Nitrogen excretion in rats on a protein-free diet and during starvation

Nitrogen balances (six days) were determined in male Wistar rats during feeding a diet with sufficient protein or a nearly protein-free diet (n = 2×24), and then during three days of starvation (n = 2×12). The objective was to evaluate the effect of protein withdrawal on minimum nitrogen excretion in urine (UN), corresponding to endogenous UN, during feeding and subsequent starvation periods. The rats fed the protein free-diet had almost the same excretion of urinary N during feeding and starvation (165 and 157 mg/kg W^0.75), while it was 444 mg/kg W^0.75 in rats previously fed with protein, demonstrating a major influence of protein content in a diet on Nexcretion during starvation. Consequently, the impact of former protein supply on Nlosses during starvation ought to be considered when evaluating minimum N requirement necessary to sustain life.     

Endogenous N-excretion and minimal protein requirement for maintenance of the common marmoset (Callithrix jacchus)

The protein requirement for maintenance of the marmoset Callithrix jacchus was investigated by factorial calculation via the N balance technique. Six adult male marmosets were fed a protein-free pelleted diet for 22 days. When a low protein diet (6%) was fed in the preperiod, only 7 days were necessary and when fed a higher protein diet (18%) 10 days were necessary to reach a minimum of N excretion during protein depletion. Body weight losses averaged 11% and food intake was 21% lower in the protein free period. The average endogenous urine N (EUN) was 62.1 mg N and endogenous fecal N (EFN) 49.2 mg N/kg W0.75. Body surface losses (BSN) were assumed to be 20 mg N/kg W0.75. The total endogenous loss of 131.3 mg N/kg W0.75 is similar to that of other species. Net protein utilization (NPU) of well balanced proteins, determined near the N equilibrium, was 51.8%. The calculated net protein requirement amounts to 313.6 mg N/kg W0.75, which corresponds to a dietary protein content of 6% in a diet of high caloric density, (about 19-20 MJ/kg dry matter) when the food intake is 3.3% of body weight.     

Energy metabolism and nutrient oxidation in young pigs and rats during feeding, starvation and re-feeding

The investigation included individual measurements of energy metabolism and oxidation of nutrients in 12 castrated male pigs (Sus scrofa) (20-40 kg) and 12 male rats (Rattus norvegicus) (65-105 g). Measurements were carried out in 5-6 days balance periods with ad libitum feeding, followed by 3-4 days of starvation and 4 days of re-feeding. O2 consumption and CO2 production were measured by open-air-circuit respiration units. In the feeding period, protein retention in relation to metabolic live mass (kg(0.75)) was identical for pigs and rats, while there was a tendency of a higher fat retention in pigs than in rats. A substantial part of digested carbohydrate was not oxidized, but transferred to fat metabolism without significant differences (P > 0.05) between pigs and rats (18% vs. 22%). During starvation, nitrogen excretion in urine decreased to 226 mg/kg(0.75) in pigs and to 429 mg/kg(0.75) in rats, indicating a lower rate of body protein degradation in pigs. Heat production was reduced to 592 and 338 kJ/kg(0.75), while the contribution of heat from oxidation of protein (OXP), carbohydrate (OXCHO) and fat (OXF) showed the same pattern for pigs and rats during all periods. Heat production during feeding and re-feeding was covered by OXP+OXCHO with no OXF and reversibly after 2 days of starvation by OXP+OXF with no OXCHO. The rat may be a suitable model for pigs regarding general patterns of quantitative nutrient partition, but any direct application of results measured with rats to pigs shall be taken cautiously, keeping in mind that modern pigs have been selected for a high growth rate and protein deposition which has not been the case for the laboratory rat.     

