Effects Of GHRP-2 And Cysteamine On Growth Improvement And Mechanisms Of Yaks (Bos Grunniens) With Growth Retardation

The yaks with growth retardation are universal in Qinghai high plateau. This situations reduce economic income of herdsman. In the experiments, Qinghai high plateau yaks were used to investigate the relationship between growth retardation and somatotropic axis hormone and study the possibility of injection GHRP-2 and cysteamine supplementary feeding to improve the growth performance of yaks with growth retardation and the possible regulatory mechanism, to provide theoretical foundation for breeding yaks with growth retardation scientifically. The paper was divided into two tests:Test 1:study of relationship between body weight and somatotropic axis hormone of yaksThirty six 1-year-old Qinghai high plateau yaks (body weight 38-83.2kg) were randomly chosen. After 7 d of preliminary feeding period, body weight and jugular blood samples were collected. The relationship between body weight and plasma GHRH, GH, IGF-1 were analyzed. The results showed GHRH, GH and IGF-1 levels of yaks were significantly rise with body weight rised (P<0.05). Body weight of yaks colony which had lighter body weight were siginficantly associated with GHRH, GH and IGF-1 (P<0.05). The results indicated yaks with growth retardation were main cause by somatotropic axis hormone secretion deficiency.Test 2:effects of GHRP-2 and cysteamine on growth performance, rumen development and muscle protein deposition of yaks with growth retardationFifteen 1-year-old Qinghai high plateau yaks with growth retardation (average body weight 54.8±9.24 kg) were randomly selected and assigned into 3 groups, with 5 yaks each group:Negative control group was feed basal diet included concentrate and oaten hay everyday. GHRP-2 injection group (GHRP-2 group) was feed the same basal diet and injected 12.5ug/kg BW GHRP-2 on 1 to 6 days,11 to 16 days and 21 to 26 days, cysteamine supplementary feeding group (Cysteamine group) was feed the same basal diet and feed 5 g/d for one yak of cysteamine on day 1-28, the administration was same to negative control group on day 29-84. In addition, another 51-year-old Qinghai high plateau yaks with normal growth performance (average body weight 75.3±2.43kg) were selected as the positive control group. The administration of positive control group was same to negative control group. After a 14 days adaptation period, body weight and jugular blood samples were collected on 0,28,56and 84 day during the formal test. After the 84 days of formal feeding test, yaks were slaughtered and sampled. The results showed as folowing:1) GHRP-2 injection and cysteamine supplementary can significantly enhanced growth of yaks with growth retardation. The whole period ADG of GHRP-2 and cysteamine groups were similar and significantly higher than positive control and negative control groups (P<0.05).GHRP-2 group had the significantly highest ADG during day 0-28 (P<0.05). The ADG of cysteamine group was significantly higher than other groups during day 29-84 (P<0.05).2) GHRP-2 and cysteamine significantly promoted rumen growth and percentage of rumen for stomachus compositus (P<0.05), of which cysteamine group had a significantly optimal effects (P<0.05). GHRP-2 and cysteamine significantly enhanced the height and width of rumen nipple (P<0.05) and had no significantly difference with positive control group (P>0.05).3) GHRP-2 and cysteamine significantly promoted rumen TVFA and acetic acid concentration (P<0.05), GHRP-2 significantly promoted rumen butanoic acid concentration (P<0.05). Cysteamine significantly enhanced rumen butyrate concentration (P<0.05) and ratio of acetic acid and propionic acid (P<0.05). The rumen NH3-N concentration of GHRP-2 and cysteamine group were significantly lower than positive control group (P<0.05) and higher than negative control group (P<0.05). The rumen MCP concentration of GHRP-2 and cysteamine group were significantly higher than positive and negative control group (P<0.05).4) GHRP-2 and cysteamine significantly enhanced the plasma GLU, BUN concentrations (P<0.05) and significantly enhanced plasma TP on trial day 28 and ALB concentration on trial day 56 (P<0.05).5) On trial day 28, Cysteamine significantly enhanced the GHRH levels and reduced SS levels of yaks (P<0.05). GHRP-2 and cysteamine enhanced the GH and IGF-1 levels significantly (P<0.05) of yaks with growth rtardation and had no significantly difference with positive group (P>0.05). The cysteamine groups had the significantly highest GHRH, GH levels on day 56 (P<0.05) and the lowest SS levels on day 84 (P<0.05).6) GHRP-2 injection significantly enhanced the mRNA expression of GHR,IGF-1 and IGF-1R in liver and skeletal muscle (P<0.05). Cysteamine feeding significantly decreased the mRNA expression of SS in hypothalamus and enhanced GHR and IGF-1 mRNA expression in liver significantly (P<0.05).7) GHRP-2 and cysteamine administration significantly enhanced the myofiber diameter, area and protein content of skeletal muscle (P<0.05), which had no significant difference with positive control group (P>0.05).8) GHRP-2 significantly enhanced the mRNA expression of IRS-1, PI3K, Akt and mTOR inskeletal muscle and significantly decreased the expression of MuRF1 gene (P<0.05). Cysteamine significantly decreased the expresson of AMPK, Atrogin-1 and MuRF1 mRNA (P<0.05).In summary, The somatotropic axis hormone secretion deficiency was one of reason for yaks with growth retardation. GHRP-2 and cysteamine can availably enhance rumen fermentation, improved the fermentation pattern and improve growth performance of yaks with growth retardation. GHRP-2 enhanced plasma GH and IGF-1 levels, induced GHR, IGF-1 and IGF-1R mRNA in liver and muscle, up regulated IRS-1, PI3K, Akt and mTOR mRNA in skeletal muscle, reduced MuRFl mRNA, enhanced the diameter and area of myofiber and growth performance of yaks with growth retardation. Cysteamine enhanced plasma GHRH levels, reduced plasma SS levels and hypothalamus SS mRNA expression, enhanced GHR and IGF-1 mRNA, reduced AMPK, Atrogin-1 and MuRFl in muscle, improved the diameter and area of myofiber and growth performance of yaks with growth retardation.