Dietary Magnesium Levels Research Articles

Influence of Dietary Levels of Magnesium on Growth, Tissue Mineral Content, and Resistance of Channel Catfish Ictalurus punctatus Challenged with Edwardsiella ictaluri

AbstractJuvenile channel catfish were fed purified diets supplemented with magnesium (Mg) from Mg sulfate at levels of 0, 200, 400, 600, 800, and 1,000 mg/kg and 0, 200, 400, 600, and 800 mg/kg in two separate feeding studies. In study I, the effect of dietary levels of Mg on growth response, vertebral mineral content, and macrophage chemotaxis were evaluated. Study II had similar objectives except that whole body mineral content was measured, and resistance of channel catfish to Edwardsiella ictaluri challenge was also determined. Fish with an average weight of 10.89 g were stocked at a rate of 50 fish/110‐L aquarium (study I). In study II, fish with an average weight of 4.14 g were stocked at rates of 40 fish/110‐L aquarium. Prior to stocking, each batch of fish was acclimated to laboratory conditions and fed the basal diet for 2 wk. The concentration of Mg in rearing water was 1.8 mg/L. Each diet was fed to fish in quadruplicate and triplicate aquaria to apparent satiation for 10 wk for studies I and II, respectively. Fish fed the basal diet started to die as early as 3 d after the study began (17 d of feeding the diet without Mg supplementation). In both studies, weight gain, survival, and feed efficiency were lowest for fish fed the basal diet but increased with increasing dietary levels of Mg. However, the differences between the values of each of these parameters for fish fed diets containing supplemental Mg were not always significant. Magnesium‐deficiency signs observed were anorexia, sluggishness, convulsions, deformed snout, vertebral curvature, muscle flaccidity, and high mortality. Vertebral and whole body ash concentrations were high, but Mg content was low for fish fed the basal and the 200‐mg Mg diets. Bone Ca content did not differ among fish fed different diets (study I), but whole body Ca tended to increase for fish fed the basal diet, suggesting the possibility of calcification of soft tissues. Macrophage chemotaxis in the presence of exoantigen was highest for fish fed diets supplemented with Mg at 400 and 200 mgkg for studies I and II, respectively. When expressed in terms of chemotaxis index, however, maximum or near maximum value was observed at a dietary Mg level of 400 mg/kg. Thus, a dietary level of Mg of 400 mg/kg from Mg sulfate was required for optimum growth and survival, maintaining high tissue levels of Mg, prevention of muscle flaccidity and skeletal deformity, and stimulating macrophage chemotaxis. Dietary levels of Mg had no effect on the resistance of juvenile channel catfish to Edwarsiella. ictaluri challenge.

The Role of Magnesium and Calcium in Eggshell Formation in Tsaiya Ducks and Leghorn Hens

Tsaiya ducks and Leghorn hens are the two major laying birds raised in Taiwan. They are all excellent egg layers. Tsaiya ducks are small in body size (1.3 kg) with bigger egg weight (65 g) and stronger eggshell breaking strength than eggs from hens. The eggshell consists mainly of calcium carbonate, hence calcium plays an important role in the eggshell formation. Magnesium is also present in eggshell in small amounts, which may have effect on maintaining eggshell quality. In comparison studies, it was shown that the duck eggshells contained higher calcium and lower magnesium content than chicken eggshells. The eggshell magnesium content was not affected by the dietary magnesium levels (690-2380 ppm) in ducks, but in hens, it increased linearly with dietary magnesium levels. The palisade layer (5000×) of the eggshell was found to have a compact form for ducks while there are many hallow vesicles in chicken eggshells. The eggshell magnesium deposition model is different for ducks and hens with ducks having a one-peak and hens having a two-peak model. The calcium deposition model is similar for both birds. Both the carbonic anhydrase specific activity and total activity in the shell gland mucosa of ducks are higher than those in hens. Ducks retain higher magnesium and lower calcium in the shell gland mucosa and secret less magnesium and more calcium into the shell gland lumen for eggshell deposition. The ATPase specific activity is maintained fairly constant during the eggshell forming stage, indicating continuous calcium transport into the shell gland lumen for eggshell formation. The magnesium content in duck eggshells is much lower than that in hens indicating that the magnesium content in the eggshell may have an effect on eggshell quality. (Asian-Aust. J. Anim. Sci. 2003. Vol. 16, No. 2 : 290-296)

Interaction of dietary magnesium level on the feeding value of supplemental fat in finishing diets for feedlot steers.

