the study period, the Novogen BT birds were found to consistently outperform those of both the Canarian and Lohmann Dual breeds, which is in line with expectations, given that this commercial hybrid has been developed to maximize its productive capacity under free-range conditions. Whereas Canarian and Lohmann Dual hens followed a similar trend up to week 40, thereafter the Lohmann Dual birds were found to have higher production rates, with a subsequent clear increase being detected from week 54 onwards. In contrast, from weeks 46 to 66, Canarian hens exhibited an asymptotic pattern in cumulative egg production, indicating a marked slowdown in egg production during this period.

Fig. 2.

Cumulative egg production (number of eggs) curves for hens of the three genotypes.

Table 3.  Productive performance of the hens of three genotypes¹

	Canarian	Lohmann Dual	Novogen BT	SEM	P-value
Feed intake (g/d)	126.93c	92.11a	117.88b	1.862	0.001
Laying rate (%)	34.56a	49.42b	68.47c	1.566	0.001
Egg mass (g)	20.21a	28.54b	41.63c	0.946	0.001
FCR	8.27b	3.85a	2.88a	0.312	0.001

^a–cMeans within the same row denoted by different superscript letters are significantly different at the P < 0.05 level.

¹Parameters determined from week 20 to 74 at the pen level.

During the experimental period, we established that Canarian and Lohmann Dual hens were characterized by the highest and lowest mean feed intakes, respectively (P < 0.01), whereas compared with those of the other two genotypes, Novogen BT hens had the highest laying rates and egg masses, with recorded values being two-fold higher than those obtained for the Canarian hens (P < 0.01). However, whereas we detected no significant differences between Lohmann Dual and Novogen BT hens with respect to FCR, with values ranging between 2.9 and 3.9, we obtained a significantly higher value of 8.2 for Canarian hens (P < 0.01).

Egg quality traits

Table 4 presents data obtained for the egg quality parameters of hens of the three genotypes. Among the three breeds, Novogen BT and Lohmann Dual hens laid the heaviest (63.4 g) and lightest (58.5 g) eggs, respectively (P < 0.01). Furthermore, the shape of eggs was significantly influenced by genotype, with Lohmann Dual hens producing eggs with a higher average shape index, indicating an overall rounder form than those laid by Canarian and Novogen BT hens. With regards to the proportions of egg components, compared with those of the other two breeds, Canarian hens laid eggs with a significantly higher proportion of yolk, whereas eggs laid by the Lohmann Dual and Canarian hens was highest and lowest percentages of eggshell (P < 0.01). Correspondingly, the shells of eggs laid by Lohmann Dual hens were assessed to have the highest strength. In addition, we identified associations between genotype and the assessed parameters of eggshell color (P < 0.01), with Canarian hens producing eggs characterized by a tinted shell coloration, whereas Lohmann Dual and Novogen BT hens laid light brown and brown eggs, respectively. With respect to yolk color traits, whereas we obtained comparable between-breed values for luminosity (L*) (P > 0.05), values for the redness (a*) and yellowness (b*) indices were significantly higher in the yolks of eggs laid by Canarian hens. Consistent with this finding, analysis of total carotenoid contents revealed that the concentrations of these pigments were approximately two-fold higher in the yolks of Canarian eggs than in those of Lohmann Dual and Novogen BT eggs (P < 0.01).

Table 4.  Egg quality traits of the hens of three genotypes¹

	Canarian	Lohmann Dual	Novogen BT	SEM	P-value
Egg weight (g)	60.92b	58.54a	63.42c	0.261	0.001
Egg shape index (%)	73.85a	77.40b	74.01a	0.217	0.001
Egg components (%)
Yolk	31.61b	28.45a	29.14a	0.181	0.001
Albumen	55.47a	56.80b	56.37ab	0.177	0.007
Eggshell	12.67a	13.97c	13.44b	0.086	0.001
Eggshell color
L*	81.55c	70.79b	62.40a	0.446	0.001
a*	5.36a	11.05b	17.32c	0.278	0.001
b*	17.83a	24.35b	27.68c	0.255	0.001
Eggshell strength (N)	28.57a	35.95c	32.41b	0.442	0.001
Yolk color
L*	58.91	59.94	58.98	0.247	0.072
a*	9.02b	6.70a	8.33b	0.198	0.001
b*	52.70b	49.05a	48.83a	0.418	0.001
Total yolk carotenoids (mg/100g)	16.09b	7.83a	7.72a	0.828	0.001

^a–cMeans within the same row denoted by different superscript letters are significantly different at the P < 0.05 level.

