| The experiment was conducted to study the effects of threonine on growth performance, immunity performance, blood metabolites in serum and protein metabolism of growing of weaned～2 month and 2～3months old meat rabbits and estimate the threonine requirement using a quadratic curve model. Two hundred weaned rabbits were allocated to individual cages and randomly divided into five groups. Animals in each group were fed with a diet with the following threonine levels: 0.49%, 0.59%,0.69%,0.79% and 0.89% in original matter basis respectively. The results were as follows.Dietary threonine levels significantly affected average daily gain (ADG) and feed/gain (P=0.0180,P=0.0248) of weaned～2 month old meat rabbits. Threonine levels had extreme significantly influence on average daily intake(ADI)(P<0.0001). Threonine levels had significantly influence on intake nitrogen (IN) (P=0.0197), but had no significantly influence on digestible nitrogen(DN), retention nitrogen(RN)and DN/IN(P>0.05),but fecal nitrogen (FN) showed positive quadratic responses to the increasing of dietary threonine level (PQ =0.0207). Lysine and methionine digestibility were not significantly affected by threonine levels (P>0.05). Dietary threonine levels had extreme significantly influence on the digestibility of aspartate , serine , glutamic , glycine , alanine , cysteine , valine and leucine(P<0.01); With the increase of threonine level, IgA, IgM and IgG concentration in serum had no significant change (P>0.05),but had a trend that first increased and then decreased. Different dietary threonine levels had significant influence on AKP in serum (P<0.05), however , threonine levels had no influence on total protein (TP), albumin (ALB) , triglyceride (TG) and serum urine nitrogen(SUN) (P>0.05). With the increasing of threonine level, the content of protein had no significant change (P>0.05), but had a trend that first increased and then decreased. Dietary threonine levels did not significantly affect the content of RNA and protein/RNA(P>0.05). Based on the average daily gain, the average daily intake and the alkaline phosphatase activities of weaned～2 month old meat rabbits , the optimal level of threonine is 0.748%,0.761%,0.710%,respectively ,when the levels of protein , threonine and DE are set at 16.12% , 0.57% and 10.18 MJ/kg in diets.Different levels of threonine had no significant difference on 2～3 month old meat rabbits'feed/gain(P=0.0894), but showed a trend of reducing (PL=0.0044,PQ=0.0179). Average daily gain (ADG) and average daily intake(ADI)were extreme significantly affected by threonine levels (P<0.0001),and average daily gain (ADG) was the highest at 0.69% level. Dietary threonine levels had no influence on nitrogen balance(P>0.05). The digestibility of methionine , aspartate , serine , glutamic , glycine , alanine , cysteine , valine and leucine were significantly affected by threonine levels (P<0.01). Different levels of threonine had no significant difference on immune organs and immune index (P>0.05), but all indexes had a trend that first increased and then decreased. Threonine levels significantly increased IgG in serum (P<0.05),but did not affect IgA and IgM(P>0.05). With the increasing of threonine level, total protein (TP), albumin (ALB) , triglyceride (TG) and alkaline phosphatase ( AKP) had a trend that first increased and then decreased, but had no significant change(P>0.05). When the threonine level was 0.69%, serum urine nitrogen (SUN) was the lowest. With the increase of threonine level, the content of protein had no significant change (P>0.05), but had a trend that first increased and then decreased. Dietary threonine levels did not significantly affect the content of RNA and protein/RNA(P>0.05). Based on the average daily gain and the average daily intake a of 2～3 month old meat rabbits , the optimal level of threonine is 0.739%,0.745%, respectively ,when the levels of protein , threonine and DE are set at 16.12% , 0.57% and 10.18 MJ/kg in diets.
|
PDF Full Text Request