Effect on Lipids in Liver and Serum,and Some Urinary Components of Dietary Supplement of Excess Lysine Given to Previously Starved or Non-starved Rats

In order to obtain further information on the changes in liver lipids, either a basal or a lysine-sexcess diet was refed to previously starved rats or fed to previously non-starved rats. Liver lipid accumulation was observed in previously starved rats refed the lysine-excess diet for 7 days, but not in rats without previous starvation. The liver lipid did not accumulate with another 8 days’ feeding (15 days⁹ refeeding). The addition of methionine alone or in combination with threonine to the lysine-excess diet had no effect on the liver lipid level. The decrease in serum triacylglycerol in rats refed the lysine-excess diet was preceded by lipid accumulation in the liver. Urinary potassium during the initial two days increased with refeeding and feeding. Marked excretion of orotate was observed for 2 days from the initiation of refeeding of the lysine-excess diet and it then decreased. Thus, such a marked increase in the urinary excretion of orotate might be associated with the stimulation of orotate biosynthesis and with lipid accumulation in the liver.     

Effect of Starvation,Refeeding and Hydrocortisone Administration on Turnover of Myofibrillar Proteins Estimated by Urinary Excretion of Nτ-Methylhistidine in the Rat

Quantitative changes in fractional catabolic and synthetic rates of the myosin-actin pool in rat muscle under starvation and refeeding, during growth or after treatment with hydrocortisone were studied by estimating urinary excretion of N^τ-methylhistidine (3-methyl- histidine; Me-His).

Following deprivation of food, urinary Me-His output increased from 0.35 mg/day to 0.45 mg/day during first 2 day in spite of decreasing body Me-His pool. This high rate of Me-His excretion was maintained for the following 4 days of starvation and then decreased. When rats were refed a 20% casein diet after 10 days of starvation, Me-His excretion continued to decrease even after 3 days of refeeding. On the fifth day of refeeding, it began to rise progressively. During starvation, fractional catabolic rate of myosin-actin was about 3.7 %/day in comparison with 2.6 %/day of fed rats. After refeeding, the fractional catabolic rate decreased rapidly to a minimum value of 1.7 %/day on the third day. After that, it reached to a value of 2.6 %/day of fed rats. On the other hand, fractional synthetic rate of myosin-actin dropped immediately after fasting and the low rate of about 0.4 %/day was maintained during starvation period. Fractional synthetic rate recovered quickly after refeeding.

Urinary output of nitrogen and creatinine rose quickly on the first day after administration of hydrocortisone and on the second day it fell to their normal value. While Me-His excretion increased after injection of hydrocortisone up to 0.52 mg/day on the second day and this high excretion rate remained until the following day. From these results, it was shown that administration of hydrocortisone to rats enhances catabolism and reduces synthesis of myosin-actin. The results also show that the effect of this hormone on myofibrillar protein catabolism appears to last longer than its effect on nitrogen metabolism in the whole body judged from urinary nitrogen output.

Fractional rates of catabolism and synthesis of rat myosin-actin were 3.3 %/day (half- life of 21 days) and 7.2%/day, respectively, at the growth stage of 129 g body weight. These rates were 2.3 %/day (half-life of 30 days) and 2.8 %/day, respectively, at the mature stage of 363 g body weight.

Under the dietary conditions in this experiment, fractional synthetic rate changed far more dramatically than catabolic rate. This suggests that mass of muscle protein is primarily regulated by the rate of synthesis, although the rate of catabolism should not be neglected.     

Using milk urea nitrogen to evaluate diet formulation and environmental impact on dairy farms

