| Feed contaminated with mycotoxins is harmful to animals. It reduces growth and depresses the immunity of animals. These effects have serious economic implications for animal producers. Further more, mycotoxins will residue in the products and tissues of animals fed with diet contaminated with them. Recent researches indicated that digestive function of intestinal tract could be changed by mycotoxins, and that ducks were more sensitive to mycotoxins than other animals. In this study, the effect of corn naturally contaminated with mycotoxins on the the growth performance, physiological function of digestive tract and its possible mechanisms were evaluated. This study consisted of 4 experiments as followed.Experiment 1 Effect of corn naturally contaminated with mycotoxins on growth performance and intestinal morphology of ducksThis experiment was conducted to study the effect of corn naturally contaminated with mycotoxins on the growth performance and intestinal morphology for ducks.192 1-d-old Charry Vally ducks were randomly allotted by body weight to 2 groups with 6 replicates of 16 ducks each (8 males and 8 females).Group 1 (control) was fed the conventional diet with the corn free of mycotoxins, and group 2 was fed the diet with the corn naturally contaminated with mycotoxins with excessive content of AFB1. The trial lasted for 28 d. At d 0,14 and 28 of experiment, the ducks were weighed and consumption of feed by replicate was calculated. At d 28, jejunum was collected from 2 ducks in each replicate to determine the intestinal morphology. The results showed that diet with the corn naturally contaminated with mycotoxins resulted in the increase of mortality and decrease of growth performance of ducks. Compared with the control group, during d 0-28, the average daily gain (ADG) and average daily feed intake (ADFI) of mycotoxins contaminated corn group significantly reduced by 19.96%(p<0.01) and 18.50%(p< 0.05) respectively, and the d 0-14 F/G (feed to gain ratio)decreased significantly (p<0.01). Jejunum villus height the ducks fed mycotoxins contaminated corn diet increased by 22.11%(p<0.O5), crypt depth decreased by 32.69%(p<0.05), the villus height to crypt depth ratio (V/C) enhanced significantly(p<0.01) and the thickness of intestine wall tended to increase. The pathological changes were also found in these ducks fed diet with moldy corn, including hydrocardia, phaeo-pigment deposition in liver, and focal necrosis, desmoplasia, lympholeukocyte and adipocyte increasing in hepatic tissue. The results indicated that corn naturally contaminated with mycotoxins could decrease growth performance and increase the mortality, induce pathological changes in liver, and change intestinal morphology in ducks.Experiment 2 Effect of different levels of corn contaminated with mycotoxins on growth performance and digestive physiology in ducksIn order to study the effect of corn naturally contaminated with mycotoxins (predominantly with AFB-1) on growth performance, intestinal development and digestive enzyme activities in ducks,384 ducks were allotted by body weight into 3 treatments with 8 replicates per treatment and 16 ducks(8 males and 8 females) per replicate. Treatment 1 (control) was fed diet with normal corn, and treatment 2 and 3 were fed the diets with contaminated corn substituted for normal com by 50% and 100% respectively. The trial lasted for 5 weeks. Growth performance, the digestive organ index and intestinal morphology at d 14 and 35, contents of DNA, RNA, protein of intestinal mucosa at d 14 and activities of digestive enzymes in brush border of jejunum and pancreas were determined. The results showed that ADFI, ADG and F/G linearly reduced (p< 0.001), and mortality linearly increased (p< 0.001) with increment of moldy com. The mortality in 100% contaminated corn group was 31.25%. At d 14 and 35, duodenum index, jejunum index and ileum index were increased (p< 0.0001) significantly, and so did the liver index at d 35. With the increasing levels of moldy corn, the V W (p<0.05), VH (p< 0.001) and VASA(p< 0.01) of jejunum mucosa increased at d 14, the CD (p< 0.01), VW (p=0.10), VH (p<0.05) and VASA (p<0.05) of duodenum mucosa also increased at d 35, content of DNA in duodenum and jejunum mucosa increased at d 14, which was opposite to that of RNA. In addition, the increment of addition levels of moldy com enhanced the activities of alkaline phosphatase (p<0.05), leucine aminopeptidase (p<0.05), trypsinase (p< 0.05) and chymotrypsin (p<0.001) at 14 d. The results indicated that the corn naturally contaminated predominantly with AFB1 could depress the feed intake, decrease body weight gain, increase mortality and reduce F/G through the changes in intestinal development and digestive enzymes activities. Experiment 3 Effect of corn contaminated with mycotoxins on the rate of chyme to pass through the digestive tract and the digestibility of nutrientsThis experiment was conducted to study the effect of corn naturally contaminated with mycotoxins on the rate of chyme to pass through the digestive tract and digestibility of nutrients. 