Further studies on the influence of genotype and dietary protein on the performance of broilers

An experiment was conducted to quantify genetic differences in response to dietary protein level of male vs female broilers. Broilers (1 d old) from a "high-yield" strain cross (Ross x Ross 208) and a "fast-growing" strain cross (Peterson x Arbor Acres) were placed on fresh pine shavings in floor pens. From Day 0 to 18, all birds were fed a 23% CP starter diet. During Days 18 to 53 male birds were fed either a 16, 18, 20, 22, 24, or 26% CP diet (3,200 kcal ME/kg) and female birds were fed the 16, 20, or 24% CP diet. Significant differences (P < 0.05) were noted in the performance of the different strains. Ross x Ross 208 male birds had a higher body weight (3.37 vs 3.16 kg), higher feed intake (7.08 vs 6.78 kg), higher breast yield (31.76 vs 29.25%), higher carcass yield (73.90 vs 71.85%), and a lower adjusted feed conversion ratio (FCR; 2.10 vs 2.16 g:g) than Peterson x Arbor Acres males at 53 d of age. As compared to Peterson x Arbor Acres females, Ross x Ross 208 female broilers also had a higher body weight (2.68 vs 2.55 kg), higher breast meat yield (33.61 vs 30.80%), higher carcass yield (75.31 vs 73.91%), and lower adjusted FCR (1.97 vs 2.04 g:g). Qualitative differences in the response of these strains were confirmed and better qualitative data is presented that can be used to predict the important output parameters from the import inputs in broiler production.     

Carry-over effects of dietary crude protein and triiodothyronine (T3) in broiler chickens

Indian River male broiler chickens growing from 7 to 30 d of age were fed on diets containing crude protein levels ranging from 120 to 300 g/kg plus 0 or 1 mg triiodothyronine (T3)/kg diet. The purpose of this study was to examine the effects of these treatments on lipogenesis after a common diet was fed (180 g crude protein/kg diet from 30 to 56 d of age). Dietary treatment groups were sampled at 30 and 56 d. In vitro lipogenesis was determined by incubating liver explants for 2 h at 37 degrees in Hanks' salts containing 25 mM-HEPES and 10 mM-[2-14C]acetate and then measuring acetate incorporation into total lipid. Growth and feed consumption from 7 to 30 d increased (P < 0.01) as dietary protein increased from 120 to 210 g/kg diet. Both measurements decreased as crude protein increased from 210 to 300 g/kg diet. T3 decreased (P < 0.01) growth and feed intake during this period. Low-protein (< 180 g/kg) diets increased (P < 0.05) and T3 decreased lipogenesis in 30-d-old chickens. Although birds given T3 from 7 to 30 d grew at the greatest rate from 30 to 56 d of age, the final body weight was still less than controls. In vitro lipogenesis at 56 d of age was not affected by either of the two dietary treatments. In contrast, the relative size of the abdominal fat pad (g/kg body weight) at 56 d was decreased by feeding T3 from 7 to 30 d. Any changes in metabolism elicited by either dietary protein levels or hormone treatments may be specific to the particular dosing interval and are not sustained when a common diet is fed during a repletion period.     

Effects of dietary protein and strain on the growth of broiler breeder pullets from zero to five weeks of age

In a series of four experiments, the effects of differences in dietary protein intake on BW, skeletal growth and the weight of the Pectoralis major muscle was studied in Hubbard Standard and Hubbard Hi-Y broiler breeder pullets. In Experiment 1, pullets were fed diets with either 15, 17, or 19% CP from 1 to 21 d. There was a linear increase in BW gain and feed consumption with each increase in CP and Hubbard Standard pullets consumed significantly more feed than Hubbard Hi-Y pullets. From 21 to 34 d, pullets were subjected to feed restriction every day (ED) or every-other-day (EOD). On Day 35, pullets were given ad libitum access to feed and ED-restricted pullets consumed significantly more feed than EOD-restricted pullets through 3.5 h postfeeding. In Experiment (Exp.) 2, pullets were fed the 19% CP diet for approximately 14 d (300 g) or 20 d (600 g) before being switched to the 15% CP diet. In Experiment 3, the 19% CP diet was fed for exactly 7 or 21 d before switching to the 15% CP diet. In all experiments, Hubbard Standard pullets weighed significantly more than Hubbard Hi-Y pullets and had increased overall skeletal growth. When the pullets from both strains were restricted to only 380 g BW at 28 d, (Exp. 3) the longer period of protein intake significantly enhanced breast muscle weight but there were no significant strain differences. When BW at 28 d was increased to 480 g, (Exp. 2), dietary protein and strain differences were observed.     

