Effect of dietary protein quality, feed restriction and short-term fasting on protein synthesis and turnover in tissues of the growing chicken

Effect of an immune challenge and two feed supplements on broiler chicken individual breast muscle protein synthesis rate

Optimization of broiler chicken breast muscle protein accretion is key for the efficient production of poultry meat, whose demand is steadily increasing. In a context where antimicrobial growth promoters use is being restricted, it is important to find alternatives as well as to characterize the effect of immunological stress on broiler chicken's growth. Despite its importance, research on broiler chicken muscle protein dynamics has mostly been limited to the study of mixed protein turnover. The present study aims to characterize the effect of a bacterial challenge and the feed supplementation of citrus and cucumber extracts on broiler chicken individual breast muscle proteins fractional synthesis rates (FSR) using a recently developed dynamic proteomics pipeline. Twenty-one day-old broiler chickens were administered a single 2H2O dose before being culled at different timepoints. A total of 60 breast muscle protein extracts from five experimental groups (Unchallenged, Challenged, Control Diet, Diet 1 and Diet 2) were analysed using a DDA proteomics approach. Proteomics data was filtered in order to reliably calculate multiple proteins FSR making use of a newly developed bioinformatics pipeline. Broiler breast muscle proteins FSR uniformly decreased following a bacterial challenge, this change was judged significant for 15 individual proteins, the two major functional clusters identified as well as for mixed breast muscle protein. Citrus or cucumber extract feed supplementation did not show any effect on the breast muscle protein FSR of immunologically challenged broilers. The present study has identified potential predictive markers of breast muscle growth and provided new information on broiler chicken breast muscle protein synthesis which could be essential for improving the efficiency of broiler chicken meat production. SIGNIFICANCE: The present study constitutes the first dynamic proteomics study conducted in a farm animal species which has characterized FSR in a large number of proteins, establishing a precedent for biomarker discovery and assessment of health and growth status. Moreover, it has been evidenced that the decrease in broiler chicken breast muscle protein following an immune challenge is a coordinated event which seems to be the main cause of the decreased growth observed in these animals.

A novel dynamic proteomics approach for the measurement of broiler chicken protein fractional synthesis rate

RATIONALE

The study of protein synthesis in farm animals is uncommon despite its potential to increase knowledge about metabolism and discover new biomarkers of health and growth status. The present study describes a novel dynamic proteomics approach for the measurement of protein fractional synthesis rate (FSR) in broiler chickens.

METHODS

Chickens received a 10 g/kg oral dose of ² H₂ O at day 21 of their life. Body water ² H abundance was measured in plasma samples using a portable Fourier transform infrared spectrometer. Free and protein-bound amino acids (AAs) were isolated and had their ² H enrichment measured by gas chromatography with mass spectrometry (GC/MS). Peptide ² H enrichment was measured by proteomics analysis of plasma and muscle samples. Albumin, fibrinogen and muscle protein FSR were calculated from GC/MS and proteomics data.

RESULTS

Ala appeared to be more enriched at the site of protein synthesis than in the AA free pools. Glu was found to be the AA closest to isotopic equilibrium between the different AA pools. Glu was used as an anchor to calculate n(AA) values necessary for chicken protein FSR calculation in dynamic proteomics studies. FSR values calculated using proteomics data and GC/MS data showed good agreement as evidenced by a Bland-Altman residual plot.

CONCLUSIONS

A new dynamic proteomics approach for the measurement of broiler chicken individual protein FSR based on the administration of a single ² H₂ O oral bolus has been developed and validated. The proposed approach could facilitate new immunological and nutritional studies on free-living animals.

