Study On Quality Deterioration Mechanism And Feeding Value Evaluation Of Native Grass Hay During Storage

Native hay is the main source of forage for herbivorous livestock in grassland pastoral areas.Forage reserve is an important measure to solve the imbalance between seasonal and annual forage supply and an important guarantee for the sustainable development of animal husbandry in grassland pastoral areas.As a strategic reserve forage,native hay is susceptible to storage methods,storage time,microbial activities,and forage metabolism during storage,resulting in quality deterioration,livestock dislike eating,forage waste,and reduced ability to resist disasters and protect livestock.Therefore,it is particularly important to study the quality deterioration mechanism of native hay during storage,determine the optimal storage mode and time of native hay,and scientifically identify the storage life and feed value of native hay for ensuring the safe storage of native hay and the healthy development of grassland animal husbandry.In this study,the typical steppe native hay in Inner Mongolia as the research object.The interdisciplinary knowledge of grassland science,microbiology,animal nutrition,detection,and other disciplines was used,and the single-factor and double-factor experimental design was adopted.The technologies of microbiology and metabolomics were used,and the multivariate statistical analysis method was combined.The changes in nutritional quality,volatile components,mycotoxins,microbial community structure,and metabolites of native hay during storage and their correlation and lamb feeding effect were studied.The quality deterioration mechanism of native hay during storage was revealed,and its feeding value was clarified,which provided the theoretical basis and technical support for the scientific storage and utilization of native hay.The main results have been reviewed as follows:(1)There was a significant effect of storage method and time on the nutritional quality,chlorophyll content,total bacterial count,and total mold count of native hay(P<0.05),Compared with outdoors storage and poncho storage,reserve storage can effectively reduce the loss of nutritional quality of native hay,reduce the number of total molds,bacteria,and toxin accumulation,and prolong the safe storage time for more than1 year.After 630 d of storage of native hay with outdoors storage and poncho storage,the total number of bacteria and molds exceeded the limits of the Chinese sanitary standards for feedstuffs by 14.61%~19.72% and 1.64%~4.29%,respectively.Compared with outdoors storage and poncho storage,reserve storage for 720 d resulted in a 28.36% and27.39% reduction in crude protein loss,71.95% and 68.29% reduction in chlorophyll loss,44.81% and 41.01% reduction in the total bacterial count and 26.02% and 20.00%reduction in total mold count for native hay,respectively.Ochratoxin and deoxynivalenol toxin were not detected in native hay stored in the Reserve.(2)A total of 60 volatile components were detected during the storage period of native hay,including 13 alkanes,13 alcohols,8 aldehydes,10 ketones,2 acids,4 esters,and 10 heterocyclic and aromatic compounds.The composition and content of volatile components in different storage periods are different.The results of principal components and orthogonal partial least squares discriminant analysis showed that the main volatile components of native hay at the beginning of storage(0 d)were p-menthol-2,8-dien-1-ol(18.98%),dihydrokiwifolide(7.14%),methyl eugenol(3.04%),eugenol(1.66%)and geranyl acetone(1.49%),with a clear hay flavour and good palatability.The main volatile components of eucalyptol(17.95%)and camphor(9.36%),which had a pungent camphor odour,were highly significantly negatively correlated with crude protein content(P<0.01)and were the characteristic volatile components for identifying deterioration in the quality of native hay during storage for 3 years(1080 d).(3)With the extension of storage years,the bacterial community diversity of native hay increased significantly(P>0.05),and the fungal community diversity increased first and then decreased.At the genus level,the dominant bacterial genera are Pantoea,Pseudomonas,Massilia,and Kosakonia;the dominant fungal genera are Didymella,Naganishia,Aspergillus,and Aureobasidium.The results of the correlation heatmap analysis showed that the main microorganisms associated with a decrease in crude protein content and an increase in volatile components of eucalyptol and camphor in native hay at late storage(1080 d)were the bacterial genera Methylobacterium,Bacteroides and Sphingomonas,and the fungal genera Aspergillus and Chaetomella.(4)A total of 401 metabolites were identified during the storage of native hay.The results of correlation thermal analysis and orthogonal partial least squares discriminant analysis showed that 112 metabolites with significant differences(VIP>1,P<0.05)were screened,mainly including 21 carbohydrates,19 organic acids and their derivatives,14 fatty acids and their derivatives,10 benzenes and their derivatives,7 nucleotides and their derivatives,and 7 flavonoids.Compared with the early storage(0 d),the relative contents of aspartic acid and urea related to protein decomposition in the late storage(1080 d)increased by 19.11 times and 7.67 times,respectively.The relative contents of succinate and L-alanine related to chlorophyll degradation increased by 2.59 times and 2.51 times,respectively.The relative contents of threonine and D-fructose-6-phosphate related to starch and sugar decomposition increased by 3.26 times and 7.20 times,respectively,indicating that the increase of the relative content of characteristic metabolites in the late storage of native hay was the influencing factor in its quality deterioration.(5)The storage period of native hay had a significant effect on the feeding effect of lambs.Compared with the native hay fed at the beginning of storage(0 d),the average daily feed intake,feed intake rate,average daily gain,and crude protein apparent digestibility of native hay lambs fed for 3 years(1080 d)decreased by 23.32 %,14.62 %,16.88 %,and 31.64 %,respectively.The contents of glutamic-pyruvic transaminase,urea nitrogen,immunoglobulin M,immunoglobulin G,and tumor necrosis factor-α were significantly increased by 10.46 %,39.86 %,8.13 %,10.69 %,and 2.98 %,respectively(P<0.05),indicating that feeding native hay with long storage life may damage the liver and heart of lambs and affect the immune function of lambs.