Effects of GHRP-2 and Cysteamine Administration on Growth Performance, Somatotropic Axis Hormone and Muscle Protein Deposition in Yaks (Bos grunniens) with Growth Retardation.

Rui Hu,Yixin Wang,Quanhui Peng,Huawei Zou,Wenhua Zhang,Suonan Zhao,Zhisheng Wang,Quanxi Niu,Xiangying Kong,Binghai Cao,Shanke Bao,Hongze Wang,Hanzhong Ji,Xiaoping Jing,Xiaoqiang Yu,Leo T.O Lee

doi:10.1371/journal.pone.0149461

Abstract

The objective of this study was to investigate the effects of growth hormone-releasing peptide-2 (GHRP-2) and cysteamine (CS) administration on growth performance in yaks with growth retardation and try to elucidate its regulatory mechanisms. Trial 1, thirty-six 1-year-old Qinghai high plateau yaks (body weight 38–83.2 kg) were randomly chosen for body weight and jugular blood samples collection. The relationship between body weight and serum GHRH (P < 0.05, R = 0.45), GH (P < 0.05, R = 0.47), IGF-1 (P < 0.05, R = 0.62) was significantly correlated in yaks colonies with lighter body weights. Trial 2, fifteen 1-year-old Qinghai high plateau yaks with growth retardation (average body weight 54.8 ± 8.24 kg) were randomly selected and assigned to negative control group (NG), GHRP-2 injection group (GG) and cysteamine feeding group (CG), with 5 yaks per group. Another five 1-year-old Qinghai high plateau yaks with normal growth performance (average body weight 75.3 ± 2.43 kg) were selected as positive control group (PG). The average daily gain (ADG) of the GG and CG were significantly higher than those in the PG and NG (P < 0.05). Both GHRP-2 and CS administration significantly enhanced the myofiber diameter and area of skeletal muscle (P<0.05). GHRP-2 significantly enhanced the serum GH and IGF-1 levels (P < 0.05), and up-regulated GHR, IGF-1 and IGF-1R mRNA expression in the liver and skeletal muscle (P < 0.05), enhanced the mRNA expression of PI3K, AKt and mTOR in the skeletal muscle (P<0.05). CS significantly reduced the serum SS levels and the hypothalamus SS mRNA expression (P < 0.05), and enhanced GHR and IGF-1 mRNA expression in the liver (P < 0.05), decreased the mRNA expression of muscle atrophy F-box (Atrogin-1) and muscle ring finger 1 (MuRF1) mRNA (P < 0.05). Conclusions: Growth retardation in yaks was primarily due to somatotropic axis hormones secretion deficiency. Both GHRP-2 and CS administration can accelerate growth performance and GH, IGF-1 secretion in yaks with growth retardation. GHRP-2 enhanced muscle protein deposition mainly by up-regulated the protein synthesis pathways, whereas CS worked mainly by down-regulated the ubiquitin-proteasome pathway.

Highlights

Bovid yaks (Bos grunniens) are primarily distributed in the Tibetan plateau
The group average serum growth hormone releasing hormone (GHRH), growth hormone (GH) and insulin-like growth factors (IGFs)-1 levels increased with the average body weight
GHRP2 injection and CS supplementary feeding significantly enhanced the expression of GHR and IGF-1 mRNA in the liver (P < 0.05)

Summary

Introduction

Bovid yaks (Bos grunniens) are primarily distributed in the Tibetan plateau. More than 20 million yaks (92 percent of the world population) are found in China. Yaks play an important role in the daily life of local herdsman and represent an important source of meat, milk, wool and fuel. Yak meat is increasingly popular and provides a significant contribution to the local economy, studies are increasingly focusing on yaks growth performance. Growth retardation is widespread in yaks due to cold temperatures, food deprivation, malnutrition, various diseases, severe plateau environmental conditions and primitive grazing methods. The phenomenon is similar to that observed in stunted children living in severely poor regions. Malnutrition and disease can cause permanently stunted growth in both children and calves [1,2,3]. Yaks with growth retardation are associated with extremely low feed conversion efficiency, great morbidity and mortality, which lead to increased yak breeding costs

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