Research notes: Sodium bicarbonate supplementation in diets for guinea fowl raised at high environmental temperatures

An experiment was designed to verify the effect of dietary NaHCO3 supplementation on performance of guinea fowl raised under high environmental temperatures (23.8 to 33.9 C) and average relative humidity of 78.7%. One hundred and forty guinea fowl in their final period of growth (56 to 84 d of age) were allotted to individual wire cages. Five isocaloric (3,000 kcal ME/kg) 16% CP diets based on corn and soybean meal and containing 0, 0.6, 1.2, 1.8, and 2.4% sodium bicarbonate were fed to the birds. The experiment followed a randomized block design with 28 birds per treatment (14 of each sex) with each bird being considered as one repetition. Results showed that weight gain, feed intake, feed conversion, mortality, blood pH, carcass yield, and carcass composition were not affected (P > 0.05) by dietary sodium bicarbonate supplementation. Weight gain, feed intake, feed conversion, carcass moisture, and fat content, however, were significantly (P < 0.05) affected by sex. Females showed 17.49% better weight gain, 7.16% greater feed intake, and 9.6% better feed conversion than males. These differences were exacerbated at supplementation levels of 1.2 and 1.8% sodium bicarbonate in the diet. Male birds showed carcass moisture values significantly (P < 0.05) greater than those of female birds; the opposite occurred with carcass fat levels. The use of sodium bicarbonate in levels up to 2.4% of the diet did not affect the performance of guinea fowl raised under the environmental conditions registered in this study.     

Body composition at farrowing and nutrition during lactation affect the performance of primiparous sows: II. Milk composition, milk yield, and pig growth

We used 35 primiparous sows to investigate the link between body fatness at farrowing and voluntary feed intake (VFI) during lactation. Two groups of sows were fed differently throughout gestation (either 2.3 kg/d of a diet containing 5.8% CP and 14.6 MJ DE/kg as fed or 1.7 kg/d of a diet containing 15.6% CP and 14.5 MJ DE/kg as fed) so that they commenced lactation at a similar body weight (158 to 152 kg) but with different body compositions: either 340 (fat) or 280 (lean) g of body fat/kg BW (P < .001). During lactation, sows were offered either a low-protein diet (7.9% CP and 15.5 MJ DE/kg as fed) or a high-protein diet (19.0% CP and 15.6 MJ DE/kg as fed) on an ad libitum basis. During lactation, VFI was measured daily, and sow body weight and backfat were measured weekly. Blood samples were collected from sows on d 110 of gestation and d 14 and 28 of lactation, and plasma was analyzed for NEFA, glycerol, insulin, glucose, and beta-hydroxybutyrate. Fat sows ate 30% less than their lean counterparts during lactation (P < .001), which corresponded to a 70% higher concentration of NEFA in plasma (P = .01) and a 30% higher concentration of glycerol (P = .15). The VFI during the first 2 wk of lactation was affected only by body fatness and not by the protein content of the lactation diet. The dietary supply of protein influenced VFI during wk 3 and 4 of lactation, possibly by affecting milk production and hence the drive to consume feed. Weight loss, particularly lean tissue loss, was minimized by feeding the high-protein diet during lactation (P < .002).     

