INTRODUCTION

Chickens are among the most important poultry species supporting food security and rural livelihoods in Indonesia, particularly for smallholder farmers who rely on them as a primary source of animal protein and household income [1]. Among the diverse native chicken populations, the Kampung Unggul Balitbangtan (KUB) chicken, developed by the Indonesian Agency for Agricultural Research and Development (Balitbangtan), has emerged as a genetically improved line with enhanced productivity, adaptability, and resilience to tropical environmental conditions [2]. KUB chickens were selectively bred from local village chickens through a systematic genetic improvement program to optimize egg production, growth rate, and feed efficiency while retaining the robust adaptive and behavioral characteristics of indigenous breeds [3]. Continuous genetic improvement is essential to sustain and enhance the performance of KUB chickens, given their dual-purpose role in egg and meat production and their socio-economic importance to smallholder poultry systems [4]. Their superior meat flavor, disease tolerance, and ability to thrive under high-temperature environments highlight their potential as a strategic genetic resource for sustainable poultry production in tropical regions.

Genetic factors governing growth and carcass traits are heritable and thus highly valuable for breeding programs aimed at enhancing productivity [5]. Investigating gene polymorphisms and their associations with economic traits offers a powerful approach for identifying candidate alleles that can be utilized as molecular markers in marker-assisted selection (MAS) programs [6]. Single-nucleotide polymorphisms (SNPs), in particular, provide high-resolution markers for studying genetic variation, yet their utility requires validation across diverse populations and breeds [7]. Among candidate genes associated with growth and muscle development, the transforming growth factor-beta 2 (TGFβ2) gene, located on chromosome 3, is recognized as a key regulator of cellular proliferation, differentiation, tissue remodeling, and immune response modulation [8, 9]. Previous studies have linked TGFβ2 gene polymorphisms to growth performance and meat quality traits in several livestock species, including cattle, pigs, and commercial chicken lines [10]. In chickens, TGFβ2 polymorphisms have been associated with growth and production traits in commercial broilers, layer lines, and several indigenous breeds. However, these findings cannot be directly extrapolated to genetically distinct native-derived populations, as breed-specific genetic architecture and selection history may influence allelic distribution and phenotypic effects [11]. To date, no study has characterized TGFβ2 genetic variation or evaluated its association with economic traits in the selectively bred KUB chicken, Indonesia’s improved native dual-purpose breed developed for tropical smallholder production systems.

Although TGFβ2 gene polymorphisms have been investigated in commercial broiler and layer lines as well as some indigenous chicken breeds, information on their occurrence, distribution, and functional significance in selectively improved native breeds such as KUB chickens is lacking. Previous studies have primarily examined associations with growth traits under standard feeding conditions, with limited attention to potential interactions between TGFβ2 variants and nutritional interventions such as multienzyme supplementation. Furthermore, integrated evaluations of TGFβ2 polymorphisms on both growth performance and meat quality traits in tropical smallholder production contexts remain scarce. This gap limits the application of MAS programs tailored to the genetic resources of Indonesian native poultry.

Therefore, the objective of this study was to characterize TGFβ2 gene polymorphisms in KUB chickens and to evaluate their associations with growth performance and meat quality traits under varying levels of dietary multienzyme supplementation. This research is expected to provide novel molecular markers and nutrigenetic insights that support precision breeding and feeding strategies for sustainable productivity in indigenous tropical chicken populations.