The Effect Of Different Growth Periods And Diurnal Cutting Times On The Ensiling Characters And Fermentation Quality Of Alfalfa

The aim of this study was to determine the rule of changes in chemical composition and epiphytic microorganisms at different growth periods and diurnal cutting times of alfalfa and their effects on fermentation quality and feeding value of the resulting silage.Primary growth of alfalfa was harvested at different diurnal cutting times(08:00 h,AM;13:00 h,M;18:00 h,PM)on a sunny day during three separated growth periods(budding period,BP;initial flowering period,IFP;full flowering period,FFP)in 2016?2017,which were used to make silage.Then the chemical composition and epiphytic microorganisms of fresh alfalfa,and fermentation quality and feeding value of the resulting silage were analyzed.The results showed that:(1)With the diurnal cutting times delaying,the dry matter(DM),water soluble carbohydrates(WSC),glucose,fructose,sucrose and starch contents of fresh alfalfa increased,whereas neutral detergent fiber(NDF)and acid detergent fiber(ADF)decreased.The fresh alfalfa relative feed value(RFV)improved from sunrise to sunset.The counts of epiphytic aerobic bacteria and lactic acid bacteria(LAB)were lower(P<0.05)in M compared to those of AM-and PM-cut alfalfa.With the increased maturity of alfalfa,the crude protein(CP)content and RFV reduced(P<0.05),while NDF and ADF increased(P<0.05).In general,the counts of epiphytic microorganisms were lower in IFP compared to those of BP and FFP alfalfa.(2)The DM,WSC,starch and lactic acid concentrations and RFV were higher(P<0.05)and the contents of NDF,ADF and NH3-N and silage p H were lower(P<0.05)for silage made with M-and PM-cut alfalfa compared to those made with AM-cut forage.With the development of alfalfa growth periods,the DM,NDF and ADF contents of silage increased(P<0.05),while the CP and WSC concentrations and RFV decreased(P<0.05).With delaying the diurnal cutting times to afternoon,alfalfa silage had higher(P<0.05)the in vitro 48 h gas production and potential gas production,acetic acid and total volatile fatty acids(T-VFA)concentrations,as well as in vitro DM digestibility(IVDMD)and in vitro NDF digestibility(IVNDFD).With the increased maturity of alfalfa,the 48 h gas production and potential gas production,the NH3-N,acetic acid,propionic acid and T-VFA concentrations produced by in vitro fermentation of silage were decreased(P<0.05).Furthermore,the silage made with BP alfalfa had higher(P<0.05)IVDMD and IVNDFD than those silages made with IFP or FFP forage.These results suggested that when preparing alfalfa silage,the budding period should be given priority and the diurnal cutting times should be delayed until afternoon.