Effect of clenbuterol on growth and body composition during food restriction in rats

Clenbuterol was administered as a dietary admixture (4 mg/kg diet) to three groups of male Wistar rats (n = 8) housed individually in metabolism cages and fed for 15 d at 110, 160, and 235% (ad libitum) of estimated requirement for energy maintenance. Untreated groups at each level of energy intake were also included. There was no effect of clenbuterol on food intake in the ad libitum group, but the drug produced significant increases in body weight, feed efficiency, and carcass weight, dressing and protein content at all three levels of energy intake. This effect of clenbuterol was particularly noticeable in the restricted animals. Clenbuterol caused changes in body composition (increased percentage of water and protein, decreased percentage of fat) in the ad libitum rats but had no effect in the restricted groups. The reduction in the growth of the viscera caused by energy restriction was not affected by clenbuterol, apart from in the 110% restricted group, where the gastrointestinal tract was 26% heavier in the clenbuterol-treated rats. The results show that the growth anabolic actions of clenbuterol can be sustained and may be even more marked in rats fed restrictively than in those given ad libitum access to feed.     

Insulin increases the daily food intake of diabetic rats on high and low fat diets

The effects of insulin dose and diet composition on daily food intake were investigated by IV infusion of insulin in doses of 2 to 5 U/day into diabetic rats consuming either a high CHO or high fat diet. The daily food intake of the diabetic rats on both diets increased significantly over baseline levels (p < .01) at the low insulin doses and was maintained at these elevated levels through the 5 U/day dose. Insulin increased the rate of weight gain from Ig/day during baseline to 2 and 2.5 g/day in high CHO and high fat fed diabetics (p < .01). These results show that treatment of diabetic rats with continuous low doses of IV insulin results in a 40% increase in daily food intake regardless of the diet consumed and this increase is accompanied by an increase in rate of body weight gain. While the high fat fed diabetics were relatively hypoglycemic, these increases in intake are not the result of insulin-induced hypoglycemia, since blood glucose concentrations are significantly elevated when the increases occur at the lower insulin doses (p < .01). Thus, peripheralinsulin infused at physiological levels stimulates rather than inhibits daily food intake.     

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.     

Effect of feeding clinoptilolite (zeolite) on the performance of three strains of laying hens

1. One hundred and twenty 16-week-old single combed pullets of three strains were fed on a diet containing 135 g protein/kg with or without 50 g clinoptilolite/kg in a trial with 20 hens per treatment. Sterile river sand replaced clinoptilotile in the control diet in order to keep the diets isoenergetic. The hens were individually caged in a naturally ventilated laying house and fed one of the two diets for ten 28-d periods. 2. Significant dietary effects of feeding clinoptilolite were observed with number of eggs laid per hen, shell thickness, efficiency of food utilisation and droppings moisture content. No significant dietary effects between treatments were observed with body weight, age at first egg, egg weight. Haugh units, food intake/hen and rate of amino acid absorption of radioactive lysine and methionine into the bloodstream. Significant differences between strains were observed with regard to all parameters except food intake/hen. There were no significant strain X clinoptilolite interactions.     

Dehydroepiandrosterone-sulfate (DHEAS) reduces adipocyte hyperplasia associated with feeding rats a high-fat diet

