Determination of the optimum dose of fats in the food of rats of different ages

Over a 14-day period, male SPF Wistar rats with an initial weight of 60, 200 and 250 g (ages 30, 75 and 90 days) were given diets with a constant protein content (10% casein) and a mounting fat content (10, 15, 20, 25, 30, 40 and 50% margarine, at the expense of the saccharides in the standard diet). The utilization parameter of protein biological value (NPU) for the various diets was determined from protein intake and the body nitrogen values. The reciprocal relation of the intake of the two nutrients was determined on the basis of linearity between th growth parameter NPR and protein and fat intake and, after substituting the optimum protein intake, was used to compute the optimum fat content of the diet. From the aspect of the maximum NPU value the optimum fat contents were 30% for 30-day-old, 15% for 75-day-old and 10% for 90-day-old animals. In all three age groups (according to the growth curve for the standard Larsen diet animals with an equal growth rate of 3 g/day), protein utilization under optimum nutritional conditions was the same. The optimum fat content of the diet computed from the reciprocal relationship of fat and protein intake is in agreement with the value obtained by the biological method - 29.4% (49.5 energy %) for 30-day-old animals, 15,8% (30.4% of the total energy value of the diet) for 75-day-old animals and 11.83% (23.7% of total energy) for 90-day-old rats. By using a biological and a mathematical method, this study contributes to the determination of optimum physiological doses of nutrients.     

Influence of the time of intake of a high fat diet on gluconeogenesis

Male Wistar rats aged 75 and 150 days were given high fat diet (36.5 weight % and 30 weight % fat) over a period of 14 days. The growth (PER, NPR) and utilization (NPU, LPU) parameters of protein biological value and liver phosphoenolpyruvate carboxykinase (PEPCK) activity were determined. In another experiment, the time dependence of liver gluconeogenesis enzyme (PEPCK and fructose-1,6-diphosphatase /FDP-ase/) and transaminase (alanine and aspartate aminotransferase /ALT, AST/) activities during 24 days' administration of the diet were determined. A 14 days' high fat intake had a negative effect on protein utilization in the organism of 75- and 150-day-old animals, which was more pronounced in the younger age group (a bigger drop in net protein utilization /NPU/ and greater stimulation of PEPCK activity). In 150-day-old animals the negative effect of a high fat intake was already manifested on the 6th to 10th day of the diet to the same degree as in the younger animals on the 14th day, as seen from the increase in all the enzyme activities. The paper presents findings on differences in the degree of the negative effect of a high fat intake on protein utilization with reference to age.     

Age-correlation of protein utilization to saccharide intake

Male Wistar rats aged 30, 90, 150 and 360 days were fed ad libitum on diets with an optimum protein and fat content for their respective ages and an increasing saccharide content. Net protein utilization (NPU) was determined from the body nitrogen and protein intake values and the course of gluconeogenesis in the liver was measured by specific phosphoenolpyruvate carboxykinase (PEPCK) activity. According to the growth curve for the standard diet, animals aged 30 and 90 days have a high growth rate (3.245 g/day), 150-day-old rats grow more slowly (1.856 g/day) and 360-day-old animals put on scarcely any weight at all (277 mg/day). In 30-day-old rats, NPU attains maximum values in the presence of a 36% saccharide content in the diet, in 3- and 5-month-old animals in the presence of 51% saccharides and in one-year-old animals in the presence of 41% saccharides in their food. The course of gluconeogenesis also corresponds to these values. PEPCK activity in the youngest age group is greatest in the presence of 31% saccharides in the food, at 90 days it is stimulated in the presence of 31-46% saccharides, at 150 days the decisive concentration is 41 and 46% and at one year proteins are used for saccharide synthesis in diet with a 31 and 36% saccharide concentration. For optimum saccharide values, PEPCK activity is reduced in every age group; together with the maximum NPU values, this indicates that proteins are used for growth and building of the organism at an early age and for the renewal of tissues and organs and maintenance of the organism in adulthood.     

