Natural Ingredient Diet Research Articles

Efficacy of iron repletion in anemic rats after the feeding of a purified or natural-ingredient diet with ferrous sulphate or carbonyl iron

We examined, in rats with iron-deficiency induced anemia, the bioavailability of iron from carbonyl iron versus ferrous sulphate that was incorporated into either a purified or natural-ingredient diet. Various assessments of iron bioavailability were used. Hemoglobin (Hb) values and Hb regeneration efficiency (HRE) after 7 days were higher when ferrous sulphate was given instead of carbonyl iron. After 15 days, there was no longer an effect of supplemental iron source, but now the purified diet produced higher Hb values than did the natural-ingredient diet. After 7 days of repletion, the feeding of the purified diet, when compared to the naturalingredient diet, resulted in higher plasma iron and transferrin saturation values. Apparent iron absorption values were higher with the purified diet. It is concluded that carbonyl iron was less effective than ferrous sulphate in the regeneration of Hb in anemic rats, but this was seen only after 7 days of iron repletion. The diet composition had effects irrespective of the source of supplemental iron. The purified diet, when compared with the naturalingredient diet, further improved the hematological parameters of iron status, raised apparent iron absorption and elevated liver iron mass.

Growth performance of pigs given a choice of natural ingredient diets containing different levels of protein and amino acid(s)

Seventy-two crossbred pigs with an initial bodyweight (BW) of 24.6 kg were assigned to 24 groups of three pigs to determine whether pigs have the ability to select a lysine intake and/or a protein intake to meet their requirements and to determine the effects of supplementation of a combination of lysine (Lys), methionine (Met), and threonine (Thr) on diet selection when pigs were given a choice of a pair of isoenergetic diets from 25 to 70 kg BW. Dietary treatments consisted of control, C, (conventional two phase feeding 16-14% crude protein), and three different choice feeding regimens: 1) protein choice, PC, (18 vs. 10% crude protein CP), 2) lysine choice, LC, (choice between a Lys-supplemented and -unsupplemented diet 0.90 vs. 0.53% lysine with 14% CP diets), 3) amino acid choice, AC, (choice between a diet supplemented with a combination of Lys, Met, and Thr on an ideal protein basis) and unsupplemented diet Lys (0.90 vs. 0.53%), Met (0.50 vs. 0.45%), and Thr (0.59 vs. 0.40%) with 14% CP diets). The diets based on ideal protein were formulated by supplementing synthetic Lys, Met, and Thr to meet a ratio relative to lysine of 65% for Thr, 55% for Met + cystine, and 18% for tryptophan. The two growth phases for the C treatment were 25 to 50, and 50 to 70 kg BW. All diets contained the same energy level (13.7 MJ DE kg −1). At any weight interval and the overall period, daily feed intake was not affected ( P > 0.05) by different feeding regimens and pigs in C and PC grew faster ( P < 0.05) and had superior ( P < 0.05) feed:gain ratio than LC or AC pigs. Supplementation of Lys or a combination of Lys, Met, and Thr did not improve pig performance when choice-fed with the unsupplemented diets. Protein choice pigs showed an extremely strong preference for the high protein diet and consumed 89.8% of the high protein diet and 10.2% of the low protein diet for the overall period. Supplementation of Lys alone or a combination with Met, and Thr did not increase feed consumption. Selection of the Lys supplemented diet and the Lys, Met, and Thr supplemented diet accounted for 35.7 and 31.8% of total feed intake for the overall period. During the overall period, dietary protein intake increased ( P < 0.05) in PC pigs compared with control pigs and there was no significant difference in dietary lysine intake between C and LC pigs and C and AC pigs, respectively. Protein choice and LC pigs required ( P > 0.05) a similar amount of dietary protein and lysine per unit gain of BW to that of control pigs. These results suggest that pigs are unable to control their protein and lysine intake to meet their requirement for growth when given a choice of two isoenergetic diets differing in protein and lysine content. Supplementation of Lys alone, or in combination with Met, and Thr did not affect the pattern of diet selection.