384 ducks were randomly assigned to 3 dietary treatments with 8 replicates per treatment and 16 ducks (8 males and 8 females) per replicate. Group 1 was fed diet with normal corn (control), group 2 was fed diet with contaminated corn (contaminated), group 3 was pair-fed group to receive the same diet as control and the same amount of feed as the contaminated ducks (pair-fed). The trial lasted for 14 d. The growth performance, digestibility of nutrients and the rate of chyme to pass through the digestive tract were determined. Compared with control, on d 0-7,8-14 and 0-14, ADFI of contaminated corn group ducks was reduced by 23.55%(p< 0.01),47.56%(p< 0.01) and 43.23%(p<0.01) respectively, ADG was decreased by 31.47%(p<0.01),41.57%(p<0.01) and 38.84%(p< 0.01) respectively, however, compared with pair-fed group, ADG of contaminated group was improved by 4.63%,18.25% and 13.83%(p< 0.01) respectively. Compared with control and pair-fed group, d 0-14 F/G was reduced 4.90%(p< 0.01) and 5.56%(p< 0.01).digestibilities of DM were increased by 3.78%(p< 0.01) and 3.75%(p< 0.01), CP was increased by 2.65% and 4.63%(p< 0.01), total amino acid was increased by 3.9%(p< 0.01) and 3.98%(p< 0.01), Furthermore, the retention time of chyme in segment of digestive tract was obviously prolonged in contaminated group. The retention time in lower segment of esophagus and jejunum were prolonged by 37.78%(p< 0.05) and 55.94%(p< 0.05) respectively. The results indicated that corn naturally contaminated with mycotoxins could depress feed intake, decrease body weight gain and. increase digestibility of nutrients, dercrease F/G by reducing the rate of chyme to pass through the digestive tract.Experiment 4. Effects of corn contaminated with mycotoxins on serum hormon levels and gene expression of Na+, K+-ATPase in ducks256 ducks were randomly allotted by body weight into 2 treatment groups with 8 replicates per treatment and 16 ducks (8 males and 8 females) per replicate to explore the mechanism for the effect of corn contaminated with mycotoxins on the digestive physiology. The trial lasted for 4 weeks. At d 14,28,2 ducks (1 male and 1 female) of average weight in each replication were selected to collect 4 mL blood from jugular vein for determining contents of neuropeptide Y(NPY), ghrelin, leptin, CCK-8, insulin and IGF-I in serum,and then to be killed by cervical dislocation to collect 2-cm jejunum sample(first quarter) for determining relative expression of Na+, K+-ATPase gene. The content of leptin (p< 0.01)and IGF-I (p< 0.01) in serum at d 14 and 28 increased significantly when ducks fed diet with moldy corn, while the content of NPY at d 28 decreased significantly (p< 0.05) Furthermore, compared with control, the relative expression of Na+, K+-ATPase gene tended to increase. The results indicated that the decrease of NPY and increase of leptin and CCK-8 content in serum of ducks fed diet with corn naturally polluted with mycotoxins could lead to the depression of feed intake and growth performance. At the same time, the increase of IGF-I content could alleviate the lesion brought from mycotoxins to keep the health of ducks.ImplicationThe results indicated that diet with corn naturally contaminated with mycotoxins (predominantly with AFB1) would increase the ducks mortality, decrease the feed intake and growth performance, and improve the feed efficiency. Futhermore, it was explored that the decrease of NPY and increase of Leptin content in serum were the main reason for depression of feed intake, and the decrease of feed intake was the main reason for depression of growth performance. At the same time, it was discovered that diet with corn naturally contaminated with mycotoxins (predominantly with AFB1) would increase the content of DNA in duodenum and jejunum mucosa and reduce that of RNA, improve VW, VH and VASA of jejunum, enhance the activities of alkaline phosphatase, leucine aminopeptidase, trypsinase and chymotrypsin, and prolong the retention time of chyme in digestive tract. It was concluded that diet naturally contaminated with mycotoxins had complicated effects on digestive end endocrine system of Ducks. |
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