Organ characteristics and Adaptive Traits of F₁ Backcross Progenies Derived from Normal-Feathered, Naked-Neck, and Frizzle Crossbred Chickens under Humid Tropical Conditions
Sustainable poultry production in the humid tropics requires genotypes with enhanced physiological adaptability to thermal stress. This study evaluated organ characteristics and adaptive traits of F₁ backcross progenies derived from crosses between indigenous chicken genotypes—Normal-feathered (NF), Naked-neck (Na), and Frizzle (F)—and an exotic broiler breeder strain (Anak) under hot–humid tropical conditions. The experiment was conducted at the Teaching and Research Farm of Michael Okpara University of Agriculture, Umudike, Nigeria (05°29′N; 07°33′E; 122 m above sea level), characterised by high ambient temperatures (27–36 °C), relative humidity of 57–91%, and annual rainfall of approximately 2,177 mm. These climatic conditions impose significant thermoregulatory and metabolic challenges on poultry, thereby providing an appropriate environment for assessing genotype-specific adaptive responses. A structured main and reciprocal crossbreeding design was employed to generate six F₁ hybrid groups: E × NF, E × Na, E × F (main crosses), and NF × E, Na × E, F × E (reciprocal crosses). Artificial insemination was adopted to minimise confounding effects of body size differences between indigenous and exotic parents. All F₁ progenies possessed approximately 50% indigenous and 50% exotic genetic background, enabling assessment of heterotic and maternal effects. Birds were managed uniformly under deep-litter housing and provided age-appropriate commercial diets and routine vaccination schedules. At six weeks of age, representative birds from each genetic group were slaughtered for organ evaluation. Internal organs—including heart, liver, gizzard, proventriculus, lungs, kidneys, pancreas, crop, and intestines—were excised and weighed. Organ weights were expressed as percentages of live body weight to eliminate size-related bias. Data were analysed using Analysis of Variance within a Randomised Complete Block Design framework, with genotype as the fixed effect and hatch as the blocking factor. Significant (P < 0.05) genotypic differences were observed in heart, proventriculus, lung, and kidney proportions, whereas liver and gizzard proportions showed no significant variation. Reciprocal crosses generally exhibited superior relative organ development compared to main crosses. Notably, the reciprocal frizzle cross (F × E) recorded the highest proportions of heart (1.02%), proventriculus (0.88%), lungs (0.69%), and kidneys (1.72%). Enhanced heart and lung development suggests improved cardiopulmonary capacity and oxygen utilisation, which are critical for sustaining metabolic activity under elevated ambient temperatures. Similarly, increased proventriculus and kidney proportions indicate enhanced digestive secretory function and osmoregulatory efficiency, respectively, key physiological processes for maintaining homeostasis during heat stress. The superior organ development observed in reciprocal crosses highlights the importance of maternal and cytoplasmic influences in shaping adaptive physiological traits. The frizzle and naked-neck genotypes, characterised by reduced feather coverage, likely exhibit improved heat dissipation, allowing metabolic energy to be redirected towards visceral organ development rather than feather synthesis. These adaptive advantages may confer improved resilience and productivity in humid tropical production systems. In conclusion, incorporation of adaptive major genes, particularly through reciprocal crossing strategies involving frizzle and naked-neck genotypes, significantly enhances organ development patterns associated with thermoregulation and metabolic efficiency. The findings underscore the value of genotype-based breeding strategies aimed at improving physiological adaptability and sustainable poultry production under hot–humid tropical conditions.
Keywords: F₁ backcross; frizzle; naked-neck; organ proportion; adaptive traits; humid tropics; poultry breeding; thermoregulation.