Modulation of exercise‐induced immunosuppression by dietary polyunsaturated fatty acids in mice

The possible interaction between intense exercise, known to suppress the immune response, and nutritive factors, such as polyunsaturated fatty acids (PUFA), was examined in inbred female C57Bl/6 mice. The animals received for 8 wk either a natural ingredient diet or a diet supplemented with 10 g/100 g linseed oil containing over 50% of 18:3 (n-3) alpha-linoleic acid. Other groups received PUFA containing only traces of 18:3 (n-3) fatty acid; beef tallow, containing mostly 18:1 (n-9) saturated fat, safflower oil, an 18:2 (n-6) PUFA, and fish oil, containing longer chain (n-3) PUFA. Each dietary group was divided into two subgroups: sedentary diet controls and exercised animals. Exercise consisted of continuous swimming at high intensity until exhaustion. It was shown in three separate experiments that (1) the primary humoral response to sheep red blood cells, determined by the plaque-forming cell (PFC) assay, was affected by PUFA diet in sedentary animals in the order beef tallow > control diet > safflower oil > fish oil > linseed oil, and (2) the PFC response was suppressed by the exhaustive exercise, as compared to sedentary controls, except for animals fed 18:3 (n-3) linseed oil, where the normal response was noted. Phagocytosis of fluorescent microspheres by peritoneal macrophages, determined by flow cytometry, was significantly lower in exercised animals receiving the linseed oil diet, whereas other diets either increased or did not significantly change the macrophage phagocytic activity, compared to the sedentary diet controls. Spleen lymphocyte subsets were unchanged in exercised animals except for a marked shift from the lymphoid peak toward the erythroid peak. Generally, our data showed a marked immunomodulatory effect of 18-3 (n-3) alpha-linoleic acid on the exhaustive exercise-related immunosuppression, as compared to the effects of other selected PUFA.

Hepa-1 enzyme induction assay as an in vitro indicator of the cyp1a1-inducing potencies of laboratory rodent diets in vivo

The Hepa-1 enzyme induction assay (assay of the induction of CYP1A1 catalytic activities in the Hepa-1 mouse hepatoma cell line by various compounds or mixtures) was evaluated as an in vitro indicator of the CYP1A1-inducing potencies of laboratory rodent diets in vivo. C57BL/6J mice were fed for three weeks four selected commercially available diets (one semisynthetic and three standard natural ingredient diets) exhibiting different enzyme-inducing effects in the Hepa-1 assay. β-Naphthoflavone mi mixed in a semisynthetic diet (33 and 330 mg/kg of diet) was used as a model inducer. CYP1A1-dependent enzyme activities (aryl hydrocarbon hydroxylase and 7-ethoxyresorufin O-deethylase) were measured in the small intestinal mucosa and liver. There was good agreement between the induction of CYP1A1 in vitro and in vivo: the rank order of the enzyme activities elicited by the diets was the same in the mice as in the Hepa-1 cells. The standard diets were less effective inducers than β-naphthoflavone in the Hepa-1 cells and in the mice, especially in the small intestinal mucosa. The Hepa-1 enzyme induction assay thus seems to be a mechanistically sound, reliable and sensitive in vitro indicator of the CYP1A1-inducing potencies of laboratory rodent diets in vivo.

Controversial Issues of Dietary Fat and Experimental Mammary Carcinogenesis

Epidemiological evidence from different countries worldwide has suggested a positive association between the availability of fat in the diet and variations in breast cancer mortality rate. A voluminous amount of information is also available in the literature linking increased fat consumption, particularly polyunsaturated fat, and stimulation of mammary tumorigenesis in animal models. In the past few years, our laboratory has been studying the impact of several confounding factors that could modulate the enhancing effect of fat on neoplastic development of the mammary gland in female rats which are treated with a carcinogen. It is our conclusion that fat promotes mammary carcinogenesis only under a very stringent set of conditions which might not be duplicated in the arena of fat intake and human breast cancer risk. Previous studies on fat and mammary cancer in experimental models have used young virgin rats which are given a dose of carcinogen at a particular age. The question arises as to whether the promoting effect of fat might be a consequence of the characteristics of the model. We have supportive evidence showing that the following criteria must be satisfied in order for fat enhancement of mammary carcinogenesis to be manifested; (a) carcinogen administered at a time when the mammary gland is exquisitely susceptible to tumor induction, (b) animals maintained on a semipurified diet, (c) ad libitum feeding necessary, and (d) unusually high requirement of linoleic acid for tumor development. On the other hand, the stimulatory effect of fat is attenuated or sometimes even negated by (a) feeding of a natural ingredient diet, (b) submaximal calorie intake, and (c) previous history of pregnancy and lactation. Given the spectrum of confounders that are inherent in epidemiological studies linking fat intake and breast cancer, including differences in lifestyle, reproductive history, eating habits, as well as complexity of the total diet, our findings suggest that there may be a need to reevaluate the validity of extrapolating animal data that are obtained under a highly defined set of conditions to the etiological significance of dietary fat in human breast cancer.

