Effects Of VitaminA On Beef Quality And Serum Bioche-Mical Indicators Of Angus×Qinchuan Crossbred Steers

The effects of dietary vitamin A concentration on beef quality and serumbiochemical indicators of Angus×Qinchuan steers and its mechanisms wereinvestigated in two experiments with randomized complete-block design.Sixteen15months old steers (BW:305±15.5kg) were equally divided into4treatments with15-A、15-B、5-C、15-D respectively known collectively as12months group; sixteen24months old steers (BW:390±16.5kg) were equally divided into4treatments with24-A、24-B、24-C、24-D respectively,known collectively as24months group.Thesteers were divided averagely into four groups according to BW respectively,andfinished individually with the same basal diets for120days. Four dietary treatmentsconsisted of the basal diet(TreatmentA),basal diet+50%of VA nutrientrequirement(Treatment B),basal diet+100%of VA nutrient requirement(TreatmentC)and basal die+200%of VA nutrient requirement (Treatment D).The results showedthat:(1) The beef cattle slaughtered characteristics, VA dose had no effects on beefslaughter rate, pure meat rate, mesenteric fat heavy/live weight, eye musle area(P>0.05); VA dose significantly affect final weight,average daily gain,back subcutaneousfat thickness, ribs subcutaneous fat thickness,average daily gain which had a tendencywas numerically greater with VA dose increment when dietary VA dose was less than2200IU/kg,back fat thickness were lowest at1100IU/kg, Marbling score were best at0IU/kg and1100IU/kg.(2) In the meat conventional ingredients (with fresh samplebased), VA dose had no significant effect on the chemical composition of LD andGM(P>0.05) except for matter and crude ash of GM,matter and crude protein of LD,vitamin A dose significantly affect (P <0.05) dry matter and longest crude proteincontent of LD、dry matter and crude ash of GM. Dry matter and Crude protein of LDwere highest at lower dose VitaminA（1100IU/kgVA）, Dry matter and Crude ash ofDM at0IU/kgVA and1100IU/kgVA were highest.(3) In the beef quality evaluationindicators, No add VA（0IU/kg DM VA）and low dose VA group (1100IU/kg DM VA) can significantly improve the beef colour、tenderness、marbling score、oxidationresistance, department of hydraulic, reducing backfat and drip loss of12monthssteers; For24months steers,2200IU/kgVA improved beef colour、oxidation resistance,department of hydrauli and drip loss were best,1100IU/kg VA improved beef qualitywere best. VA dosage significantly influence on the hanging matureLD and GM totalhip muscles pigment content,TBARS and drop of water loss（P<0.05. Among them,the total pigment content of LD and GM at1100IU/kgVA were highest, TBARSvalue in the LD at2200IU/kg VA and in the GM at1100IU/kg VA were lowest.(4)Serum biochemical indicators: VA dose had signifiacantly effect on an serum insulinand plasma glucagons, growth hormones, T3and cortisol concentration (P <0.05), butit does not exist obvious dose dependent effect, and were influenced by steers age andfattening time length. Considering above results, the effect was the best when thesteers were fed with the diet contained1100IU/kg DM.