Study On Production Performance And Optimal Dietary Protein Level Of Crossbreed Sheep With Different Breeds

In this study,the fattening effects of three crossbreed sheep were compared,and the optimal protein level of their diets was investigated.Firstly,the growth performance and nutrients digestibility of Dorper×Han,Dorper×Mongolian and Dorper×Mongolian×Suffolk crossbreed sheep were measured through feeding experiment and digestion experiment.After the feeding experient,the slaughter experiment was carried out to determine the slaughter performance and meat quality.Then,the effects of dietary protein levels on growth performance and apparent digestibility of nutrients were measured by feeding Dorper×Mongolian×Suffolk crossbreed sheep with total mixed pellet diets with different protein levels,and the optimal dietary protein level of crossbreed sheep was preliminarily explored.The study is divided into three parts:Part 1.Effects of crossbreed of different breeds on growth performance and nutrient digestibility of sheepThe experiment selected sixty Dorper×Han,Dorper×Mongolian,and Dorper×Mongolian×Suffolk crossbreed sheep with similar age,healthy and good body condition for research.According to the breed,they were divided into three groups,with twenty sheep in each group.Each group was divided into four replicates with five sheep in each replicate.The growth performance of sheep was measured on the30 th,50th,65 th and 90 th days of the experiment.Feed and fecal samples were collected three days before the end of the experiment to determine the digestibility of nutrients,and stored at-20℃ until assay.The results showed that,in the early stage of fattening,the average daily feed intake of DMSS group and DDMM group was significantly higher than that of DDHH group(P<0.01).And there was no significant difference in the later stage of fattening(P>0.05).In the total fattening stage,the average daily gain of DMSS group was significantly higher than that of DDHH group and DDMM group(P<0.05),and the F/G was the best.For the apparent digestibility of nutrients,during the two-stage fattening stage of the three groups of sheep,there were significant differences in the apparent digestibility of nutrients(P<0.05),and DMSS was the best.The results showed that the Dorper×Mongolian× Suffolk crossbreed sheep had the best growth performance,its daily weight gain was as high as 363.68 g/d,and its digestibility of various nutrients was significantly higher than other groups,which highlighted the heterosis of the Dorper×Mongolian×Suffolk crossbreed sheep of growth performance.Part 2.Effects of crossbreed of different breeds on slaughter performance and meat quality of sheepThe experimental design was the same as that of part 1.After the feeding experiment,two healthy and disease-free experimental sheep with similar weight were randomly selected from each group for slaughter.And the live weight before slaughter is recorded.After slaughter,the carcass weight and the weight of each organ are weighed according to the halal slaughter method,and the slaughter performance is measured.Then the sample of Longissimus Dorsi Muscle was collected to determine the meat quality.The results showed that the body weight,carcass weight,carcass rate,GR value,testicular weight and abdominal fat weight in DMSS group and DDMM group were significantly higher than those in DDHH group(P<0.05).The head weight,the ratio of head to body weight and the ratio of hoof to body weight in DMSS group and DDMM group were significantly lower than those in DDHH group(P<0.05);The weight of heart and liver and liver index in DMSS group were significantly higher than those in DDHH group(P<0.05)and DDMM group(P<0.01).The weight of spleen in DMSS group was significantly higher than that in DDHH group(P<0.05).There was no significant difference in other organ indexes(P>0.05).In terms of meat quality,there was no significant difference in the indexes of nutritional components of muscle among the groups(P<0.05),but the content of EE increased;For the indexes of muscle physical and chemical properties,the muscle shear force in DDMM group and DMSS group was significantly lower than that in DDHH group(P<0.01);However,the lightness of meat in DDMM group was significantly higher than that of DDHH group(P<0.05).The results showed that under the experimental conditions,Dorper×Mongolian crossbreed sheep and Dorper×Mongolian×Suffolk crossbreed sheep showed better slaughter performance and meat quality than Dorper×Han crossbreed sheep.Part 3.Effects of different dietary protein levels on growth performance and nutrient digestibility of crossbreed sheepThe experiment selected twenty four Dorper ×Mongolian×Suffolk crossbreed sheep with similar age,healthy and good body condition for research.The sheep was randomly divided into three groups according to their body weight,with eight sheep in each group.They were fed with three protein level diets of 13.44%,14.57% and15.25% respectively,which were recorded as 13% CP,14% CP and 15% CP.The transition period was five days,and the trial period was twenty five days.The daily feed intake was recorded every day.After the experiment,the sheep were weighed and the growth performance was measured.Feed and fecal samples were collected three days before the end of the experiment to determine the nutrients digestibility.The results showed that when the dietary protein level was 14.57%,the ADFI and ADG of Dorper×Mongolian×Suffolk crossbreed sheep were the highest,while the F/G was the best when the dietary protein level was 15.25%.The DM digestibility decreased significantly with the increase of dietary protein level(P<0.05),the digestibility of CP and EE increased first and then decreased with the increase of dietary protein level(P<0.05).The NDF and ADF digestibility showed a significant trend of decreasing first and then increasing with the increase of dietary protein level(P<0.05).The results showed that the optimum protein level of Dorper×Mongolian×Suffolk crossbreed sheep was 15.25% from the economic point of view.