Effects of diet type on incidence of spontaneous and 2-acetylaminofluorene-induced liver and bladder tumors in BALB/c mice fed AIN-76A diet versus NIH-07 diet

Diet is a major influence on the responses of experimental animals to drugs, toxins, and carcinogens. Two diets used widely in toxicological and/or nutritional studies, and considered to be nutritionally adequate, were compared with respect to their influence on growth, body weight, lifespan, spontaneous neoplasia, and neoplastic responses to 2-acetylaminofluorene (2-AAF). Both sexes of weanling BALB/c mice were fed either a purified diet (AIN-76A) or a nonpurified, natural ingredient diet (NIH-07), with or without 2-AAF for up to 2 years. Dosages of 2-AAF were administered to males at 0, 20, 40, or 60 ppm in each diet and to females at 0, 100, 125, or 150 ppm. Each group consisted of 96 mice. In most instances, males and females fed purified diet (AIN-fed) gained weight more rapidly, attained higher maximum body weights, and died earlier than their nonpurified diet (NIH-fed) counterparts. 2-AAF inhibited weight gain significantly only in AIN-fed females. Thus, females receiving 150 ppm 2-AAF gained little more than their NIH-fed counterparts. At the dosages used in males, 2-AAF did not induce liver neoplasia but the AIN diet was clearly associated with a higher spontaneous frequency of liver neoplasia than the NIH diet. Although 2-AAF induced liver tumors in females fed either diet at all dosages, a higher frequency and earlier appearance of liver tumors among AIN-fed females than their NIH-fed counterparts was apparent mainly at the lowest dosage. 2-AAF induced bladder neoplasia in both sexes. AIN-fed males were much more sensitive to this effect than NIH-fed animals; however, diet had no impact on the induction of bladder neoplasia in females. This study dramatically shows the importance of diet selection on the outcome of carcinogenicity studies. However, the results suggest that dietary differences may not be consistently found among different sexes or strains and that differences between purified and nonpurified diets in the carcinogenic response to a carcinogen may be related to their differential effects on body weight.

Natural dietary ingredients (oats and alfalfa) induce covalent DNA modifications (I-compounds) in rat liver and kidney.

Mammalian tissue DNA has recently been found, via 32P postlabeling, to contain complex profiles of age-dependent bulky carcinogen adductlike covalent modifications, which have been termed I-compounds, referring to their apparent indigenous origin without exposure to exogenous carcinogens. I-compound patterns are highly species, sex, tissue, and diet specific. As shown here, the presence of certain plant ingredients in diet, i.e., ground oats and alfalfa meal, significantly contributed to the formation of these DNA derivatives. Six groups of weanling female Sprague-Dawley rats were fed one of the following diets for three months: a natural ingredient diet containing neither oats nor alfalfa (Wayne MRH 22/5 Rodent Blox), Wayne diet supplemented with oats or alfalfa or both, a purified semisynthetic diet (AIN-76A), and AIN diet supplemented with oats. The natural ingredient diet produced more complex patterns and higher levels of I-compounds than purified diet in both liver and kidney DNA. Supplementation of either diet with oats elicited the formation of four additional oats-specific I-compounds in liver DNA. Oats and alfalfa, individually and in combination, tended to significantly raise nonpolar and diminish polar I-compound levels. To determine whether the oats-related extra spots were derived from mycotoxin contamination, two groups of rats were fed either Wayne diet or Wayne diet containing zearalenone (0.05 mg/kg) for three weeks. Zearalenone significantly increased the uterine weight but did not induce any DNA adduct formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Macronutrients on Segmented Filamentous Bacteria in the Small Intestine of Mice

