Effects Of Dietary Vitamin A Supplementation On Growth Performance,Morphology And Enzyme Activity Of Gastric And Intestine Tissue Of Broilers

This thesis mainly studied the effects of different levels of vitamin A(V_A)supplemented on the performance of broilers,slaughter performance and meat quality,as well as the morphology of digestive tract tissue and enzyme activity.Results provide theoretical basis for scientifically supplement V_A and establishing nutrient regulation measures for healthy of broilers.In this study,a single-factor complete randomized trial design was used.Two hundred and forty one-day-old healthy AA broilers were randomly divided into five groups.Each treated had six replicates with eight chickens.The experimental chickens Free intake and drinking during test period of 42 days.The treatment diets included corn,soybean meal with 5 different levels of V_A(3 000,6 000,15 000,30 000 and 45 000 IU/kg).This thesis mainly contained four parts.1.Experiment 1 mainly studied the effect of different dietary V_A levels on the performance of broilers.The results showed that dietary V_A supplementation had a significant effect on the average daily weight gain of broilers from 22 to 42 days(P=0.035).The 3 000 IU/kg group had the lowest weight gain and significantly lower than the 15 000 IU/kg group.The average daily feed intake of different V_A treatment groups was significantly different during the 22 to 42-day and 1 to 42-day experimental period(P=0.019,P=0.019)and linearly increased(P=0.057,P=0.022),and higher in the 30 000IU/kg and 45 000 IU/kg groups.V_A at different levels had a significant effect on the feed-to-gain ratio during 22-42 days(P=0.065).The feed-to-gain ratio tend to be significantly lower in 6 000 IU/kg and 15 000 IU/kg groups than 45 000 IU/kg group.The feed-to-meat ratio increased linearly from 1 to 42 days with the increase of dietary V_A(P=0.091).2.Experiment 2 mainly studied the effect of dietary supplementation with different V_A levels on slaughter performance and meat quality of broilers.The results showed that different dietary V_A levels had no effect on the slaughter performance of broilers(P>0.05).The loss of water,shear force,and drip loss of Pectoral muscle were significantly or tended to be significantly different among diets with different V_A(P=0.004,P=0.052,P=0.087).Water loss rate linearly increased(P=0.038)and drip loss decreased quadraticly(P=0.002)with increasing dietary V_A levels.Water loss rate and drip loss were higher in the 30 000 IU/kg and 45 000 IU/kg groups and lower in the 3000to 15 000 IU/kg group.The difference in a*and L*values,shear force,drip loss,and cooking loss among the different V_A treatment groups significant or tended to be significant(P<0.05 or P<0.10).The meat color a*value and cooking loss increased quadraticly(P=0.049,P=0.043)and the pH value at 45 min showed a linear increase(P=0.034)with the increase of dietary V_A level.They were lower in the 3 000 IU/kg and6 000 IU/kg groups.3.Experiment 3 focused on the effect of different dietary V_A levels on digestive tract enzyme activity in broilers.The results showed that the activity of duodenal trypsin and chymase decreased linearly with the increase of dietary V_A on the 21st day of experiment(P=0.093,P=0.025),and they were higher in 6 000 IU/kg and 15 000 IU/kg groups and lower in 45 000 IU/kg group.The chymase activity was significantly higher in the 3 000 to 15 000 IU/kg group than 45 000 IU/kg group(P=0.025).For the jejunum,the chymotrypsin and amylase activities were significantly different among the V_A treatment groups(P=0.032,P=0.038),and all were higher in the 6 000 IU/kg and 15 000IU/kg groups.The jejunal lipase activity decreased quadraticly(P=0.037)with V_A level increased and higher in the 3 000 IU/kg and 6 000 IU/kg groups;The activity of ileal amylase was tended to be significantly different among different V_A treatment groups(P=0.066).The ileal amylase activity was tended to be significantly higher in 6 000IU/kg group than 15 000 IU/kg group.The ileal chymotrypsin activity tended to be significantly higher in the 6 000 IU/kg group than 3 000 IU/kg and 30 000 IU/kg groups(P=0.075)during 42 d of the test period,and higher in the 15 000 IU/kg group.With the increase of dietary V_A level,the activity of chymotrypsin in jejunum decreased linearly(P=0.036).The duodenal lipase activity tended to be significantly higher in the 6 000~30 000 IU/kg group than 3 000 IU/kg group(P=0.085).The ileal lipase activity decreased linearly when dietary V_A increased(P=0.022)and tended to be significantly higher in the 6 000 IU/kg group than 30 000IU/kg and 45 000 IU/kg groups(P=0.074).4.Experiment 4 mainly studied the effects of different dietary V_A levels on digestive tract tissue morphology in broilers.In 21 d of the experimental period,the ratio of villous height(VH)and villus height to crypt depth(VH/CD)was decreased linearly(P=0.037)or the quadraticly(P=0.025)with increasing dietary V_A levels.The VH values were higher in the 6 000 IU/kg and 15 000 IU/kg groups,and VH/CD values were higher in the 3 000 IU/kg and 15 000 IU/kg groups.The jejunal VH and VH/CD values linearly decrease(P=0.036,P=0.089),and higher in the 6 000 IU/kg and 15 000 IU/kg groups.The ileal VH/CD and CD values were significantly or tended to be significantly different among different V_A treatment groups(P=0.014,P=0.085).The ileal VH and decreased linearly(P=0.022)and was higher in 6 000 IU/kg group with the increase of the daily V_A level.Inversely,CD increased linearly(P=0.060)and was lower in 6 000 IU/kg group.On the 42d day of the trial period,different dietary V_A levels had a significant or significant effect on the jejunal CD value and VH/CD value(P=0.033,P=0.066).The CD value was lowest in the 6 000 IU/kg group and significantly lower than 3 000 IU/kg and30 000 IU/kg groups.VH/CD values was higher in 6 000 IU/kg and 15 000 IU/kg groups and significantly higher than 3 000 IU/kg group.The ileal CD values was significant difference(P=0.017)and significantly lower in the 6 000 IU/kg and 15 000 IU/kg groups than in 3 000 IU/kg group.Based on the changes of growth performance,slaughter performance,meat quality,digestive tract histomorphology,and enzyme activity indexes in this paper,it is concluded that the addition of 6 000 IU/kg V_A to the diet can improve the performance of broilers,meat quality,and digestive function,but excessive addition of V_A(30 000 to 45000 IU/kg)has negative effect on broiler growth and digestive function.