A feeding trial involving 160 crossbred steers (357 kg) and a metabolism trial involving eight Holstein steers (189 kg) cannulated in the rumen and proximal duodenum were conducted to evaluate the interaction of dietary Mg level (.18 vs .32%, DM basis) and supplemental fat (0% supplemental fat vs 4% tallow [T], yellow grease [YG], or griddle grease [GG]) on growth performance and NE value of the diet. Dietary Mg level did not influence (P > .10) growth performance. Daily weight gain was lower (11%, P < .05) for steers fed GG than for those fed YG. Supplemental fat decreased (5%, P < .10) DMI and increased (P < .05) gain efficiency (7%). There was a fat x Mg level interaction (P < .01) for dietary NE. The increase in dietary NEg with T and YG supplementation was similar (8.6 vs 8.0%) for diets containing .18 and .32% Mg. In contrast, the increase in dietary NEg with GG supplementation was 8.9% with .18% dietary Mg, but the NEg value of the diet did not increase when GG was added to diets with .32% dietary Mg. Dressing percentage was lower (1.5%, P < .1) and retail yield was greater (2.2%, P < .05) for steers fed GG- than for steers fed YG-supplemented diets. Increasing dietary Mg level increased kidney, pelvic, and heart fat (5.5%, P < .05). There was a fat x Mg level interaction (P < .1) for marbling score. With diets containing no supplemental fat, increasing dietary Mg decreased (15.2%) the marbling score, and with diets containing supplemental fat, increasing dietary Mg increased (7.2%) the marbling score. Fat supplementation decreased (P < .01) ruminal and total tract digestion of OM (10 and 3.5%, respectively) and NDF (37 and 17%, respectively). Supplemental fat did not affect (P > .10) Ca digestion but decreased (41.7%, P < .01) apparent Mg digestion. Increasing dietary Mg level increased (77.7%, P < .05) apparent Mg digestion. There were no treatment effects (P > .10) on postruminal fatty acid digestion. Fat supplementation decreased (17.3%, P < .01) the acetate:propionate molar ratio. Total ruminal protozoal counts were increased (12.7%, P < .05) by increasing dietary Mg level and decreased (12.9%, P < .05) by fat supplementation. We conclude that supplemental fats may depress Mg absorption. Increasing dietary magnesium levels beyond current recommendations may increase marbling scores in cattle fed fat-supplemented diets but may not affect growth performance or dietary NE. The NE value of fat is a predictable function of level of fat intake.

Effects of dietary magnesium level on calcium absorption in growing male rats

The effects of dietary magnesium level (0.025, 0.05, and 0.15% magnesium) on calcium absorption were studied in growing rats fed the diets containing 0.5% calcium. The apparent calcium absorption rate and the retention rate of rats fed diets containing 0.15% magnesium were significantly lower than those of rats fed diets containing 0.05% magnesium. On the other hand, apparent magnesium absorption and retention were significantly increased dose-dependently. Femoral bone mineral density (BMD) of rats fed diets containing 0.15% magnesium was significantly lower than that of rats fed diets containing 0.025% and 0.05% magnesium. The amounts of femoral calcium of rats fed diets containing 0.15% magnesium also tended to be lower than those of rats fed diets containing 0.025% and 0.05% magnesium. These results suggested that dietary magnesium and calcium competed with each other in intestinal absorption; therefore 0.05% dietary magnesium level was preferable compared with 0.15% dietary magnesium if the diet contained 0.5% calcium. On the other hand, the amounts of femoral magnesium of rats fed diets containing 0.15% magnesium were significantly higher than those of rats fed diets containing 0.025% magnesium, and the femoral breaking energy of rats fed diets containing 0.15% magnesium was significantly higher than that of rats fed diets containing 0.025% magnesium. These results also suggested that magnesium might have an effect on bone metabolism other than calcium absorption.

Detrimental effect of dietary sodium and beneficial effect of dietary magnesium on glomerular changes in cyclosporin-A-treated spontaneously hypertensive rats.

