Effects Of Rumen-Protected Methionine,Leucine,Isoleucine Supplemental On Growth And Digestive Performance Of Heifers In Low-Protein Diets

It has been shown that some amino acids have a metabolic regulatory effect and that the addition of these amino acids in rumen protected form in Ruminant Diet can appropriately reduce dietary protein levels,improve dietary N conversion efficiency and reduce fecal and urinary N emissions without affecting production performance.So far,relevant research has focused on lactating cows,with little research on heifers.Investigating the feasibility of low protein diets + metabolism-regulated amino acids for use on back-up cows was the aim of this topic.In the present study,the 7-month-old Holstein reserve heifers were used as test animals to observe the effects of low-protein dietary supplementation with rumen-protected methionine,leucine and isoleucine(RPMet,RPLeu,RPIle)on growth,digestion,blood biochemical index and nitrogen balance.40 7-month-old reserve heifers with average day age of 211.5±1.5d and initial weight of 219.6±5.8kg were divided into five treatment groups according to the principle of similar weight and day age,and eight heifers in each group by randomized blocks design.The experimental treatments were: high-protein positive control group with a diet CP content of 14.6%(HP);low-protein negative control group with a diet CP content of 11.6%(LP);low-protein diet + RPMet(LP+M);low-protein diet + RPMet and RPIle(LP+IL);low-protein diet + RPMet,RPIle and RPLeu(LP+MIL).The energy content of the test-treated diets was similar.The trial was conducted for 70 d,with a pre-feeding period of 10 d and a positive trial period of 60 d.The results showed that there was no significant difference between the groups for body height and body length(P>0.05)at 30 and 60 days.The differences in measured bust circumference were similarly insignificant at 30 days.Chest circumference at 60 th day,LP+MIL was not significantly different from the HP and LP+M groups(P>0.05)and was significantly higher than the LP group(P<0.05)Body weight did not differ significantly between groups in each period(P>0.05).The ADG from 1 to 60 d was not significantly different between HP and LP+MIL groups(P>0.05),and all were significantly higher than the LP group(P<0.05).Protein consumption per kilogram of gain was lower in the LP+MILgroup at both 30 and 60 days.No significant effect of experimental treatment on serum TG,LB,TP,ALP,AST,ALT,PRL,GH,P,E,IGF-1(P>0.05).Serum Urea levels were extremely different between the groups at day 30(P<0.01),with the HP group significantly higher than the other groups.The LP+M group was higher than the LP and LP+IL groups and did not differ significantly from the LP+MIL group.When the 60 th day,there was no significant difference between HP group and LP+IL group and LP+MIL(P>0.05).Serum GLN content,30 th day,LP+MIL group was extremely significantly lower than the rest of the groups(P<0.01).As the feeding time increased to 60 d,there was no significant difference between the groups(P>0.05),but the LP+MIL group was numerically relatively low.?INS levels were not significantly different between groups at day 30(P>0.05),but at day 60 the LP+MIL group was extremely significantly higher than the rest of the groups(P<0.01).The experimental treatment did not affect DM,EE and ME intake;Also did not affect the content of DM,CP,ADF,NDF in faeces and the apparent digestibility of each nutrient(P>0.05).Protein intake decreases with lower dietary protein levels.There was a trend for NDF intake to differ between groups at 30d(0.05<P<0.1),however at day 60,the NDF intake in the LP group was extremely significantly lower than that in the remaining groups(P<0.01).Urine of N intake,LP group tends to be lower than HP,IL+M at 30 d,numerically lower than LP+IL,LP+MIL group,but the difference is not significant;between-groups difference is not significant at 60 d.The amount of digested N was extremely significantly higher in the HP group than in the rest of the group at day 30(P<0.01),with longer feeding times The difference between the HP group and the LP+MIL group was not significant at day 60.In summary,the addition of Met,Leu and Ile to the diet in the form of perioromegaly protection did not affect the growth performance after the appropriate reduction of the diet protein level,which improved the diet nitrogen conversion efficiency and reduced fecal and urinary nitrogen emissions to some extent.Low-protein diets supplemented with rumen-protected Met+Leu+Ile group can significantly increase ADG,improve blood glucose level and increase serum insulin content.