The Effect Of Protein Level On Growth Performance And Nutrient Metabolism Of Heat-stress Meat Rabbits

The experiment was conducted to study the effect of different protein levels in diets on the production performance, nutrient metabolism indexes, antioxidant capacity, immunity and HSP70level of heat-stress meat rabbits. The objectives were to clarify the effect of heat stress on the production performance and metabolism of meat rabbit by feeding different protein levels in diets. Therefore, it is to provide a theoretical basis of appropriate dietary protein for meat rabbits under heat stress.The complete crossover trial design was used in our experiment. It was to be set two kinds of temperature and humidity environments that were heavy heat stress (THI:28.9-30) and comfortable environment (THI:22.2-23.2). Based on NRC (1977) that was the standard of nutritional needs of meat rabbits, five crude protein levels of the meat rabbits dietary were designed (Ⅰ:CP12.0%; Ⅱ:CP14.0%; Ⅲ:CP16.0%; IV:CP18.0%; V:CP20.0%).300New Zealand weaned pups, the start weight, of which were almost same (0.825±0.054kg), were selected in our study. All the pups were randomly allotted into10groups and thirty meat rabbits in each group with five replicates of six meat rabbits (half male and half female). After all groups were administered for35days, production performance and indexes of nutrient metabolism were determined. After experiment of15days, six meat rabbits, which were randomly selected from every group and placed in metabolic cages, were used to measure the feed nutrients digestion. The results were as followed:1. Feed protein level decreased feed intake and daily gain of meat rabbits, while increased F/G of meat rabbits. During the period of the heat stress, daily gain increased first with the rising of protein levels, then decreased, The daily gain of group Ⅱ was higher than that of groups else (P<0.05), group Ⅲ was no significant difference with group Ⅳ (P>0.05). For F/G, it decreased first with the rising of protein levels, and then increased. F/G of group Ⅱ, group Ⅲ and group Ⅳ was lower than groups else (P＜0.05), there was no significant difference between group Ⅰ and group V (P＜0.05).2. Feed protein level affected DM digestibility and CP digestibility in the diets of heat-stress meat rabbits. During the heat stress period, the digestibility of DM, EE, Ash and CF increased first with the rising of protein levels, and then decreased. While the digestibility of DM, EE, Ash in group Ⅱ and Ⅲ were higher than that of groups else (P<0.05), there was no significant difference between group Ⅱ and group Ⅲ (P>0.05). The CF digestibility of group Ⅱ and Ⅲ were no significant difference (P>0.05), the CF digestibility of group Ⅱ, group Ⅲ was higher than that of groups else (P<0.05). When diet protein levels improved, the digestibility of CP decreased under heat stress, while group Ⅰ was higher than that of groups else (P<0.05), the CP digestibility of group Ⅱ, group Ⅲ and group IV were higher than that of group V (P<0.05), there were no significant difference among group Ⅲ, group Ⅲ and group IV (P>0.05).3. Feed protein level affected serum biochemical of heat-stress meat rabbits. TP, ALB, CHOL increased with the rising of protein levels. The TP, ALB content of group II and III were higher than that of groups else (P＜0.05). There was no significant difference between group II and group III (P>0.05). The CHOL content of group Ⅰ, group Ⅱ, group Ⅱ were lower than that of group V (P<0.05), while there was no significant difference between group V and group IV (P>0.05). The levels of BUN and AKP first decreased with the rising of protein levels, then increased, while the BUN content of group Ⅱ and group Ⅲ were significant difference among that of groups else (P＜0.05) and there was no significant difference between group Ⅱ and group Ⅲ (P>0.05). The BUN content of group Ⅰ, group Ⅱ and group Ⅲ were lower than that of groups else (P＜0.05), there was no significant difference among group Ⅰ, group Ⅱ and group Ⅲ (P>0.05).4. The feed protein level had an obvious effect on anti-oxygen indexes of heat-stress meat rabbits. During the period of heat stress, CAT, T-AOC, SOD and GSH-PX levels increased first with the rising of protein levels, and then decreased, while CAT content was no significant difference among all the groups (P＜0.05), the CAT content of group Ⅲ was the highest among all the groups, also does the T-AOC content. The T-AOC content of group Ⅲ and group Ⅳ were no significant difference (P>0.05), while group Ⅲ and Ⅳ were significant difference among that of groups else. The SOD content of group Ⅱ was higher than group Ⅲ, group Ⅳ and group V (P＜0.05), There was no significant difference between group Ⅰ and group Ⅱ (P>0.05). The GSH-PX levels of group Ⅱ, group Ⅲ were higher than that of groups else (P＜0.05), and there was no significant difference between group Ⅱ and group Ⅲ (P>0.05). The content of MDA first decreased with the rising of protein levels, then increased, while the MDA content of group II was lower than that of groups else (P＜0.05).5. Feed protein level affected the level of IgG, C3, C4in the blood of heat-stress meat rabbits, but it had small effect on IgA (P>0.05). The level of C3and C4increased first with the rising of protein levels then decreased, while the C3level of group III was higher than that of groups else (P<0.05). The C4level of group III and II were no significant difference (P>0.05), but group II and group III were higher than that of groups else (P<0.05). The level of IgG was increased when protein levels improved, while IgG level of group V was higher than that of group I, group II and group III (P<0.05), but there was no significant difference between group V and IV (P>0.05). The level of IgA was no significant difference among all the groups (P>0.05).6. During the heat stress period, the feed protein level affected HSP70of meat rabbit tissues. The HSP70level of group I, IV and V were lower than group II, group III (P<0.05), the protein levels of diets improved the HSP70level of meat rabbit tissues, enhanced the anti-heat-stress ability of meat rabbits.In summary, the protein levels of diets influenced the growth of meat rabbits, when meat rabbits were in the situation of heavy heat stress. The protein levels of diets in moderation promoting the utilization of dietary, it enhanced antioxidant capacity, also it improved the ability of oxidative stability and HSP70expression of meat rabbit tissues, and thereby it enhanced the anti-heat-stress ability of meat rabbits and reduced the negative impact of heat-stress of meat rabbits.