Fasting and Its Impact on Skin Anatomy, Physiology, and Physiopathology: A Comprehensive Review of the Literature

Skin serves as the first protective line and barrier of the body. Like many other organs, skin can be affected by several disorders in response to external factors such as pathogens, ultraviolet light, and pollution, as well as endogenous alterations related to aging and/or oxidative stress disturbance. Researchers have reported new insights into how skin cells are altered in response to caloric restriction diets in mammals. One of the most well-known caloric restriction diets is the Ramadan intermittent fasting, which is a radical change in the diet plan of practitioners for the period of one lunar month. Ramadan fasting represents the fourth of the five pillars of the Islamic creed. Even though infirm individuals are waived to take part in this religious duty, patients with various health problems, including those with different skin disorders, might choose to share this event with peers and family members. No standardized protocols or guidelines exist, however, to advise their physicians on the proper management of their patients' condition during fasting. With an increasing Muslim population living in Western countries, this topic has started to draw substantial attention, not only of Middle-Eastern physicians, but also of clinicians in the West. For this purpose, we carried out a comprehensive overview on the topic. Our main findings are that: (1) there is a strong need for evidence-based suggestions and guidance. Literature on the impact of the Ramadan fasting, as well as of other kinds of fasting, on skin diseases is scarce and of poor quality, as well as the information available from the Internet; (2) patients willing to fast should be advised about the importance of taking proper treatments or consider alternative options including administration of trans-dermal/topical drugs, as they are permitted during daylight hours. Further, non-compliance has important, clinical and economic implications for an effective patient management.

Estimation of endogenous amino acid losses in growing chickens given soya-bean meal supplemented or not with DL-methionine

An experiment was carried out in growing chickens to study the effect of supplementation of a semi-synthetic diet containing soya-bean meal as the sole protein source with DL-methionine, to improve its biological value, on the excretion of endogenous protein and amino acids measured in lower ileum and total tract using traditional methods. Thirty-two White Rock male broilers (10 days old) were randomly divided into eight groups each of four birds, of similar body weight (mean live weight: 142·8 (s.e. 0·68) g), and individually housed in metabolism cages. Following a paired-feeding design based on metabolic body weight (kgM0·75), each group of birds was given, for an experimental period of 20 days, each of four levels of protein (60, 120, 180 or 240 g/kg; 5 days each) in two groups of isoenergetic (14·5 kJ metabolizable energy per g dry matter) and semi-synthetic diets based on soya-bean meal, either not supplemented or supplemented with 2 g/kg DL-methionine (diets S and SM, respectively). After 3 days of each treatment excreta were collected for 48 h, frozen and stored at –20ºC. At the end of the fourth treatment three chickens of each group were killed and their lower ileal contents collected. The remaining chick of each treatment was fasted for 24 h and given a protein-free diet for 8 days and excreta were collected for the last 4 days. Then (day 39 of age), chickens were killed and lower ileum contents removed and stored at –20ºC. Samples of excreta and lower ileum contents were subjected to nitrogen (N) analysis by Kjeldahl procedure and amino acid (AA) analysis by high-performance liquid chromatography. Supplementation with DL-methionine of the soya-bean meal-based diets halved total tract endogenous AA losses. Regression analysis produced a higher estimation of ileal and faecal endogenous AA excretion than feeding a protein-free diet. Endogenous AA excretion determined in the lower ileum was higher than in excreta no matter which estimation procedure was utilized. In conclusion, supplementation of dietary protein with the first limiting AA to improve its protein quality, causes an important drop in endogenous AA losses, that may have an important effect on the N economy and energy requirements in poultry. The use of regression analysis on excreta data where graded amounts of protein are given to growing chickens, seems a suitable method for determining endogenous AA losses provided that good quality proteins are used.

The effect of nutritional status and muscle fiber type on myogenic satellite cell fate and apoptosis

