Analysis of Growth Hormone Gene Polymorphism and Its Association with Growth Traits in Kenguri Sheep
Abstract
The present study investigated polymorphisms of the growth hormone (GH) gene and their association with morphometric traits in Kenguri sheep, an important meat-type breed of Karnataka, India. A total of 60 adult sheep (16 males and 44 females) were sampled for genomic DNA isolation using a modified high-salt method. The GHgene fragment (422 bp) spanning exon 2–3 was amplified through polymerase chain reaction (PCR) and genotyped by PCR–restriction fragment length polymorphism (PCR-RFLP) using the HaeIII enzyme. Two genotypes, AAand AB, were detected, while BBwas absent. The frequencies of AAand ABgenotypes were 0.417 and 0.583, respectively, with allele frequencies of 0.708 (A) and 0.292 (B). Chi-square analysis indicated significant deviation from Hardy–Weinberg equilibrium (χ²=10.29, p<0.05). Morphometric traits including body weight, body length, height at wither, and chest girth were recorded. Males showed significantly (p<0.05) higher body weight and chest girth than females, while other traits were comparable. Within genotypes, no significant association (p>0.05) was found between GHpolymorphisms and body measurements in either sex. The findings confirm the presence of GHgene variability in Kenguri sheep, with predominance of heterozygotes, although no strong phenotypic association was evident. This suggests that while the GHgene harbours genetic variability, additional markers or larger populations may be required to elucidate its role ingrowth performance. The study provides baseline molecular information that could support marker-assisted selection (MAS) strategies for sheep improvement programs in India.
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Introduction
India harbours one of the world’srichest livestock genetic resources, with 65 million sheep distributed across diverse agro-climatic regions [1]. Sheep playa vital role in rural livelihood through meat, wool, and skin production. In recent decades, the demand for mutton has increased steadily, underscoring the need for scientific breeding strategies that improve productivity while conserving indigenous breeds. Kenguri sheep, primarily reared in the Koppal and Raichur districts of Karnataka, are a medium-to-large sized mutton-type breed characterized by their adaptability, disease resistance, and increasing popularity in stall-feeding systems [2]. Despite their potential, genetic improvement efforts in Kenguri sheep remain limited. Molecular markers, particularly those associated with growth, offer an opportunity to accelerate breed improvement. The growth hormone (GH) gene, synthesized by somatotroph cells of the pituitary gland, is a crucial regulator of postnatal growth, lactation, reproduction, and metabolism [3,4]. It influences body weight, height, and carcass quality both directly and through the insulin-like growth factor (IGF) pathway [5]. Due to its central role, GHhas been widely investigated as a candidate gene for marker-assisted selection (MAS) in livestock [6].
Polymorphisms in GHhave been reported in several sheep breeds worldwide, including Indian populations such as Nellore, Patanwadi, and Vembur [7–9]. However, the extent of GHvariability in Kenguri sheep and its association with growth traits has not been systematically studied. So this study was designed to detect polymorphisms of the GHgene in Kenguri sheep using PCR-RFLP, estimate genotype and allele frequencies and test Hardy–Weinberg equilibrium and assess associations between GHpolymorphism and morphometric traits (body weight, body length, chest girth, and height at wither).
Conclusion
This study documents the presence of GHgene polymorphism in Kenguri sheep, identifying two genotypes (AAand AB) with a predominance of heterozygotes and absence of BB. The population deviated significantly from Hardy–Weinberg equilibrium, suggesting non-random mating or selection effects. Although no significant associations were detected between GHpolymorphism and morphometric traits, the findings provide baseline molecular information useful for breed conservation and genetic diversity studies. Future research with larger populations and multiple candidate genesis required to clarify the role of GHand related markers ingrowth performance and to establish effective marker-assisted selection strategies in Kenguri sheep. CONFLICT OF INTEREST Author declares no conflict of interest