Reducing nitrogen (N) excretion by dairy cattle is the most effective means to reduce N losses (runoff, volatilization, and leaching) from dairy farms. The objectives of this review are to examine the use of milk urea nitrogen (MUN) to measure N excretion and utilization efficiency in lactating dairy cows and to examine impacts of overfeeding N to dairy cows in the Chesapeake Bay drainage basin. A mathematical model was developed and evaluated with an independent literature data set to integrate MUN and milk composition to predict urinary and fecal excretion, intake, and utilization efficiency for N in lactating dairy cows. This model was subsequently used to develop target MUN concentrations for lactating dairy cattle fed according to National Research Council (NRC) recommendations. Target values calculated in this manner were 8 to 14 mg/dl for a typical lactation and were most sensitive to change in milk production and crude protein intake. Routine use of MUN to monitor dairy cattle diets was introduced to dairy farms (n = 1156) in the Chesapeake Bay watershed. Participating farmers (n = 454) were provided with the results of their MUN analyses and interpretive information monthly for a period of 6 months. The average MUN across all farms in the study increased in the spring, but the increase was 0.52 mg/dl lower for farmers receiving MUN results compared to those who did not participate in the program. This change indicated that participating farmers reduced N feeding compared to nonparticipants. Average efficiency of feed N utilization (N in milk / N in feed x 100) was 24.5% (SD = 4.5). On average, farmers fed 6.6% more N than recommended by the NRC, resulting in a 16% increase in urinary N and a 2.7% increase in fecal N compared to feeding to requirement. N loading to the Chesapeake Bay from overfeeding protein to lactating dairy cattle was estimated to be 7.6 million kg/year. MUN is a useful tool to measure diet adequacy and environmental impact from dairy farms.     

Heat production and substrate oxidation in rats fed at maintenance level and during fasting

A total of 36 Wistar rats were fed a commercial diet to a stipulated live weight of 75 g (Group A), 100 g (Group B) and 225 g (Group C). All rats were measured in energy balance experiments, in which the animals were fed near maintenance level, followed by a period of fasting with measurements of the gas exchange. The rats in Group A, B and C were fasted for 2, 3 and 4 days, respectively. The minimum heat production on the last day of fasting for all groups was proportional to metabolic body weight (kg0.75) with a regression: heat production, kJ day-1 = 321 x kg0.75 (R2 = 0.994). In rats fed near maintenance level, heat production was provided by oxidation of carbohydrates in 80-85%, oxidation of protein was 10-15%, while oxidation of fat contributed less than 10%. It is suggested that in the fasting period, the contribution to the total heat production from oxidized carbohydrate and fat depended on the size of the fat depots, a large fat depot giving rise to fat oxidation. On the last day of fasting, 24, 51 and 90% of the total heat originated from fat oxidation in Group A, B and C, respectively.     

Effect of a soy protein diet on protein and energy metabolism and organ development in protein-restricted growing pigs

Two feeding experiments were carried out with castrated male pigs weighing between 10 and 30 kg to study acute and persisting dietary effects on growth and on protein and energy metabolism in growing pigs. Pigs were fed semi-synthetic isoenergetic and isonitrogenous diets at 50% protein requirement with either soy protein isolate (SPI) or casein (CAS) as sole protein source. Intake of protein and ME amounted to 9% w/w and 1800 kJ x kg BW (-0.62) x d(-1) in Exp. 1, respectively, and 9% w/w and 1430 kJ x kg BW(-0.62) x d(-1) in Exp. 2. The CAS diet was supplemented by Lys, Met, Thr and Trp. In Exp. 1 (acute effects), 18 pigs received the CAS diet for 24 days (period 1); 9 pigs were then switched to a SPI diet whereas 9 pigs continued on the CAS diet for another 31 days (period 2). In Exp. 2, a third period of 31 days was added in which the SPI group was switched back to CAS diet. The control group was fed on the CAS diet throughout Exp. 2 (86 days). Altogether the majority of parameters were not affected neither comparing SPI with CAS in Exp. 1 nor inspecting possible persistence of effects in Exp. 2. In detail, in Exp. 1 SPI compared to CAS feeding resulted in a lower efficiency of protein utilisation and lower protein retention. Attendant upon the lower protein retention an increased energy retention as fat was only observed in tendency. SPI feeding caused a decreased body weight, thyroid weight and increased hepatic carbohydrate content that persisted after the diet was changed back to CAS (Exp. 2).     

