Effect And Mechanism Of Dietary Energy Level On Growth,Finishing And Slaughter Performance And Meat Quality Of Donkeys

Dietary energy level is an important limiting factor that limits animal growth and development performance,but current research on meat donkeys is rarely reported.In this study,it was discussed the effect of dietary energy level on the performance of growth,finishing,and slaughter,meat quality,and muscle amino acid composition of donkeys.The completely single-factor test design was adopted in this study.Thirty-six meat donkeys(male)aged 1 years with similar weight(150±25 kg)were randomly divided into three treatment groups including low-energy group(E1),middle-energy group(E2),high-energy group(E3).Each treatment group included 4 repicates with 3 donkeys each replicate.The experiment included 10 days pre-trial period,and the trial period was 135 days,which was divided into early finishing(1-45 d),middle finishing(46-90 d)and late finishing(91-135 d).Donkeys were weight once half every 15 days.Digestion experiment was done three times,and blood was collected in the experimental period.All donkeys were slaughtered after keeping fasting for 12 h,and samples were collected.The test was mainly divided into four parts:The experiment 1 mainly investigated the effects of dietary energy levels on performance of growth,finishing and slaughter of meat donkeys.The results indicated that the dietary energy level had no significant effect on the weight,average daily weight gain and feed conversion rate of meat donkeys during the early stage of fattening(P≥0.10).The weight,average daily weight gain and feed conversion rate in E2 group was significantly higher than that in E1 and E3 groups during the middle of fattening(P<0.05).During the late fattening period,the weight of E2 group was significantly greater than that of E1 and E3 groups,but the difference between El and E3 groups was not significant.No significant difference exsited in daily gain and feed conversion efficiency between E2 and E3,but these parameters were significantly higher than those in the E1 group(P<0.05).Throughout the test period,the total weight gain and average daily weight gain were E2>E3>E1(P<0.05),but there was no significant difference in feed intake.It indicated that the diet in the medium energy group promotes the growth and fattening performance and feed conversion efficiency of the meat donkeys.The low energy and high energy diets were not beneficial to the development of growth and fattening performance,especially the low energy diets.The live weight before slaughter and carcass weight were E2>E3>E1(P<0.05),but the meat-to-bone ratio and eye muscle area meat donkeys in the E3 group were significantly or tended to be significantly lower than those of the E1 and E2 groups(P<0.05,P=0.075).The weight of greater omentum fat,mesenteric fat,perirenal fat and intra-abdominal fat and GR value in group E3 were significantly higher than those in group E1(P<0.05),and those parameters above were greater in E2 than El(except large omentum fat)(P<0.05).It indicated that high-energy diets promoted the fat deposition and the thickness of the back fat of the meat donkeys,and the middle-energy diets came second.Dietary energy levels could significantly increase the weight of the lungs,and which was in E3 group is significantly higher than the other two groups(P<0.05);the proportion of total organ weight to the live weight before slaughter in E1 and E3 groups tend to be significantly higher than that in E2 group(P<0.05).Dietary energy level had no significant effect on the pH of the cecum(P≥0.10),and had a significant effect on the total weight of the digestive tract,ileum weight,rectal weight,and digestive tract weight before the slaughter,compared with the E2 group,the E1 group The total digestive tract weight,ileum weight,and total intestinal length of the E3 group were significantly decreased(P<0.05),and the proportion of jejunum weight,rectal weight,and total digestive tract weight to live weight before slaughter and rectal weight were significantly increased(P<0.05).).This shows that the diet with medium energy level promotes the development of the digestive tract,but the organ development is better with the low energy and high energy groups.The weight of the lungs in E3 group was significantly higher than that in the other two groups(P<0.05).The proportion of total organ weight to the live weight before slaughter in El and E3 groups tended to be significantly higher than that in E2 group(P=0.092).Dietary energy level had no significant effect on the pH of the cecum(P≥0.10),but had a significant effect on the total weight of the digestive tract,ileum weight,rectal weight,and digestive tract weight before the slaughter,and compared with the E2 group,the total digestive tract weight,ileum weight,and total intestinal length of the E1 and E3 group significantly decreased(P<0.05),and the proportion of jejunum weight,rectal weight,and total digestive