Segmented filamentous bacteria (SFBs) in the ileum of mice were poorly present after the feeding of milk powder as sole source of nutrition, but were abundant in animals fed on a diet based on natural ingredients. Twenty-one different purified diets were formulated so that clues could be obtained to identification of the macronutrients that may be responsible for the differential SFB promoting effects of milk powder and the natural ingredient diet. None of the purified diets induced the appearance of SFBs, suggesting that the type and amount of fat, the type ofcarbohydrate and the amount and type of fibre in the diet do not influence SFB colonisation. Alternatively, the purified diets could have lacked a substance which was present in the natural ingredient diet and is essential for SFB colonisation. Thus, although we were not able to identify nutritional factors of SFBs, it is clear that the composition of the diet is at least one factor that determines whether or not SFBs appear in the ileum of mice. Colonisation levels of SFBs in mice fed experimental diets were not associated with relative caecal weight, the percentage of fusiform-shaped bacteria in the caecum or the number of Enterobacteriaceae present in faeces. The latter three parameters were however, significantly influenced by the composition of the purified diets. Keywords: Segmented filamentous bacteria; Intestinal bacteria; Macronutrients; Mouse.

Increased incidence of spontaneous and 2-acetylaminofluorene-induced liver and bladder tumors in B6C3F1 mice fed AIN-76A diet versus NIH-07 diet

Diet is a major influence on the responses of experimental animals to drugs, toxins, and carcinogens. Two diets used widely in toxicological and carcinogenic studies, and considered to be nutritionally adequate, were compared with respect to neoplastic responses to 2-acetylaminofluorene (2-AAF). Both sexes of weanling B6C3F1 mice were fed either AIN-76A (a purified diet) or NIH-07 (a natural ingredient diet), with or without 2-AAF, for up to 2 years. Dosages of 2-AAF were administered to males at 0, 40, 60, or 80 ppm in each diet and to females at 0, 150, 200, or 250 ppm. Each group consisted of 96 mice, except the groups of females dosed at 0 and 150 ppm, which consisted of 120 and 72 mice, respectively. The incidence of malignant liver tumors was significantly greater in all AIN-fed groups compared to corresponding NIH-fed groups, as was the total incidence of tumors (malignant + benign). Similarly, the incidence of malignant and total bladder tumors was greater in AIN-fed groups of mice administered the two high doses of 2-AAF for each sex compared to NIH-fed groups. No malignant bladder tumors were observed among any of the groups of mice receiving control diets. This was also true for the males on low dosages (40 ppm) of 2-AAF. The AIN-fed group of low dose females (150 ppm) developed 4% incidence of malignant bladder tumors. This study dramatically showed the importance of diet selection in chronic carcinogenic studies and suggests that results obtained with the use of a purified diet may differ both qualitatively and quantitatively from results obtained with a natural ingredient diet.

Life Span, Morphology, and Pathology of Diet-Restricted Germ-Free and Conventional Lobund-Wistar Rats

The effect of germ-free life and dietary restriction (DR) on life span and pathology was investigated in isolator housed germ-free (GF) and conventional (CV) Lobund-Wistar rats fed either ad libitum or restricted to 12 grams per day (70% of adult ad libitum intake) of a natural ingredient diet from weaning. The median length of life of ad libitum CV and GF rats was 31.0 and 33.6 months respectively, while DR increased the median length of life of CV and GF rats to 38.6 and 37.8 months respectively. DR reduced the frequency or postponed the occurrence of diseases which eventually lead to death in the Lobund-Wistar rat. This was especially true of prostate adenocarcinoma, prostatitis, and mammary fibroma. The reduced early food intake and smaller body weight of adult GF rats may be the reason ad libitum fed GF rats live slightly longer than their CV counterparts, but GF life was without additional effect on life span when food intake was restricted.

Interrelationships of dietary sodium, potassium and chloride on growth in young swine.

