Effects Of Dietary Nutrition Levels On Growth Performance,Plasma Parameters,Rumen Fermentation,Carcass Characteristics And Meat Quality Of Holstein Bulls

The objectives of these experiments were to investigate:a)Effects of dietary forage to concentrate ratio and forage length on nutrient digestibility,ruminal fermentation and fecal microflora of Holstein calves;b)Effect of dietary crude protein levels on nutrient digestibility,N metabolism,rumen fermentation,bacterial protein level and growth performance of young Holstein bulls;c)Effect of dietary concentrate levels on nutrient intake,carcass characteristics and meat quality of Holstein finishing bulls.The first experiment was to investigate the effects of dietary forage to concentrate ratio(F:C)and forage length on nutrient digestibility,blood metabolites,ruminal fermentation and fecal microflora.Twenty-eight Holstein weaned calves were randomly allocated to four treatment in 2 x 2 factorial arrangement:whole-length forage(WL)with low F:C(50:50),WL with high F:C(65:35),short length forage(SL)with low F:C(50:50)and SL with high F:C(65:35).Dry matter(DM)and organic matter(OM)intake were increased by increasing both F:C(P<0.01)and forage length(FL)(P<0.05),while the WL enhanced the NDF digestibility of calves(P<0.01).Cholesterol(CHO)(P<0.01),leptin(LP)(P<0.05)and growth hormone(GH)(P<0.01)concentration in blood was increased as the dietary F:C increased.A significant increase for blood triglyceride(TG)and GH(P<0.01),and significant decrease for insulin(INS)(P<0.05)levels was observed with decreasing the dietary FL.Ruminal pH of bulls fed with low F:C diets were significantly lower than those in high F:C treatment(P<0.05).Inereasing the F:C enhanced ruminal acetic acid(P<0.05)and acetic acid/propionic acid(P<0.01).Fecal Lactobacillus content was significantly higher,while Escherichia coli was significantly lower in WL and high F:C groups(P<0.05).Fecal Salmonella was significantly lower in high F:C group(P<0.05).Lower fecal scores(higher diarrhea rate)were observed in calves offered with SL hay compare to WL hay(P<0.05).DGGE band and richness index(S)were significantly affected by interaction between F:C and FL,and their values in WL with high F:C treatment was significantly higher than other treatments(P<0.05).Integrated the results of this study,we conclude that the WL with high F:C(65:35)diet is suitable for weaned calves.The second experiment was to investigate the effects of crude protein levels in diet on nutrient apparent digestibility,N metabolism,blood metabolites,ruminal fermentation,bacterial protein level and growth performance of Holstein bulls.Twenty-one Holstein young bulls were equally divided into three groups and were offered diets formulated with low crude protein(LCP;10.21%CP),medium crude protein(MCP;12.35%CP)and high crude protein(HCP;14.24%CP).Yellow corn silage was used as the unique forage source in the present study,mixed with concentrate and the moisture content adjusted appropriately(about 55%DM).The mixed feed was supplied ad libitum.Results indicated that CP intake,blood urea nitrogen,N intake,total N excretion,N balance and deposition rate of digestible N increased linearly with an increase in dietary CP(P<0.05).Meanwhile,ruminal pH and NH3-N concentration in MCP and HCP treatments were significantly higher compared to LCP group(P<0.05).Bulls that received HCP diet had significantly higher ruminal bacterial protein level,butyrate,propionate,acetate and the TVFA concentrations than those that received LCP diet treatment(P<0.05).Moreover,dietary CP had positively significant effect on the final BW,ADG,G/F,body height(and increment)and waist increment of bulls(P<0.05).Correlation analysis showed that ruminal pH was positively correlated with CP digestibility(r = 0.78)but was negatively correlated with DM digestibility(r =-0.80)and total VFA concentration(r =-0.76)(P<0.05).A strongly positive correlation was observed between bacterial protein level and DM digestibility(r = 0.82)and CP digestibility(r = 0.80)(P<0.01).With respect to N metabolism,a positive correlation was observed between total N loss and CP intake(r = 0.90)and NH3-N concentration(r = 0.82)(P<0.01).Furthermore,N balance was positively correlated with CP intake(r = 0.97,P<0.01)and NH3-N concentration(r = 0.79),but was negatively correlated with total N loss(r =-0.77)(P<0.05).Therefore,it could be concluded that HCP supplementation in the diet would be optimal for bulls during the growing period.The third experiment was to determine the effects of dietary concentrate levels on nutrient intake,blood metabolites,carcass characteristics and meat quality of Holstein finishing bulls.Twenty-four Holstein fattening bulls were offered feed mixture ad libitum with two concentrate to forage ratios designated as low concentrate(LC;35:65)and high concentrate(HC;65:35).Dry matter and crude protein intake were increased,while NDF and ADF intakes were decreased as dietary concentrate level increased(P<0.01).Furthermore,slaughter weight,carcass weight,and back fat thickness were greater in bulls fed high dietary concentrate level than those fed high forage treatment(P<0.05).Shear force decreased with increasing concentrate level while intramuscular fat content in longissimus muscle of bulls fed HC treatment was greater than for bulls fed LC treatment(P<0.01).Increasing dietary concentrate level decreased ruminal pH,while enhanced the concentration of volatile fatty acid,C1 6:0,C18:0,C20:0,C18:2cis-9,12,C20:3n-6,saturated fatty acid(SFA),PUFA,n-6 and total fatty acid(FA)in ruminal fluid(P<0.01).In particular,the correlation coefficients appeared that bacterial C16:0 in HC group was negatively associated with ruminal pH(P<0.01),which was not significant in LC group.It showed that PUFA in both LC and HC correlated negatively with ruminal pH(P<0.05 and P<0.01,respectively),which indicated that high concentrate diet exacerbated this negative correlation between bacterial PUFA and ruminal pH.In terms of the fatty acid composition of longissimus muscle,concentrations of C12:0,C14:0,C16:0,C18:0,C20:0,C14:1cis-9,C18:1trans-11,C18:1Cis-9,SFA,MUFA,n-3 and total FA were greater in bulls fed the HC diet than the LC diet(P<0.01).In contrast,the PUFA/SFA was lower for bulls offered the HC diet than for those offered the LC diet(P<0.01).The correlation results between concentrations of LCFA in longissimus muscle and other evaluated parameters showed that the C16:0,C18:0,C18:1 trans-11 and C18:1cis-9 in longissimus muscle were positively linked to the concentration of backfat thickness,intramuscular fat,and ruminal C16:0,C18:2cis-9,12,total FA,glucose,triglycerides,acetate,propionate,total VFA,and negatively with ruminal pH(P<0.05).The correlation analysis showed that SFA,MUFA,PUFA,total FA longissimus muscle correlated positively with C16:0,SFA,total FA,glucose,triglycerides,acetate,total VFA,backfat thickness,intramuscular fat,and negatively with ruminal pH(P<0.05).The overall results of present experiments reveal that increasing dietary concentrate levels fed to Holstein bulls had modest effects on carcass quality and fatty acid composition.