Cyclosporin A (CsA) causes renal magnesium wasting, hypertension, and occasionally irreversible renal damage. We examined the effect of dietary sodium and magnesium on renal histology in spontaneously hypertensive rats (SHR) receiving CsA. Forty-six 8-week-old SHR were divided into six groups and given different dietary levels of sodium (low 0.3%, high 2.6%) and magnesium (low 0.2%, high 0.6%). Low-dose CsA (5 mg/kg/d) was given subcutaneously for 6 weeks in four groups. Systolic blood pressure, serum creatinine, degree of proteinuria, and renal tissue CsA and calcium concentrations were determined. Kidney wet weight to total body-weight ratio was calculated as an index of renal hypertrophy. Renal histological alterations were scored according to glomerular changes: 100 glomeruli were assigned for severity of change a score from 0 to 3. The number of affected glomeruli was multiplied by the damage score to obtain a damage index. In the CsA-treated high-sodium diet group systolic blood pressure and glomerular damage index were increased, and renal hypertrophy was the most common. These changes were prevented by oral magnesium supplementation. The glomerular damage index correlated positively with increases in systolic blood pressure, serum creatinine, proteinuria, and renal calcium concentration. Dietary sodium enhanced CsA-induced functional and morphological renal changes in SHR and aggravated hypertensive renal arteriolar and glomerular lesions. Dietary magnesium supplementation protected against the deleterious effects of sodium and CsA.

Magnesium requirement of Atlantic salmon (Salmo salar L.) parr in seawater-treated fresh water1

This experiment was undertaken to establish the magnesium (Mg) requirement in young Atlantic salmon, Salmo salar L., in seawater-treated fresh water. In Norwegian hatcheries it is a common practice to add sodium hydroxide and/or sea water (1-2%) to improve pH and conductivity of the natural fresh water. Parr with initial weight of 8 g, were divided in six triplicate groups in brackish water containing 54 mg Mg L(-1) and fed a basal casein-gelatine diet supplemented with minor amounts of krill and fish meal (containing 200 mg Mg kg(-1)) for an initial period of 3 weeks. Thereafter the fish were fed this diet supplemented with either 0, 100, 200, 300, 400 or 500 mg Mg kg(-1) (as MgSO4) for 12 weeks. Growth and feed efficiency were recorded. Concentrations of Mg and other divalent cations (Ca and Zn) were measured in whole fish, serum and vertebrae. Sodium concentration in vertebrae was also measured. Growth and feed efficiency were unaffected by the levels of dietary magnesium used in the experiment. Magnesium concentrations in the whole body, serum and vertebrae Mg appeared to be more sensitive than growth and feed efficiency to differences in dietary Mg intake. The group fed the unsupplemented diet showed significantly lower Mg concentration in these tissues than the other groups. Whole-body calcium concentration was negatively correlated with dietary Mg and Ca:Mg ratios in the vertebrae were significantly affected by the dietary Mg levels. Zinc concentration in whole body, serum and vertebrae was not altered by the dietary Mg levels. Further, vertebral Na concentration did not vary between the dietary treatments. In conclusion, a minimum Mg supplementation level of 100 mg kg(-1) dry diet (in total, 326 mg kg(-1)) was needed to maintain Mg concentration in the whole body and serum and for proper bone mineralization.

Effect of dietary magnesium level on nephrocalcinosis and growth in rats.

We studied the extent of kidney calcification by varying dietary levels of Mg, based on pathological examinations and calcium (Ca) and magnesium (Mg) balance tests. AIN-76 diets containing varying levels of Mg--0.3 (-M), 1.3 (1/20M), 2.4 (1/10M), 9.2 (1/5M), 19 (control), 38 (2M), 102 (5M), and 187 (10M) mmol/kg diet--were fed to 3-week-old male Fischer-344 rats for 14d. Although the magnitude of abnormality was highest in kidney of rats fed the -M diet, the damage was normalized as the dietary level of Mg increased, with increasing serum Mg concentration and urinary excretion of Mg. We found almost no deposition of Ca in rats fed the 10M diet. The mechanism by which the high dietary Mg induces these effects most likely involves a competition between Mg and Ca for reabsorption in proximal and/or distal tubules, since these diets increased the urinary excretion of Ca. However, these high Mg diets decreased food intake and body weight gain compared with the control diet, although these indices were not decreased in rats fed the 2M diet. The results suggest that a dietary magnesium level approximately twice the normal level effectively reduces kidney calcification while maintaining normal growth in rats.

Influence of dietary magnesium level on growth-performance and metabolic responses of Holstein steers to laidlomycin propionate.