¹Forty eggs per genotype were used for assessments, with the exception being the determination of total yolk carotenoids, for which we used 12 eggs per genotype.

Carcass and meat quality traits

Table 5 presents data obtained for the assessed carcass and meat quality parameters of hens of the three genotypes. In line with expectations, when measured at 74 weeks, we recorded slaughter and carcass weights that were significantly higher in Canarian hens and significantly lower in Lohmann Dual hens, reflecting their differing rates of growth. In addition, there were differences between Canarian and Novogen BT hens regarding dressing percentage, with the commercial breed being characterized by a lower percentage than the local breed (P < 0.01). With respect to the yields of the main carcass components, Lohmann Dual hens were found to have the highest proportion of breast meat, whereas Novogen BT hens had the highest percentage leg (drumstick + thigh) muscle (P < 0.01). However, we detected no significant differences among the genotypes with respect to the values of pH at 24 h post-slaughter, which ranged between 5.7 and 5.9. Contrastingly, genotype was established to have a significant influence on the color of skin and breast meat (P < 0.01), with Canarian hens being characterized by lighter skin but darker meat compared with the other two breeds. Furthermore, for both skin and meat, Lohmann Dual hens had the highest values of the redness (a*) index, whereas in Canarian hens, both tissues types were characterized by elevated yellowness (b*) values. In addition, compared with hens of the other two breeds, the breast meat of Canarian hens was established to undergo the lowest cooking losses (P < 0.01), whereas in terms of the texture of the cooked breast meat, compared with Canarian hens, we recorded significantly lower shear force values in the meat of Lohmann Dual hens, which is taken to be indicative of a more tender meat.

Table 5.  Carcass and meat quality traits of the hens of three genotypes^1,2,3

	Canarian	Lohmann Dual	Novogen BT	SEM	P-value
Slaughter weight (kg)	2.52c	1.57a	1.95b	0.064	0.001
Carcass weight (kg)	1.54c	0.95a	1.14b	0.041	0.001
Dressing (%)	61.01b	60.11ab	58.73a	0.281	0.003
Commercial cuts
Breast (%)	18.37b	20.31c	15.86a	0.319	0.001
Drumstick + thigh (%)	31.56a	32.69a	39.09b	0.573	0.001
pHu	5.85	5.79	5.77	0.015	0.096
Skin color
L*	75.82c	73.10b	69.51a	0.458	0.001
a*	2.05a	3.16b	1.34a	0.174	0.001
b*	20.13b	18.64b	11.69a	0.638	0.001
Meat color
L*	51.95a	55.17b	57.95b	0.562	0.001
a*	2.16b	3.93c	1.44a	0.171	0.001
b*	3.57b	2.38a	1.37a	0.212	0.001
Cooking loss (%)	15.86a	19.03b	17.85b	0.358	0.001
Shear force (N)	34.67b	28.98a	32.78ab	0.779	0.008

^a–cMeans within the same row denoted by different superscript letters are significantly different at the P < 0.05) level.

¹Commercial cut percentages are expressed relative to carcass weight.

²pH_u, color parameters, cooking loss and shear force were determined in breast meat.

³Twenty animals per genotype were used for assessments.

Fat content and fatty acid profiles of egg yolk and breast meat

Table 6 presents the total fat percentages and fatty acid profiles of egg yolks and breast meat from the Canarian, Lohmann Dual, and Novogen BT hens. The genotype of hens appeared to have no significant influence on the fat contents in yolk and meat (P > 0.05). The mean values for yolk fat ranged from 31.8% to 32.4%, whereas those for the fat in meat were between 8.2% and 8.8%. No significant differences were detected in the percentages of fatty acids in yolk and meat with respect to genotype (P > 0.05). The fatty acid profiles predominantly comprised monounsaturated fatty acids (MUFA), followed by saturated fatty acids (SFA) and polyunsaturated fatty acids (PUFA).

