The Appropriate Level Of Dietary Threonine And Tryptophan For New Zealand Growing Meat Rabbit

The aim of this study was to investigate the effects of dietary Threonine and Tryptophan on the growth performance and serum biochemical indices of New Zealand growing rabbits, basing on a certain level of measured digestible energy (DE).We measured and analyzed the appropriate level of dietary Threonine and Tryptophan for growing meat rabbits, provided some basic data to the requirement of Threonine and Tryptophan of the growing meat rabbits and fulfilled the data of the appropriate ratio to other essential amino acids.The experiment contained 3 main test portions. The aim of test Ⅰ was to DE termine the DE of each feed ingredients through digestion experiments, and then the measured data were used in Test Ⅱ and Test Ⅲ. In order to determine the suitable demand of Thr and Trp at certain DE level,5 Threonine levels and 8 Tryptophan levels were set for Test Ⅱ and Test Ⅲ, respectively, based on the parameters confirmed from Test Ⅰ.Experiment 1 The determination of DE of feed ingredientsIn this experiment, the replacement method was used to determine the DE of all feed ingredients. Forty-two healthy New Zealand growing white rabbits at day 45 of age, with an average body weight of 904.17±50.87 g were randomly divided into 7 groups, with differences in Corn, Wheat bran, Soybean meal, Corn germ meal, Alfalfa powder, Peanut shells and Basis of each group. Each group has 6 replicates with 3 males and 3 females reared seperately in the cage. The preliminary trial lasted for 6 days and the experiment lasted for another 6 days. The results showed that the DE values of Corn, Wheat bran, Soybean meal, Corn germ meal, Alfalfa powder rand Peanut shells were 14.18 MJ/kg,9.37 MJ/kg,14.23 MJ/kg,13.60 MJ/kg,7.99 MJ/kg and 4.73 MJ/kg, respectively.Experiment 2 The appropriate level of dietary Threonine for the rabbitOne-factor completely random design was used in this trial. We add synthetic Thr to the basic diets with DE level of 10.48MJ/kg and Lys level of 0.85%, set 5 kinds of feed with different levels of Threonine (0.60%,0.65%,0.70%,0.75%,0.80%). A total of 100(50 male and 50 femal) healthy New Zealand growing meat rabbits at day 45 of age, with an average body weight of 1004.89±50.41g were randomly assigned to 5 groups with 20 replicates, Each group had 10 male and 10 female. All animals were reared in separated cages with conventional breeding management and immune disinfection procedures, natural lighting and ventilation. Rabbits were fed twice daily during the experimental period and had ad libitum access to food and water.The experiment was lasted for 28 days after a 7-day adaptation period. In every group, four rabbits with similar average body weight were chosen for the blood collection at the last day of the experiment. The blood collected was used to determine the serum total protein (TP), albumin (ALB), serum urea nitrogen (SUN) and insulin-like growth factor-I (IGF-I) content. Rabbits were weighed separately according to different replicates in the early morning of the beginning and the end day of the experimental period with an empty belly. We collected the total amount of feed consumed during the whole experiment period and the results were used to calculate the average daily feed intake (ADFI), average daily gain (ADG) and feed to gain ratio (F/G) of each treatment.The results are as follows:1) Based on the high similarity of born weight(P>0.05), dietary Threonine level had significant affection on ADFI (F<0.01),and had significant influence on ADG and F/G (P<0.05), The ADFI and ADG of each treatment were quadratically elevated which were first increased and then decreased with the increasing level of Threonine, while the F/G was quadratically elevated which were first decreased and then increased. The optimum values of the growth performance were in 0.70%.2) Dietary Threonine level had significant influence on the content of IGF-I (P<0.01) and SUN(P<0.05), but had no significant influence on the contents of TP and ALB in serum (P>0.05). The IGF-I content of the group with the feed containing 0.70% Threonine was the highest, which is significantly higher than Threonine level of 0.60%,0.65% and 0.80%(P<0.01).The SUN content had the minimum value in the group with the diet containing 0.70% Threonine., which is significantly higher than Threonine level of 0.60%and 0.80% (P<0.05).The TP and ALB content of the group with the feed containing 0.70% Threonine was also the highest. Combining analysis of variance and regression, the appropriate level of dietary Threonine is 0.70%.Experiment 3 The appropriate level of dietary Tryptophan for the rabbitOne-factor completely random design was used in this trial. We added synthetic Typtophan to the basic diets with DE level of 10.48 MJ/kg and Lys level of 0.85%, set 8 kinds of feed with different levels of Typtophan (0.17%,0.18%,0.19%,0.20%, 0.21%,0.22%,0.23%,0.24%). A total of 112(56 male and 56 female) healthy New Zealand growing meat rabbits at day 45 of age, with an average body weight of 1099.14±54.01 g were randomly assigned to 8 groups with 14 replicates, each group had 7 male and 7 female. All animals were reared separately in the cage, with same conventional breeding management and immune disinfection procedures, natural lighting and ventilation. All rabbits were fed twice daily during the experiment and had ad libitum access to food and water. The experiment was lasted for 28 days after a 7-day adaptation period. In every group, four rabbits with similar average body weight were chosen for the blood collection at the last day of the experiment. The blood collected was used to determine serum total protein (TP), albumin (ALB), serum urea nitrogen (SUN) and insulin-like growth factor-I (IGF-I) content. Rabbits were weighed separately according to different replicates in the early morning of the beginning and the end day of the experimental period with an empty belly. We collected the total amount of feed consumed during the whole experiment period and the results were used to calculate the average daily feed intake (ADFI), average daily gain (ADG) and feed to gain ratio (F/G) of each treatment.The results were as follows:1) dietary Typtophan level had significant affection on ADFI (P<0.01),and had significant influence on ADG and F/G (P<0.05), The content of ADFI and ADG in the group with the diet containing 0.21% Typtophan were the highest, while the F/G in the group with the diet containing 0.21% Typtophan was the lowest.2) Dietary Typtophan level had significant influence on the content of IGF-I and SUN (P<0.01), when dietary Typtophan is 0.21%, the IGF-I, TP and ALB content had the maximum value, while the SUN had the minimum value. Combining analysis of variance and regression, the appropriate level of dietary Typtophan is 0.20%-0.21%.To sum up, the appropriate level of dietary Threonine and Typtophan are 0.70% and 0.20%-0.21% when the dietary DE is 10.48 MJ/kg and the dietary Lysine is 0.85%.