We used 216 Holstein steers (151 kg) in a 262-d trial to evaluate the influence of dietary magnesium level (.19, .25, and .32%) and laidlomycin propionate (LP; 0 vs 11 ppm, air-dry basis) on growth performance and NE value of the diet. During the initial 112 d of the trial, LP increased (P < .01) ADG (6.3%) and feed efficiency (4.2%). From d 112 until slaughter, LP increased (P < .05) ADG (9.7%) and feed efficiency (4.5%). Across the 262-d feeding period, LP supplementation enhanced (P < .01) ADG (8.9%) and feed efficiency (6.3%). There was an interaction (P < .05) between dietary Mg and LP on NE value of the diet. The enhancement in NE value of the diets owing to LP with .19, .25, and .32% dietary Mg were .5, 3.0, and 5.9%, respectively. Six Holstein steers (302 kg) were used in a 6 x 6 Latin square experiment to evaluate treatment effects on characteristics of ruminal and total tract digestion. There were no treatment interactions (P > .10) on site and extent of digestion of OM, starch, and N. Supplemental Mg increased (quadratic effect, P < .10) ruminal OM digestion. Neither LP nor dietary Mg level affected (P > .10) ruminal digestion of starch and feed N. Supplemental LP decreased (15%, P < .05) ruminal microbial efficiency. Total tract digestion of OM and N increased (linear effect, P < .01) with increasing dietary Mg level. There were interactions between LP and dietary Mg level on ruminal soluble-Mg concentration (linear effect, P < .01) and Mg absorption (quadratic effect, P < .05). Apparent total tract Mg digestion increased owing to LP (P < .01) and dietary Mg level (linear effect, P < .01). There were no treatment effects (P > .10) on ruminal pH. Dietary Mg level did not influence (P > .10) ruminal VFA concentrations or molar proportions. Supplemental LP increased (14%; P < .10) total ruminal VFA concentration but did not affect (P > .10) VFA molar proportions. We conclude that LP will increase daily weight gain and feed efficiency of calf-fed Holstein steers and that this response may be enhanced by increasing dietary Mg level.

Effects of dietary magnesium excess in White Leghorn hens

The effects of excess dietary magnesium on White Leghorn laying hens were investigated in two experiments and a third experiment looked at the effect of dietary phosphorus on excess magnesium in the diet. In Experiment 1, magnesium levels of 0.15, 0.8, and 1.2% were fed in a diet containing 2.5% calcium to hens 30 wk of age for 5 wk. A control diet with 3.5% calcium and 0.15% magnesium was also fed. In Experiment 2, hens 65 wk of age fed 3.5% calcium were fed dietary magnesium levels of 0.15, 0.36, 0.53, 0.76, and 0.91% for 4 wk. In these two experiments, excess magnesium reduced egg production, decreased feed consumption, decreased body weight, decreased percentage eggshell, reduced plasma calcium, and increased plasma magnesium and tibia magnesium but changes seen in tibia weight, percentage ash, and tibia calcium and phosphorus were variable. More changes from feeding excess magnesium were seen in the young, high producing hens in Experiment 1. In Experiment 3, hens 50 wk of age were fed a marginal calcium level (2.5%) with an excess of magnesium (0.8%) and a control level of available phosphorus (0.45%) and this was compared to a low (0.25%) and a high level (0.9%) of available phosphorus for a 4-wk experimental period. At the end of the experimental period, hens fed low phosphorus had lower egg production and lower feed consumption than the hens fed higher levels of phosphorus. Body weight was lower in the hens fed the two lower levels of phosphorus. Percentage eggshell was lower than the controls when fed low phosphorus and higher when fed high phosphorus. These results suggest that high phosphorus diets are better than low phosphorus diets when excess magnesium is fed to laying hens. Further study is needed to investigate the role of phosphorus when excess magnesium is fed.

Influence of dietary magnesium level on metabolic and growth-performance responses of feedlot cattle to laidlomycin propionate.

