The meat production industry encounters challenges in augmenting carcass and meat quality attributes, significantly influencing consumer preferences and demand amid the global upsurge in meat consumption [1,2]. Key attributes encompassing body morphology, skeletal architecture, vertebral characteristics, muscular development, tenderness, and adipose deposition in livestock species hold paramount significance in governing both meat quality and quantity [3,4,5,6,7,8,9].

In the domain of livestock breeding, the pursuit of augmenting traits related to body size has emerged as a central objective, particularly in China, due to its substantial influence on meat production and carcass traits [10,11,12]. Recent research underscores the economic significance of vertebral count in determining carcass length, weight, and body size traits [10,11,12,13]. Variations in body size have emerged within and between domestic animal species or breeds during livestock evolution [14]. Notably, the number of thoracolumbar vertebrae plays a crucial role in carcass characteristics, particularly carcass length [15]. Across different pig breeds [16], sheep breeds [17], donkeys [10,18], and yaks [19], variations in the number of thoracolumbar vertebrae have been observed. This trait has been considered a selection criterion in commercial animal breeding due to its strong correlations with growth and meat production, exhibiting high heritability (0.60–0.62) and a positive correlation with body length [15].

China has made significant advancements in livestock genetic improvement, particularly in pig breeding [20]. However, enhancing breeding efficiency and accuracy remains a challenge. Molecular marker techniques, such as marker-assisted selection (MAS), have emerged as a rapid and effective approach [21,22,23]. MAS relies on the linkage between phenotypic traits and molecular markers within the genome, enabling the swift and accurate identification of individuals with desired traits, thus improving breeding efficiency. Identifying candidate genes and their polymorphisms associated with vertebral traits holds scientific and economic significance, providing markers for genetic enhancement in livestock.

The influence of genetic factors and signaling pathways on multi-vertebrae traits in livestock is a complex and multifaceted area of research. Several studies have shed light on the genetic underpinnings of these traits, with a focus on genes such as PLAG1, VRTN, PRKG2, MMP4, NR6A1, LTBP2, DCAF7, NCAPG-LCORL, ActRIIB, and TGFβ3, as well as their associations with specific vertebral characteristics in various livestock species, especially pigs, donkeys, and sheep. Consistently, Yan et al. [10] and Liu Z et al. [18] emphasized the quantitative nature of these traits, indicating that they are influenced by multiple genes and intricate biological signaling pathways. This highlights the polygenic nature of multi-vertebrae traits, where numerous genetic factors interplay to determine the final outcome. The genes PLAG1 and NCAPG-LCORL, originally known for their roles in human height, carcass weight, and body length, have emerged as key players in livestock vertebral traits, underscoring their pleiotropic effects [24]. Furthermore, specific mutations in genes like ActRIIB and TGFβ3 have been linked to variations in vertebral number in sheep and pigs, respectively. Liu J et al. [25] identified a point mutation in intron 4 of the ActRIIB gene in Small-Tailed Han sheep associated with vertebral number variation. Similarly, Yue J et al. [26] reported that the mutation g.105179474 G  > A in the TGFβ3 gene was associated with rib and thoracolumbar vertebrae numbers in pigs, highlighting the genetic diversity that can underlie these traits. In Beijing Black pigs, Niu N et al. [27] identified a significant link between variant-g.19034 A  >  C of the VRTN gene and multiple thoracic vertebrae numbers, further exemplifying the genetic complexity of vertebral traits in sheep and pigs.

Donkeys are a comparatively less explored area in this context and have shown promising insights. Shi et al. [28] reported significant associations between specific genetic loci, HOXC8 g.15179224C  >  T and g.15179674G  >  A, with lumbar vertebrae length and the number of lumbar vertebrae. This highlights the potential for genetic selection and breeding strategies to influence vertebral traits in donkeys, similar to other livestock species. Nevertheless, the existing body of literature to date has exclusively focused on the investigation of genetic markers associated with vertebral traits in donkeys, sheep, and pigs. However, it is noteworthy that comprehensive investigations into the association of genetic markers with vertebral traits in cattle and horses have been absent from the existing body of research. Drawing upon the aforementioned evidence, it becomes evident that variations in vertebral traits among livestock species (donkeys, sheep, and pigs) can significantly influence changes in body size, carcass length, and weight. Furthermore, it is essential to recognize that vertebral traits are inherently quantitative in nature, controlled by a complex interplay of multiple genes. Thus, the exploration and screening of genes associated with these vertebral traits hold substantial potential for enhancing meat production within the livestock sector, thereby making a notable contribution to the meat industry.

2. Genetic Markers Associated with Number of Vertebrae in Pigs, Donkeys, and Sheep

2.1. Genetic Markers Associated with Number of Vertebrae in Pigs

2.2. Genetic Markers Associated with Number of Vertebrae in Donkeys

2.3. Genetic Markers Associated with Number of Vertebrae in Sheep