Changes in body composition in broilers by a sulfur amino acid deficiency during growth.

In the factorial approach, amino acid (AA) requirements are determined using the AA composition of retained protein, which is assumed to be constant. However, this hypothesis may not be valid because the AA composition of body protein can be affected by the diet. The objective of this study was to quantify the changes in chemical body composition of broilers receiving diets either deficient (TSAA-) or sufficient (TSAA+) in TSAA. Diet TSAA+ was formulated according to the Ross recommendation. Diet TSAA- provided 36% true digestible Met:Lys and 64% true digestible TSAA:Lys, which were, respectively, 34 and 22% lower compared with diet TSAA+. Performance and tissue weight gain between 7 and 42 d of age were not affected by the TSAA supply. In TSAA- chickens, protein gain was lower in the carcass (P < 0.01) and tended to be lower in the empty body (P = 0.06) and pectoralis major muscle (P = 0.10). Compared with TSAA+ chickens, lipid gain in TSAA- chickens was 78% greater in the pectoralis muscle (P < 0.001), 28% greater in abdominal fat (P < 0.05), and 10% greater in the carcass (P = 0.10). In the pectoralis muscle, there was a tendency for an increase in the redness value (a*; P = 0.10). The TSAA supply affected the AA composition of tissues and tissue gain, but the Met and Cys concentrations were changed only in the offal (P = 0.08). The deficient TSAA supply resulted in an increase in the Ser concentration in the empty body, carcass, and pectoralis muscle (P < 0.05). In contrast, it resulted in a decrease in the concentrations of Lys and Glu in the empty body, of Phe, Tyr, Gly, and Glu in the pectoralis muscle, and of Ala in the offal (P < 0.05). This indicates that although chickens cope with a TSAA deficiency predominantly by changing the protein and lipid concentration in the body, the AA composition is also affected. This calls into question the use of a constant ideal AA profile in poultry nutrition.

Insulin signaling in chicken liver and muscle.

This review addresses the control exerted by insulin through its receptor on the general metabolism and gene expression in chicken liver and muscle. Compared with mammals, chickens have similar concentrations of circulating insulin, but still maintain high plasma glucose levels. This may be a consequence of the low sensitivity of the chicken to exogenous insulin. In order to determine whether this low sensitivity is the result of differences in insulin receptor signaling between mammals and birds, insulin receptors have been characterized in several chicken tissues and two insulin receptor substrates (IRS-1 and Shc) have been described in liver and muscle. Compared with mammals current knowledge of insulin signaling in birds is incomplete. This is particularly evident when considering the number of isoforms of the components involved in the insulin cascade (IRSs, AKT, ERK and others) many of which may have not been characterized in the chicken. Despite these shortfalls in available data, it appears that insulin signaling in chicken liver is similar to that in mammals, but is unlike that in mammals in muscle. In leg muscle, chickens differ from mammals in the early steps of the insulin signaling cascade (IR, IRS-1 and PI3K) where PI3K activity is about 30-fold greater in the chicken than in the rat. This "constitutive" hyperactivity of PI3K in chicken muscle may over-stimulate a feedback inhibitory pathway described in mammals thereby desensitizing chicken muscle to insulin.

Changes in body composition and meat quality in response to dietary amino acid provision in finishing broilers.

In order to control and optimize chicken quality products, it is necessary to improve the description of the responses to dietary amino acid (AA) concentration in terms of carcass composition and meat quality, especially during the finishing period. The aim of this study was to investigate the effects of Lysine (Lys, i.e. a limiting AA used as reference in AA nutrition) and AA other than Lys (AA effect). In total, 12 experimental diets were formulated with four levels of digestible Lys content (7, 8.5, 10 and 11.5 g/kg) combined with either a low (AA-), adequate control (AAc) and high (AA+) amount of other essential AA (EAA) expressed as a proportion of Lys. They were distributed to male Ross PM3 from 3 to 5 weeks of age. No significant AA×Lys interaction was found for growth performance or carcass composition. Body weight and feed conversion ratio were significantly improved by addition of Lys but were impaired in broilers receiving the AA- diets, whereas breast meat yield and abdominal fat were only affected by Lys. No additional benefit was found when the relative amount of other EAA was increased. There was a significant AA×Lys interaction on most of the meat quality traits, including ultimate pH, color and drip loss, with a significant effect of both AA and Lys. For example, AA- combined with reduced Lys level favored the production of meat with high ultimate pH (>6.0), dark color and low drip loss whereas more acid, light and exudative meat (<5.85) was produced with AA+ combined with a low Lys level. In conclusion, growth performance, carcass composition and meat quality are affected by the levels of dietary Lys and AA in finishing broilers. In addition, interactive responses to Lys and AA are found on meat quality traits, leading to great variations in breast pHu, color and drip loss according AA balance or imbalance.

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.

Effects of thermal manipulation during early and late embryogenesis on thermotolerance and breast muscle characteristics in broiler chickens.