tract weight to live weight before slaughter and rectal weight significantly increased(P<0.05).These results suggested that the medium energy diet promoted the development of the digestive tract,but the low energy and high energy diet showed the better effect for the organ development.The experiment 2 mainly studied the effect of dietary energy level on apparent digestibility and digestive tract enzyme activity of meat donkeys.The results showed that in the middle finishing period the digestibility of DM,CP,EE,Ca,and P of meat donkeys in the E2 group was higher,and was higher than that in the El and E3 groups(P<0.05).The digestibility of DM,ADF,NDF,Ca and P in E2 and E3 group was significantly higher than that of E1 group in the late finishing period(P<0.05).The lipase activity in ileum and jejunum,chymotrypsin activity of ileum and amylase activity in duodenum in the E2 group were significantly higher than those in the E1 and E3 groups.The amylase activity of ileum in the E3 group was significantly higher than that in the E2 and E1 groups.The activity of trypsin in ileum and jejunum was significantly higher than that in E1 and E3 groups(P<0.05).The activity of trypsin and lipase in duodenum and amylase activity in jejunum in E2 and E3 were significantly higher than those in E1 group(P<0.05).It indicated that both medium-energy and high-energy dieta could promote the activity of digestive enzymes in the small intestine,and had a higher digestibility of nutrients,especially the medium-energy diet had the greater effect.The Experiment 3 mainly studied the effects of dietary energy levels on the physical and chemical characteristics and the nutrients content of donkey meat.The results showed that muscular cooking loss and shearing force in E3 group tended to be significantly lower than those in E1 group(P=0.092,P=0.074),and E2 group was second.The a*and b*values in E3 group were significantly lower than those in E1 and E2 groups(P<0.05).Dietary energy levels had no significant effects on the crude protein content of donkey muscle(longissimus,triceps brachii,glutinous muscles,Biceps femoris)(P>0.10).The ether extract content in the E2 and E3 groups was significantly higher than those in the El group(P<0.05).It indicated that the medium energy and high energy diets could promote the deposition of fat in muscles,and increase the tenderness and water retention performance of muscles,especially the high energy diet showed the better effect.The effect of dietary energy levels on the content of mineral elements in muscles of meat donkeys varies with different muscle parts and mineral element speciesThe experiment 4 mainly studied the effects of dietary energy levels on blood biochemical indexes and amino acid composition in blood and muscles of meat donkeys.The results found that the contents of TAA,EAA,NEAA and DAA in the triceps brachii and the contents of NEAA,DAA and TAA in the gluteal muscle and TAA,EAA,NEAA,DAA,FAA,BCAA and NEAA,EAA/TAA and EAA/NEAA of biceps femoris in group E2 were significantly higher than those in the E3 group(P<0.05),but there was no significant difference between E2 the E1 group.The contents of Asp,Ser and Arg in biceps femoris and the contents of Thr,Ser,Glu,Ala and Tyr in gluteal muscles and Glu,Gly,Ala,Val,Met,Leu,Tyr,Phe,Lys,Pro,His and Arg in triceps brachii of E1 and E2 groups were significantly higher than those in the E3 group,but there were no difference in the above indicators between the E1 and E2 groups.All of these results indicated that donkey muscle in the low-energy and medium-energy groups had better AA balance and higher protein nutritional value,in particular,donkey muscle in the low energy group had the best AA balance.The plasma levels of Glu,Ala,Met,Pro,His,NEAA,BCAA,FAA and DAA and EAA/NEAA in E2 and E3 groups significantly increased compared with E1 group(P<0.05),but EAA/NEAA,EAA/TAA and Asp content significantly decreased or tended to decrease(P=0.016,P=0.051,P=0.085).At the middle and late stages of finishing,the serum levels of GLU,CHOL,HDL-C and LDL-C in the E2 and E3 groups were significantly higher than those in the E1 group(P<0.05),and the serum levels of ALB,TP,D3HB and NEFA in the E2 group were significantly higher than the El and E3 groups(P<0.05).In conclusion,the medium energy diet promoted the performance of growth,fattening and slaughter of the meat donkeys,and the development of the digestive tract and the digestion and absorption of nutrients.The A A balance of the muscle and the nutritional value was higher,and fat deposition was lower,and the economic benefits was the best in medium energy dietary group.Although the low energy diet reduced the fat deposition and improved the amino acid balance of the muscle,and the high energy diet increased the water retention and tenderness,the high energy diet and the low energy diet reduced the growth,fattening and slaughtering performance of the meat donkey,especially the low energy diet showed the bad effect.