OBJECTIVE: To determine if chronic administration of a low level of dehydroepiandrosterone-sulfate (DHEAS) (10 micrograms/ml drinking water) attenuates adiposity in male Osborne-Mendel rats fed low-fat (11% of kcals) vs high fat (46% of kcals) diets. DESIGN: Rats were randomly assigned to one of four treatment groups for 6 wk in this 2 x 2 factorial study. The main effects tested were diet (low vs high fat) and DHEAS (- or +). SUBJECTS: Male Osborne-Mendel rats (initial body wt approximately 265 g). MEASUREMENTS: Adipocyte mass, size and number from two major fat depots (retroperitoneal, epididymal); mass of one subcutaneous adipose depot (inguinal); serum levels of triglycerides, insulin, glucose and DHEAS; brown adipose tissue (BAT) mass; body weight gain, food and water consumption, and residual carcass composition. RESULTS: DHEAS treatment had no effect on weight gain, food consumption or water intake. DHEAS-treated rats fed the high-fat diet had smaller fat pads containing fewer adipocytes and less carcass lipid than the non DHEAS-treated rats fed the high-fat diet. In contrast, DHEAS-treated rats fed the low-fat diet had similar levels of adipose tissue mass and cellularity compared to control animals fed the low-fat diet. CONCLUSION: Administration of a low dose of DHEAS (10 micrograms/ml or 0.8 mg/kg body wt/d) in the drinking water of young male Osborne-Mendel rats fed a high-fat diet for 6 wk reduced carcass lipid, fat depot mass and retroperitoneal and epididymal adipocyte number compared to their high-fat-fed cohorts. In this study, the antiobesity effects of DHEAS were specific to the level of dietary fat used.     

Resistant starch decreases serum total cholesterol and triacylglycerol concentrations in rats

Rats were meal-fed semipurified diets containing a low (0.8 g/MJ) and a high (9.6 g/MJ) amount of resistant starch (RS) or various amounts of RS (0.8 to 9.6 g/MJ) and guar gum (0 to 8.8 g/MJ). In one experiment, rats were fed the low and high RS diets in three dietary regimens (ad libitum consuming, 12 h ad libitum/12 h food deprived, and meal fed). Effects of RS and guar gum on serum postprandial and postabsorptive concentrations of total cholesterol (TC) and triacylglycerol (TAG), growth, hydrogen excretion, tissue weights and contents of small intestine and cecum, and pH of cecal contents were investigated. In addition, effects of RS on food intake, de novo hepatic synthesis of fatty acids and neutral sterols, and on lipoprotein lipase activity and weight of epididymal fat pads were investigated. Compared with feeding the low RS diet, the high RS diet reduced the serum TC and TAG concentrations, with these effects observed after 1 and 2 wk of feeding, respectively. The dietary regimen did not influence the effect of RS on the serum TC and TAG concentrations, but it did affect the serum TAG concentration. Resistant starch had no effect on the hepatic synthesis of fatty acids and neutral sterols or on the lipoprotein lipase activity in epididymal fat pads. Guar gum also reduced the serum TC concentration, but it had no effect on serum TAG concentration. The tissue weights and contents of small intestine and cecum as well as hydrogen excretion increased with increasing amounts of dietary RS and guar gum, whereas the pH of cecal contents decreased. No effects of RS on food intake and total body weight gain were found, whereas guar gum decreased weight gain. Feeding the high RS diet also led to a lower weight of the epididymal fat pads. We conclude that dietary RS can reduce serum TC and TAG concentrations and fat accretion.     

Supplemental arginine and ornithine do not affect splenocyte proliferation in surgically treated rats

The present study was designed to determine whether arginine or ornithine supplementation enhanced immune responsiveness in surgically stressed rats. Young rats (130 to 150 g; n = 72) were fed one of three nonpurified diets: control, arginine-supplemented (30 g/kg of diet), or supplemented with ornithine on an equimolar basis to supplemental arginine. Control and ornithine-supplemented diets were made isonitrogenous to the arginine-supplemented diet with alanine. Food intake and body weight were monitored throughout the experimental period. Eight days after initiation of dietary treatments, 36 rats were given dorsal skin wounds. Rats were killed 7 days later. Blood was collected, spleen and thymus were weighed, and splenocytes were isolated to measure proliferation in response to mitogens and interleukin-2 production. Food intake, body weight gain, and thymus weight were lower in rats subjected to surgery than in controls rats (p < .01). Neither supplemental dietary arginine nor ornithine affected food intake, body weight gain, thymus weight, splenocyte proliferation, or splenocyte interleukin-2 production in any treatment group (p < .1). These data suggest that low-level dietary supplementation of arginine and ornithine did not ameliorate detrimental effects of minor surgery in rats.     

