Guanidinoacetic acid (GAA) is the only precursor for the creatine synthesis of vertebrates. Creatine (Cr) and phosphocreatine (PCr) are able to provide energy for the rapid growth and development of the muscle tissue. This study evaluated the effects of dietary different levels GAA on growth performance, GAA absorption and creatine metabolism of lambs. Twenty-four 3-month-old healthy Kazakh male lambs (body weight = 27.35± 0.58 kg) were randomly divided into four groups with 6 lambs in each group. The lambs were fed with the basal diets supplemented with 0 (0 mg/kg group), 500 (500 mg/kg group), 1000 (1000 mg/kg group) and 1500 mg (1500 mg/kg group) GAA per kg diet (DM basis), respectively. The results showed that, as the GAA content of the diet increased, there was a quadratic change in DMI, with the lowest in the 500 mg/kg group and the highest in the 0 mg/kg group. The CK enzyme activity and ATP content in quadriceps muscle increased linearly with increasing levels of diary GAA in the diet. PCr levels and ADP levels in the longest dorsal muscle increased linearly with increasing levels of GAA in the diet. The relative expression of SLC6A6 and SLC6A8 mRNA in the jejunum and ileum mucosa showed a quadratic change as the dietary GAA level increased, with the lowest relative expression in both the 1500 mg/kg group. With the increase of dietary GAA level, both Cr concentration in hepatic vein plasma and the portal plasma GAA concentration shows a quadratic change, with the highest concentration in the 500 mg/kg group and the lowest concentration in the 0 mg/kg group. Therefore, dietary supplementation with 500~1000 mg/kg DM GAA is recommended for lambs.

The purpose of this study is to investigate the potential effects of 5-hydroxytryptophan (5-HTP) duodenal perfusion on melatonin (MT) synthesis in the gastrointestinal (GI) tract of sheep. 5-hydroxytryptophan is a precursor in the melatonin synthetic pathway. The results showed that this method significantly increased melatonin production in the mucosa of all segments in GI tract including duodenum, jejunum, ileum, cecum and colon. The highest melatonin level was identified in the colon and this indicates that the microbiota located in the colon may also participate in the melatonin production. In addition, portion of the melatonin generated by the GI tract can pass the liver metabolism and enters the circulation via portal vein. The current study provides further evidence to support that GI tract is the major site for melatonin synthesis and the GI melatonin also contributes to the circulatory melatonin level since plasma melatonin concentrations in 5-HTP treated groups were significantly higher than those in the control group. In conclusion, the results show that 10–50 mg of 5-HTP flowing into the duodenum within 6 h effectively improve the production of melatonin in the GI tract and melatonin concentration in sheep blood circulation during the day.

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<sec> Context <sc>L</sc>-citrulline (<sc>L</sc>-Cit) does not degrade in the rumen and has the ability to form peptide bonds in the body; however, it does not participate in protein synthesis. </sec> <sec> Aims This study aimed to evaluate the effects of <sc>L</sc>-Cit on the reproductive performance of Hu ewes. </sec> <sec> Methods In total, 30 ewes were randomly categorised into five groups. The control group was fed with a basic diet, whereas the Experimental Groups I, II, III, and IV were provided feed supplemented with 5, 10, 15, and 20g/day of <sc>L</sc>-Cit respectively. Blood samples of ewes were collected 4h after feeding on Day 21 of the experiment and before feeding on Day 30. The optimal supplementary feeding dose was selected on the basis of blood biochemical indexes. Overall, ninety 2-year-old ewes were classified into two groups. The control group was fed with a basic diet and the experimental group was fed with a diet supplemented with 10g/day of <sc>L</sc>-Cit. After 30days of supplementary feeding, reproductive performance of ewes was determined. </sec> <sec> Key results The plasma concentrations of Cit, ornithine, and arginine in ewes increased linearly with an increase in the level of <sc>L</sc>-Cit supplementation. The plasma concentrations of gonadotropin-releasing hormone, luteinising hormone, and follicle-stimulating hormone in the experimental group increased significantly compared with those in the control group. The plasma total antioxidant capacity and catalase, superoxide dismutase, and glutathione peroxidase in the experimental group were significantly higher than those in the control group, whereas the concentrations of malondialdehyde in all experimental groups were significantly lower than those in the control group. The conception, lambing, and double lambing rates of the experimental group were increased by 28.76%, 15.90%, and 40.21% respectively. </sec> <sec> Conclusions Supplementation with different doses of <sc>L</sc>-Cit can improve the concentrations of some plasma amino acids and reproductive hormones as well as antioxidant capacity of ewes. Supplementary feeding with 10g/day of <sc>L</sc>-Cit could increase the lambing and double lambing rates of ewes. </sec> <sec> Implication <sc>L</sc>-Cit can improve the reproductive performance of ewes. </sec>

Context L-citrulline (L-Cit) does not degrade in the rumen and has the ability to form peptide bonds in the body; however, it does not participate in protein synthesis. Aims This study aimed to evaluate the effects of L-Cit on the reproductive performance of Hu ewes. Methods In total, 30 ewes were randomly categorised into five groups. The control group was fed with a basic diet, whereas the Experimental Groups I, II, III, and IV were provided feed supplemented with 5, 10, 15, and 20 g/day of L-Cit respectively. Blood samples of ewes were collected 4 h after feeding on Day 21 of the experiment and before feeding on Day 30. The optimal supplementary feeding dose was selected on the basis of blood biochemical indexes. Overall, ninety 2-year-old ewes were classified into two groups. The control group was fed with a basic diet and the experimental group was fed with a diet supplemented with 10 g/day of L-Cit. After 30 days of supplementary feeding, reproductive performance of ewes was determined. Key results The plasma concentrations of Cit, ornithine, and arginine in ewes increased linearly with an increase in the level of L-Cit supplementation. The plasma concentrations of gonadotropin-releasing hormone, luteinising hormone, and follicle-stimulating hormone in the experimental group increased significantly compared with those in the control group. The plasma total antioxidant capacity and catalase, superoxide dismutase, and glutathione peroxidase in the experimental group were significantly higher than those in the control group, whereas the concentrations of malondialdehyde in all experimental groups were significantly lower than those in the control group. The conception, lambing, and double lambing rates of the experimental group were increased by 28.76%, 15.90%, and 40.21% respectively. Conclusions Supplementation with different doses of L-Cit can improve the concentrations of some plasma amino acids and reproductive hormones as well as antioxidant capacity of ewes. Supplementary feeding with 10 g/day of L-Cit could increase the lambing and double lambing rates of ewes. Implication L-Cit can improve the reproductive performance of ewes.