Early visual experience of food does not appear to reduce subsequent feed neophobia in turkeys.

Turkeys may reduce their feed intake because of neophobia toward a new diet; however, their feeding behavior is not well known. The aim of this study was therefore to investigate the effects of diet color on behavior and feed intake in turkeys. For 2 wk, 2 groups of 1-day-old turkey chicks were fed diets varying in color but of the same composition: light-colored crumbles (LC group) or dark-colored crumbles (DC group). Both groups (total n = 144) were then fed a novel diet of green crumbles for the next 2 wk. On d 30, the original groups were each divided into 3 groups and received light, dark, or green pellets. We postulated that neophobia on d 30 would be reduced for chicks fed 1) green pellets compared with diets of other colors because of the effect of recent experience, and 2) a diet of a color that was previously encountered over the first 2 wk of life. Behavior and feed intake were measured on the days before and during each feed transition at 5 min after the changeover feed to observe the short-term reaction. On the first transition day, birds in the LC group decreased their feed intake significantly at 5 min, unlike birds in the DC group, which increased their feed intake. Exploratory behavior increased in both groups when they received green crumbles on the transition day, indicating a response to the color. The changeover to pellets induced a reduction in feed intake in all groups at 5 min, but, in line with our first hypothesis, behavioral changes were less pronounced in birds receiving green pellets. However, turkeys in the DC group did not eat more dark-colored pellets than those in the other groups, and turkeys in the LC group did not eat more light-colored pellets. In the present experiment, we conclude that previous visual experience did not reduce subsequent feed neophobia but that color continuity facilitated a diet change from one feed form to another.

Sequential feeding with variations in energy and protein levels improves gait score in meat-type chickens.

Feeding broilers by alternating different diets for 1 or 2 days is known as sequential feeding, and it possibly reduces leg problems since it slows down early growth and may enhance general activity. The present study compared continuous feeding with a standard diet (C: metabolisable energy = 12.55 MJ/kg, crude protein = 190 g/kg) with alternations of a high-energy/low-protein diet (E+P-:+7% ME; -20% CP) and a low-energy/high-protein diet (E-P+: -7% ME,+20% CP) and investigated its effects on growth, behaviour and gait score in 352 male Ross broiler chickens. Sequential feeding was carried out during ten 48-h sequential-feeding cycles from 8 to 28 days of age. Three treatments were compared: complete diet (C) and two alternations of diets varying in protein and energy contents (S1: E+P- followed by E-P+; and S2: E-P+ followed by E+P-). Chickens received the same feed during the starter and finisher periods (0 to 7 and 29 to 38 days of age). Body weight (BW), feed intake, general activity and gait score, bone quality and carcass conformation were measured to evaluate leg condition and general performance. Sequential feeding significantly reduced BW at 28 days of age (S1: -9.1%; S2: -3.7%/C group; P < 0.05) and S1 were lighter than S2. In both sequential groups, time spent standing increased (C: 28%; S1:33%; S2: 35%; P < 0.05) and leg abnormalities decreased (mean gait score: C: 2.61; S1: 2.45; S2: 2.38; P < 0.02). This improvement was not related to changes in bone quality. BW at slaughter was impaired in Group S1 only, and the feed conversion ratio throughout the rearing period was not significantly impaired by sequential feeding. However, abdominal fat was higher in the S2 group. Sequential feeding using diets varying in energy and crude protein can be a useful method of reducing leg problems in broilers since it improves gait score without impairing growth performance when used as early as 8 days of age and up to not less than 8 days before slaughter in order to compensate for reduced growth. This improvement can be explained by reduced early growth and enhanced motor activity. However, it appears that the low-energy diet should be given first in order to avoid a reduction in BW at slaughter.

Effects of various energy and protein levels during sequential feeding on feed preferences in meat-type chickens.

