| Present study was conducted to evaluate adsorption of dietary mercury by nanometer silicate(NS) in the gastrointestinal tract of growing/finishing pigs on the basis of better adsorption capacity of NS in vitro, and consequent role on reducing mercury residues on muscles, liver, kidney and other organs and alleviating deleterious effects of mercury on growth performance, meat quality, immune competence, anti-oxidative ability, endocrines, hepatic & renal function, and so on.A total of 96 cross bred pigs (DurocxLandracexlarge white, 48 barrows and gilts respectively), with similar initial weight (27.87±1.15 kg), were used in this study. The animals were randomly assigned to two concentrations of mercury (0.1 and 0.3 ppm from HgCl2) and two levels of NS (0 and 0.3%) in a 2×2 factorial arrangement of treatments. Each group has 3 pens (replications), and each pen has 8 pigs (4 barrows and 4 gilts). The pigs were allowed ad libitum access to diets and water during the experiment, which last 90 days, 45 days in growing phase and 45 days in finishing phase.Body weights and feed intake were recorded to calculate average daily gain (ADG), average daily feed intake (ADFI) and feed/gain (F/G) for each pen on the 83rd day. Blood was collected via anterior vena cava venipuncture from two random selected pigs in each pen for a total of 24 pigs sampled (6 pigs per group) on d30 (the 30th day), d45, d60, d75 and d90 respectively. And the 24 pigs were vaccinated for hog cholera. Those blood samples were obtained at about 08:00 each time and kept in freezer until analysis. Ten days before ending of the feeding trial, digestion experiment was conducted by the method of total fecal collection. Upon termination of the feeding trial, 6 randomly selected pigs (3 barrows and 3 gilts) from each treatment were slaughtered after a 24-hour fast. And related tissues samples were collected and kept until analysis. After determination of all sample and statistically analysis of the data, main results were obtained as follows:Mercury residues in tissues were subject to the extent of dietary mercury exposure. With the increase of Hg exposure, there was a marked enhancement of Hg contents in blood,muscle, renal cortex, renal medulla, liver, heart, brain and hair (P<0.05). Average Hg content in muscle of pigs fed with 0.1 mg/kg Hg contaminated diet came to 45.56 ug/kg, a little lower than maximum limit (50 ug/kg) of National Pork Hygiene Standard. Muscular Hg residue reached 57.25 ug/kg, a bit higher than the standard, for pigs with 0.3 mg/kg Hg supplementation. For pigs exposed to 0.1 ppm Hg, NS addition lowered Hg residues by about 47.18% in longissmus dorsi muscle (P<0.05), 39.81% in semimembranosus muscle (P<0.05), 53.32% in biceps femoris muscle (P<0.05), 49.93% in serratus muscle (P<0.05). When pigs fed with 0.3 ppm Hg diet, NS addition consistently lowered Hg residues by about 32.12%(P<0.05), 30.54%(P<0.05), 34.38% (P<0.05) and 33.79%(P<0.05) in the four tissues respectively. And average Hg levels were 23.91 ug/kg and 38.51ug/kg for the two NS addition groups, much lower than the national standard. Furthermore, the levels of Hg retention in the four different muscular tissues were quite consistent. Mercury residues in renal cortex, renal medulla and liver decreased significantly in pigs with NS on the basis of 0.1 mg/kg Hg supplementation, by 55.86%(p<0.05), 37.67%(p>0.05) and 67.56%(p<0.05). And 45.05%(p<0.05), 42.53%(p<0.05) and 40.245(p<0.05) for pigs with NS on the basis of 0.3 mg/kg Hg. Compared with pigs in Tl & T3 group, Pigs in T2 & T4 had lower Hg residues by 21.24% (p<0.05) in blood, 50.24% (p<0.05) in hair, 24.36% (p>0.05) in brain, 17.95% (p>0.05) in heart and 3.72% (p>0.05), 48.21% (p<0.05), 26.65% (p>0.05), 18.73% (p<0.05) respectively. No obvious changes were found for Hg contents among the four groups(p>0.05). In the early phase of the trial, blood Hg levels increased gradually with the increase of Hg exposure time. But it's level didn't continue to increase much in the late phase. Blood Hg contents were lower markedly on d30, d45, d60, d75 and d90 in T2 than those in Tl (p<0.05). A little decrease in T4 for various exposure period compared with that in T3 (p>0.05).Digesta Hg concentration in varied intestinal tracts, as well as Hg in feces, urine and bile, were markedly higher in pigs with 0.3 mg/kg Hg supplementation than that in 0.1 mg/kg group (P<0.05). For pigs exposed to 0.1 ppm Hg, NS addition promoted digesta Hg concentration by about 19.06% in stomach (P<0.05), 20.11% in duodenum (p>0.05), 40.42% in jejunum (P<0.05), 39.58% in ileum (P<0.05), 