The Study Of Suitable Diet Energy Level Of Growing Yak Fattening By Barn-feeding And Regulation Of Meat Quality

In this study,the diets of three different concentrate energy levels were designed to explore the effect of production performance,blood biochemical parameters,apparent digestibility of nutrients,the situation of the ruminal fermentation and the beef qualiy in three years old yaks by three barn-feeding experiments.Experiment 1 Effect of diet energy levels on production performance and blood biochemical parameters18 heads of Growing health castrated Yaks were randomly divided into three treatment groups（n=6）.The three different diets were low-energy diets（metabolizable energy 8.36MJ/kg）,middle-energy diets（metabolizable energy 11.15MJ/kg）and high-energy diets（metabolizable energy13.58MJ/kg）,were fed three treatment groups,and the roughage was oat hay.After the pre-feeding period of 40 days and the formal period of 180 days,the results showed that:The final weight of low-energy group,middle-energy group and high-energy group compared to the initial weight of yak were increased by 31.20%,49.63% and 51.31% respectively;the average daily gain of the middle-energy group and the high-energy group were significantly higher than the low-energy group（P<0.05）;The most economical feeding time of middle-energy and high-energy groups is respectively 169 d and 92 d;With the extension of feeding time,the content of urea nitrogen（BUN）were significantly increased（P<0.05）,the rest of the biochemical indexes had no significant changes within the normal range.The experimental conclusion was that the higher diet energy level,the better daily weight gain.But in combination with economic benefits,middle-energy group was more suitable for application in practical production.All stabling for a long time,the rest of the blood biochemical indexes were not affected significantly except for BUN.Experiment 2 Effect of concentrate energy levels on apparent digestibility of nutrientsThe animals of the test were selected 4 heads of yaks from each treatment groups in experiment 1,and the diets was the same as experiment 1.After pre-feeding period of 7 days,the test was began to collect the feces continuously for 3 days.The results showed that: the DM,OM and CP apparent digestibility of middle-energy group were higher quanlitively than low-energy group and high-energy group,which was not significant（P>0.05）;EE apparent digestibility in high-energy group were significantly higher than other groups（P<0.05）;ADF and NDF apparent digestibility of middle-energy group and low-energy group were significantly higher than high-energy group（P<0.05）;Ca apparent digestibility in high-energy and middle-energy were significantly higher than that in low-energy group（P<0.05）,and the middle-energy group was the highest.The experimental conclusion was that the rate of carbohydrate digestion was reduced with the increasing of diet energy levels.But the ability to digest for other nutrients were increased.Experiment 3 Effect of concentrate energy levels on the situation of the ruminal fermentationThe design was the same as experiment 1.But the trial was contained pre-feeding period of 15 days and formal period of 15 days.At the last day of the formal period,the test began to collect the rumen fluid from the mouth.The results showed that:With the increase of energy levels,the pH and concentration of NH₃-N,MCP were significantly increased（P<0.05）;However,TVFA and Protozoa were significantly decreased（P<0.05）;The total dehydrogenase activity were significantly increased at middle-energy group（P<0.05）,and dropped to the level of the middle-energy group at high-energy group;The fatty acid contents of each treatment groups had no significant difference（P>0.05）.The experimental conclusion was that high fat levels of diet could inhibit the energy metabolism,which had a significant impact on rumen fermentation index within the normal range.Experiment 4 Effect of concentrate energy levels on the beef qualityAfter the experiment 1,Concentrated slaughter experiment was carried out.The longissimus muscle between 12 ～ 14 ribs on the right side was collected to determine indicators.The results showed that:The effect of concentrate energy levels on beef incarnadine,pH and slaughter rate were not significant（P>0.05）;The shear force of middle-energy group were significantly higher than the high-energy group（P<0.05）.The experimental conclusion was that appropriate energy level can improve the tenderness of the beef.To sum up,as the rise of the diet energy level,the daily gain increased significantly.And the middle-energy group worked best.In combination with apparent digestibility of nutrients,the situation of the ruminal fermentation,the beef quality and economic benefits,middle-energy group（metabolizable energy 11.15MJ/kg）was more suitable for application in practical production.