Table 6.  Total fat percentage and fatty acid profiles of egg yolk and breast meat for the hens of three genotypes¹

	Canarian	Lohmann Dual	Novogen BT	SEM	P-value
Egg yolk2
Fat (%)	32.41	31.78	32.36	0.245	0.517
∑SFA (%)	34.79	35.45	35.31	0.212	0.410
∑MUFA (%)	50.05	49.68	51.27	0.300	0.075
∑PUFA (%)	13.74	13.49	12.50	0.338	0.292
Breast meat3
Fat (%)	8.82	8.25	8.15	0.241	0.477
∑SFA (%)	28.91	29.66	29.52	0.225	0.367
∑MUFA (%)	51.77	50.93	50.17	0.298	0.086
∑PUFA (%)	18.30	18.38	19.26	0.275	0.290

¹SFA: saturated fatty acids; MUFA: monounsaturated fatty acids; PUFA: polyunsaturated fatty acids.

²Twenty egg yolks per genotype were used for assessments.

³Twenty meat samples per genotype were used for assessments.

Sensory evaluation

The results obtained from the organoleptic assessments of eggs and meat are presented in Table 7. Although the eggs produced by Canarian hens received a higher score (7.75) compared with those given to the eggs Lohmann Dual (6.70) and Novogen BT (7.10) hens, there were no significant differences among the three genotypes with respect to the external traits and overall palatability. Similarly, among the three breeds, the aroma of meat produced by Canarian hens was rated the highest (5.98; P < 0.05), although we detected no significant differences regarding the taste of the eggs produced by the different genotypes. However, compared with the meat produced by Novogen BT hens, that of Canarian hens was rated to be juicier (3.49 vs. 4.26) and greasier (2.17 vs. 2.96). With respect to overall palatability, compared with the meat produced by Novogen BT hens (5.13), the panelists gave equivalent higher scores to the meats of Canarian (6.15) and Lohmann Dual (6.15) hens.

Table 7.  Sensory analysis of eggs and meat from the hens of three genotypes

	Canarian	Lohmann Dual	Novogen BT	SEM	P-value
Egg
External assessment	7.43	7.30	7.59	0.107	0.672
Internal assessment	7.75a	6.70b	7.10b	0.111	0.001
Overall palatability	7.69	7.16	7.13	0.114	0.085
Meat
Aroma	5.98a	4.87b	5.13b	0.176	0.030
Taste	4.74	4.96	4.74	0.171	0.823
Juiciness	4.26a	4.00ab	3.49b	0.129	0.040
Greasiness	2.96a	2.53ab	2.17b	0.123	0.034
Overall palatability	6.15a	6.15a	5.13b	0.164	0.012

^a–bMeans within the same row denoted by different superscript letters are significantly different at the P < 0.05 level.

Discussion

Growth performance

In this study, we applied a non-linear Gompertz equation to characterize the body growth of Canaria, Lohmann Dual, and Novogen BT hens, with relatively high R² values being obtained for the fitted curves. Differences among model parameters indicated distinct growth patterns among the genotypes, with Canarian hens showing later maturation and higher asymptotic body weights than Lohmann Dual and Novogen BT hens. Asymptotic weight has been established to be strongly influenced by genotype and environmental conditions[32], and the asymptotic weight of Canarian hens (2.2 kg) assessed in the present study was found to be higher than that previously reported for certain other traditional breeds, such as Ardennaise and Fulani[33,34], and similar to values obtained for Portuguese and Italian local breeds[35,36]. In contrast, commercial dual-purpose breeds are generally characterized by higher asymptotic weights, which is presumed to reflect the influence of genetic selection and more conducive rearing conditions[34,37].