Satellite cells (SC) are multipotential stem cells that can be induced by nutrition to alter their cellular developmental fate, which may vary depending on their fiber type origin. The objective of the current study was to determine the effect of restricting protein synthesis on inducing adipogenic transdifferentiation and apoptosis of SC originating from fibers of the fast glycolytic pectoralis major (p. major) and fast oxidative and glycolytic biceps femoris (b. femoris) muscles of the chicken. The availability of the essential sulfur amino acids Met and Cys was restricted to regulate protein synthesis during SC proliferation and differentiation. The SC were cultured and treated with 1 of 6 Met/Cys concentrations: 60/192, 30/96 (control), 7.5/24, 3/9.6, 1/3.2, or 0/0 mg/L. Reductions in Met/Cys concentrations from the control level resulted in increased lipid staining and expression of the adipogenic marker genes peroxisome proliferator-activated receptor gamma and stearoyl-CoA desaturase during differentiation in the p. major SC. Although b. femoris SC had increased lipid staining at lower Met/Cys concentrations, there was no increase in expression of either adipogenic gene. For both muscle types, SC Met/Cys, concentration above the control increased the expression of peroxisome proliferator-activated receptor gamma and stearoyl-CoA desaturase during differentiation. As Met/Cys concentration was decreased during proliferation, a dose-dependent decline in all apoptotic cells occurred except for early apoptotic cells in the p. major, which had no treatment effect (P < 0.05). During differentiation, decreasing Met/Cys concentration caused an increase in early apoptotic cells in both fiber types and no effect on late apoptotic cells except for an increase in the p. major 7.5/24 mg/L of Met/Cys treatment. In general, the viability of the SC was unaffected by the Met/Cys concentration except during proliferation in the p. major 0/0 mg/L of Met/Cys treatment, which increased SC viability. These data demonstrate the effect of nutrition on SC transdifferentiation to an adipogenic lineage and apoptosis, and the effect of fiber type on this response in an in vitro context.

The effects of early-age thermal manipulation and daily short-term fasting on performance and body temperatures in broiler exposed to heat stress

This study was conducted to investigate the effects of thermal manipulation at 5 days of age and short-term fasting during the warmest part of the day on responses to prolonged heat stress of broilers. A total of 240-day-old Ross 308 female broiler chicks were divided into three groups: control, thermal manipulation (chicks were exposed to 36 °C for 24 h at 5 days of age) and short-term fasting during the warmest part of the day (10.00-17.00 h). Prolonged heat stress was induced daily from 28 to 42 days by heating until the ambient temperature reached 32-35 °C between 10.00 and 17.00 h. Both thermal manipulation and short-term fasting resulted in a decrease in rectal temperatures and haematocrit values at 35 and 41 days of age. Thermal manipulation improved body weight, feed consumption and feed conversion. However, short-term fasting caused a reduction in body weight and a deterioration in feed conversion. Short-term fasting lowered the percentages of carcass, whereas thermal manipulation highered breast yield. Both thermal manipulation and short-term fasting decreased heart mass and abdominal fat.

Free amino acid concentrations in plasma, muscle and liver as indirect measures of protein adequacy in growing chickens

An experiment was carried out to study the effect of changes in either the quality or the quantity of dietary protein intake on the free essential amino acid profiles in plasma, muscle or liver of growing chickens. Following a randomized paired-feeding design based on metabolic body weight (kg M0·75), White Rock male broilers were allocated to one of three isoenergetic (14·5 kJ metabolizable energy per g dry matter (DM)) semisynthetic diets containing different levels of protein (60, 120, 180 or 240 g/kg DM). All diets were based on soya-bean meal, as the sole source of protein, either unsupplemented (diets S) or supplemented with 20 g/kg L-lysine (diets SL) or 2 g/kg DL-methionine (diets SM). Samples of blood, biceps muscle and liver were taken and amino acid analysis was determined by high performance liquid chromatography. Plasma was only adequate to detect the effect of the supplementation with methionine to balance the dietary amino acid (AA) profile. Plasma concentrations of free methionine significantly increased as a result of the supplementation with methionine (P < 0·001) and remained unaffected by the amount of protein ingested. When lysine was added to diets S to induce an AA imbalance, a significant increase in muscle concentrations of free valine, isoleucine and phenylalanine (P <0·05) and a significant decrease in liver concentrations of free arginine and phenylalanine were observed (P<0·05). The supplementation with DL-methionine gave rise to a significant fall in the concentrations of free histidine, glycine and threonine (P < 0·05) and increased those of isoleucine and methionine in the skeletal muscle (P < 0·05), while in liver it significantly lowered the concentrations of free arginine, valine, leucine, phenylalanine and methionine (P < 0·001 to P < 0·05) and raised that of free glycine (P < 0·001). The ratios lysine: phenylalanine, lysine: valine and methionine: glycine in muscle together with that of methionine: glycine in liver seem to be appropriate indexes of the adequacy of the dietary AA profile to requirements.

