Poultry production is an integral component of agriculture. It serves as the most important and quickest source of animal protein and household income, thereby improving family nutrition, health, and the livelihood of high- and low-level farmers in rural and urban communities [1,2,3,4]. In Nigeria, one of the traditional poultry species is the helmeted guinea fowl (Numida meleagris) [5]. Economically, guinea fowl are more attractive in the tropics due to less demand with respect to diet and better adaptation to the traditional poultry system when compared to chicken [6,7]. There is a high value for the eggs of guinea fowl because of their nutrient contents, thick shells, longer shelf life, and the premium prices they attract compared to chickens [5,8]. The bird is a seasonal bird, and its breeding activity peaks in the summer period. During this period, which coincides with the rainy season in the tropics, there are a variety of plants and insects for the birds to feed on [9,10].

In spite of the benefits derived from guinea fowl, its characterization in the tropics is poor, thereby limiting the exploitation of its full potential for sustainable economic growth and development [7]. In Nigeria, previous research and development endeavors such as the Programme for Emerging Agricultural Research Leaders (PEARL) and African Chicken Genetic Gains (ACGG) focused on chicken, while other poultry species like guinea fowl have been neglected. Also, reproductive performance (fertility and hatchability characteristics), which are crucial to guinea fowl profitability [11], and egg quality traits of guinea fowl [12,13,14] in the country have not been widely exploited. Such information is vital to unraveling the potential of the underutilized poultry genetic resource in order to map out appropriate selection and breeding strategies for improvement in the production and productivity of the birds. It has been reported that egg quality indices are useful for breed assessment and standardization [15]. The establishment of a relationship between traits and the prediction of egg weight from egg quality parameters is also of interest [16]. Additionally, in the poultry egg industry, egg quality parameters affect consumer preference, quality grading, price, fertility, hatchability, and weights of newly hatched birds [17]. Based on this, the current study aimed to characterize the fertility, hatchability, and egg quality parameters of indigenous helmeted and exotic guinea fowls.

The exotic birds performed better than their indigenous counterparts in terms of hatchability and fertility. This may be a result of a differential genetic constitution. According to Zeleke et al. [13], the differences among genetic groups of guinea fowl in terms of fertility and hatchability could be a reflection of previous interventions on selection and breeding. However, the values obtained in the indigenous stock are comparable to the hatchability range of 58.9–76.7% and fertility rate of 49.2–70.0% reported by Obike et al. [34]. In the current study, the fertility value of the Nigerian indigenous stock was higher than the values of 55.97% [35] and 57% reported by Zeleke et al. [13]. Also, the indigenous stock had a higher hatchability value compared to the 50.4% reported by Atawalna et al. [36]. However, a lower hatchability percentage was obtained in comparison with the hatching rates of 72.92 and 82.2% reported by Yakubu et al. [35] and Adu-Aboagye [37], respectively. In other studies, the fertility of guinea fowl eggs has been reported to range from 70 to 85% [38,39], while hatchability ranges from 72 to 80% [40,41]. The observed variations in the indigenous guinea fowls of Africa could possibly be due to environmental factors (as they were reared in different agro-ecosystems), varying management systems, health status, sex structure, age and weight of guinea hens, egg size, and incubator conditions. Also, the guinea fowls of the current study were naturally mated; there is every possibility that if artificial insemination is adopted, better results would be obtained. This is congruous with the submission of Hudson et al. [42] that artificial insemination is a veritable tool in the improvement of guinea fowl’s fertility and hatchability.

Guinea fowls are highly valued for their eggs because of their nutritional and health benefits. On average, eggs from the exotic birds seemed to be better than those from their indigenous counterparts in most parameters investigated. The superior edge in egg quality characteristics of the exotic birds, especially egg weight, is not surprising considering the fact that the birds have been subjected to artificial selection. According to Krunt et al. [15], higher egg weight is a product of the selective process involving birds of superior advantage in terms of performance. Therefore, there is every possibility that if the indigenous birds are upgraded using the exotic gene pool, there may be an improvement in the egg quality parameters, with an emphasis on egg weight, which has been reported as a crucial indicator for breed standardization, quality grading, and consumer evaluation [43,44]. The mean egg weight value of 41.50 g in exotic birds is comparable to the value of 40.37 g reported for French Broiler Guinea Fowl guinea fowl strain in Kastina State, Nigeria [45], but less than 43.44 g and 51.68 g reported by Krunt et al. [15], and Kouame et al. [46], respectively. The egg weight value of 34.1 g in indigenous birds is lower than the 37.3 and 37.5 g reported for guinea fowl in Sarki and Birnin Kebbi, Nigeria, by Idowu et al. [14]. However, apart from genetics, other non-genetic factors such as age, nutrition, and the system of management can influence egg quality parameters [47,48].

The estimates of correlation are comparable to those reported in similar studies [16,24,49,50]. The strong and positive association of egg weight with egg width, egg length, shell, yolk and albumen weights, and shell thickness is in consonance with the submissions of earlier workers [24,27]. The negative correlation between egg weight and haugh unit is consistent with the findings of Bernacki et al. [27] and Khaleel [28]. The strong relationship existing between egg weight and some egg parameters may be useful as a selection criterion, as it is possible that they have the same gene action. This, therefore, provides a basis for the genetic manipulation and improvement of the indigenous guinea stock for better egg quality traits. High correlation coefficients among the variables also make it possible to predict egg weight from egg quality parameters.

Three principal components were extracted (out of a total of sixteen original independent variables), which were able to account for a good percentage of the generalized variance in the egg quality parameters investigated. These, according to Malfatti et al. [51], can be used to assess the relationship between the different egg quality indices as well as their assignment into various groups. The stepwise regression revealed the importance, especially of egg width, in the prediction of egg weight. However, due to the problem of multicollinearity, the ordinary least squares method (stepwise regression) estimates may be biased compared to estimates from the principal component factor scores and ridge regression [30,52]. Also, in the CHAID model, egg width alone and in combination with albumen weight were the best predictors of egg weight in indigenous and exotic guinea fowls. The CHAID model, which is non-parametric, does not impose assumptions on the independent variables compared to multiple linear regression. In this study, the CHAID model was more consistent in the estimation of egg weight in both genetic groups. Therefore, it might be an indispensable tool in the poultry industry with regard to egg quality classification. This is in accordance with earlier reports [32,53]. Egg width can easily be measured. This becomes imperative as this information could be exploited in estimating egg weight where resources are limited. The prediction of egg weight from other egg quality parameters has been reported [16]. Albumen weight, as observed in the present study, has also been reported to be a good indicator of egg weight [27].