We also observed differences among the assessed genotypes with respect to inflection points. Previous studies have reported inflection points at approximately 10 to 12 weeks for local and dual-purpose hens[34,35,36,38,39], and our observations of earlier inflection points in Lohmann Dual and Novogen BT hens indicate an earlier attainment of maximum growth rate compared with that in some local breeds. Maximum growth rates reported in the literature differ considerably among local and dual-purpose genotypes[35,36,37], which is assumed to be associated with differences in genetic background and production purpose. In general, however, meat- and laying-type hens have characteristically distinct growth profiles, reflecting differences in tissue deposition and reproductive development[40].

It should also be noted that our experimental design included different approaches regarding breed acquisition, with Novogen BT birds being obtained as day-old chicks, whereas birds of the other two genotypes were derived from locally incubated eggs. Conceivably, this may have introduced early-life variability associated with the establishment of a resident microbiota or exposure to stress, potentially influencing later growth performance.

Laying performance

Egg production curves, which describe laying patterns over time, can be useful for evaluating age-related variation in laying performance[41]. Hens of the three genotypes assessed in the present study showed distinct laying patterns, reflecting their different genetic backgrounds and productive purposes. Canarian chicken are a rustic dual-purpose breed traditionally valued for small-scale household production[42], whereas Lohmann Dual is a modern dual-purpose breed selected for both male fattening and female laying[43], and Novogen BT hens are robust layers optimized for free-range egg production.

The values obtained for feed intake in this study are generally consistent with those reported for comparable genotypes under different production systems[18,43,44,45], with the feed intake of Canarian hens being comparable to those of other traditional heavy breeds, whereas the values obtained for Lohmann Dual and Novogen BT hens were within the expected ranges for dual-purpose and commercial layer breeds, respectively.

The low percentage of laying among Canarian hens (35%) could be explained in term of the broodiness trait of this breed, which was observed during several weeks of the experimental period, contributing to a substantial reduction in laying activity. Broodiness is a commonly observed behavior among indigenous breeds associated with temporary cessation of laying[46,47], and although this trait results in a reduction in egg output, it remains relevant in rural and smallholder systems, in which natural incubation contributes to the sustainability of flocks and household resilience[48].

The laying percentages of Lohmann Dual and Novogen BT hens recorded in this this study are somewhat lower than those previously reported for these and other commercial layer genotypes under the conditions imposed by intensive or cage systems[43,44,45]. These differences may be associated with differences in rearing conditions, management practices, and/or diet formulation. Egg mass values thus reflect the observed differences in laying rate among the hens of different genotypes.

Under the free-range conditions provided in this study, Novogen BT and Lohmann Dual hens were characterized by relatively efficient FCRs, whereas the higher FCR observed in Canarian hens is indicative of the lower productive efficiency of this breed compared with specialized layer and dual-purpose breeds, and is consistent with previous findings for this genotype[22]. Compared with intensive systems, free-range conditions are generally associated with greater levels of activity and lower rates of feed efficiency[49], with FCR values of close to 2 kg of feed per kg of eggs produced typically being obtained for intensively reared flocks of laying hens[50,51]. Nevertheless, recent genetic selection has contributed to enhancing the feed conversion efficiency of modern dual-purpose breed, with values reaching levels comparable with those of commercial layers[43].

Egg quality traits

According to the European egg classification standards[52], Novogen BT eggs are categorized as large, whereas Canarian and Lohmann Dual eggs were classified as medium-sized. Consistent with this distinction, previous studies have reported that under comparable rearing conditions, native breeds produce lighter eggs than commercial layers[4,9]. Given the general consumer preference for larger as opposed to smaller eggs[53], it is presumed that the selection of modern lines of laying hens has contributed to an increase in egg weight[6]. Considerable variability in egg weight has been described among native, dual-purpose, and commercial layer genotypes[4,9,43,45,54,55,56,57,58,59], confirming the strong influence of genotype on this trait[13]. Moreover, the weights of eggs laid by Canarian hens in the present study were found to be higher than those previously reported for this breed[22].