Histidine maintenance requirement and efficiency of its utilization in young pigs

An experiment was conducted in young pigs (initial BW 10.1 kg) to estimate the maintenance requirement for histidine and its efficiency of utilization for protein accretion using a comparative slaughter technique. Three groups of six pigs each were fed a purified diet supplying 0, 14 or 56 mg histidine per kg BW0.75. Following 21 d of feeding, pigs were killed for whole body compositional analysis. A representative group of six pigs was killed at the beginning of the experiment. Retention of histidine and total N were the main criteria of response. Histidine retention (R2 = 0.73) and N retention (R2 = 0.78) were linear functions of histidine intake (p < 0.001). Histidine requirement for zero histidine retention was 15.5 mg/kg BW0.7, whereas histidine required for zero N retention was 4.1 mg/kg BW0.75. At zero histidine retention, the pigs retained daily 82 mg N/kg BW0.75, presumably due to the degradation of histidine-rich compounds such as haemoglobin and/or carnosine. The slope of the regression line relating histidine retention to N retention indicated that 105 mg of histidine was deposited per gram of total N which was considerably less than the estimated histidine concentration in body protein (179 mg/g N). Based on the slopes of regression equations for histidine and N retention, marginal efficiency of histidine utilization was calculated to be 0.94 and 1.34, respectively.     

The effect of iron overload on urinary excretion of immunoreactive prostaglandin E2

The effect of in vivo lipid peroxidation on the excretion of immunoreactive prostaglandin E2 (PGE2) in the urine of rats was studied. Weanling, male Sprague-Dawley rats were fed a vitamin E-deficient diet containing 10% tocopherol-stripped corn oil (CO) or 5% cod liver oil (CLO) with or without 40 mg dl-alpha-tocopheryl acetate/kg. To induce a high, sustained level of lipid peroxidation, some rats were injected intraperitoneally with 100 mg of iron as iron dextran after 10 days of feeding. Iron overload stimulated in vivo lipid peroxidation in rats, as measured by the increase in expired ethane and pentane. Dietary vitamin E reversed this effect. Rats fed the CLO diet excreted 9.5-fold more urinary thiobarbituric acid-reactive substances (TBARS) than did rats fed the CO diet. Iron overload increased the excretion of TBARS in the urine of rats fed the CO diet, but not in urine of rats fed the CLO diet. Dietary vitamin E decreased TBARS in the urine of rats fed either the CO or the CLO diet. Iron overload decreased by 40% the urinary excretion of PGE2 by rats fed the CO diet, and dietary vitamin E did not reverse this effect. Iron overload had no statistically significant effect on urinary excretion of PGE2 by rats fed the CLO diet. A high level of lipid peroxidation occurred in iron-treated rats, as evidenced by an increase in alkane production and in TBARS in urine in this study, and by an increase in alkane production by slices of kidney from iron-treated rats in a previous study [V. C. Gavino, C. J. Dillard, and A. L. Tappel (1984) Arch. Biochem. Biophys. 233, 741-747]. Since PGE2 excretion in urine was not correlated with these effects, lipid peroxidation appears not to be a major factor in renal PGE2 flux.     

Effect of alcohol on microsomal cortisol 4en-5 alpha-reductase in the liver of rats fed on a standard or low protein diet

Alcohol feeding (40% of total calories over a period of 9 days) increases microsomal cortisol-5 alpha-reductase activity in rat liver distinctly. It is assumed that this is an adaptive response to an increased release of cortisol caused by alcohol administration. Cortisol-5 alpha-reductase activity is decreased to one third of control values in rats fed an isocaloric, low protein diet. The response to alcohol feeding is susta ined in these animals. Phenobarbital treatment (80 mg/kg x day) stimulates 5 alpha-reduction of cortisol per g of microsomes almost twofold. The activity calculated per total liver increases 4-fold. Alcohol administration has no additional effect on cortisol-5alpha-reductase in phenobarbital-treated rats.     