Muscle (pectoralis major) protein turnover in young broiler chickens fed graded levels of lysine and crude protein

An evaluation of muscle (pectoralis major) protein turnover using the phenylalanine flood dose technique was assessed in broiler chicks fed graded dietary lysine levels with CP at 170, 210, 250, and 290 g/kg diet. Chicks at 21 d old were injected with 1 mL/100 g BW of a phenylalanine solution (120 micromol L-[ring-2H5)]-phenylalanine). Muscle protein gain was assessed in chicks at 19 and 23 d of age. No differences were found in weight gain at lysine levels higher than 1.22% of the diet. Dietary lysine levels affected fractional synthesis rate (FSR, %/ d) of muscle with 170 and 210 g of CP/kg diet but not with 250 and 290 g of CP/kg. However, there was increasing FSR with increasing diet lysine levels at 290 g of CP/ kg. Breast muscle protein deposition (absolute growth rate, AGR, mg/d) reached a plateau with 1.22% dietary lysine at CP levels of 170,210, and 290 g/kg diet, confirming the observation on gross muscle weight. In terms of absolute synthesis rate/AGR with minimal absolute breakdown rate (ABR), the diet containing 210 g of CP/kg with 1.22% lysine was the most appropriate for chicks to 21 d. Levels of lysine influenced protein synthesis more so than protein degradation. These data suggest that both protein synthesis and breakdown increase at levels of dietary lysine and CP above those required for maximizing growth.

Is ribosomal capacity a potential metabolic marker of muscle development? Measurement by muscular biopsy

Metabolic markers of muscle metabolism could help geneticists and nutritionists predict the breast meat development of chickens. The aim of the current study was to test the ribosomal capacity (CS), a potential metabolic marker, and to evaluate a simple biopsy method on the pectoralis major muscle. Ribosomal capacity was measured in three commercial meat chicken genotypes differing in their growth rate. Fast-, medium-, and slow-growing male chickens were fed using three commercial dietary programs of increasing energy and protein concentration (nine treatments). Biopsy was performed at 4 wk of age on the p. major 12 chickens per treatment. Fast-, medium-, and slow-growing chickens were slaughtered at market weight, i.e., 6, 8, and 12 wk of age, respectively, and breast meat (right and left p. major + minor) was dissected. A significant reduction in BW at slaughter (-1 to -3%) and breast meat yield (-4%) occurred only in biopsied medium-growing chickens but not in the other two types. Slow-growing chickens had a significantly lower CS (8.75 microg/mg) than the two other chicken types (9.40 and 9.46 microg/mg for fast- and medium-growing chickens, respectively). No significant dietary effect or interaction of dietary treatment with genotype was measured. The CS was not significantly correlated to breast meat development. Under conditions of the present experiment, CS may not be a relevant marker of subsequent breast meat development at 4 wk of age. The biopsy technique can easily be applied to other markers.

Muscle and liver protein metabolism in rats fed raw or heat-treated pea seeds

Raw or extruded pea (Pisum sativum, cv. Ballet) diets with or without supplementary amino acids were fed for 15 days to young growing rats and the effects on tissue weights, liver and muscle protein metabolism and hormone levels monitored. Body weight gain, liver and gastrocnemius muscle weights and protein contents were reduced and some key hormones altered when rats were fed unsupplemented raw pea diets. This appeared to be a result of amino acid deficiencies in the diet, the action of antinutritional factors and the refractory nature of the reserve proteins and other seed components. However, this did not in itself improve the nutritional performance of the rats due to the overriding effects of the amino acid deficiencies in the pea diets. After supplementation, extruded peas supported much higher rates of growth and skeletal muscle deposition than did supplemented raw peas. Despite this, the weight gains remained less than achieved on a high quality control diet. Protein synthesis and degradation rates in skeletal muscles and total protein contents were similar to control values. The lower growth rate did not appear to be due to impaired deposition of skeletal muscle. Deposition of other body components, possibly lipids, may have been lowered by supplemented extruded pea diets. Liver protein levels were reduced in rats fed supplemented raw peas and blood corticosterone was elevated. In conclusion, extrusion treatment of peas in combination with amino acid supplementation appeared to abolish the negative effects of peas on skeletal muscle deposition.