Short-term feed preferences were studied in individually caged chickens fed sequentially in order to understand a previously described imbalance in the intake of diets offered. Sequential feeding (SF) was carried out for four 48 h cycles in male broiler chickens. The diets varied in energy (2800 (E-) and 3200 kcal/kg (E+)) and protein (230 (P+) and 150 g/kg (P-)) contents. SF was compared to standard feeding (C) (3000 kcal/kg ME and CP = 190 g/kg). In experiment 1, three treatments were used: C, SE (E- followed by E+) and SE' (E+ followed by E-). Four treatments were used in experiment 2: C, SP (P+ followed by P-), SE and SEP (P+E- followed by P-E+). Total feed intake was measured during the SF period. After this, short-term preferences were evaluated with a choice test on chickens previously fed with the same feeds during the SF period (experienced birds) and in C chickens (naïve birds). In both experiments, total feed intake was similar among treatments and the percentage of each feed consumed was not significantly different from controls (50%). In experiment 1, SE and SE' chickens over-consumed E+ and under-consumed E- diets only during the first 15 min of the fourth cycle. The choice test indicated that experienced chickens preferred E+, while naïve chickens preferred E-. Similarly, in experiment 2, chickens over-consumed E+ and E+P- during the first 15 min of the fourth cycle, but the intake of diets varying in protein content was not different from controls. During the choice test, as in experiment 1, experienced chickens preferred E+, while naïve chickens preferred E-. There was a slight preference for the protein-poor diet in naïve birds and there was no preference in the diet varying in both protein and energy contents. Experience modified choice between feeds varying in energy content but not in protein. When feeds were known, preference for energy affected the feed intake immediately after switching from one diet to the other, although lower with the diet also varying in protein, it did not influence the total intake of each diet. Interactions between the nutritional properties and sensorial cues of feed could explain these results.

Forty-eight-hour cycle sequential feeding with diets varying in protein and energy contents: adaptation in broilers at different ages.

Sequential feeding is a cyclic feeding program with 2 diets for 1 or several days used to induce lower feed costs or to improve welfare quality. The aim of the present study was to investigate the effects of energy [2,800 (E-) and 3,200 kcal/kg (E+)] and protein [230 (P+) and 150 g/kg (P-)] content on daily feed intake and growth in 900 male broiler chickens, and to compare these results with standard feeding (CP = 190 g/kg and ME = 3,000 kcal/kg). Sequential feeding was carried out during 48-h cycles in 2 periods (period 1 = 10 to 17 d of age, period 2 = 18 to 29 d of age). Four treatments were compared during periods 1 and 2: 1) complete diet (C), 2) alternation of diets varying in CP (SP = P+ followed by P-), 3) in energy (S(E) = E- followed by E+), 4) in protein and energy contents (S(EPA) = P+E- followed by P-E+). A fifth treatment (S(EPB)) used an alternation in protein and energy contents during period 2 only. All chickens received the same feed during the finishing period (30 to 35 d of age). Feed intake was similar with sequential feeding and complete feed, but in proportion to total feed intake, chickens overconsumed high energy feeds (E+ and E+P-) during each period, and P- only for period 2 (P < 0.01). During period 2, overconsumption was greater with S(EPA) than S(EPB) (P < 0.01). Weight gain was similar for all treatments during period 1. At 35 d of age, S(E) chickens were heavier than S(EPA) and S(EPB) (P < 0.01). Feed to gain ratio was similar for all treatments for period 1 and increased for S(P), S(EPA), and S(EPB) compared with C and S(E) for period 2 (P < 0.01). Walking ability, carcass conformation, breast yield, and abdominal fat did not differ between treatments, but ultimate pH of breast meat was improved with S(P). In conclusion, growth and slaughtering performances similar to standard feeding can be reached with 48-h cycle sequential feeding using diets varying in protein and energy contents.

Short-term number of pecks and feed intake levels: a link with the physical characteristics of feed in four-week-old turkeys.

Short-term reactions of young turkeys to changes in the physical characteristics of their feed sometimes give rise to problems of adaptation in the field. Specific feeders were designed for this study to automatically count the number of pecks given at feed by 4-wk-old male turkeys during 95-min sessions. The lighting program was intermittent (0140L:0100D). In experiment 1, 4 series of 12 birds were tested 4 times/day from 28 to 31 d of age. Four control turkeys were consistently tested with 1 feed, and 8 experimental turkeys ate 1 of 32 commercial feeds (30 as pellets and 2 as crumbs) with a distinct feed for each test (16 replicates/experimental feed). Feed intake, total number of pecks, and pecking efficiency (mg/peck) were recorded for each test and normalized for each turkey. The effects of series, day, and test were not significant for controls. The number of pecks and pecking efficiency differed among feeds (P < 0.001) but not feed intake. Hierarchical Cluster Analysis for these variables distinguished 3 groups of feed: group 3 (6 crumb and small pellets) resulted in high pecking and low efficiency. However, group 1 (10 feeds) were pecked at less but more efficiently than group 2 (16 feeds) for similar feed intake, although the average sizes of the pellets were similar (6.23 and 6.16 mm, respectively), as were the average bulk density, hardness, resistance to abrasion, and color characteristics of the pellets for both groups. Two feeds of each of these 2 groups were compared in a second experiment for 12 turkeys receiving the 4 feeds successively each day over 4 d in varying order. The turkeys consistently pecked the feeds of group 1 less and less efficiently compared with group 2. The automated measurement of pecking, combined with a more detailed image analysis of feed particles, might enhance the evaluation of the effects of feed technology on the behavior of turkeys and thus become a useful tool for the feed industry.