A metabolism trial and a growth-performance trial were conducted to evaluate the interaction of dietary magnesium level (.18 vs .32%) and laidlomycin propionate (LP) (0 vs 11 ppm, airdry basis) on utilization of a high-energy finishing diet by feedlot steers. There were no treatment effects (P > .10) on ruminal and total tract digestion of OM and ADF. However, there was an interaction (P < .05) between magnesium level and LP on ruminal starch digestion. With LP, magnesium level had no effect on ruminal starch digestion. Without LP, increasing dietary magnesium decreased ruminal starch digestion. Laidlomycin propionate decreased (P < .10) ruminal degradation of feed N (13.9%) and microbial efficiency (8.9%) and increased (P < .10) total tract N digestibility. There were no treatment interactions (P > .10) on site and extent of magnesium digestion. Magnesium absorption decreased with increased dietary magnesium (11.6%, P < .05) and LP (16.9%, P < .01). There was an interaction (P < .10) of treatments on postabomasal calcium absorption. With the low magnesium level LP increased calcium absorption, whereas with the higher magnesium level LP decreased calcium absorption. There was an interaction between magnesium level and LP on ruminal pH at .5 h (P < .05) and 8 h (P < .10) after feeding. In general, ruminal pH increased with LP supplementation at the lower magnesium level and decreased with LP supplementation at the higher magnesium level. There were interactions (P < .05) between magnesium level and LP on ruminal VFA molar proportions and estimated methane production. At the lower magnesium level, the effects of LP on VFA molar proportions were small. At the higher magnesium level, however, LP decreased (13.2%) molar proportions of acetate and increased (26.5%) molar proportions of propionate. There was an interaction (P < .05) between magnesium level and LP on feed intake. At the lower magnesium level, LP increased (3.9%) feed intake; at the higher magnesium level LP decreased (4.4%) intake. Increasing dietary magnesium enhanced ADG (6%, P < .10). Both magnesium and LP enhanced (2.8%, P < .10) diet NE, and this effect was strictly additive. There were no effects (P > .10) of magnesium level or LP on plasma magnesium concentrations. Plasma calcium concentrations were decreased by supplemental magnesium (15.2%, P < .05) and increased by LP (16.0%, P < .01). We conclude that dietary magnesium levels modulate the metabolic and performance responses of feedlot steers to supplemental LP.

Effect of dietary magnesium level on urinary and faecal excretion of calcium, magnesium and phosphorus in adult, ovariectomized cats

Dietary Mg restriction is generally considered to contribute to the prevention of struvite urolithiasis in cats, but its effects on faecal and urinary excretion of Ca and P have not been systematically investigated. The present study seeks to fill the gap. In a 4 x 4-week crossover study, ovariectomized cats were fed on purified diets containing either 0.40, 0.79, 1.59 or 3.17 mmol Mg/MJ (0.19, 0.38, 0.76 and 1.52 g Mg/kg diet). Increasing the dietary Mg level from 0.40 to 3.17 mmol Mg/MJ by the addition of extra MgCO3 raised urinary and faecal excretion of Mg from 0.14 to 0.68 mmol/MJ and from 0.28 to 1.66 mmol/MJ respectively. The 8-fold increase in Mg intake significantly raised urinary excretion of Ca from 0.06 to 0.09 mmol/MJ. Apparent absorption and urinary excretion of P were depressed by 13 and 25% respectively when the dietary Mg level was raised from 0.40 to 3.17 mmol/MJ. A dietary level of 0.40 mmol Mg/MJ (0.19 g Mg/kg diet) was found to be sufficient to maintain Mg balance in the adult ovariectomized cats fed on the purified diet.

Dietary and serum magnesium levels in patients with acute myocardial infarction, coronary artery disease and noncardiac diagnoses.

To study the relation of dietary and serum levels of magnesium (Mg) in acute myocardial infarction (AMI) and its complications in relation to noncardiac diagnoses. Case control study in a primary and secondary care center for AMI patients. The study included 460 subjects with definite AMI (n = 335, group A), possible AMI (n = 64, group B), unstable angina (n = 19, group C) and controls with noncardiac chest pain (n = 42, group D). Demographic variables, dietary intake, and clinical and biochemical data were compared. Mean age, sex, body weight, and body mass index were comparable in all the groups. Dietary fat and cholesterol intakes were significantly higher and carbohydrate intakes were lower in group A, B and C patients with coronary artery disease compared to control group D. Dietary consumption of Mg was comparable in all groups; however, in 85 patients in group A (272.5 mg/day) and 17 in group B (280.4 mg/day) in whom ventricular arrhythmias were present, Mg intake was relatively lower compared to control group D (316.6 mg/day). Serum Mg levels in group A (1.66 mEq/L), B (1.65 mEq/L), and C (1.66 mEq/L) were within normal (1.74 mEq/L) limits, but were significantly lower than in control group D. Lower serum Mg in group A, B and C patients was attributed to increased demand during AMI, although in patients with complications (ventricular arrhythmias), Mg deficiency may in part result from relatively lower Mg intake, a hypothesis which requires further study.