With regards to the shape of eggs, values obtained for the indices of Canarian and Novogen BT eggs were within the normal range for commercial layers[59], whereas Lohmann Dual eggs tended to be rounder, consistent with previous observations for this genotype[43]. However, although round eggs may provide greater shell stability[60], they are less compatible with standard packaging systems and may be more susceptible to breakage during transport[61].

Our findings regarding differences in the proportions of the yolk, albumen, and shell of eggs laid by hens of different genotypes are consistent with the previously reported strong influence of genetics on the proportional distribution of egg components[13,57,62]. Although such differences may have limited relevance for consumers, they are important factors from the perspective of food-processing applications, in which yolk or albumen is used as the main ingredient.

Consistent with previous findings, we found the color of eggshells to be strongly influenced by genotype[43,63]. The pigmentation of eggshells has been established to be dependent primarily on the relative proportions of protoporphyrin and biliverdin[64]. Commercial brown-egg breeds, such as Novogen BT, have been genetically selected for darker shell hues[57], and consistent with previous findings associating darker shells with heavier eggs[43,59], the eggs laid by Novogen BT hens in the present study had lower L* values and a greater weight compared with those of eggs laid by the other two breeds.

Eggshell quality traits, including the proportion, thickness, and strength of shells, are also strongly influenced by genetics[9,55,57], and we speculate that the greater strength of the shells of Lohmann Dual eggs may be attributable to their rounder shape, which has been associated with a greater resistance to breakage[61]. In contrast, eggs laid by the hens of genetically less selected breeds, such as Canarian, generally have shells of lower resistance than those of commercial brown layer breeds[13,45]. The findings of previous studies have also indicated that certain differences in mineral composition contribute to the greater strength of the shells of darker brown eggs[64].

Yolk color is an important quality trait that is mainly influenced by the composition of the feed consumed[65,66]. Given that all hens assessed in the present study were reared under the same conditions and received the same diet, the observed differences in the redness (a*) and yellowness (b*) of yolks of eggs laid by the different genotypes were somewhat unexpected. Whereas the findings of some studies have indicated an absence of any genotypic effects on yolk color[4,22,55,59], others have reported differences associated with genotype-dependent foraging behavior during access to outdoor environments[13]. However, the limited vegetation available in the outdoor areas used in the present study would tend to imply that dietary intake of natural pigments was probably low. Consequently, it is conceivable that the higher carotenoid concentrations observed in Canarian eggs may reflect genetic differences influencing the absorption, metabolism, or deposition of carotenoids[9,67,68,69].

Carcass and meat quality traits

As anticipated, we found that among the three assessed breeds, Canarian hens were characterized by higher slaughter and carcass weights at 74 weeks, consistent with their greater body growth. However, their weights were lower than those reported for some autochthonous meat-type breeds slaughtered at similar ages[18,59], indicating that body weight may be considered a key criterion when local hens are intended for meat production after the laying period[17]. In contrast, values obtained for the slaughter and carcass weights of Novogen BT hens were similar to those previously reported for commercial brown layer strains[45,70], reflecting the genetic improvements in carcass traits even in egg-producing breeds.

Although the slaughter and carcass weights of Lohmann Dual hens were found to be lower than those previously reported for this breed[45], which may be associated with the presence of a sex-linked dwarf gene limiting female growth[71], the carcasses of these hens were assessed to have satisfactory meatiness, particularly the breast muscle, which is consistent with previous findings reported for this genotype[45].

With respect to pH measured at 24 h post-mortem, whereas the values obtained were within the normal ranges reported in the literature[18,45,59,70], it has, nevertheless, been established that final muscle pH may also be influenced by genetic differences in susceptibility to stress and depletion of muscle glycogen content during pre-slaughter handling[17,72].

Compared with the two commercial breeds, both the skin and meat of Canarian hens were characterized by higher yellowness (b*) values, which is consistent with previous observations for this genotype[15], and may be associated with genetic differences in pigment deposition and muscle composition[18,73]. Skin and meat yellowness are considered important quality traits in free-range poultry products, as consumers often associate these features with naturalness and product authenticity[74,75].

