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Simple Summary: Ashidan yak is a new breed of hornless yak developed by Chinese scientists, which has an important economic value. However, little is known about the growth of Ashidan yaks. This study analyzed the body weight and body size measurements of 260 female Ashdan yaks and compared the performance of five nonlinear models (Logistic model, Gompertz model, Brody model, von Bertalanffy model and Richards model). Our results showed that the early growth and development of Ashidan yak change with the seasons, and the Richards model performs better among the five models. Understanding animal growth plays an important role in improving animal genetics and breeding. In order to explore the early growth and development law of Ashidan yak, the body weight (BW), wither height (WH), body oblique length (BL) and chest girth (CG) of 260 female Ashidan yaks were measured. These individuals grew under grazing conditions, and growth traits were measured at 6, 12, 18 and 30 months of age. Then the absolute growth and relative growth of Ashidan yak were calculated, and five nonlinear models (Logistic model, Gompertz model, Brody model, von Bertalanffy model and Richards model) were used to fit the growth curve of Ashidan yak. The fitting effect of the model was evaluated according to MSE, AIC and BIC. The results showed that the growth rate of Ashidan yak was the fastest from 12 to 18 months old, and the growth was slow or even stagnant from 6 to 12 months old. The AIC and BIC values of the Richards model were the lowest among the five models, with an AIC value of 4543.98 and a BIC value of 4563.19. The Richards model estimated body weight at 155.642 kg. In summary, the growth rate of female Ashidan yak changes with the seasons, growing faster in warm seasons and slower in cold seasons. Richards model is the best model to describe the growth curve of female Ashidan yak in five nonlinear models. [ABSTRACT FROM AUTHOR]

Simple Summary: As a domestic animal living in the Qinghai-Tibet Plateau at high altitudes from 2000 to 5000 m, the growth rate of the yak is slow under extremely harsh natural environmental conditions, such as high altitude, low temperatures, and low oxygen. Compared with conventional selection, using molecular markers in breeding to improve yak growth traits is more efficient. Many studies have indicated that CNV mutations can significantly affect the phenotypic traits of livestock and poultry. This study explored the association between the growth traits and CNVs of SOX5 and SOX8 in 326 Ashidan yaks. Our results showed that CNVs and the CNV combination of SOX5 and SOX8 were significantly associated with withers height and chest girth (p < 0.05), suggesting these mutations could be new markers for the selection of yak growth traits. Copy number variation (CNV) is a structural variant with significant impact on genetic diversity. CNV has been widely used in breeding for growth traits, meat production or quality, and coat color. SRY-like box genes (SOXs) are a class of transcription factors that play a regulatory role in cell fate specification and differentiation. SOX5 and SOX8 belong to subgroups D and E of the SOXs, respectively. Previous studies have shown that SOX5 and SOX8 are essential in the development of bones. In this study, we explored the association between the growth traits and CNVs of SOX5 and SOX8 in 326 Ashidan yaks and detected mRNA expression levels in different tissues. Our results illustrated that CNVs of SOX5 and SOX8 were significantly associated with withers height at 18 months of age and chest girth at 30 months of age (p < 0.05). The CNV combination of SOX5 and SOX8 was significantly associated with withers height at 18 months of age (p < 0.01). SOX5 expression in the lung was significantly higher than in the heart, spleen, kidney, and muscle (p < 0.05). SOX8 expression in the lung was significantly higher than in the liver and muscle (p < 0.05). Our results provide evidence that the CNVs of SOX5 and SOX8 genes could be used as new markers for the selection of yak growth traits. [ABSTRACT FROM AUTHOR]

Simple Summary: Yak is the dominant animal species in China's plateau regions. The development of the yak industry is conducive to protecting the ecosystem of the Qinghai–Tibet Plateau and promoting local economic development. However, the slow growth and development of yak have seriously affected the development of the yak industry. Structural variation (SV) has been widely applied in livestock breeding for growth traits. Therefore, it is of great significance to use SV to improve yak growth traits in yak breeding. Meanwhile, the GHR gene plays an important role in the formation and normal development of bones. This study associated the correlation between the yak GHR SV gene and growth traits and confirmed that GHR-SV can be used as a molecular marker for the early reproduction of yaks. This study provides a theoretical basis for the early growth and development of yaks. The growth hormone receptor (GHR) is a member of the cytokine/hematopoietic factor receptor superfamily, which plays an important role in the growth and development, immunity, and metabolism of animals. This study identified a 246 bp deletion variant in the intronic region of the GHR gene, and three genotypes, including type II, type ID, and type DD, were observed. Genotype analysis of structural variation (SV) was performed on 585 individuals from 14 yak breeds, and it was found that 246 bp deletion was present in each breed. The II genotype was dominant in all yak breeds except for SB yak. The association analysis of gene polymorphisms and growth traits in the ASD yak population showed that the 246 bp SV was significantly associated with body length at 6 months (p < 0.05). GHR messenger RNA (mRNA) was expressed in all the tested tissues, with significantly higher levels in the liver, muscle, and fat than in other organs. The results of transcription activity showed that the luciferase activity of the pGL4.10-DD vector was significantly higher than that of the pGL4.10-II vector (p < 0.05). Additionally, the transcription-factor binding prediction results showed that the SV in the runt-related transcription factor 1 (Runx1) transcription-factor binding site may affect the transcriptional activity of the GHR gene, regulating yak growth and development. This study showed that the novel SV of the GHR gene could be used as a candidate molecular marker for the selection of the early growth trait in ASD yak. [ABSTRACT FROM AUTHOR]