The measurement of muscle protein synthesis in broilers with a flooding dose technique: use of 15N-labelled phenylalanine, GC-MS and GC-C-IRMS

An experiment was carried out to measure fractional muscle protein synthesis rates (k(s)) in broilers with injection of a flooding dose of phenylalanine (1 ml/100 g body weight of 150 mM phenylalanine; 38 atom percent excess (APE) [15N]phenylalanine). K(s) was calculated from the [15N] enrichment in phenylalanine of tissue-free and protein-bound phenylalanine using both gas chromatography mass spectrometry (GC-MS) and gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) for measurements after a 10 min isotope incorporation period. The tertiary-butyldimethylsilyl (t-BDMS) derivatives of phenylalanine were used for gas chromatographic separation in both systems. GC-MS and GC-C-IRMS were calibrated for a range of 7 to 37 [15N]APE and 0 to 0.62 [15N]APE, respectively, and for sample sizes of 0.45 to 4.5 nmol phenylalanine and 7 to 40 nmol phenylalanine, respectively. Reproducibility of standards as a measure of precision varied from 0.06 to 0.29 [15N]APE and from 0.0004 to 0.0018 [15N]APE in GC-MS and GC-C-IRMS, respectively. K(s) was measured in the m. pectoralis major of broilers fed rye based diets (56%) which were provided either unsupplemented (-) or supplemented (+) with an enzyme preparation containing xylanase. K(s) in breast muscles was significantly increased from 21.8%/d to 23.9%/d due to enzyme supplementation. It can be concluded from the study that the measurement of protein synthesis in broilers with the flooding dose technique can be carried out by using [15N]phenylalanine, GC-MS and GC-C-IRMS.

Dietary alterations in protein, carbohydrates and fat increase liver protein-turnover rate and decrease overall growth rate in the rainbow trout (Oncorhynchus mykiss)

We have determined the protein-turnover rates and nucleic-acid concentrations in the liver of trout (Oncorhynchus mykiss) fed on two different isocaloric diets: low-protein/high-fat and non-carbohydrate/high-fat. Compared to controls, the partial replacement of protein with fat significantly decreased the protein accumulation rate and protein-retention efficiency in the liver whilst increasing the fractional protein-synthesis and protein-degradation rates as well as protein-synthesis efficiency. The complete replacement of carbohydrates with fat significantly lowered the protein-accumulation rate and protein-retention efficiency, but enhanced both the protein-synthesis and protein-degradation rates as well as protein-synthesis capacity. The protein:DNA and RNA:DNA ratios decreased considerably on both diets. Total DNA decreased in fish on a low-protein/high-fat diet but did not change in those on a non-carbohydrate/high-fat diet. The absolute protein-synthesis rate registered no significant change under any of the nutritional conditions. Both the experimental diets did however raise the fractional protein-synthesis rate significantly, due to enhanced protein-synthesis efficiency when protein was partially replaced with fat and to enhanced protein-synthesis capacity when carbohydrates were completely replaced with fat. Our results show the capacity of the liver to adapt its turnover rates and conform to different nutritional conditions. They also point to the possibility of controlling fish growth by dietary means.

Replacement of soybean oil with tallow in rye-based diets without xylanase increases protein synthesis in small intestine of broilers

