| The aim of this study was to investigate the effects of different levels of rumen-protected methionine(RPMet)on the performance,main nutrients digestibility and composition of plasma free amino acids in Liaoning Cashmere goats.The effects of RPMet on plasma growth hormone(GH)and insulin-like growth factor(IGF-1),hair follicles development and the expression of IGF-1 and IGR-1R gene m RNA in skin tissue were further studied too,to determine the effect of RPMet on cashmere growth and its regulation in Liaoning cashmere.Twenty-four Liaoning Cashmere male goats(35.41±1.13 kg)age about 1.5 years old were used in the experiment.The single factor randomized trial design was used.RPMet was added at 4 levels,namely 0%(Control group),0.1%,0.2% and 0.3%.The nutritional levels of each group were same,and the environmental conditions were the same.The animals were offered diets twice per day and drinked water freely.The experiment was was 16 weeks.The results showed that:(1)Production performance:,Average daily gain of Liaoning Cashmere goats increased quadratically(P<0.001)and linearly(P<0.05)when 1% to 3% RPMet was added to the diet,but Feed/Gain decreased significantly in quadratially(P<0.01)and linearly(P< 0.01)which showed that 0.2% RPMet group goats had the best growth condition.RPMet levels of diets were no difference in the length,diameter of cashmere fiber and cashmere weight of the plot(P>0.05).(2)Nutrients digestion: OM intake(P<0.05)and digested(P<0.05)increased in quadratically with the increase of dietary of RPMet levels,and OM intake for 0.2% RPMet group was significantly higher than the other groups,digested OM for 1% and 0.2% groups were significantly higher than for Control group,but t no difference with 0.3% group.Dietary RPMet levels had no significant effect on the intake and digestibility of DM,NDF and ADF(P>0.05).During the period of fecal collection,dietary RPMet added levels linearly reduced fecal nitrogen(P<0.01)and urinary nitrogen/nitrogen intake(P<0.01),linearly increased digestible nitrogen(P<0.05),retained nitrogen(P<0.05)and retained nitrogen/nitrogen intake(P<0.05),and the apparent digestibility of nitrogen increased significantly(P<0.01).Supplementation of 1% to 3% dietary RPMet,The plasma urea nitrogen significantly decreased at quadratic(P<0.01)and linear(P<0.01),compared with 3.99 mmol/L for control group,and 2.73,1.96 and 2.91 mmol/L for the other group respectively.(3)Plasma free amino acid composition: The dietary RPMet levels significantly increased plasma free Met content(Linear and Quadratic P<0.01).Dietary RPMet levels linearly reduced plasma Ile(P<0.01),Leu(P<0.01)and Lys content(P<0.05).RPMet levels significantly linearly reduced branched-chain amino acids and total amino acids(P<0.01),and linearly reduced essential and non-essential amino acids(P<0.05).(4)Plasma hormone: Dietary RPMet levels linearly increased plasma GH in the mid-(P<0.01)and final experiment(P<0.05),with the highest concentration for 0.3% RPMet.However,there was no difference for plasma IGF-1 content(P>0.05).(5)Skin hair follicle morphology,expression of IGF-1 and IGF-1R m RNA: Compared with control group,dietary RPMet levels increased primary(linear P<0.05,secondary P< 0.01)and secondary hair bulb width(Quadratic,P<0.01),the widths of primary and secondary hair bulb for 0.2% RPMet group were the largest(199.01 and 73.33 μm,respectively).There were an increasing trend on secondary hair follicle depth(Quadratic,P= 0.093),hair follicle activity(Linear,P=0.055)and S/P ratio(Linear,P=0.07),and the highest means were 1281.69 μm,95.83% and 13.5for the 0.2% RPMet group,respectively,There was no difference on the expression of IGF-1 and IGF-1R m RNA in skin(P>0.05).Based on the above results,the growth performance and apparent digestibility of nutrients were improved,nitrogen deposition and daily gain was increased,and the total essential amino acid concentration of plasma reducedby RPMet supplementation.Dieraty RPMet also improved hair follicle growth in skin tissue,and promoted GH levels.Adding 2% RPMet to the diet was optimum for Liaoning Cashmere goat. |
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