Broiler short-term feed preferences measured with SRAbox, a new feed choice procedure.

Three dietary compositions and 3 methods of pellet preparation were used in different choice situations to improve our understanding of the factors perceived by broiler chickens in the physical structure of their diet. Within the same visual field, broiler chickens were offered 8 microfeeders containing different pelleted feeds that could be reached from the same position of the bird. Chickens were daily tested during 5-min tests following a 45-min period of feed withdrawal, after adaptation to individual cages and experimental feeders. Two feeds (4 microfeeders/feed in alternate positions) were weighed prior to and after the test. Behavior of the chickens was videotaped during the test to count the number of pecks given to each microfeeder. In a first experiment, 2 feeds of distinct composition were either steam or cold-pelleted. The tests of choice were repeated daily from 22 to 25 and from 35 to 38 d of age on 96 male broiler chickens. Significant preferences were measured from the first test. Similar preferences were measured when chickens received the same choice or alternating choices from one test to another. Differences of feed intake between 2 feeds during 5 min were significantly correlated to differences of number of pecks (R2 = 0.85). In most cases, preferences were established within the first minute of pecking. Steam pellets were significantly preferred to cold pellets for one feed composition but not for the other. Preferences for compositions were consistent whatever the pellet preparation and probably associated with the color of the feeds. A second experiment confirmed that 38-d-old broiler chickens seemed to prefer light colors. Short-term preferences of a chicken for a feed were rather influenced by physical characteristics of feed particles (size, color, hardness) than by the origin of raw materials. Feed pecking may change because of feed composition itself, because of its consequences on color or texture cues, or both.

Analysis of variability in nutrient digestibilities in broiler chickens.

1. Forty commercial broiler chickens from two different breeding origins were used for individual measurements of growth performance from d 7 to d 21. From d 21 to d 24 a balance experiment was carried out for the measurement of metabolisable energy (ME), digestibilities of lipids, starch and amino acids, viscosity of excreta water-extract, and amount of water loss. After this, the weight and length of the different parts of the gastrointestinal tract were measured for each bird. During the experiment, the birds were fed with an experimental diet containing 5 g/kg of guar gum in order to increase the variability of responses. 2. There were no significant (P < 0.05) differences between the two breeds in 21 d live weight, food:gain ratio, ME value or the digestibilities of lipids, starch and total amino acids. Significant (P < 0.05) differences between the two breeds were observed for caecal size, excreta guar gum degradation measured using viscosity measurements, and vent score. 3. Pooling all the individual data, individual ME values were correlated (r2 = 0.33) with individual food:gain ratios, which shows that a great part of ME variation was associated with individual variation. 4. Several significant (P < 0.05) correlations were observed between individual digestibilities and individual anatomical characteristics of the gastrointestinal tract. The most significant were concerned with the duodenum weight:length ratio correlated with ME (r = 0.474) and the caeca weight:body weight ratio correlated with guar gum degradation (r = 0.495). Covariance analyses were carried out when correlations were significant and did not show significant interactions with the breeding origin of chickens.

Increased responsiveness to dietary lysine deficiency of pectoralis major muscle protein turnover in broilers selected on breast development.