Plasma lipid physical properties in swine fed margarine or butter in relation to dietary magnesium intake.

Plasma lipids obtained from swine which had been fed butter or margarine at two dietary magnesium (Mg) levels indicated that the level of dietary Mg was more significant to plasma total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) levels than was the presence of butter or margarine. At 270 mg Mg/kg, which is considered adequate for swine, there was a significant difference in the plasma TC between swine fed margarine and those fed butterfat (105 and 126 mg %, respectively). Plasma LDL-C was higher in swine fed butter than in those fed margarine (88 and 71 mg %, respectively). In swine fed an additional 247 mg Mg/kg, however, there was no significant difference in plasma TC between those fed margarine or butter. Although at 247 mg Mg/kg, however, there was no significant difference in plasma TC between those fed margarine or butter. Although at 247 mg Mg/kg plasma LDL-C was higher in swine fed margarine and HDL-C was higher in those fed butter, there were no significant differences in the order parameters of LDL and HDL. Studies in which the influences of dietary fats on plasma cholesterol were first noted were carried out on liquid diets deficient in Mg. Mg, a cofactor in the enzymes involved in desaturation of saturated fatty acids, is also necessary in desaturation of linoleic to arachidonic acid.

The effect of dietary magnesium level on the eggshell quality in laying Tsaiya duck and Leghorn hen

The effect of dietary magnesium level on the eggshell quality in laying Tsaiya duck and Leghorn hen

The effect of dietary magnesium level on the magnesium metabolizability in laying Tsaiya duck and Leghorn hen

The effect of dietary magnesium level on the magnesium metabolizability in laying Tsaiya duck and Leghorn hen

The humoral immune response in marginally and severely magnesium deficient rats

The effects of severe, moderate, and mild magnesium deficiencies on plasma proteins, immunoglobulin M (IgM), immunoglobulin G (IgG), and specific antibody response were studied. Forty male Sprague-Dawley rats were fed diets containing 50, 160, 280, and 400 μg magnesium/gram for either three or eight weeks. Eight of the rats were fed the control diet but were pair fed with the 50 μg/gram treatment group. All rats were immunized once with sheep red blood cells. Plasma magnesium levels reflected the dietary levels of magnesium, and bone magnesium highly correlated with plasma magnesium. The severely deficient rats had significantly enlarged spleens, while all other groups were similar to controls. The severe magnesium deficiency significantly decreased total plasma proteins. Additionally, immunoglobulin M and G levels were significantly reduced in the severely deficient rats. The mean log antibody titer for the severely deficient rats was approximately half that of the controls, but was not statistically different from the other dietary groups. Conversely, total plasma proteins were not lowered by the suboptimal levels of magnesium. Immunoglobulin M levels in the marginally deficient animals correlated with their plasma magnesium concentrations, and lower immunoglobulin G levels were found with the moderate magnesium deficiencies. Antibody response was not altered by the suboptimal levels of dietary magnesium.

Effects of Dietary Magnesium on Growth and Tissue Magnesium Content of Blue Tilapia Oreochromis aureus

AbstractJuvenile blue tilapia Oreochrornis aureus (mean weight 0.5 ± 0.05 g) were stocked into 38 liter glass aquaria receiving Row‐through well water containing 0.1 mg magnesium/L and fed semipurified, casein‐based diets containing graded levels of magnesium (0.003, 0.008, 0.023, 0.037, 0.050 and 0.065% magnesium, dry weight). Magnesium supplements were provided as anhydrous magnesium sulfate (MgSO4). No treatment‐related mortalities occurred and no visible magnesium deficiency symptoms were observed in any treatment group during the 18 week experimental period. Magnesium concentrations in scale and bone of tilapia fed diets containing 0.023 to 0.065% magnesium were greater (P &lt; 0.05) than in fish fed diets containing 0.003 to 0.008%. Scale and bone magnesium concentrations did not differ (P &gt; 0.05) among fish that received dietary magnesium levels of 0.023% or greater. The magnesium content of muscle was higher (P &lt; 0.05) in fish fed 0.037 to 0.065% magnesium than in those fed 0.003 to 0.008% magnesium. Muscle magnesium concentrations did not differ (P &gt; 0.05) among fish that received 0.037% or more dietary magnesium. Adequate weight gain and superior feed efficiency occurred in fish fed 0.05 to 0.065% magnesium. Results indicated that diets for O. aureus should contain at least 0.05% magnesium (500 mg Mg/kg dry diet) for optimum growth and normal tissue mineralization.