The Effect of Dietary Protein on the Renal Gluconeogenic Capacity of Rats

Kidney cortex slices and homogenates of rats fed a high protein diet for 7 to 14 days had higher gluconeogenic capacity from fructose or oxaloacetate and fructose 6-phosphate or fructose 1, 6-diphosphate, respectively, than those of rats fed a high carbohydrate diet containing adequate protein. Levels of gluconeogenic enzymes, especially glucose 6-phosphatase and phosphoenolpyruvate carboxykinase, are good indicators of an increased capacity of renal gluconeogenesis of rats fed the high protein diet. Activities of renal glycolytic enzymes and glutamic-oxaloacetic and glutamic-pyruvic transaminases did not change and citrate concentrations of rat kidney decreased by feeding the high protein diet. Urinary excretion of ammonia of rats fed the high protein diet increased.     

Effects of Feeding a Histidine-excess Diet and Subsequent Starvation on Liver and Muscle Glycogen,and on Serum Glucose

The effects of feeding with a histidine-excess diet and subsequent starvation on liver and muscle glycogen, and on serum glucose were investigated in young and adult rats.

Feeding with a histidine-excess diet resulted in the accumulation of liver glycogen in both young and adult rats. The hepatic glycogen continued to decrease during starvation, and the liver became almost totally depleted of glycogen after starvation for 48 hr. Glycogen in the liver of young rats starved for 24 hr after previous feeding with a histidine-excess diet was significantly higher than that of young rats starved for 24 hr after previous feeding with a basal diet.

Muscle glycogen after feeding and subsequent starvation was not affected by the types of diets fed previously, muscle glycogen during starvation showing a slight decrease in young rats and a slight increase in adult rats.

Feeding with a histidine-excess diet caused a significant decrease of serum glucose in young rats, but not in adult rats. Serum glucose in young rats was markedly reduced by starvation after previous feeding with a basal diet, but not after previous feeding with a histidine-excess diet. In adult rats, there were no changes in serum glucose between rats starved after feeding with either a basal diet or a histidine-excess diet, and serum glucose was decreased slightly by starvation after feeding with the test diets.

The overall results indicate that the maintenance of serum glucose in young rate even during starvation after previous feeding with a histidine-excess diet might be partially concerned with the export of glucose from the accumulated glycogen in the liver due to the diet.     

Lysine maintenance requirement and efficiency of its utilisation in young pigs as estimated by comparative slaughter technique

An experiment was carried out on weaner pigs (initial BW 10.8 kg) to estimate the maintenance requirement for lysine (Lys) and its marginal efficiency of utilisation using a comparative slaughter technique. Three groups of six pigs each were fed purified diets for 21 days supplying Lys at 19.5, 78 or 195 mg/kg W0.75, which corresponded to 50, 200 or 500% of the assumed maintenance requirement. All other essential amino acids were given at 50% excess. At the end of the experiment, pigs were killed for whole-body nitrogen (N) and amino acid analysis. A representative group of six pigs was analysed at the beginning of the experiment. Based on regression equations, relating Lys or N retention to Lys intake, Lys requirement for zero Lys retention was estimated to be 121 mg/kg W0.75, while Lys requirement corresponding to zero N retention was 41.7 mg/kg W0.75. At N equilibrium, the pigs lost 65 mg of Lys per kg W0.75 daily while at zero Lys retention, the daily N retention was 156 mg/kg W0.75 . The marginal efficiency of lysine utilisation was 0.91. It is concluded that zero lysine retention is a better criterion of lysine maintenance requirement than zero N retention.     

Effect of wheat bran on excretion of radioactively labeled estradiol-17 beta and estrone-glucuronide injected intravenously in male rats.