It has been previously established that growth and carcass qualities of chicks are modified by genotype and dietary amino acid supply. In this study, we evaluated the effects of lysine deficiency and genetic selection on muscle protein metabolism. Chicks originating from an experimental line selected for breast development (QL) and its control line (CL) were provided ad libitum access to isoenergetic diets containing 20% crude protein but differing in their lysine content (0.75 or 1.01%). Protein fractional synthesis rates (FSR) were measured in vivo in the pectoralis major and sartorius muscles of 3-wk-old chickens (flooding dose of [3H]phenylalanine). Fractional breakdown rates (FBR) were estimated as the difference between synthesis and deposition. Lysine deficiency reduced (P < 0.001) growth performance and muscle weights and increased (P < 0.05) muscle FSR, capacity for protein synthesis (muscle RNA:Protein, Cs) and FBR. Although QL birds grew faster and had heavier pectoralis major muscles than CL birds (P < 0.05), there was no line difference in sartorius weight (P = 0.15). No difference between the lines was observed in sartorius protein metabolism (P > 0.14). In the pectoralis major muscle, chicks of both lines receiving an adequate lysine intake also exhibited similar protein turnover rates. However, in chicks fed the lysine-deficient (0.75% lysine) diet, FSR and Cs were higher in QL than in CL chicks (P < 0.05), and FBR tended (P = 0.07) to be higher in QL chicks. This increased protein turnover in the QL birds on the lysine-deficient diet suggests that the responsiveness of muscle protein metabolism to amino acid supply is modified by genetic selection for breast development.

Muscle protein turnover during early development in chickens divergently selected for growth rate.

To explore the mechanisms involved in the genetic control of muscle growth and protein gain, protein metabolism was assessed in the pectoralis major muscle of two chicken lines selected for either fast or slow growth. Protein synthesis was measured in vivo at various ages from 1 to 4 wk, using a flooding dose of L-[4-3H] phenylalanine. Protein degradation was estimated as the difference between synthesis and deposition. Over the experimental period, BW were about 2-fold greater (P < 0.001), and pectoralis major muscle weights were 2.4- to 3.6-fold higher (P < 0.001), in chicks from the fast-growing line (FGL) than those from the slow-growing line (SGL). Independent of age, absolute rates of protein deposition, synthesis, and breakdown were higher in FGL than in SGL chickens. Fractional rates of muscle protein synthesis clearly decreased with age. When comparing birds of the same age, fractional rates of muscle protein synthesis tended to be lower in the FGL. Fractional degradation rates (KD) were significantly lower in FGL chickens during the first 2 wk of post-natal growth, whereas KD were similar between lines in older chickens. In this experimental model of chicken lines divergently selected for BW, the greatest line-related difference in muscle protein metabolism was in KD, and was observed in the early growth phases.

The effects of dietary protein independent of essential amino acids on growth and body composition in genetically lean and fat chickens.

1. Growth performance between 28 and 49 d of age and carcase composition at 49 d in genetically lean (LL) and fat (FL) broilers fed on diets varying in non-essential amino acid (NEAA) concentrations were compared in 2 experiments. In experiment 1, 3 crude protein (CP) contents (133, 155, and 178 g/kg) were compared. In experiment 2, 4 CP levels (131, 150, 170 and 189 g/kg) were compared. All diets were supplemented with synthetic amino acids to cover the EAA requirement of the LL birds. 2. Weight gains of FL chickens were not affected by dietary treatments, while those of LL increased when CP level increased. 3. Reducing CP content always increased body lipids, abdominal fat and food conversion ratio in both lines in both experiments; however, the effect on abdominal fat was more pronounced in the FL birds. 4. Reducing CP concentration always decreased breast muscle proportion in both lines in both experiments, even when growth rate was not affected by CP. 5. It is concluded that LL chickens require diets more concentrated in NEAA than fat chickens and that there seems to be an effect of NEAA on breast muscle development.

Does excess dietary protein improve growth performance and carcass characteristics in heat-exposed chickens?

The effects of two environmental temperatures (22 and 32 C, constant) and five dietary protein contents (10 to 33% CP) were investigated in 4- to 6-wk-old broiler chickens. High ambient temperature reduced growth rate, feed efficiency, and breast muscle proportion and increased abdominal fat proportion. Irrespective of ambient temperature, increasing dietary protein content improved growth performance and carcass characteristics. At 32 C, there was a greater heterogeneity of the data, and bird responses were lower than at 22 C. We concluded that under conditions of chronic heat exposure, diets containing the highest protein levels, 28% and 33% compared with 20% CP, slightly improved chick performance. However, the effect was low and, in our experimental conditions, modifying dietary protein supply (variations in the total quantity of protein) is not sufficient to help broilers to withstand hot conditions.

Chronic heat exposure alters protein turnover of three different skeletal muscles in finishing broiler chickens fed 20 or 25% protein diets.