Factors affecting body tissue mobilization in early lactation dairy cows. 1. Effect of dietary protein on mobilization of body fat and protein

Twenty Holstein cows were fed diets that were formulated with 16 or 19% crude protein (CP) that contained, respectively, 6 and 9% ruminally undegradable protein (RUP) (dry matter basis) to study the effect of increased RUP on tissue mobilization and production parameters. Cows were enrolled in the study from -14 to 114 d postpartum. Body composition measurements using the D2O dilution technique were made at -2, 5, and 12 wk postpartum. Maximum loss of body tissue occurred between wk 2 prepartum and wk 5 postpartum during which time cows fed both treatments mobilized a mean of 54 kg of body fat and 21 kg of body protein. Cows continued to mobilize 18 kg of body fat through wk 12 postpartum, but the amount of body protein was unchanged. One unit of change in body condition score corresponded to about 40 kg of empty body fat. Partitioning of empty body energy between empty body fat and protein indicated that, for each unit of change in body energy, 93% was lost or gained as body fat, and body protein accounted for only 7%. Increasing RUP in the diet had no effect on the postpartum amounts of empty body protein, empty body fat, or empty body energy. Milk production was 39.8 kg for cows fed the 16% CP diet and 42.4 kg for cows fed the 19% CP diet. There was an interaction of treatment by week postpartum. Both dry matter intake and milk production were lower during the first 6 wk postpartum but were greater thereafter for cows fed the 19% CP diet than for cows fed the 16% CP diet. Milk CP percentage was higher (3.08% vs. 2.89%), and milk CP yield tended to be greater (1.29 vs. 1.15 kg/d), for cows fed the 19% CP diet.     

Performance and tissue zinc and metallothionein accumulation in chicks fed a high dietary level of zinc

Four experiments were conducted to identify several factors that might improve the accuracy and reproducibility of Zn bioavailability assays for chicks. Response of tissue Zn and metallothionein (MT) concentrations to various elevated levels and soluble sources of dietary Zn were measured, as well as the effect of delaying high Zn administration until 7 d posthatching to alleviate the detrimental effect of Zn sulfate on feed intake to 3 wk of age. Bone Zn increased (P < 0.01) in all experiments in response to increasing dietary Zn concentrations. Liver and pancreas MT were affected (P < 0.01) by a source by age interaction and variability that made this criterion unsuitable for bioavailability assays. Lastly, 1-d-old chicks were used to study the effect of delaying feeding of a high-Zn diet up to 7 d of age. The basal diet was fed continuously for 21 d as a control. A diet containing 1,000 ppm Zn was either fed continuously from Day 1, or started on Day 3, 5, or 7. Chicks given high Zn on Day 3, 5, or 7 decreased (P < 0.01) feed intake within 24 h of feeding. Delayed feeding of high dietary Zn might help to alleviate decreased feed intake observed in previous studies. Delaying the onset of high Zn feeding by several days may help alleviate feed intake problems observed with Zn sulfate. Use of either Zn gluconate or Zn acetate as a standard in assays or use of MT synthesis as a bioavailability criterion will probably not be useful to improve accuracy of the estimates.     

Energy restriction with high-fat diet enriched with coconut oil gives higher UCP1 and lower white fat in rats

