Effect Of Dietary Protein Level On Growth Performance, Nitrogen Metabolism And Protease Activities Of Growing Rex Rabbits

This experiment was conducted to research the effects of dietary crude protein (CP)levels on growth performance, nitrogen metabolism, serum biochemical index, serumhormone and protease activities of growing Rex rabbits. Two hundred weanling rabbits withan average weight of (629±138)g were randomly divided into5groups with40replicates ineach groups,each replicate contain1rabbit. They were fed each diet with CP at14.5%,16%,17.5%,19%and20.5%. There was a pretrial period of7days and experimental period of53days. The results showed as follows: dietary crude protein (CP) level had extremelysignificant affects on average daily gain (ADG)(P<0.01), and did significant influence onaverage daily intake(ADI) and feed/gain (F/G)(P<0.05), in19%CP treatment F/G has theminimum (3.46), ADI in20.5%groups was significant higher than other4groups. Dietarycrude protein (CP) level did significant affect on fur area(P<0.05)，but had no influence on theweight of fur (P>0.05)；Dietary crude protein (CP) level did significant affect nitrogenintake,nitrogen retention and digestible nitrogen (P<0.05), but had no significant influence onfecal nitrogen output, urine nitrogen and nitrogen apparent digestibility, biological value ofnitrogen and nitrogen utilization rate (P>0.05). The dietary crude protein (CP) level did notsignificant affect Trypsin and Chymotrypsin(P>0.05), The maximum value of Trypsin was ingroup17.5%and Chymotrypsin in16%. The dietary crude protein (CP) level had nosignificant influence on serum cholesterol content, total protein, albumin, urea nitrogen andcholesterol (P>0.05), but had significant influence on globulin (P<0.05).The growthhormone,IGF-1and insulin in serum were not significant affected by dietary crude proteinlevel(P>0.05). The express of GHR in muscle had significant influence(P<0.05). The expressof GHR in liver had no significant influence (P>0.05), the dietary of lower CP level werehigher than that higher CP level; the express GHR in liver has the highest value in19%group.Based on the F/G, nitrogen retention and fur area, the estimated requirement of portion levelwere19%, but the optimal portion level estimated by MLIN were18.51%,19.45%.and18.33%Dietary crude protein (CP) level in3~5month old rabbits had extremely significant affect average daily gain, and in19%CP treatment was the highest(P<0.05).Had nosignificant influence on average daily intake (ADI) and feed/gain (F/G)(P>0.05), in19%CPtreatment F/G has the maximum.in19%CP treatment F/G has the minimum. Dietary CP leveldid significant affect on Rex fur skins weight (P<0.05), But there was no affect on area of Rexfur skins (P>0.05), and also had the highest in19%. Dietary crude protein (CP) level hadsignificant affect nitrogen intake (IN) and digestible nitrogen (DN)(P<0.05). It has noinfluence on fecal nitrogen output(FN), nitrogen retention(RN), urine nitrogen(UN) andnitrogen apparent digestibility,biological value of nitrogen and nitrogen utilization rate(P>0.05). RN was increased with the CP increased; nitrogen apparent digestibility was firstincreased and then decreased. PH, drip loss, shear force, L, a*and b*, whole net carcassrate,Muscle protein contend were not changed significantly(P>0.05),whole net carcass rate inlow protein diet was advanced to high protein diet; Shear force showed was first increasedand then decreased; drip loss expressed downward trend; PH was first decreased and thenincreased. Dietary crude protein (CP) level had no significant affect small intestine protease.Dietary CP level had no significant affect TP, ALB, GLB, A/G and CHO (P>0.05);Dietary CPlevel did influence on SUN (P<0.05), and the highest at19%. Dietary CP level had significantaffect growth hormone (GH)(P<0.05), the highest at17.5%;dietary CP level had nosignificant affect insulin and IGF-Ⅰ(P>0.05), in17.5%had the highest. The express of GHRin muscle and liver had extremely significant influence (P<0.01), the express GHR in muscleincreased gradually; the express GHR in liver has the highest value in16%group. Based onthe ADG and GH, the estimated requirement of portion level was19%and17.5%, but theoptimal portion level estimated by MLIN was19.09%and17.32%.