Effect of a high fat intake on protein utilization during ontogenetic development

Male rats (Wistar strain, Velaz, Prague) aged 30, 90 and 150 days were fed 14 days ad libitum on a high fat diet (containing 40% margarine) and their growth (PER, NPR) and utilization (NPU, LPU) parameters of protein (casein) biological value were compared with those of animals given a standard gel containing 10% margarine (the diets were isoenergetic). The course of gluconeogenesis in their liver was also determined by measuring phosphoenolpyruvate carboxykinase (PEPCK) activity. A high fat intake had a negative effect on the growth parameters of protein biological value, PER and NPR, in all three age groups and on the utilization parameters NPU and LPU in 30- and 90-day-old rats. The nonsignificant increase in NPU and LPU in the oldest animals was evidently related to the equal protein intake compared with the control, indicating that proteins need to be utilized more economically in the presence of a raised fat intake; owing to their far lower fat intake compared with 90-day-old animals on a high fat diet, the fat had a less negative effect on their protein utilization than in the younger age group. The negative effect of a high fat intake was confirmed by high activation of gluconeogenesis in 30- and 90-day-old animals and by raised phosphoenolpyruvate carboxykinase activity in 150-day-old rats, in which the supposition that gluconeogenesis would be highly activated if the diet were administered for a period other than 14 days cannot be ignored. The biological and biochemical methods employed in this study can be used with a wider perceptual range of dietary nutrients to determine optimum nutrient values under different conditions.     

Determination of optimum fat intake

In a 14-day experiment, adult rats weighting 250-260 g were given ad libitum diets with a constant protein content [casein - 10 %] and a mounting fat content [margarine - 0, 10, 20, 30 and 40 % - added at the expense of carbohydrates]. The growth parameters of protein biological value - PER and NPR - were determined and together with weight increments in correlation to protein an fat intake [a linear correlation] they were used on the basis of their regression equations to calculate the reciprocal relationships of fat and protein intake [for equality y]. By substituting the optimum protein intake [43.3 g/14 days - according to NPU], the optimum fat intake for adult rats was found to correspond to dietary fat concentrations of 9.72 % [y = weight increments], 12,82 % [y = PER] and 11.83 % [y = NPR]. These results wee verified in a biological experiment in which adult animals, for 14 days, were given a limited amount [31 g/animal per day] of diets containing 10 % protein [casein] an d9, 10, 11, 12, and 13 % fat [margarine - at the expense of carbohydrates] with the aim of studying the effect of a mounting fat intake on optimum protein intake [43.4 g/14 days]. The correctness of the mathematical method for determining the optimum fat intake was verified by a biological method [the optimum net protein utilization , NPU, which is highest in diets containing 11 % fats, i.e. 22.5 % of the total energy value of the diet]. It was also found that this method, both along and in conjunction with other methods [especially the one using the NPR parameter], was suitable for the determination of optimum nutrient values.     

Effect of feed intake on heat production and protein and fat deposition in milk-fed veal calves

Energy requirements for veal calves have not been updated recently despite the increased age at slaughter and the predominance of the Prim'Holstein breed in Europe. The objectives of this study were to determine the effects of four feeding levels (FLs) on protein and fat deposition and heat production in milk-fed calves at three stages of fattening and to determine energy requirements of calves. At each stage, 16 Prim'Holstein male calves (mean body weight (BW): 73.4, 151.6 and 237.4 kg) were fed a milk replacer at 79%, 87%, 95% or 103% of a reference FL. Measurements for one stage were conducted over 4 successive weeks in two open-circuit respiration chambers and consisted of a 6-day nitrogen and energy balance followed by a fasting day for estimating fasting heat production (FHP) of the calves. Heat production (HP) measurements were analyzed using a modeling approach to partition it between HP due to physical activity (AHP), feed intake (thermic effect of feeding (TEF)) and FHP. There was no effect of FL and stage on apparent digestibility coefficients, except for a tendency for increased digestibility coefficient of fat as animals got older. The metabolizable energy (ME)/digestible energy (DE) ratio did not depend on FL but decreased (P < 0.01) as animals got older in connection with marked increases in urinary glucose and urea excretion. The AHP and TEF components of HP were not affected by stage or FL and averaged 8.4% and 7.8% of ME intake, respectively. The FHP, expressed per kg BW0.85, increased with increasing FL, suggesting that also ME requirement for maintenance (MEm) may depend on FL. For an average intake of 625 kJ ME/kg BW0.85 per day (95% of the reference FL), FHP was 298 kJ/kg BW0.85 per day. Energy retention as protein and fat increased with increasing FL resulted in higher BW gain. But the rate of increase depended on stage of growth. The slope relating protein deposition to FL was lower in the finishing phase than in the growing phase, while the slope for lipid deposition was greater. Protein and fat contents of BW gain were not affected by FL but increased as animals got older. From these results, the energy requirements of veal calves are proposed according to a new approach, which considers that MEm (expressed per kg BW0.85) depends on ME intake (kJ/kg BW0.85) according to the following relationship: MEm = 197 + 0.25 × ME intake. The corresponding marginal efficiencies of ME utilization for protein and fat deposition are then 82% and 87%, respectively.     

