| Effects of different protein level on growth performance,nutrient digestibilities,immunology ,protein enzyme activities in small intestine and biochemical fraits in serum on weaning~2 month-old and 2~3 month-old New Zealand White rabbit were investigated,and compared the differents of these results between two kinds of age. Nutrient content of five kinds of experimental diets is resemble except protein level(13.50%,15.55%,17.56%, 20.20%,21.93%).The results are as follows: Experiment One: During weaning~2 month-old ,growth performance,nutrient digestibilities,protein content in seurmof New Zealand White rabbit ascended first with the improvment of protein levels,then descended.Daily gain in 20.20% CP treatment is highest but feed conversion rate was lowest,which was 34.93 g/d and 2.74:1 respectively;CP digestibility in 17.56%CP treatment was 72.08% and get to the maximun(p>0.05 or p<0.05);But CF digestibility in 15.55% CP treatment was highest ,which was 28.36%,and had significant difference than other treatments(p<0.01);Amino acid digestibility was consistent with CP digestibility as a whole;RN increased with the improvement of protein level(p>0.05),which was highest on 20.20%CP treatment (1.49g/d),effect of protein level on RN/DN was little.In15.55%CP treatmeant,spleen indices,thymus indices,chymotrypsin activity,trypsin activity of meat rabbit were highest ,which were 0.95g/kg,2.80g/kg,15.67U/g,125.68U/g respectively,but had no significant difference(p>0.05),so immunology indices and protein enzyme activities in small intestin of weaning~2 month-old meat rabbit had no obvious change with different protein level;CHO and BUN of meat rabbit in 21.93%CP treatment are highest ,which are 2.12g/L and 10.68mmol/L respectively,so the protein level of 21.93% of meat rabbit is excessive in this experiment.In a word, the diet of 17.56%~20.20% CP was suited to weaning~2 month-old meat rabbit. Experiment Two:During 2~3 month-old ,growth performance,nutrient digestibilities,protein content in seurm of New Zealand White rabbit ascended first with the improvment of protein levels,then descended.Daily gain in 20.20% CP treatment is highest(30.30g/d), and had no significant difference (p>0.05);Feed conversion rate got to the minimum(4.12:1) in 21.93%CP treatment.CP digestibility was highest in 20.20%CP treatment,which is 74.43%,but had no significant difference (p>0.05) with 15.55%CP treatment and 17.56%CP treatment;CF digestibility reached the maximum (32.34%) in 15.55%CP treatment; Amino acid digestibility was consistent with CP digestibility as a whole.RN in15.55%CP treatment was reasonable for daily gain profit;RN/DN had no significant difference among five treatments(p>0.05);Carcass rate is highest in 17.56%CP treatment ,which is 55.90%;Regarding as daily gain profit economic situation of 2~3 month-old meat rabbit in 15.55%CP treatment is idealest;Effect of experimental diets on chemical content of meat was little;Shearing force and water holding capacity in 20.20%CP treatment were highest and lowest,which were 961.53g and 43.12% respectively. Spleen indices and thymus indices in 20.20%CP treatment were highest(0.89g/kg and 2.60g/kg respectively),but had no significant difference among all treatment(p>0.05); chymotrypsin activity,trypsin activity of meat rabbit in 17.56%CP treatment got to maximum,which were 14.14U/g and 129.18U/grespectively;CHO and BUN in 21.93%CP treatment were highest(2.36g/L and 8.52mmol/L respectively).In a word, the diet of 15.55%~20.20% CP was suited to 2~3 month-old meat rabbit. Experiment Three: Contrasting the results between experiment one and experiment two,daily gain of weaning~2 month-old meat rabbit was higher than of 2~3 month-old meat rabbit,and feed conversion rate was lower than of 2~3 month-old meat rabbit;Nutrient digestibilties of 2~3 month-old meat rabbit were higher than of weaning~2 month-old meat rabbit;Immunology indices had obvious change between two kinds of age,but protein enzyme activities descended with the addition o...
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