Effects Of Supplemental Rumen Protected Amino Acids In Low-protein Diets On Growth Performance,Slaughter Performance And Nutrient Digestibility Of Mutton Sheep

In this experiment,different levels of low-protein diets were supplemented with rumen-protected amino acids,and the effects of low-protein diets in amino acid balance mode on growth performance,slaughter performance,digestive and metabolic performance,and meat quality on Dorper and thin-tailed Han crossbred mutton lambs were studied.The research content is divided into the following three parts:Experiment 1:The aims of this study were to investigate the effects of different levels of low-protein diet supplemented with rumen protected amino acids on growth performance,slaughter performance on Dorper and thin-tailed Han crossbred mutton lambs,the aim of this study was to reduce the protein level of the diet.One hundred and fifty Dorper and thin-tailed Han crossbred mutton lambs（weight about 33 kg）were divided into 5 groups（3 replicates in each group,10 mutton lambs per replicate）.The experimental treatments were as follows:control group,dietary CP16%;LP14 group,dietary CP14%;LP12 group,dietary CP12%;LP10 group,dietary CP10%;and LP12+NPN group,dietary CP12%+NPN.The experimental groups were supplemented with rumen protected lysine,methionine,threonine and arginine respectively to reach the corresponding amino acid level in the control group.The adjustment period lasted for 10 days and the experiment period lasted for 80 days.The results showed that:1)There was no significant difference in daily weight gain,feed conversion ratio,live weight,slaughter rate,GR value and eye muscle area of the mutton lambs in each treatment group（P>0.05）.2)In terms of the weight and proportion of each segment of the gastrointestinal tract,the weight of the valvular and large intestine of the LP10group and their pre-slaughter live weight were significantly higher than the other groups（P<0.05）.The results showed that supplementation of amino acids in low-protein diets under the conditions of this experiment did not affect the growth performance and slaughter performance of mutton lambs.Experiment 2:The aims of the present study were to investigate the effect of low-protein diets of different levels supplemented with rumen-protected amino acids on contents of protein and hormone in serum and meat quality in Dorper and thin-tailed Han crossbred mutton lambs.The experimental design was the same as experiment 1.At the end of the experiment,six mutton lambs in each group were selected for slaughter,and the longest muscle samples of the mutton lambs were taken for meat quality testing.The results showed that:1)There was no significant difference in serum concentrations of Total Protein（TP）,Globin（GLB）,Growth Hormone（GH）and Insulin-Like Growth Factor-I（IGF-I）among the 5 groups（P>0.05）.However,Blood Urea Nitrogen（BUN）concentrations in the low-protein groups were significantly lower than that of control group（P<0.01）.2)There was no significant difference among the 5groups in the length of longissimus dorsi muscle,in terms of flesh color,drip loss,pH₀,pH₂₄,cooked meat rate and shearing force（P>0.05）,There was no significant difference in amino acid content of longissimus muscle in mutton lambs among the 5 groups（P>0.05）.The results showed that supplementation of amino acids in low-protein diets under the conditions of this experiment would not affect the quality of meat and improve protein utilization.Experiment 3:The aim of this study was to investigate the effect of different levels of low-protein diet supplemented with rumen-protected amino acids on nutrient digestion and metabolism of fattening Dorper and thin-tailed Han crossbred mutton lambs.When the average weight of the lambs in the control group reached 44kg,4lambs in each group were selected for digestive metabolism trial,the pre-test period was5 days,and the trial period was 5 days.The results showed that:1)The dry matter intake（DMI）and the apparent digestibility of dry matter（DM）,organic matter（OM）and CP in each group of lambs were not significantly different（P>0.05）,and the low protein group was slightly different in value.Higher than the control group.2)There was no significant difference in total energy intake,fecal energy and urine energy discharge,digestive energy,metabolic energy,total energy metabolism rate and digestive energy metabolic rate among the groups（P>0.05）.3)Compared with the control group,low protein diets reduced the nitrogen intake of mutton lambs except for the LP12+NPN group（P=0.093）.There was no significant difference in fecal nitrogen,urinary nitrogen and nitrogen excretion between the groups（P>0.05）.The nitrogen,urinary nitrogen and total nitrogen expulsion of the LP10 group were the lowest.There was no significant difference in apparent digestible nitrogen,sediment nitrogen,nitrogen utilization rate and nitrogen biological value between the groups（P>0.05）.The results showed that supplementation of amino acids in low-protein diets under this experimental condition could improve the nutrient digestion and metabolism of mutton lambs to some extent.In summary,after reducing the dietary crude protein level of fattening Dorper and thin-tailed Han crossbred mutton lambs by 1 to 4 percentage points and supplementing the rumen lysine,methionine,threonine,arginine and urea,to some extent it can improve the protein utilization rate of the diet without reducing the growth performance,slaughter performance and meat quality of the fattening mutton lambs.It shows that low-protein supplemental amino acid diets are feasible in fattening lambs,and can save protein feed ingredients.