Nutrition and energetics of the canary (Serinus canarius)

Canaries appear to be primarily seed-eaters, although there are no reports of their feeding ecology in the wild. In captivity, they are offered seed-based diets, preferring to consume seeds such as canary, rapeseed and millet. The mean daily dry-matter intake ranges from 3 to 4 g, which corresponds to a mean gross energy intake of approximately 70 kJ per bird per day. The efficiency of dietary metabolism is high (0.85), which equates to individual metabolizable energy intakes of 45-75 kJ per bird per day. For a canary of average body weight (22 g) the data can be fitted to a regression equation to predict a requirement of 62 kJ ME per day. This corresponds to published information on the energy requirements of other passerine species, but deviates from the predictive equation for poultry. The digestibility values for protein, fat and carbohydrate are similar to those obtained for the budgerigar, although it is likely that the digestibility coefficient is dependent upon the seed type and alimentary tract lipase and amylase activities. Nutrient requirements of canary chicks have not yet been determined, although recent studies have provided data on the nutrient intakes of developing chicks. The newly-hatched canary chick has a rapid growth rate, achieving 90% of its asymptotic body mass by 11 days of age. Gross energy intake is approximately 3 kJ per day following hatching and by day 10 is equivalent to that of an adult canary. It appears that the protein intake should lie between 16.5 and 21.9% of the diet (as is), with peak intake occurring between 8 and 10 days of age.     

Energy and protein requirements of Belgian Blue double-muscled bulls

Energy and protein requirements were determined for Belgian Blue double-muscled (BB dm) bulls based on the results of two feeding trials and a trial with serial slaughtering. The results of the serial slaughter experiment allowed calculation of chemical composition and energy content of the empty body, as well as protein and energy deposition at various live weights between 350 and 650 kg. Protein requirements were calculated based on the protein requirements for maintenance, the protein mass accreted and the efficiency of protein accretion. Efficiency of protein deposition (g protein accretion/g protein intake for accretion) was derived from the feeding experiments based on marginal protein levels; it decreased from 0.53 to 0.44 with increasing live weight. Energy requirements were also derived from the same database. Net energy for maintenance was estimated, with these animals that received an optimum energy/protein ratio, by subtracting the net energy retained from the net energy intake. Requirements were then determined by summation of the energy requirements for maintenance and the energy requirements for accretion. Conclusively, energy and protein requirements were determined for BB dm bulls for live weights from 350 to 650 kg and for different growth rates. As such, surpluses of energy and protein that BB dm animals require compared to other beef breeds, were quantified.     