An evaluation of plasma and erythrocyte magnesium concentration and the activities of alkaline phosphatase and creatine kinase as indicators of magnesium status

Rats were fed diets containing magnesium at concentrations ranging from 3.3 to 26.7 mmol/kg of diet (80 to 650 mg/kg). The magnesium concentration of their plasma and erythrocytes, and the activities of plasma alkaline phosphatase and creatine kinase were investigated to determine their usefulness as indices of magnesium status. All the indices increased with increasing dietary magnesium levels. The best correlations were observed between dietary intake and plasma concentration of magnesium (r = 0.846, p less than 0.001) and between intake and femur concentration (r = 0.811, p less than 0.001). There was an extremely high correlation between plasma concentration and femur concentration (r = 0.930, p less than 0.001). Although significant, the correlations between intake and the enzyme activities were not strong. It is concluded that plasma magnesium concentration is the most useful indicator of magnesium status and that the activities of the two magnesium-requiring enzymes can only be used for the purpose of diagnosing severely deficient magnesium status.

Effects of temperature, and dietary magnesium and nickel levels on magnesium and nickel concentrations during the moult - cycle inOniscus asellus(Porcellionidae, Isopoda, Crustacea)

Mean magnesium concentrations in intermoult Oniscus asellus, caged at 20 degrees C for 10 days, ranged from 1,059.15 +/- 51.9 ppm on diets containing 10 ppm nickel, to 6,827.6 +/- 314.1 ppm on a mixture of 500 ppm magnesium + 10 ppm nickel. Mean nickel concentrations ranged from 89.4 +/- 4.3 ppm on diets containing 500 ppm magnesium, to 314.0 +/- 14.8 ppm on a mixture of 500 ppm magnesium + 10 ppm nickel. At 30 degrees C, magnesium tissue concentrations ranged from 4,149.8 +/- 153.5 ppm on diets with 10 ppm nickel to 12,602.6 +/- 529.3 ppm on 500 ppm magnesium. Nickel concentrations at 30 degrees C varied from 156.8 +/- 6.7 in isopods in the control to 490.5 +/- 23.5 ppm on those on 500 ppm magnesium + 10 ppm nickel. Magnesium in intermoult isopods was mainly stored in other tissues, including the exoskeleton, and nickel in the hepatopancreas. Differences in both magnesium and nickel concentrations between males and females were not significant. Magnesium and nickel concentrations in postmoult isopods, on the average, amounted to 367.6 +/- 16.5 ppm and 18.7 +/- 0.7 ppm, respectively, at 20 degrees C, and 369.9 +/- 16.3 ppm and 30.9 +/- 1.3 ppm, respectively, at 30 degrees C. Differences between males and females, and between various treatments were not significant at P greater than 0.01. It is suggested that both hepatopancreas and other tissues, including the exoskeleton, are used as sinks to get rid of excessive tissue magnesium and nickel during the moult-cycle.

Effect of dietary magnesium on Ascaris suum infections of mice

Low amounts of dietary magnesium affected the inflammatory tissue response in nonimmunized mice differently than in immunized mice. Eosinophil numbers and LPL activity in lung tissue following infection with A. suum larvae were altered by the level of magnesium in the diets of mice. Average or higher dietary levels of magnesium resulted in decreased numbers of lung larvae indicating an overall protective effect. Increases in eosinophil numbers or LPL activity were not directly related to the numbers of larvae/lungs. Larvae/livers, eosinophil numbers, and LPL activity were affected by the types of magnesium diets that mice received. Nonimmunized mice had differences in larvae/liver (at 2 days and 7 days pi) and LPL activity (at 2 days pi). Immunized mice had varying findings at 2 days pi but a direct relationship between dietary magnesium and numbers of larvae, numbers of eosinophils, and liver LPL activity at 7 days pi.