45.40% in cecum (P<0.05), 37.42% in colon (P<0.05) and 34.56% in rectum (P<0.05) respectively, and feces Hg by40.52%(P<0.05). When pigs fed with 0.3 ppm Hg diet, NS addition consistently enhanced Hg concentration by 4.93 (p>0.05), 20.87% (p<0.05), 35.51% (p<0.05), 48.69% (p<0.05), 50.77% (p<0.05), 47.65% (p<0.05), 41.86% (p<0.05) and 40.86% (p<0.05) in a variety of gastrointestinal digesta and feces respectively. Hg concentrations in bile and urine reduced obviously by 70.47%(p<0.05) and 45.15%(p>0.05) in T2 than those in Tl. And a decrease by 37.53%(p<0.05) and 13.30%(p>0.05) in T4 compared with those in T3.There were no obvious differences for ADG, F/G and ADFI among four groups (p>0.05). Apparent digestibility of crude protein decreased by 9.99% (p<0.05) in T3 compared with that in Tl. Other differences for nutrient digestibility were not found (p>0.05).Higher Hg supplementation resulted in a reduction on muscular A a value & myoglobin concentration, and a increase on dripping-loss in longissimus dorsi of pigs in T3 than those in Tl(p<0.05). And NS addition improved muscular a a value & myoglobin concentration to some extent(p>0.05), and reduced significantly dripping-loss in pigs of T4 than that in T3(p<0.05).The analysis of endocrine showed that pigs fed with the diet containing 0.3mg/kg mercury had lower serum FSH by 20.00% (p<0.05) and E2 by 8.89% (p<0.05) than those fed 0.1 mg/kg Hg. With the addition of NS, the two lowered endocrine increased a bit(p> 0.05). As for GH, T3, T4, LH and P4, no obvious differences were observed (p>0.05).With the increase of Hg supplementation, pigs had much lower activities of serum SOD, hepatic SOD, renal SOD, serum CAT, blood GSH-Px, hepatic GSH-Px and renal GSH-Px (p<0.05). NS addition made these decreased enzyme activities increase obviously (p<0.05). The same changes were observed on serum T-AOC, blood GSH and blood SH (p<0.05). Higher MDA contents were induced in serum, liver and kidney when pigs exposed to higher mercury(p<0.05). Pigs had lower MDA contents due to addition of NS(p<0.05).When fed with 0.3 mg/kg Hg, pigs had markedly decreased peripheral blood lymphocyte proliferation and serum hog cholera antibody titer than those in Tl(p<0.05). With the addition of NS, the two immune indexes significantly increased(p<0.05). However, no changes for weight ratios of immune organs were found(p>0.05).The analysis of zinc, iron, copper and selenium retentions in tissues showed that pigs in T3 had lower zinc concentrations in serum, muscle, liver & kidney, and lower ironconcentrations in muscle, liver & kidney, and higher serum copper content, and higher selenium concentrations in the four tissues, than those in Tl, respectively (p<0.05). For pigs in T4 and T2, these changes withdrew obviously due to the addition of NS (p<0.05).No obvious changes for weight ratios of liver, kidney & other organs were found among four groups (p>0.05). In contrast to pigs fed 0.1 mg/kg Hg, pigs with 0.3mg/kg Hg had lower GST activities & MT contents in liver & kidney, and higher GST activity, LDH activity, BUN content & creatinine content in serum (p<0.05). NS addition made the changes in these indexes be alleviated effectively (p<0.05). But, the changes and alleviations were not obvious for ALP, GPT, GOT and other serum biochemical indexes (p >0.05). There appeared that irregular shapes of liver lobules, blurry border between liver lobules, irregular array of liver cell cords and some cells with vacuole-like metamorphism for pigs fed 0.3 mg/kg Hg in microscopical examination. And the pigs had thicker basolateral membrane in glomerulus and a little loss of cell luminal membrane in the pars recta of the proximal tubule at the microscopic level. Pigs in T3 had lower crude ash contents and Ca concentration in femur than those in Tl (p<0.05). And there was a marked improvement after NS addition (p<0.05).In summary, all the results implied that the addition of non-nutritive sorptive material, NS, could effectively reduce the gastrointestinal absorption of mercury via its specific adsorption, with a consequent reduction of mercury residues in body tissues, which include muscles, liver, kidney and other organs, alleviated adverse effects of mercury on growth performance, meat quality, immune competence, anti-oxidative ability, endocrines, hepatic & renal function, and so on. No doubt it would be of great significance to apply NS to solve the problem of Hg pollution in animal production industry. NS had provided an encouraging solution to produce safe and low-residue animal products with mercury contaminated feed.
|
PDF Full Text Request