Determination of the optimum proportion of saccharides in the diet of adult rats

SPF male Wistar rats weighing 250-260 g and aged 90 days were fed 14 days on diets with a constant 10% protein (casein) content, a constant 11% fat (margarine) content and mounting saccharide (rice starch: sugar: potato starch - 6.4: 1.2: 1) contents of 31, 36, 41, 46, 51, 56, 61 and 66%. Protein intake and the body and liver nitrogen values were used to determine the utilization parameters of protein biological value, i.e. NPU (body) and LPU (liver), for the individual diets. Liver gluconeogenesis was also studied by measuring specific phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1.6-diphosphatase (FDP-ase) activity. On the basis of linearity between the growth parameter NPR and protein and saccharide intake we determined the reciprocal relationship of the intake of the two nutrients and used it to compute the optimum saccharide concentration for the diet. The 51% saccharide diet gave the best protein utilization (the maximum (net) protein utilization value) in the 90-day-old rat organism. This was confirmed by the course of gluconeogenesis, which was significantly activated in the presence of 31-46% saccharide diets. By substituting the optimum protein intake in the reciprocal saccharide-protein intake relationship we obtained the optimum saccharide intake, which corresponded to a 49% concentration in the diet. With its use of a biological, biochemical and computation method, the study is a contribution to the determination of optimum nutrient values.     

The effect of lysine intake on energy partitioning and utilization in growing pigs

An experiment utilizing 12 castrated male pigs within a body weight range of 23 - 147 kg was conducted to ascertain whether the alteration of protein quality by varying the level of lysine intake is influencing total energy retention, heat production and therewith efficiency of energy utilization for growth. The animals were allotted to two treatments of a constant medium (11.5 g/d) or high lysine intake (13.5 g/d) level on the basis of an isonitrogenous diet at an energy intake level of 1.3 MJ ME/kg BW0.75. Representing a tool for determining body composition, at target body weights of 35, 55, 80, 115 and 145 kg measurements of deuterium dilution space were undertaken. Protein and lipid accretion were calculated by difference, assuming accretion to contain 23.8 and 39.0 kJ/g, respectively. The results show a significant effect (p < 0.05) between treatment groups for the values of energy retained in protein, thus ensuring the intended alteration by protein quality. Furthermore total energy retention, heat production (difference between ME intake and energy retention) and therewith energy utilization demonstrate independence from the composition of body weight (BW) gain. These observations confirm earlier results, but however, seem to be in contrast to the supposition of a constant efficiency for protein (kp) and fat (kf) accretion, respectively. This may be attributed to a variable kp, in fact to a smaller kp at minor values for protein accretion due to an increased whole body protein turnover. Lacking evidence from experimental data for advantages in using constant values for kp and kf to determine the accurate energy requirement for growth, a uniform value for the efficiency of total energy retention seems to be more adequate.     

The responses of rats to various combinations of energy and protein. II. Diets made from natural ingredients

Natural diets with metabolizable energy levels of 8.5, 10.0, 11.5 or 13.0 MJ/kg and protein:energy ratios of 1:1, 1.33:1, 1.67:1 or 2:1 %:MJ/kg were fed ad libitum for 28 days to male and female weanling rats. Records of food intake and bodyweight were maintained weekly, and at post mortem examination body length, abdominal fat, liver and kidney weights were measured. Food intake was reduced when dietary energy level increased but this reduction was not sufficient to prevent energy intake increasing, especially in males. Female rats showed only small increases in energy intakes as dietary energy levels rose. The increase in energy intake at higher dietary energy levels increased food conversion efficiency, weight gain and abdominal fat deposition. The responses of male rats were greater than females. Protein intake had a smaller and less consistent effect than energy intake. Increased protein:energy ratio resulted in higher absolute and relative liver and kidney weights and greater body length. This reflected the increase of bodyweight gain at higher protein:energy ratios.     

Fatty acid oxidation and fatty acid synthesis in energy restricted rats

The importance of fat oxidation and fatty acid synthesis were examined in rats fed approximately one half their ad libitum food intake for a period of 13 days followed by 7 days of ad libitum feeding (refed rats). This study was undertaken because previous reports demonstrated that refed rats rapidly accumulated body fat. Our results confirmed this observation: refed rats accrued body fat and body weight at rates that were approximately 3 times higher than controls. Evidence for a period of increased metabolic efficiency was demonstrated by measuring the net energy requirement for maintenance over the refeeding period: refed rats had a reduced metabolic rate during the period of energy restriction (approximately 30% lower than control) and this persisted up to 2 days after the reintroduction of ad libitum feeding. The major factor responsible for the rapid fat gain was a depressed rate of fatty acid oxidation. Calculations of protein and carbohydrate intake over the refeeding period showed that the simplest explanation for the decrease in fatty acid oxidation is fat sparing. This is possible because of the large increase in dietary carbohydrate and protein intake during the refeeding period when metabolic rates are still depressed. The increased carbohydrate and protein may adequately compensate for the increasing energy requirements of the ER rats over the refeeding period affording rats the luxury of storing the excess dietary fat energy.     