In a preliminary experiment, pigs fed a purified diet gained at the same rate as pigs fed a natural ingredient diet if the purified diet was formulated to provide 150% of the Na, K and Cl requirements. Subsequent experiments were designed to determine the interrelationships of dietary Na, K and Cl. Pigs were fed diets with Na (.03% to .60%), K (.1% to 1.0%) and Cl (.03% to .60%) levels arranged in a three-factor central composite design. Over the range of Na levels, predicted gain increased by .07 kg/d. Within this dietary range no interactions between Na and K or Na and Cl were observed, but changes in growth due to dietary K level were dependent on the dietary Cl level. Using canonical analysis of the response surface, a minimax of the observed K and Cl interaction was calculated to be .57% K and .27% Cl. An imbalance of dietary K and Cl was predicted to depress gain, and an increase in gain was predicted by a 1:1 addition of K and Cl above or below the minimax. The results of a third experiment failed to confirm that additions of K and Cl in a 1:1 ratio above the minimax altered gain (P greater than .10). Experiment 4 confirmed that an imbalance of K and Cl altered growth of pigs. At .1% K, an increase in dietary Cl from .03% to .57% depressed gain by .07 kg/d; at 1.1% K the same increase in dietary Cl improved gain by .16 kg/d (P less than .07). These results suggest that dietary K and Cl levels have an interactive effect on pig growth.

Prevention of prostate cancer and liver tumors in L-W rats by moderate dietary restriction

Aging conventional (CV) and germfree Lobund-Wistar (L-W) rats developed spontaneous tumors, predominantly in the prostate, liver, and adrenal glands. In CV L-W rats a 30% reduction of daily intake (natural ingredient diet L-485) had the following effects: (1) reduction of the incidence of metastatic prostate adenocarcinomas (PA) from 25.7% to 6.3% and extension of the average latent periods from 26.6 to 36.7 months; and (2) reduction of the incidence of hepatomas from 59% to 26% and extension of the average latent periods from 31.3 to 34 months. Adrenal medullary tumors developed in approximately 60% of rats older than 19 months, regardless of dietary intake and microbial status. Stromal hyperplasia developed among 36 of 78 (46%) rats older than age 30 months. Rats with PA were free of stromal hyperplasia, and the reverse was also true. Germfree L-W rats developed all of the above tumors, but the diet-related differences were not as significant as those among the conventional counterpart rats. The incidence of prostatis was reduced from 22% to 6% among the diet-restricted rats, but this lesion did not develop among the germfree rats.

Measurement of the proliferative status of colonic epithelium as a risk marker for colon carcinogenesis: Effect of bile acid and dietary fiber

The proliferative status of mouse colonic epithelium, as affected by dietary fibers with or without cholic acid (CA), was studied by autoradiography and the metaphase arrest technique. In the first study, groups of mice were fed natural ingredient (laboratory chow) or semisynthetic diets containing 0% (control) or 0.2% (test) CA. After the mice were fed two weeks, the effect of CA was significantly more pronounced in the semisynthetic diet group than in the natural ingredient diet group with respect to labeled cells/crypt section (7.8 +/- 0.8 vs. 2.9 +/- 0.4) and mitotic figure (MF)/crypt section (3.0 +/- 0.5 vs. 1.8 +/- 0.2). In the second study, diets formulated to contain 5 or 10% cellulose (C), pectin (P), or wheat bran (WB) with or without CA (0.2%) were fed to animals for two weeks and colonic proliferative indices were measured. When compared with 5% C group, the 10% WB group exhibited lower labeling index (LI) values (4.2 +/- 0.5 vs. 6.4 +/- 1.0) and the 10% P group exhibited higher LI values (10.0 +/- 1.1 vs. 6.4 +/- 1.0). CA-induced increases in the LI and MF values responded independently in some cases to dietary fiber. Among the CA-treated groups, only the 10% P diet resulted in lower LI when compared with the 5% C group (p less than 0.05) (7.4 +/- 0.8 vs. 12.5 +/- 2.8) but had no effect on MF/crypt section. However, the 5 or 10% WB diet resulted in lower MF values (1.7 +/- 0.2 and 1.8 +/- 0.6 vs. 2.6 +/- 0.3). A long-term feeding study comparing 10% P with 10% C diets also demonstrated that the LI was elevated in the 10% P group without any effect on the mitotic activity of the colonic epithelium. This paradoxical finding suggests that the value of the LI and/or mitotic index as a risk marker of colon carcinogenesis should be further investigated.