Urinary and fecal estrogen excretion were studied in male rats fed a non-fiber wheat starch diet (dietary fiber less than 1%; NF group; n = 4), a low-fiber wheat flour diet (dietary fiber 2%; LF group; n = 4) or a high-fiber wheat bran diet (dietary fiber 11.6%; HF group; n = 3). Short-term effects of the experimental diet on estrogen excretion were studied after i.v. injection of 5 microCi (0.185 MBq) of [14C]estradiol-17 beta (E2) into the tail vein of the rats fed the diets for 2 days. After 3 weeks on the experimental diets, the long-term effects were studied after injection of 5 microCi of [14C]E2 and 10 microCi of [3H]estrone-3-glucuronide (E1-gluc). The diet was found to affect estrogen excretion. The short-term effect indicated that rats fed the HF diet excreted a relatively large amount of labeled compounds in the feces during the first day after injection, while rats fed the NF or the LF diets excreted about half that amount over the same period. On the other hand, urinary excretion of labeled compounds was significantly higher in the NF and LF rats. The long-term effect resulted in steeper slopes (P less than 0.05) of the fecal excretion profiles of rats fed the HF diet as compared with rats fed the NF and LF diets, indicating an accelerated fecal excretion of labeled compounds in the HF rats. The kinetic profiles of 14C and 3H radioactivity in blood plasma indicated a fast decrease (t1/2 of less than 2 min) for both [14C]E2 and [3H]E1-gluc. It was concluded that, owing to the short-term effect of wheat bran intake, during the first 24 h after i.v. administration relatively large amounts of radioactively labeled compounds are excreted in feces of rats fed the HF diet. In contrast, excretion is lower in urine of these rats. When the microflora is adapted to the experimental diet the wheat bran diet still results in an accelerated fecal excretion of labeled compounds, which might be attributed to an interruption of the enterohepatic circulation of estrogens. This might result in lowered plasma and/or tissue estrogen levels and hence a decreased exposure of estrogen-sensitive tissue to estrogens, which might decrease risk on mammary (breast) cancer development.     

Effect of dietary protein level and source on bone mineralization in rats

Bone mineralization was studied in rats. Animals were divided into three feeding groups: LCP - diet with 13.5% crude protein in DM (5% of gluten, 10% of casein), HCP - diet with 21.2% CP in DM (8% of gluten, 10% of casein), and LSM - diet based on grain meals and meat-bone meal (21% CP in DM). After 28 days feeding, animals were euthanased by cervical dislocation and femur bones were collected, weighed and kept frozen until analyses. Diets with 21% protein (HCP, LSM) significantly increased weight of femur bones. Despite of the substantially higher ash level (7.1%) in the LSM diet than in the LCP diet (3.4%), rats of both groups had the similar bone concentration of Ca (15.7 +/- 1.1 vs. 17.4 +/- 1.1 g/kg) and Zn (178.7 +/- 7.9 vs. 173.0 +/- 8.5 mg/kg). However bone density in LSM rats was significantly higher than in LCP ones. Although rats fed HCP diet had intermediate bone density, the bone concentration of Ca (11.4 +/- 0.5 g/kg) and Zn (145.1 +/- 2.9 mg/kg) was significantly lower, than in animals fed LCP and LSM diets. This was related to the very wide protein/calcium (37:1 g/g) and protein/zinc (5.3:1 g/mg) ratios in HCP diet. Those ratios were narrowest in the LSM diet: 16.2:1 (CP/Ca) and 2.6:1 (CP/Zn). It can be conluded that protein/mineral ratio in a diet is a very important factor in bone development, besides dietary protein and ash contents itselves.     

A high-selenium diet induces insulin resistance in gestating rats and their offspring