Heat-exposed chickens exhibit a lower growth rate and a depressed protein retention which may result from an alteration in protein metabolism. A high-protein diet seems to be beneficial under hot conditions because it tends to improve growth. Effects of high ambient temperature (32 vs. 22 degrees C) and dietary crude protein (25 vs. 20%) on muscle protein turnover were investigated in finishing broiler chickens. At 5-6 wk of age, protein synthesis was measured in vivo in the Pectoralis major, Sartorius and Gastrocnemius muscles (flooding dose of [(3)H]-phenylalanine). Protein breakdown was determined in the same muscles as the difference between protein synthesis and deposition. Chronic heat stress markedly reduced protein synthesis, irrespective of muscle type (P < 0.05). This was mainly related to the lower capacity for protein synthesis (muscle RNA/Protein) (P < 0.01). Chronic heat exposure also decreased protein breakdown in the P. major and Sartorius; this effect was not observed in the GASTROCNEMIUS: Protein synthesis was more affected than breakdown, leading to reduced protein deposition, at least in the P. major and Gastrocnemius muscles. Increasing dietary protein content had no significant impact on muscle protein turnover. Particularly at 32 degrees C, the high-protein diet did not significantly modify either protein synthesis, ribosomal capacity or translational efficiency. However, it favored muscle protein deposition, which was probably related to reduced proteolysis. In conclusion, we showed that chronic heat exposure decreased muscle protein deposition, mainly by reducing protein synthesis. Under these conditions, the impaired protein synthesis was not restored by a 5% higher protein intake.

Comparative responses of genetically lean and fat broiler chickens to dietary threonine concentration.

Genetically lean (LL) or fat (FL) male broiler chicken's were fed on 5 diets containing either 3.80, 4.27, 4.75, 5.22 or 5.70 g true digestible threonine per kg. Threonine deficiency induced a more pronounced reduction in growth in the LL than in the FL but did not influence abdominal fat and breast muscle proportions in either line. Plotting weight gain or protein gain against threonine intake suggests that the requirement of both lines is very similar in terms of mg per g of gain. Thus food intake or appetite should account for differences between genotypes. Requirement for true digestible threonine was estimated as 10.70 mg per g of weight gain or 63.8 mg per g of protein gain, using a linear regression approach. The quadratic polynomial equations suggest that the requirements are 13.9 and 12.4 mg digestible threonine per g of gain for LL and FL respectively.

Effects of chronic heat exposure and protein intake on growth performance, nitrogen retention and muscle development in broiler chickens.

The respective effects of ambient temperature, dietary crude protein and feed intake were investigated in finishing chickens and the consequence of protein supplementation under high temperature conditions was analysed in particular. Heat-related reduction in growth was associated with decreased nitrogen retention (-30 or -35% according to the diet), which could not be explained by the observed lower feed intake alone. Tissue samples performed in 5- to 6-week-old chicks showed varying effects of heat according to the muscles studied: at 32 degrees C, the proportion of Pectoralis major muscle (in percentage of body weight) appeared slightly reduced (reduction lower than 10%), whereas the proportion of two leg muscles were increased (+10 to +15% for the Sartorius muscle; +5% for the gastrocnemius muscle). At 32 degrees C, providing a high protein diet significantly (P < 0.05) increased weight gain and feed efficiency, and slightly improved whole body protein deposition.

Response of chick lines selected on carcass quality to dietary lysine supply: live performance and muscle development.

Broiler carcass quality can be improved by conventional selection techniques. In this regard, an experimental "quality" line (QL) was selected for high breast meat yield. We analyzed the effects of this selection on the dietary lysine requirement in chicks from 0 to 3 wk. Control (CL) and QL chicks were provided ad libitum access to isoenergetic diets containing 20% crude protein but differing in their lysine content (0.75, 0.88, 1.01, and 1.13%). Two-way ANOVA showed a significant effect (P < 0.01) of genotype on body weight, growth rate, feed intake, and weight of Pectoralis major and Gastrocnemius muscles. Conversely, the Sartorius muscle weight was not modified (P = 0.21) by genotype. Lysine deficiency markedly reduced body weight, growth rate, and feed intake, and increased feed conversion ratio (P < 0.001). Low dietary levels of lysine also depressed the weight of Gastrocnemius, Sartorius, and P. major (P < 0.001). The body or muscle weight response to diet lysine concentration depended on the line, with QL chicks appearing less sensitive to lysine deficiency. Consequently, their dietary requirements could be lower. Finally, when weight gain and P. major muscle protein deposition were plotted against lysine intake, QL chicks appeared to be more efficient than CL chicks. The underlying mechanisms responsible for this await clarification.

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.