OBJECTIVE: To investigate the effects of overfeeding on a high fat diet, enriched in coconut oil, and the influence of food restriction on the uncoupling protein (UCP1) expression and on body fat content. DESIGN AND SUBJECTS: In experiment I, female Wistar rats were fed ad libitum either a normal-fat diet (control group, C) or a high-fat diet (HF), enriched in coconut oil, for 7 weeks. In experiment II, HF rats after finishing experiment I were fed (for 3 weeks) either the normal-fat diet (group CAHF, Control After High Fat) or food restricted diets which provided 60% of the energy intake of group CAHF: a group fed a low-energy, normal-fat diet (LENF) and another fed a low-energy, high-fat diet (LEHF). MEASUREMENTS: Body and fatty depot weights. Food intake. Protein and UCP1 levels of interscapular brown adipose tissue. RESULTS: High-fat diet feeding promoted an increase in body fat content, body weight and UCP1 levels. Energy restriction induced similar body weight reduction in groups LENF and LEHF. However, some adipose depots were more strongly reduced in the rats fed the high-fat diet enriched in coconut oil (group LEHF) than in the rats fed the normal-fat diet (Group LENF). Specific UCP1 was 2.0 (group LENF) and 3.4 (group LEHF) times higher than in controls (group CAHF). CONCLUSION: The coconut-oil enriched diet is effective in stimulating UCP1 expression during ad libitum feeding and in preventing its down regulation during food restriction, and this goes hand in hand with a decrease of the white fat stores.     

Methionine requirement of channel catfish fed soybean meal-corn-based diets

A soybean meal-corn-based diet was used to determine dietary methionine (Met) required by 14-g channel catfish (Ictalurus punctatus) in a 42-d experiment at 25 degrees C. The basal diet with balanced limiting amino acids relative to the catfish whole-body amino acid profile contained 277 g of CP, 3.6 g of Met, 4.0 g of cystine (Cys), and 10 MJ of DE/kg of DM. DL-Methionine was added to the basal diet from 0 to 12.0 g/kg in 2-g intervals at the expense of L-glutamic acid to produce seven isonitrogenous and isocaloric diets. A reference diet contained 331 g of CP, 8 g of Met, 5 g of Cys, and 10 MJ of DE/kg of DM (included 8% fish meal). Seven graded Met levels resulted in quadratic responses (P < .01) of weight gain, specific growth rate, feed or GE intake, feed or energy efficiency, protein or energy retention, protein efficiency ratio, and apparent net protein or energy utilization. Channel catfish required 9.4 g of Met/kg of DM (34.1 g/kg of CP) with a total 11.3 g/kg of calculated digestible sulfur-containing amino acids based on multiple regression dose-response models or 270 mg of Met/kg of fish per day based on a broken-line response of protein gain to Met intake. At the adequate Met level, catfish with the lowest (P < .05) liver lipids showed feed intake and protein or energy utilization efficiency similar (P > .05) to that of catfish fed the reference diet. Catfish fed all-plant-protein diets require more dietary methionine than previously reported. Catfish fed corn-soybean meal diets fortified adequately with methionine result in performance that approaches that of fish fed a fish meal-based diet.     

Hematologic response of adult brown mink to oxidative stress

We evaluated the response of mink to oral administration of the oxidant compound propylene glycol (PG) to better understand the relative susceptibility of mink red blood cells (RBC) to oxidant injury. Feeding a diet containing 12% PG to 6 mink for 1 w resulted in a 17% decrease in hematocrit, a 21% decrease in RBC count and a 4.8-fold increase in reticulocyte count. A marked increase in Heinz body and eccentrocyte numbers was consistent with oxidative injury to RBC. Because of high food intake, mink ingested approximately twice the quantity of PG/kg body weight compared to domestic cats fed diets containing 12% PG. Therefore, the severity of the hematologic dyscrasia in mink may be the result of greater intake of PG rather than unique sensitivity of mink RBC of oxidative injury. However, the high food intake and the mink's position at the top of the food chain may increase its exposure to environmental contaminants.     

Protein requirements of sheep in late pregnancy: partitioning of nitrogen between gravid uterus and maternal tissues