Although supranutrition of selenium (Se) is considered a promising anti-cancer strategy, recent human studies have shown an intriguing association between high body Se status and diabetic risk. This study was done to determine if a prolonged high intake of dietary Se actually induced gestational diabetes in rat dams and insulin resistance in their offspring. Forty-five 67-day-old female Wistar rats (n=15/diet) were fed a Se-deficient (0.01 mg/kg) corn-soy basal diet (BD) or BD+Se (as Se-yeast) at 0.3 or 3.0mg/kg from 5 weeks before breeding to day 14 postpartum. Offspring (n=8/diet) of the 0.3 and 3.0mg Se/kg dams were fed with the same respective diet until age 112 days. Compared with the 0.3mg Se/kg diet, the 3.0mg/kg diet induced hyperinsulinemia (P<0.01), insulin resistance (P<0.01), and glucose intolerance (P<0.01) in the dams at late gestation and/or day 14 postpartum and in the offspring at age 112 days. These impairments concurred with decreased (P<0.05) mRNA and/or protein levels of six insulin signal proteins in liver and muscle of dams and/or pups. Dietary Se produced dose-dependent increases in Gpx1 mRNA or GPX1 activity in pancreas, liver, and erythrocytes of dams. The 3.0mg Se/kg diet decreased Selh (P<0.01), Sepp1 (P=0.06), and Sepw1 (P<0.01), but increased Sels (P<0.05) mRNA levels in the liver of the offspring, compared with the 0.3mg Se/kg diet. In conclusion, supranutrition of Se as a Se-enriched yeast in rats induced gestational diabetes and insulin resistance. Expression of six selenoprotein genes, in particular Gpx1, was linked to this metabolic disorder.     

Fertility response of yearling beef heifers after prebreeding energy manipulation, estrous synchronization and timed artificial insemination

The effect of dietary energy and weight class on the fertility of yearling beef heifers (Angus, Hereford, and Angus x Hereford) was investigated over 2 years. In year 1, heifers (n=58) were classed as heavy (HW; > or =340 kg) or light weight (LW; <340kg) and then assigned to receive either a low (LE; 0.23 kg/day) or high energy (HE; 0.68 kg/day) diet. In year 2, heifers (n=60) were also classified as heavy (> or =335kg) or light weight (<335 kg), but the energy content of the diet was raised so that heifers on the LE and HE were targeted to gain 0.46 and 0.79 kg/day, respectively. Heifers in the four groups, LELW (n=14 and 12), LEHW (n=16 and 17), HELW (n=13 and 15), and HEHW (n=15 and 16) received restricted amounts of concentrate (HE > LE) and free choice hay over 47 or 42 days (year 1 and year 2, respectively). To synchronize estrus, heifers were fed capsules containing MGA (0.5 mg/animal each day) beginning 11 days before the end of the feeding trial (day 0), PGF(2alpha) (25mg i.m.) and estradiol benzoate (Ebeta; 400 microg i.m.) was given on days 8 and 10, respectively. Estrous behavior was observed (days 10 and 11) and all heifers were inseminated on day 11. Following AI, heifers were re-grouped and a bull was introduced (days 27-39) for the second service in both years. Pregnancy diagnosis for the first (days 41-42) and second services (days 69-97) was performed by transrectal ultrasonography. Transrectal ultrasonic observations of ovarian follicle number and size were completed for a subset of heifers (n=5-8) from each experimental group at the end of the feeding trial. The effect of year was not significant for any of the reproductive performance variables measured. The mean ADG was (0.72 +/- 0.04 kg/day) and was greater in LW than HW heifers and in heifers in the HE than LE treatment groups (P <0.05). In heifers receiving the LE diet, ADG was lower in HW than LW heifers (weight x diet; P=0.02; 0.54 +/- 0.04 and 0.62 +/- 0.03 kg/day for HW and LW heifers, respectively). The diameter of the largest follicle was greater in heifers receiving the HE diet (P < 0.05; 11.3 +/- 0.4 mm) than those on the LE diet (10.3 +/- 0.3), and in LW (P <0.05) compared to HW heifers. The HE diet increased the size of the largest follicle in LW but not HW heifers (diet x weight, P <0.05). The percentage of pubertal heifers at the end of the feeding period (59.3%), estrous response (56.4%), conception rate (47.7%), ovulation rate (88.9%), and first service pregnancy rate (36.2%) were not significantly affected by initial weight or diet. There was a tendency for first service pregnancy rates to be greater in LW than HW heifers consuming the LE diet (diet x weight, P <0.1; 54.2 +/- 15 and 30.3 +/- 10% for LELW and LEHW heifers, respectively). Pregnancy rate after two services was greater (P=0.01) in LW (82 +/- 10%) than in HW (64.5 +/- 10%). The LE diet achieved moderate rates of gain and allowed high level of reproductive performance in LW but not HW heifers.     