Quantitative partition of protein,carbohydrate and fat pools in growing pigs

A model combining data from balance experiments with data from oxidation of nutrients demonstrating the pools of protein, carbohydrate and fat and their partition in the body was presented.

Data from more than 200 experiments with growing pigs were used to fill up the “black boxes”; in the model and to discuss the pattern between catabolic and anabolic processes of the different nutrients.

With a ME‐intake of 1.3 MJ/kg^0.75 the proportion of retained protein from the protein pool varied from 50 to 75% depending on the age of animals and the protein quality. At a low protein intake and ME of 0.6 MJ/kg^0.75 the utilization of protein was reduced to about 25% as a substantial part of the protein pool was oxidized.

The carbohydrate group from the protein sources constituted less than 5% of the carbohydrate pool. The oxidation of carbohydrates was between 50–75% of the pool in all experiments, while the rest was used for lipogenesis. Even on a low feeding level the pattern occurred indicating a requirement for specific substances formed in the body.

Lipogenesis constituted 46–96% of the fat pool depending of the amount on digested fat in the different experiments. No oxidation of fat was observed in experiments with pigs (30–90 kg LW) on a high feeding level in spite of the broad variation in the amount of digested fat, indicating a complete storage of the fat pool into body fat. In experiments with piglets (3–9 kg LW) on the same energy intake fat oxidation of about 30% occurred, probably caused by the high energy requirement of the piglets. With a ME‐intake of 0.6 MJ/kg^0.75 the oxidation of fat was higher than the fat pool for pigs between 30–60 kg LW, thereby causing oxidation of body fat to cover the energy requirements.     

Changes in body composition in obese patients on a low-calorie diet

Energy balance was studied on 4 obese hospitalized subjects kept on hypocaloric diet (489 Kcal - 54% CHO, 10,6% Fat, 35,4% Protein) for 18 +/- 3,7 days. Energy expenditure was measured trough heart-rate monitoring (individual calibrations before and after the study were performed) and nitrogen balance was computed to establish protein loss. Individual qualitative composition of body weight loss was then assessed: 71,4 +/- 5,23% could be attributable to fat loss, 9,38 +/- 3,32% to protein loss, 18,2 +/- 5,5% to water loss. Part of this last figure could be attributable to a slight under-estimation of the method utilized to measure the energy expenditure (heart-rate monitoring).     

Determination of the optimum doses of nutrients in a diet.

For 14 days, SPF male Wistar rats with an initial weight of 60 g were given isocaloric diets (1.7 MJ/100 g diet) containing 10% protein (casein) and 5, 10, 25 and 40% fat (margarine). Two utilization parameters of the protein biological value--net protein utilization (NPU) and liver protein utilization (LPU)--were determined from protein intake and body and liver nitrogen. These results were supplemented by a study of the course of the antithetical processes of gluconeogenesis and glycolysis, of the citric acid cycle and transamination processes and of the liver and muscle amino acid spectrum. A high (40%) fat diet significantly reduced the protein biological value parameters NPU and LPU and liver and muscle amino acid values, stimulated gluconeogenesis and inhibited glycolysis and the citric acid cycle, together with associated transamination processes in the liver. Activation of these processes in the muscles provided substrates for increased gluconeogenesis. The negative effect of a low fat + high carbohydrate diet was less marked. The optimum diet for weaned rats is thus a diet containing 10% protein and 10--25% fat. The study, which submits several possible ways of determining optimum nutrient intakes under different physiological conditions shows that diets with more detailed nutrient concentrations should be used.     

