| The shortage of forage feed is one of the main factors that limits the sustainable development of animal husbandry in China.At present,there have amounts of potential feed resources such as crop by-products in China,but they were less efficient for feed utilization.The planting area and yield of ramie in China has occupied the first place in the world for many years.As by-product of fiber crop,stems and leaves of ramie showed great potential for feeding due to its high level of crude protein.In addition,they were rich in amino acids,as well as their favorable amino acids composition,which were essential and benefit to animal growth.However,there were few studies of ramie on feeding safety,rumen degradation characteristics and feed utilization in large ruminants.Therefore,to determine the main anti-nutritional factors,ramie stems and leaves and their silage were analyzed.To evaluate the feeding safety of ramie stems and leaves,acute toxicity and 28-day sub-acute toxicity test were administered to SD mice and rats.To determine the rumen degradation characteristics of ramie stems and leaves,the semi-in vivo digestion experiment in cannulated cattle was carried out.To study the feeding effect of ramie silage,150-day feeding test was conducted to Yunling bull.All experiments above and,the study intended to systematically and comprehensively evaluated ramie stems and leaves,in order to provide theoretical basis and reference for ramie utilizing as a feed.The results showed that:1.In acute toxicity test,the maximum dose of ramie stems and leaves was administered to mice.No death and toxicity symptoms were observed in the treated group and the control group during the experimental period.Body weight showed no difference between treated group and control group during intragastric administration time.And there were no abnormal lesions occurred in the main organs or tissues in mice after the experiment finishing.Under this test condition,the maximum dose of ramie stems and leaves to mice was up to 12g/kg·BW,which can be determined that the stems and leaves of ramie were non-toxic substances.2.In 28-days sub-acute toxicity test,the same volume of ramie stems and leaves in high dose,low dose and control(2g/kg·BW,1g/kg·BW,0 g/kg·BW)were orally administrated to SD rats.There were no abnormal changes on general behavior,body weight,feed intake,hematology,coagulation,serum biochemistry,and histopathology in high dose group,low dose group and the control group.Changes on hematology were found both in the three groups,but these changes could not considered to be toxicological.Histopathological examination was performed on the high dose group and control group.It showed that some lesions were found both in the high dose group and the control group,but the lesions were mild.Therefore,they could be judged as a common spontaneous lesion,and not related to ramie administration.Under the condition of this experiment,the non-toxic dose(NOAEL)of ramie was up to 2.00 g/kg in SD rats through orally administrating for 28 consecutive days.3.Through the analysis of limiting factors in ramie feeding utilization,it showed that the level of tannin,crude fiber,neutral detergent fiber and acid detergent fiber in ramie stems and leaves were high.Their contents in ramie stems and leaves were 0.48%,31.30%,55.80% and 42.07%,respectively.The value of its calcium/phosphorus was 17.99,which indicated it was unbalanced in calcium and phosphorus content.However,the content of tannin and fiber in ramie decreased after silage,but the ratio of calcium/phosphorus was still very high.4.Rumen degradation test of ramie stems and leaves showed that the contents of its conventional nutrients such as dry matter,organic matter and crude protein were high,which were 94.31%,87.86% and 16.61%,respectively.The degradation rate of dry matter,organic matter,crude protein,neutral detergent fiber and acid detergent fiber increased,while ramie stems and leaves' retention time increased in rumen.And all of them reached the highest at 72 h,which were 63.05%,62.68%,83.09%,23.89% and 38.93%,respectively.The effective degradation rates were 43.87%,42.93%,60.15%,14.72%,and 20.65%,respectively.5.In feeding test,three treatments that ramie silage replaced different proportion of corn silage(0%,20%,40%)were conducted to Yunling cattle for 150 days.Compared with the control group,the average daily weight gain of the T2 group was 0.81 kg,which showed a little higher than another two groups although there was no significant difference.Aspartate transaminase(AST),alanine aminotransferase(ALT),total protein(TP),albumin(ALB),globulin(GLB),albumin/globulin ratio(A/G)and triglyceride(TRIG)in three groups showed no significant difference.The content of serum urea nitrogen(BUN)in the two groups of 20% replacement and 40% replacement was significantly lower than that in the control group,which indicated they could utilize the protein more effectively.Therefore,it was feasible to use ramie silage instead of 20% and 40% corn silage to feed beef cattle.Considering the growth performance and blood biochemical indexes of beef cattle in this test and the perspective of actual production efficiency,ramie silage replacing 20% of corn silage to feed beef cattle was better.In summary,there had restrictive factors for feeding such as high tannin and fiber,high ratio of calcium to phosphorus in stems and leaves of ramie.There was non-toxic of ramie stems and leaves.And at a maximum dose of 2g/kg·BW,ramie stems and leaves showed no adverse effects on SD rats.As the retention time of ramie stems and leaves in the rumen of beef cattle increased,the degradation rate of each nutrient component increased.That ramie silage replacing 20% and 40% of corn silage for feeding cattles,did not produce adverse effects on their production performance and health.In addition,silage could effectively improve the feeding value of ramie stems and leaves.In the future,it has greatly potential for ramie stems and leaves to develop and utilize as a large ruminant feed resource. |
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