| Nutrition regulation technology can improve the nitrogen utilization rate of pigs,thereby reducing the nitrogen emission,and it is a fundamental way to solve the environmental pollution of swine production.The efficiency of amino acid utilization by animals,in addition to being affected by the composition and levels of amino acids in the diet,is also closely related to the dynamics of amino acid release in the body.Therefore,clarifying the impact of different amino acid releasing dynamic protein sources on nitrogen utilization in pigs is crucial for the scientific formulation of pig diets.This study investigated the protein sources of different amino acid release dynamics and the effects of protein levels on growth performance and nitrogen utilization in piglets.We selected casein(CAS),which has a faster amino acid release rate,and corn gluten meal(CGM),which has a slower amino acid release rate,and formulated three different protein diets with different amino acid release rates at two protein levels,which were normal protein level casein(NCAS)and normal protein level corn gluten meal(NCGM),normal protein level mixed diet(NBlend),low protein level casein(LCAS),low protein level corn protein meal(LCGM)and low protein level mixed deit(LBlend).We first measured the dynamics of amino acid release from the six diets using an in vitro experiment,and subsequently used a 2 × 3 full factorial test design,48 weaned piglets(Doric×Landrace×Large White)weighing 7.45±0.58 kg were selected and randomly divided into six treatment groups with eight replicates,one pig per replicate.The results of the trial showed that:In vitro digestion experiment showed that the total area between single amino acid release percentage curve and total amino acids release percentage curve in CGM group was significantly larger than that in CAS group and Blend group(P<0.05).However,there was no significant difference in the total area between the single amino acid release percentage curve and the total amino acids release percentage curve between CAS group and Blend group(P>0.05).Animal test showed that although the low protein diets increased nitrogen digestibility,nitrogen utilization,as well as nitrogen biological value and decreased nitrogen emission(P<0.05),their average daily gain(ADG)and plasma total protein(TP)were still lower than those of the normal protein diets(P<0.05),and F: G was also higher than that of the normal protein diet(P<0.05).The low protein diets had reduced(P<0.05)phosphorylation of ribosomal protein S6 kinase(S6K1)and e IF4 E binding protein 1(4E-BP1),downstream factors of the mammalian target of rapamycin complex 1(m TORC1)pathway,compared with the normal protein diets.However,the expression levels of muscle atrophy F-box(MAFbx)and muscle ring finger 1(Mu RF1),key proteins of the ubiquitin-proteasome pathway(UPP),were not significantly different(P>0.05).Either at a normal protein level or at a low protein level,the CGM group had significantly(P<0.05)increased F: G,nitrogen emission,IGF-1,and expression of Mu RF1 and MAFbx compared with the CAS group and Blend group,and decreased ADG,TP,nitrogen digestibility,nitrogen utilization,as well as nitrogen biological value(P<0.05),whereas the phosphorylation levels of S6K1 and 4E-BP1 were not significantly different(P>0.05).In addition,the growth performance,nitrogen deposition,nitrogen biological value,plasma biochemical indexes,phosphorylation levels of S6K1 as well as 4E-BP1,and the expressions of Mu RF1 and MAFbx were not significantly different between the CAS group and Blend group(P>0.05).In summary,(1)the more balanced CAS group and Blend group with amino acid release improved growth performance,nitrogen utilization,and decreased the protein expression of the UPP pathway and nitrogen emission in piglets,(2)the low protein diet with a protein level of 14.85%(SID)improved nitrogen digestion and utilization in piglets,but reduced their growth performance. |
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