The objective of this study was to quantify effects of maternal protein nutrition on N accretion or loss in conceptus and maternal tissues of ewes during late pregnancy. Ewes, pregnant with twins, were fed low (LP, 79 g CP/kg DM), medium (MP, 116 g CP/kg DM), or high (HP, 157 g CP/kg DM) protein diets, each with an estimated ME concentration of 2.7 Mcal/kg DM, between d 111 and 140 of pregnancy; all ewes had been fed the same diet (2.7 Mcal ME, 120 g CP/kg DM) for the previous 30 d (d 80 to 110). Dry matter intakes were varied (LP = 1.0, MP = 1.2, and HP = 1.4 kg/d) according to predicted energy costs of protein deposition for each diet. Nitrogen accretion was estimated by comparative slaughter (d 140 minus d 110) and by collection of excreta between d 120 and 130. Fresh weights of maternal and gravid uterine tissues were measured at slaughter, before proximate analysis of these components. Whole-body N retention was directly and linearly related to N intake, but efficiency of deposition of apparently absorbed N decreased linearly with increasing N intake (LP, .79; MP, .70; HP, .62). Nitrogen accretion in the gravid uterus, maternal viscera, and mammary gland was significantly less in LP than in MP or HP ewes. Nitrogen balance in maternal carcass tissues was linearly related to N intake, ranging from a negative value in LP ewes to a positive value in HP ewes (LP, -63 g; MP -39 g; HP, 55 g). These data provide the basis for estimating N requirements for protein accretion in the conceptus and in maternal tissues during late pregnancy. They also highlight the capacity of maternal carcass tissues to mobilize or deposit amino acids in response to variations in dietary protein supply.     

Decreased plasma insulin but normal glucagon in rats fed low protein diets

Plasma glucagon and insulin were determined in rats fed three diets, one control and two low protein (LP 1 & LP 2). In LP 1, the protein omitted was replaced by carbohydrate while in LP 2, fat and alpha-cellulose replaced the omitted protein. Among rats fed LP diets ad libitum, food consumption decreased and body weight loss occurred. In order to separate the effects of reduced food intake and weight loss from the effects of LP diet alone, paired feeding and paired weight experiments were conducted. In another experiment, ingestion of a LP diet for 8 to 10 days was followed by refeeding the control diet for 5 days. The results demonstrate that plasma insulin was reduced in LP rats compared to the full-fed controls and pair-fed controls, the lowest levels being observed in rats fed LP 2 diet. Furthermore, the paired feeding experiment revealed that the diminished food consumption plays no significant role in lowering plasma insulin in LP rats. The refeeding experiment showed that the decline in plasma insulin in LP rats is a transient phenomenon and the plasma insulin promptly reverts to normal upon resumption of feeding the control diet. Plasma glucagon was unaltered throughout these dietary manipulations.     

Effects of dietary retinoic acid on skin papilloma and carcinoma formation in female SENCAR mice

Previously we have shown that dietary retinoids are essential for papilloma formation induced by either an initiation-promotion or a complete skin carcinogenesis protocol. The present study was conducted to further determine the effect of dietary retinoic acid (RA) on papilloma formation and the conversion of papillomas to carcinomas. Skin tumors were induced in 3 week old female SENCAR mice by an initiation-promotion protocol with one application of 20 micrograms of 7,12-dimethylbenz[a]anthracene (DMBA), followed by 20 weekly applications of 2 micrograms of 12-O-tetradecanoylphorbol-13-acetate (TPA). Mice were fed RA at one of the three doses: 0.3 (nutritionally marginal dose), 3 (near physiological) and 30 (pharmacological) micrograms/g of diet. Mice fed 30 micrograms of RA/g of diet had the same survival rate as the other two groups despite a lower body weight and all three groups had similar papilloma incidence, which reached 100% at age 18 weeks. Mice fed 3 micrograms of RA/g of diet had the highest papilloma yield (approximately 14 papillomas/mouse) of all groups and it peaked between weeks 18 and 38 of age. These papillomas later regressed such that mice from all three groups had about the same papilloma yield at week 44 of age. Mice fed 30 micrograms of RA/g of diet failed to develop any visible carcinoma, while mice fed 0.3 or 3 micrograms/g showed 1.9% conversion of papillomas to carcinomas. Therefore, dietary RA at 30 micrograms/g of diet inhibited the conversion of papillomas to carcinomas without affecting papilloma incidence. In addition, dietary RA at 30 and 0.3 micrograms/g of diet lowered papilloma yield.