We examined the effects of dietary fat type (10% of either soybean oil, S, or beef tallow, T)(3) and xylanase supplementation (-, without; +, with 1 g of Avizyme 1300 per kg diet) in rye- based diets (56%) on tissue protein synthesis in male broilers. Birds were injected with a large flooding dose of a phenylalanine solution (150 mmol/L, 38 atom percentage excess [(15) N] phenylalanine) and tissues were obtained after a 10-min incorporation period. [(15) N]-enrichment in tissue free phenylalanine and tissue protein bound phenylalanine were measured by gas-chromatography mass-spectrometry and by gas-chromatography combustion isotope ratio mass-spectrometry, respectively in order to calculate tissue specific fractional rates of protein synthesis (k(s)). The k(s) (%/d) in (S-), (S+), (T-) and (T+)-fed birds were 56, 64, 84 and 61 (SEM = 3.7) in duodenum, 51, 52, 75 and 58 in jejunum (SEM = 3.1), 66, 67, 105 and 68 (SEM =7.0) in jejunal mucosa cells, 53, 56, 68 and 50 (SEM = 3.7) in ileum and 52, 45, 118 and 39 (SEM = 20.2) in pancreas, respectively. Significant fat, enzyme or interaction effects in these tissues were mainly caused by the elevated k(s) in (T-)-fed birds which was closely associated with intestinal viscosity. We conclude that the effect of soluble nonstarch polysaccharides (NSP) and of NSP-hydrolyzing enzymes may be explained partially by modification in tissue protein synthesis of the intestinal tract.

Various macronutrient intakes additively stimulate protein synthesis in liver and muscle of food-deprived chicks

We investigated the influence of refeeding food-deprived chicks with either protein, carbohydrate, fat or combinations thereof on the rates of liver and muscle protein synthesis. After 2 d of food-deprivation, chicks were given individual or mixed protein, carbohydrate and fat. At 30 min after refeeding, the protein fractional synthesis rate (K(s)) was measured by a large dose injection of L-[2,6-(3)H]phenylalanine. When chicks were food-deprived for 2 d, liver K(s) was 67% lower and muscle fractional synthesis rate was half that of well-fed controls. Upon refeeding starved chicks a complete diet, K(s) in the liver and muscle returned to the level of fed controls within 30 min. When food-deprived chicks were refed protein alone or two of the three macronutrients, liver and muscle K(s) were significantly higher than those in the starved group. There was no effect of refeeding with carbohydrate or fat alone. Plasma glucose concentration was significantly greater than in fed or starved groups in chicks refed the complete diet, carbohydrate or carbohydrate mixed with either protein or fat. Refeeding chicks with the various macronutrients did not affect the plasma insulin or insulin-like growth factor-I concentrations. These results suggest that intakes of individual macronutrients additively increase liver and muscle protein synthesis and that the acute increase in muscle protein synthesis after refeeding chicks diets containing the three macronutrients was mainly regulated by the change in ribosomal efficiency.

Natural abundance variations in stable isotopes and their potential uses in animal physiological ecology

Chemical, biological, and physical processes lead to distinctive "isotopic signatures" in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use of naturally occurring stable isotopes as tracers. Here we provide a review of the current and potential uses of naturally occurring stable isotopes in animal physiological ecology. We outline the physical and biological processes that lead to variation in isotopic abundance in plants and animals. We summarize current uses in animal physiological ecology (diet reconstruction and animal movement patterns), and suggest areas of research where the use of stable isotopes can be fruitful (protein balance and turnover and the allocation of dietary nutrients). We argue that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques. We also argue that animal physiologists can make an important contribution to the emerging field of stable isotopes in biology by testing experimentally the plethora of assumptions upon which the techniques rely.

Relative responses of protein turnover in three different skeletal muscles to dietary lysine deficiency in chicks

1. The effect of lysine deficiency was analysed on muscle protein turnover in 2-, 3- and 4-week-old growing broilers. Protein fractional synthesis rates (FSR, in %/d) were measured by a reliable in vivo technique (flooding dose of L-[4-3H] phenylalanine) in the Pectoralis major (PM), the Anterior latissimus dorsi (ALD) and the Sartorius (SART) muscles. Protein fractional breakdown rates (FBR, in %/d) were estimated as the difference between the synthesis rates and the growth rates of tissue protein. 2. Lysine deficiency resulted in significant increases in muscle FSR and FBR. When expressed in absolute rates (g/d), tissue protein deposition was reduced whatever the tissue. This phenomenon was accompanied by decreased protein synthesis (ASR). 3. The protein turnover responsiveness to the lysine deficiency appeared to depend on the studied muscle, since the PM muscle was the most sensitive whereas the SART and ALD muscles presented a lower sensitivity.