Alteration of dietary fat intake to prevent weight gain: Jayhawk Observed Eating Trial

Objective: To examine the effects of ad libitum diets with three distinct levels of fat intake for the prevention of weight gain in sedentary, normal‐weight and overweight men and women. Methods and Procedures: Three hundred and five participants were randomized to one of three diets. The diets targeted <25% of energy from fat (low fat (LF)), between 28 and 32% of energy from fat (moderate fat (MF)), or >35% of energy from fat (high fat (HF)). Participants consumed two meals per day on weekdays and one meal per day on weekends in a university cafeteria over a 12‐week period. Energy and nutrient content of cafeteria foods were measured by digital photography. All meals and snacks consumed outside the cafeteria were measured by dietary recall. All analysis of energy and nutrient content was completed using Nutrition Data System for Research (NDS‐R) version 2005. Results: Two hundred and sixty participants completed the study. LF gained 0.1 ± 3.1 kg, MF gained 0.8 ± 2.5 kg, and HF gained 1.0 ± 2.2 kg and there was no gender or age effect. Longitudinal mixed modeling indicated a significant difference among the groups in weight over time (P = 0.0366). When adjusting for total energy intake, which was a significant predictor of weight over time, the global effect for the group was eliminated. Thus, increasing weight was a function of increasing energy but not increasing percentage of fat intake. Discussion: Energy intake, but not percentage of energy from fat, appears responsible for the observed weight gain. LF diets may contribute to weight maintenance and HF diets may promote weight gain due to the influence of fat intake on total energy intake.     

Production and composition of Iberian sow's milk and use of milk nutrients by the suckling Iberian piglet

Sixteen purebred Iberian (IB) sows were used in two consecutive trials to determine the efficiency of conversion of sow's milk into piglet body weight (BW) gain and the relationship between milk protein and body protein retention and between milk energy yield and body energy retention in the nursing IB piglet. In each trial, four sows were selected in order to evaluate their milk production, litter growth and nutrient balance measurements, together with four additional sows for milk sampling. Litter size was equalized to six piglets. Daily milk yield (MY) was determined weekly by the weigh-suckle-weigh technique over a 34-day lactation period. Piglets were weighed individually at birth and then weekly from day 5 of lactation. Milk samples were collected on days 5, 12, 19, 26 and 34 post partum. The comparative slaughter procedure was used to determine piglet nutrient and energy retention. One piglet from each litter was slaughtered at birth and four on the morning of day 35. Total MY was on average 5.175 ± 0.157 kg/day. The average chemical composition (g/kg) of the milk was 179 ± 4 dry matter, 53.4 ± 1.0 CP, 58.5 ± 3.8 fat, 10.4 ± 0.3 ash and 56.9 ± 2.3 lactose. Milk gross energy (GE) was 4.626 ± 0.145 MJ/kg. Milk intake per piglet tended to increase in trial 2 (832 v. 893 g/day; P = 0.066). Piglet BW gain contained (g/kg) 172.1 ± 1.3 protein, 151.5 ± 3.5 fat, 41.4 ± 0.6 ash and 635 ± 3 water and 10.127 ± 0.126 MJ GE/kg. Throughout the 34-day nursing period, the piglets grew at an average rate of 168 ± 3 g/day. The ratio of daily piglet BW gain to daily MY was 0.195 ± 0.002 g/g and the gain per MJ milk GE intake was 41.9 ± 0.5 g/MJ. The overall efficiency of protein accretion (g CP gain/g CP milk intake) was low and declined in trial 2 (0.619 v. 0.571; P = 0.016). Nutrient and energy deposition between birth and weaning were 27.4 ± 0.5 g/day protein, 24.2 ± 0.8 g/day fat and 1615 ± 40 kJ/day energy. Piglet energy requirements for maintenance were 404 kJ metabolizable energy (ME)/kg BW0.75. ME was used for growth with a net efficiency of 0.584. These results suggest that poor efficiency in the use of sow's milk nutrients rather than a shortage in milk nutrient supply might explain the low growth rate of the suckling IB piglet.     