Energy metabolism and protein balance in growing rats fed different levels of dietary fibre and protein

A study was performed to investigate the effect of different levels of dietary fibre (DF) and dietary protein on visceral organ size, digestibility, nitrogen balance and energy metabolism in rats. Thirty-six male Wistar rats, initial body weight about 76 g, were used in a factorial design consisting of three levels of DF (low, 100 g/kg DM; medium, 250 g/kg DM and high, 290 g/kg DM) and two levels of dietary protein (low, 120 g/kg DM and high, 223 g/kg DM). The added fibre source was soybean hulls and Danish fish meal was used as sole source of dietary protein. Measurements of gas-exchange were done on six rats (one group) while urine and faeces were collected individually. The ratio of food/empty body gain increased (P < 0.05) with increasing DF and decreasing levels of dietary protein. The weight of the digestive tract was larger (P < 0.05) in rats fed the high fibre diet than in those fed the low fibre diet. The digestibility of nutrients and energy decreased linearly with increasing level of soybean fibre (P < 0.05). An increased intake of DF was associated with a concomitant loss of protein and energy to faeces. The microbial degradation of NSP and other unabsorbed carbohydrates caused considerably changes in N metabolism of the colon. In rats fed the low protein diets increased levels of DF decreased N excretion in urine and increased N excretion in faeces, while the ratio of retained/digested protein remained constant. When rats were fed the high protein diet protein retention dropped in response to DF both absolute and relative to digested amount, indicating that energy intake could be a limiting factor. Heat production as a percentage of metabolizable energy (HP/ME) was higher (P < 0.05) in rats fed the low protein diet than in rats fed the high protein diet, but no significant difference was found among DF levels.     

PPARalpha activation and increased dietary lipid oppose thyroid hormone signaling and rescue impaired glucose-stimulated insulin secretion in hyperthyroidism

The aim of the study was to investigate the impact of hyperthyroidism on the characteristics of the islet insulin secretory response to glucose, particularly the consequences of competition between thyroid hormone and peroxisome proliferator-activated receptor (PPAR)alpha in the regulation of islet adaptations to starvation and dietary lipid-induced insulin resistance. Rats maintained on standard (low-fat/high-carbohydrate) diet or high-fat/low-carbohydrate diet were rendered hyperthyroid (HT) by triiodothyronine (T(3)) administration (1 mg.kg body wt(-1).day(-1) sc, 3 days). The PPARalpha agonist WY14643 (50 mg/kg body wt ip) was administered 24 h before sampling. Glucose-stimulated insulin secretion (GSIS) was assessed during hyperglycemic clamps or after acute glucose bolus injection in vivo and with step-up and step-down islet perifusions. Hyperthyroidism decreased the glucose responsiveness of GSIS, precluding sufficient enhancement of insulin secretion for the degree of insulin resistance, in rats fed either standard diet or high-fat diet. Hyperthyroidism partially opposed the starvation-induced increase in the glucose threshold for GSIS and decrease in glucose responsiveness. WY14643 administration restored glucose tolerance by enhancing GSIS in fed HT rats and relieved the impact of hyperthyroidism to partially oppose islet starvation adaptations. Competition between thyroid hormone receptor (TR) and PPARalpha influences the characteristics of GSIS, such that hyperthyroidism impairs GSIS while PPARalpha activation (and increased dietary lipid) opposes TR signaling and restores GSIS in the fed hyperthyroid state. Increased islet PPARalpha signaling and decreased TR signaling during starvation facilitates appropriate modification of islet function.