The influence of exogenous antigenic stimulation on the specificity repertoire of background immunoglobulin-secreting cells of different isotypes

The total number of spontaneously occurring (“background”) IgM-, IgG-, and IgA-secreting cells and the frequency of antigen-specific IgM-, IgG-, and IgA-secreting cells were determined in germ-free BALB/c mice fed a chemically defined ultrafiltered diet (GF-CD), in specific pathogen-free BALB/c mice fed an autoclaved natural ingredient diet (SPF-NI), and in conventional BALB/c mice fed nonautoclaved natural ingredients (CV-NI). This was done by means of the ELISA-plaque assay. The results did not show differences among the various groups of mice with regard to the total numbers of IgM-secreting cells in the various lymphoid organs. Also the frequencies of IgM-secreting cells specific for DNP27-BSA and the anti-idiotypic monoclonal antibodies Ac38 and Ac146 did not differ significantly among GF-CD, SPF-NI, and CV-NI mice. GF-CD mice, however, did show substantially decreased numbers of IgG- and IgA-secreting cells in their lymphoid organs. Furthermore, there were striking differences in the frequencies of antigen-specific IgG- and IgA-secreting cells between GF-CD mice and the two other groups of mice. These results indicate that exogenous antigenic stimulation has a great effect on both the total numbers and the specificity repertoires of background IgG- and IgA-secreting cells. Such an influence could not be detected with regard to the background IgM-secreting cells. This suggests two distinct compartments of background Ig-secreting cells: a very stable, endogenously regulated compartment consisting mainly of IgM-secreting cells, and another compartment, consisting mainly of IgG- and IgA-secreting cells, whose numbers and specificity repertoire appeared to be influenced by exogenous antigenic stimulation.

Pancreatic carcinogenesis in azaserine-treated rats: Inhibition by a solvent mixture in the diet

The growth of azaserine-induced foci and nodules in a 4-month experiment and the incidence of carcinomas in a 15-month experiment were greater in LEW/CrlBR inbred rats fed a purified diet (AIN-76A) than in rats fed a natural-ingredient diet (chow). Addition of a mixture of several solvents to either diet reduced the incidence of adenocarcinomas in the pancreas in the long-term study but failed to reduce the number or size of pancreatic atypical acinar cell foci in the experiments of 4 months and 6 months (chow only) duration. Apparently, some component of the solvent mixture inhibits a late stage in the development of pancreatic carcinoma. Glyceryl monooleate and propylene glycol are implicated as the components of the mixture most likely to be responsible for the inhibitory effect, but neither the identity of the critical component nor the mechanism of the inhibition is known. The solvent mixture also contained ethanol and trioctanoin.

Adequacy of Chemically Defined, Water-Soluble Diet for Germfree BALB/c Mice Through Successive Generations and Litters

To determine dietary adequacy, germfree BALB/cAnN mice were fed ad libitum an ultrafiltered solution of chemically defined, water-soluble, low-molecular-weight nutrients. They received a measured daily supplement of membrane-filtered, distillation-purified soy oil containing vitamins A, D, E and K. Mice were kept on ash-free filter paper bedding, which they freely consumed. On this regimen, germfree BALB/c mice reproduced through nine generations, and through eight litters in one generation. Average number born per litter was 4.1, compared with 5.1 in control BALB/c mice, which had a conventional microflora and were fed a natural ingredient diet. From 21 to 32 d of age, the experimental mice gained more slowly than controls. After 32 d, experimental mice gained more rapidly than controls; their weights tended to be lower than controls at 45 d and equal to controls at 56 d. Intake-limiting effects of the diet appeared responsible for reduced growth rates and litter size. Experimental females showed a low incidence of deaths from cecal volvulus. Experimental males experienced a high incidence of deaths from colonic impaction of cecally-formed trichobezoars; this site of formation appeared to be unique to BALB/c males on the experimental regimen. These losses were judged to be unrelated to nutritional deficiency. No overt signs of nutritional deficiency developed in female mice which were fed CD diet up to 18 mo of age.