Although observed differences among the three breeds with respect to cooking loss are consistent with the findings of some previous studies[17,70,73], others have reported no genotypic effect[18,45,59,72]. This trait reflect differences in the water-holding capacity of tissues, which are primarily associated with differences in myofibrillar proteins and are influenced by both genetic and environmental factors[76,77].

In contrast to our findings in this study, several authors have reported no significant differences in breast meat shear force among the hens of different breeds reared under similar conditions[17,20,45,70]. Nevertheless, the tenderness of meat has been established to associated with breed-related differences in sarcomere length, muscle fiber diameter, and muscle structure[73].

Fat contents and fatty acid profiles of egg yolk and breast meat

Our findings regarding the fat contents and fatty acid profiles of egg yolk and breast meat are consistent with those of several studies that have reported no significant differences in total fat content or fatty acid profiles of egg yolks[22,55,58] and breast meat[18] among hens of different genotypes, although others have detected differences in the proportions of monounsaturated, saturated, and polyunsaturated fatty acids[9,44,68]. However, owing to differences in diet, age, and rearing conditions, comparisons among studies in this regard are generally difficult. Although genetic background may influence lipid metabolism and the composition of fatty acids[55,68], the composition of dietary fatty acids is generally considered the main determinant of the lipid profiles in eggs and meat[4,44]. Accordingly, previous authors have suggested that identical diets and management conditions may contribute to minimizing genotypic differences in the fatty acid composition of poultry products[57,78].

Sensory evaluation

Despite differences in the size and shell color of eggs laid by the hens of different breeds, panelists tasked with performing sensory evaluations assigned similar scores for the external appearance of the eggs produced by these hens. Although consumer preferences for egg traits differ among countries and markets, the color of egg yolk is generally considered one of the most influential quality attributes[65]. In the present study, the eggs laid by Canarian hens received the highest internal quality scores, which can mainly be ascribed to the more intense yolk coloration, which is associated with higher carotenoid concentrations and redness and yellowness values. These findings are consistent with those previously reported indicating that consumers in Southern European countries prefer intensely colored (golden-orange) yolks[67].

With regards to the evaluation of hen meat, the higher intensity of the aroma perceived for the meat of Canarian hens contrasts with previous reports describing the more intense aroma of meat produced by commercial hybrids compared with that of local breeds[70]. However, other authors have reported that meat from heavier hens may have a more intense aroma and flavor[17]. Although the panelists in the current study were unable to evaluate the tenderness of meat, as samples were presented in burger form, they were, nonetheless, able to assess juiciness and greasiness, which are associated with certain physicochemical characteristics of meat. Given that spent hen meat is often characterized by a lower tenderness due to age- and breed-related changes in muscle structure[18], presenting the meat in burger form may contribute to gaining consumer acceptability and represent a useful strategy for valorizing these products.

Ethical approval

All animal procedures performed in this study were conducted in accordance with the European Directive 2010/63/EU and Spanish RD53/2013 regulations on the protection of animals used for scientific purposes. The animals were reared and slaughtered (in an official slaughterhouse) following standard commercial farm practices without applying any experimental or invasive procedures beyond routine management. The animal study protocol was approved by the Institutional Animal Welfare and Ethics Review Committee of Canary Islands Institute for Agricultural Research/Canary Government (approval code: CEEA-ICIA-2025-003; approval date: 7^th March 2025).

Funding

This research was funded by Fundación CajaCanarias and Obra Social La Caixa (Proyecto 2018 Patri31).

Acknowledgements

The authors thank the Association of Breeders of Canarian Chickens, Grupo Capisa, and Grupo Sada for their contribution to the experimental procedures. We also wish to thank Nicolas Darmanin and Julian Hernández (ICIA) for their valuable assistance in animal care and sensory analysis.

Author contributions

Serezade Sigut, Eva Dorta, and Alexandr Torres conducted the experiments; Alexandr Torres and Maria Fresno performed data analysis; María Fresno acquired funding; Maria Fresno, Sergio Álvarez, and Noemi Castro supervised the experimental design and animal welfare; Alexandr Torres wrote the manuscript.

Conflict of interest

The authors declare that they have no conflicts of interest.

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