Long-term effects of a fatty acid synthase inhibitor on obese mice: food intake, hypothalamic neuropeptides, and UCP3

Short-term treatment of lean and obese mice with the fatty acid synthase (FAS) inhibitor, C75, alters expression of hypothalamic neuropeptides thereby reducing food intake, body weight, and body fat. Here we report the long-term effects of C75 on obese (Ob/Ob) mice. A low dose of C75 administered every third day for 30 days reduced food intake by 62% and body weight by 43% whereas body weight of ad lib-fed controls increased by 11%. Loss of body weight correlated with decreased adipose and liver tissue mass. Decreased food intake correlated with decreased expression of hypothalamic neuropeptide mRNAs for NPY, AgRP, and MCH and an increased expression of neuropeptide mRNAs for alphaMSH (i.e., POMC) and CART. Consistent with increased energy expenditure, C75 treatment caused greater weight loss than pair-fed controls and increased expression of skeletal muscle UCP-3 mRNA. Lowered blood glucose was due largely to restriction of food intake. C75 blocked the normal fasting-induced rise in blood free fatty acids and ketones due either to decreased adipose tissue lipolysis and hepatic ketogenesis or increased fatty acid and ketone utilization by peripheral tissues, notably skeletal muscle.     

Precision feeding can significantly reduce lysine intake and nitrogen excretion without compromising the performance of growing pigs

This study was developed to assess the impact on performance, nutrient balance, serum parameters and feeding costs resulting from the switching of conventional to precision-feeding programs for growing–finishing pigs. A total of 70 pigs (30.4±2.2 kg BW) were used in a performance trial (84 days). The five treatments used in this experiment were a three-phase group-feeding program (control) obtained with fixed blending proportions of feeds A (high nutrient density) and B (low nutrient density); against four individual daily-phase feeding programs in which the blending proportions of feeds A and B were updated daily to meet 110%, 100%, 90% or 80% of the lysine requirements estimated using a mathematical model. Feed intake was recorded automatically by a computerized device in the feeders, and the pigs were weighed weekly during the project. Body composition traits were estimated by scanning with an ultrasound device and densitometer every 28 days. Nitrogen and phosphorus excretions were calculated by the difference between retention (obtained from densitometer measurements) and intake. Feeding costs were assessed using 2013 ingredient cost data. Feed intake, feed efficiency, back fat thickness, body fat mass and serum contents of total protein and phosphorus were similar among treatments. Feeding pigs in a daily-basis program providing 110%, 100% or 90% of the estimated individual lysine requirements also did not influence BW, body protein mass, weight gain and nitrogen retention in comparison with the animals in the group-feeding program. However, feeding pigs individually with diets tailored to match 100% of nutrient requirements made it possible to reduce (P<0.05) digestible lysine intake by 26%, estimated nitrogen excretion by 30% and feeding costs by US$7.60/pig (−10%) relative to group feeding. Precision feeding is an effective approach to make pig production more sustainable without compromising growth performance.     

Protein appetite is increased after central leptin-induced fat depletion

Leptin reduces body fat selectively, sparing body protein. Accordingly, during chronic leptin administration, food intake is suppressed, and body weight is reduced until body fat is depleted. Body weight then stabilizes at this fat-depleted nadir, while food intake returns to normal caloric levels, presumably in defense of energy and nutritional homeostasis. This model of leptin treatment offers the opportunity to examine controls of food intake that are independent of leptin's actions, and provides a window for examining the nature of feeding controls in a "fatless" animal. Here we evaluate macronutrient selection during this fat-depleted phase of leptin treatment. Adult, male Sprague-Dawley rats were maintained on standard pelleted rodent chow and given daily lateral ventricular injections of leptin or vehicle solution until body weight reached the nadir point and food intake returned to normal levels. Injections were then continued for 8 days, during which rats self-selected their daily diet from separate sources of carbohydrate, protein, and fat. Macronutrient choice differed profoundly in leptin and control rats. Leptin rats exhibited a dramatic increase in protein intake, whereas controls exhibited a strong carbohydrate preference. Fat intake did not differ between groups at any time during the 8-day test. Despite these dramatic differences in macronutrient selection, total daily caloric intake did not differ between groups except on day 2. Thus controls of food intake related to ongoing metabolic and nutritional requirements may supersede the negative feedback signals related to body fat stores.