EFFECTS OF FEEDING SPENT BLEACHING CLAY FROM CANOLA OIL REFINING TO GROWING MICE AND RATS

The spent bleaching clay from canola (rapeseed) oil processing might be a useful ingredient in livestock feeds but little is known about possible metabolic effects of the clay. Experiments with growing mice and rats were designed to study effects of spent clay on weight gains, feed utilization and gross anatomy. In exp. 1 clay was mixed 1:1 with cornstarch or canola meal. These premixes were incorporated into purified and natural ingredient diets to provide clay levels of 0, 0.3, 0.6, 1.2 and 2.4%. Eighty weanling mice were randomly allotted to the 20 diets which were fed for 28 d. Liver weights and liver: body weight (%) increased (P &lt; 0.05) with increasing levels of clay fed in purified diets. Otherwise clay treatments had no effect on the responses:weight gain, feed:gain ratio, plasma urea nitrogen or kidney weights. Experiment 2 involved weanling rats fed three different clay samples at dietary levels of 1, 2 and 4%, with and without an antioxidant (ethoxyquin) for a 28-d period. Using the same criteria as in exp. 1, clay samples, levels and use of antioxidant had no effect on animal responses. The data demonstrated that up to 4% spent bleaching clay could be included in natural ingredient diets without either beneficial or harmful effects to growing mice and rats. Key words: Spent bleaching clay, mice, rats, feeding trials, bentonite, rapeseed

The effect of microbial flora, diet, and age on the tumoricidal activity of natural killer cells.

This study examined the effects of diet (chemically defined vs natural-ingredient), age, and microbial flora on the tumoricidal activity of natural killer (NK) cells from the spleens of mice. Results from a 4-h 51Cr-release assay indicate the following: Germfree C3H/HeCr mice raised on a chemically defined diet had significantly greater NK cell activity than their germfree or "clean-conventional" (i.e., barrier-maintained) counterparts who were raised on a sterilized natural-ingredient diet. The NK activity of germfree mice was dramatically increased after their alimentary tract was colonized with a complex intestinal flora. Conventional mice raised under clean (barrier) conditions had significantly less NK cell activity than nonbarrier-maintained mice. Switching germfree mice from a chemically defined diet to a sterile natural-ingredient diet did not enhance NK cell activity. No significant differences in NK activity were evident with C3H/HeCr mice of different (6-10 wk vs 29-36 wk) ages. These results indicate that diet and microbial flora can modulate the NK cell activity of mice.

Energy/protein ratio in natural-ingredient diets for weanling rats. II. Energy and protein retention and efficiency of retention.

A 3 x 3 factorial experiment was carried out, in which natural ingredient diets formulated at 3 digestible energy levels (DE) (100, 90 and 80% of NRC, 1978 recommendations) and at 3 energy: protein ratios (EPR) (63, 71 and 79 kJ DE/g crude protein (CP)) were fed to 8 weanling male Wistar rats/group. Half of these animals were sacrificed at the end of the 6-week experimental period and their body composition analyzed. Retentions of protein and energy were assessed by difference from a similar group of 8 rats killed and analyzed at the beginning of the experiment. No interaction was found between the 2 factors studied. Main results showed a decrease in intake and retention of both energy and protein, without affecting the efficiency of retention when energy level of diets was reduced by 20%. An increase in the EPR of the diets led to a decrease in protein intake and to an increase in efficiency of protein retention, without affecting the amount retained. No changes in body composition, nor in composition of live weight gains were found as a result of treatments. It is concluded that a 10% reduction in DE level of the diet is of no consequence, and that an EPR of 79 kJ/g leads to more efficient use of the dietary protein without detrimental effects over any other nutritional indicator.

Modifying effect of vitamin A on benzo[a]pyrene-induced respiratory tract tumours in hamsters.

Groups of 40 hamsters of each sex were fed natural ingredient diets containing 600, 4000 or 100 000 IU vitamin A/kg. After an adaptation period of 170 days on the diets, respiratory tract tumours were induced by intratracheal instillation of benzo[a]pyrene + ferric oxide suspended in saline. Mortality was statistically significantly increased in the high dose group as compared with the mid (control) and low dose group. Microscopy of the respiratory tract did not reveal any significant differences in tumour response between the various dose groups. However, the incidence of preneoplastic respiratory tract lesions was distinctly inversely correlated with the oral vitamin A dose. The serum retinol values were similar in the various dose groups, without any indication of a dose related increase. It was concluded that under the experimental conditions used vitamin A did not influence benzo[a]pyrene-induced respiratory tract cancer in hamsters.