Study On The Effect Of Feed Nutrient Level On Sheep Meat Quality And SCD Gene Expression

Jilin Province is an important part of the national"Advantageous Producing area of mutton sheep in the Central and Eastern farming-husbandry interleaved zone",and the mutton sheep industry is one of the leading industries in the region,among which fattening sheep is one of the main business projects of the mutton sheep industry in the region.Therefore,how to use the feed resources in the region to optimize the optimal dietary structure suitable for fattening sheep in the growing period and improve the production efficiency of mutton sheep?It is one of the effective ways to break the bottleneck of efficient development of meat sheep industry in restricted areas.In this study,according to the appropriate metabolizable energy（ME）and crude protein（CP）requirements of sheep in growing and fattening period stipulated in Nutrient Requirement of Meat Sheep（NY/T 816-2021）,and based on local feed raw material resources,the diet was designed（energy and protein intake was 100%of nutrient requirement）.At the same time,the energy protein level of the control group was adjusted by 10%,and the experimental group was fed the 2×2 factor design.4 groups were fed different protein and energy levels experimental diets:GroupⅠ（110%CP,90%ME）,groupⅡ（90%CP,90%ME）,groupⅢ（110%CP,110%ME）and groupⅣ（90%CP,110%ME）.Thirty 4-month-old healthy Australian white sheep and small-tailed Han sheep cross F1 ewe were randomly divided into groupⅠ,groupⅡ,groupⅢ,groupⅣand control group,with 6 ewes in each group.The control group was standard energy protein group,which was fed for 2 months under the same feeding conditions.Growth traits,slaughter performance,mutton quality,content of flavor precursors,volatile flavor substances and SCD gene expression levels regulating meat quality were compared between experimental groups and control groups,so as to explore the effects of different energy and protein levels on meat production and meat quality of growing mutton sheep,so as to provide reference for the development of scientific and reasonable fending plan for mutton sheep.The research results are as follows:1.Study on the effects of different Nutrient levels on growth traits and slaughter performance of sheepCompared with the control group,the daily gain and body length increase of groupⅢ（high energy and high protein group）were significantly increased（P<0.05）,and the body length increase of groupⅡ（low energy and low protein group）was significantly decreased（P>0.05）.There were no significant differences in body height,chest circumference,chest width and slaughter performance（P>0.05）.In summary,the growth performance of groupⅢ（high energy and high protein group）was superior to other groups.2.Study on the effects of Different Nutrient Levels on Meat Quality and Flavor Substance Content of SheepCompared with control group,p H_24hvalue and tenderness of longissimus dorsi muscle in groupⅠ（low energy and high protein group）were significantly increased（P<0.05）.There were no significant differences in meat color and cooked meat percentage among 5 groups（P>0.05）.The meat quality of Longissimus dorsi muscle in groupⅠ（low energy and high protein group）was the best.A total of 16 amino acids,including 7 essential amino acids（EAA）and 9non-essential amino acids（NEAA）,were detected in longissimus dorsi muscle of sheep in each group.Compared with the control group,the contents of glycine,lysine and tyrosine in groupⅡ（low energy and low protein group）were significantly decreased（P<0.05）,and the contents of methionine in groupⅣ（high energy and low protein group）were significantly decreased（P<0.05）.The muscle flavor of groupⅡ（low energy and low protein group）decreased,and the protein value of longissimus dorsi muscle in groupsⅠ（low energy and high protein group）,Ⅲ（high energy and high protein group）andⅣ（high energy and low protein group）was excellent.A total of 11 fatty acids were detected in longissimus dorsi muscle of sheep,including 5saturated fatty acids（SFA）,4 monounsaturated fatty acids（MUFA）and 2 polyunsaturated fatty acids（PUFA）.No C15:1 was detected in longissimus dorsi muscle of sheep in groupⅠ（low energy and high protein group）.Compared with control group,the contents of C16:1 and C17:1in muscle of groupⅡ（low energy and low protein group）were significantly decreased（P<0.05）.The content of C17:0 in groupⅣ（high-energy low protein group）was significantly higher than that in groupⅢ（high-energy high protein group）（P<0.05）.The C16:1 and PUFA contents in groupⅢ（high energy and high protein group）were significantly higher than those in groupⅡ（low energy and low protein group）（P<0.05）.The content of C18:2n-6 in groupⅢ（high energy and high protein group）and groupⅣwas significantly higher than that in groupⅠ（low energy and high protein group）（P<0.05）.The SFA content of groupⅣ（high energy and low protein group）was significantly lower than that of groupⅡ（low energy and low protein group）.The PUFA content in groupsⅢ（high energy and high protein group）andⅣwas significantly higher than that in groupⅡ（low energy and low protein group）（P<0.05）.In terms of fatty acid composition,groupⅢ（high-energy high-protein group）and groupⅣ（high-energy low-protein group）had the highest nutritional value.Compared with control group,inosine content in experimental groups had no significant difference（P>0.05）.In conclusion,the musculature of longissimus dorsi muscle in groupⅠ（low energy and high protein group）was the best,and the nutritional value of longissimus dorsi muscle in groupsⅢ（high energy and high protein group）was the best.Compared with the control group,the contents of 4-methyl-caprylic acid,4-methyl-nonanoic acid,hexal,nonaldehyde and 2,4-decadienal in groupⅠ（low energy and high protein group）were significantly increased（P<0.05）;The contents of 2,4-decadienal and nonaldehyde in groupⅡ（low energy and low protein group）were significantly increased（P<0.05）;The contents of 2,4-decadienoaldehyde and nonaldehyde in groupⅢ（high energy and high protein group）were significantly increased（P<0.05）.The nonaldehyde content in groupⅣ（high energy low protein group）was significantly increased（P<0.05）.No 1-pentene-3-ol was detected in groupⅢ（high-energy high-protein group）,groupⅣ（high-energy low-protein group）and control group.The odor substances and volatile flavor substances in groupⅠ（low energy and high protein group）were significantly increased,and the flavor was not good.The content of funky fatty acids in groupⅣ（high energy low protein group）was the lowest.The correlation between fatty acids and volatile flavor compounds was found that 4-methyl-caprylic acid was negatively correlated with cil-10-15-enoic acid and stearic acid.There was a negative correlation between nonaic acid and stearic acid,oleic acid and linoleic acid,but a positive correlation between nonaic acid and oleic acid.2,4-sebacedienal was negatively correlated with cis-10-heptaenoic acid and stearic acid.3.Study on the effects of different nutrient levels on SCD gene expressionHE staining was used to observe the histological morphology of longissimus dorsi muscle of sheep,and the study showed that there were no significant differences in muscle fiber density and muscle fiber diameter of longissimus dorsi muscle of sheep in 5 groups（P>0.05）.Immunohistochemistry and Quantitative Real-time PCR（real-time PCR）method were used to study the expression and localization of SCD protein was found to be expressed in the cell membrane,cytoplasm and connective tissue of 5 groups of sheep muscle cells,and there was no significant difference in the m RNA level of SCD gene in sheep muscle of the 5 groups（P>0.05）.But the trend of groupⅣ（high energy and low protein group）>control group>groupⅡ（low energy and low protein group）>groupⅢ（high energy and high protein group）>groupⅠ（low energy and high protein group）.