Dietary lysine deficiency greatly affects muscle and liver protein turnover in growing chickens

We analysed the respective influences of age and lysine deficiency on skeletal muscle and liver protein turnover. Growing male broilers were fed ad libitum on isoenergetic diets containing 200 g crude protein/kg which varied in their lysine content (7.7 or 10.1 g/kg). Fractional rates of protein synthesis (FSR) were measured in vivo in the liver and the pectoralis major muscle of 2-, 3- and 4-week-old chickens (flooding dose of L-[4-3H]phenylalanine). Fractional rates of proteolysis (FBR) were estimated for the same tissues as the difference between synthesis and growth. Over the 2-week period liver FSR and FBR were unchanged, whereas muscle FSR decreased with age. This developmental decline was related to the lower capacity for protein synthesis (Cs) without any modifications of the translational efficiency. Whatever the age, lysine deficiency resulted in significant decreases in body weight, tissue protein content and tissue protein deposition, apparently because of reduced amounts of proteins synthesized. We recorded a difference in the response of the two tissues to lysine deficiency, the pectoralis major being more sensitive than the liver. When comparing birds of the same age, liver FSR and FBR were not modified by the diet, whereas muscle FSR, Cs and FBR were higher in chicks fed on a lysine-deficient diet than in the controls. Conversely, when chicks of similar weights were compared, the main effect of the dietary deficiency was an increase in muscle FBR. The results suggest that lysine deficiency not only delayed chick development so that protein turnover was affected, but also induced greater changes in metabolism. Thus, the principal mechanism whereby muscle mass decreased appeared to be a change in FBR.

Age-related changes of protein turnover in specific tissues of the chick

The effect of age on muscle and liver protein turnover was analyzed in growing broilers. Protein turnover was compared in the Pectoralis major (PM), the Anterior Latissimus dorsi (ALD), and the Sartorius (SART) muscles, as well as in the liver in broilers at three ages (2, 3, and 4 wk). Protein fractional synthesis rates (FSR, in percentage per day) were measured by a flooding dose of L-[4-3H] Phe. Protein fractional breakdown rates (FBR, in percentage per day) were estimated as the difference between FSR and the gain rates of tissue protein. When expressed in absolute rates (grams per day), tissue protein deposition increased during chick growth (approximately 1.7-fold, whatever the tissue). This phenomenon was accompanied by increased protein synthesis (ASR) and proteolysis (ABR) in the PM and in the ALD muscles as well as in the liver. However, ASR and ABR did not seem to be significantly modified in SART. The FSR in skeletal muscles significantly decreased with age. This developmental decline was associated with decreases in RNA content and RNA: protein ratio (Cs, capacity for protein synthesis). In contrast to muscle, we found no significant variation in liver FSR between 2 and 4 wk of age. In addition, liver Cs and translational efficiencies were not decreased. Finally, in muscle as in liver, FBR did not show any clear age-related pattern.

Effect of dietary protein quality on energy metabolism in growing chickens

A slaughter experiment was carried out to study the effect of dietary protein quality on maintenance energy requirements and energy costs for protein accretion and fat deposition in fast-growing broiler-type male chickens. Three isonitrogenous (200 g crude protein/kg DM) and isoenergetic (14 kJ metabolizable energy (ME)/g DM) semipurified diets based on soyabean meal unsupplemented (diet S) or supplemented with 20 g L-lysine/kg (diet SL) or 2 g DL-methionine/kg (diet SM), in order to promote a decrease or an increase in growth rate respectively, were selected and given at four feeding levels (ad lib. or restricted to 40, 28 and 18 g DM/d, on average) to 10-d-old fast-growing male broiler-type chicks for 2 weeks. Both the efficiency with which ME was used to support growth (kg) and the maintenance requirements (MEm) significantly decreased inversely to the biological value of the dietary protein (kg = 0.660, 0.600 and 0.572; MEm = 597, 522 and 464 kJ/kg W0.75 per d, for diets SL, S and SM respectively). The partial efficiencies of use of ME for protein accretion (kp) or fat deposition (kf) were also inversely related, the former increasing with the quality of the protein offered. An alternative procedure was used to try to overcome the statistical problems inherent in the partition of ME between fat and protein.