Genetic selection has significantly improved the muscle development of fast-growing broiler chickens in the last 50 yr. However, improvement in muscle growth has coincided with relatively poor development of visceral systems, resulting in impaired ability to cope with high environmental temperatures. The aim of this study was to elucidate the effects of thermal manipulation (TM) during different periods of embryogenesis on chick hatchability, BW and thermoregulation upon hatching, on their ability to cope with thermal challenge at 42 d of age, and on carcass and breast meat traits. Control embryos were incubated at 37.8 degrees C. The TM embryos were incubated at 37.8 degrees C and treated for 3 h at 39.5 degrees C on the following days of embryogenesis: E8 to E10 [early (EA)], E16 to E18 [late (LA)], and both E8 to E10 and E16 to E18 (EA-LA). Body weight and body temperature (T(b)) were measured at hatching and throughout the growth period as well as during exposure of 42-d-old chickens to a thermal challenge at 35 degrees C for 6 h. The LA and EA chicks exhibited significantly lower T(b) than control chicks (37.9 vs. 38.2 degrees C) at hatching, but during the growth period, differences in T(b) between treated and control chicks decreased with age. Significant hyperthermia (over 44 degrees C) was monitored in all groups during the thermal challenge, but mortality was higher in treated than in control chickens. No effect of treatments on BW was found during the entire growth period. However, breast yield was higher in LA chickens than in controls at slaughter. The EA and EA-LA treatments slightly decreased the ultimate pH of breast meat, whereas the LA treatment had no effect. In conclusion, none of the TM conditions tested in the present study were able to improve long-term thermotolerance in chickens. Late treatment favored breast muscle growth without affecting ultimate pH and drip loss of breast meat.

Reducing the CP content in broiler feeds: impact on animal performance, meat quality and nitrogen utilization.

Reducing the dietary CP content is an efficient way to limit nitrogen excretion in broilers but, as reported in the literature, it often reduces performance, probably because of an inadequate provision in amino acids (AA). The aim of this study was to investigate the effect of decreasing the CP content in the diet on animal performance, meat quality and nitrogen utilization in growing-finishing broilers using an optimized dietary AA profile based on the ideal protein concept. Two experiments (1 and 2) were performed using 1-day-old PM3 Ross male broilers (1520 and 912 for experiments 1 and 2, respectively) using the minimum AA:Lys ratios proposed by Mack et al. with modifications for Thr and Arg. The digestible Thr (dThr): dLys ratio was increased from 63% to 68% and the dArg:dLys ratio was decreased from 112% to 108%. In experiment 1, the reduction of dietary CP from 19% to 15% (five treatments) did not alter feed intake or BW, but the feed conversion ratio was increased for the 16% and 15% CP diets (+2.4% and +3.6%, respectively), while in experiment 2 (three treatments: 19%, 17.5% and 16% CP) there was no effect of dietary CP on performance. In both experiments, dietary CP content did not affect breast meat yield. However, abdominal fat content (expressed as a percentage of BW) was increased by the decrease in CP content (up to +0.5 and +0.2 percentage point, in experiments 1 and 2, respectively). In experiment 2, meat quality traits responded to dietary CP content with a higher ultimate pH and lower lightness and drip loss values for the low CP diets. Nitrogen retention efficiency increased when reducing CP content in both experiments (+3.5 points/CP percentage point). The main consequence of this higher efficiency was a decrease in nitrogen excretion (-2.5 g N/kg BW gain) and volatilization (expressed as a percentage of excretion: -5 points/CP percentage point). In conclusion, this study demonstrates that with an adapted AA profile, it is possible to reduce dietary CP content to at least 17% in growing-finishing male broilers, without altering animal performance and meat quality. Such a feeding strategy could therefore help improving the sustainability of broiler production as it is an efficient way to reduce environmental burden associated with nitrogen excretion.

Is there peripheral or ovarian insulin action alteration in broiler breeder hens fed ad libitum?

We investigated whether a change in peripheral glucose homeostasis, a local change in the insulin-related ovarian regulatory system, or both occurred in ad libitum-fed broiler breeder hens compared with feed-restricted counterparts. Feed-restricted (R, from 5 to 16 wk of age) and ad libitum-fed (A) hens from a standard commercial line (S) and an experimental dwarf genotype (E) were studied. Basal and stimulated plasma insulin and glucose concentrations were measured during the prebreeding and laying periods. In the basal state (after 16 h fasting) plasma glucose concentrations were significantly lower in SA chickens (-5% at 17 wk, -7.5% at 32 wk) compared with EA, SR, and ER chickens, with no difference in plasma insulin concentrations (n = 16). In 17-wk-old SA birds, 30 min after oral glucose loading, plasma glucose concentrations increased significantly compared with the basal state and were also significantly lower as compared with SR but did not differ significantly from EA and ER. Plasma insulin concentrations did not differ significantly between genotypes or regimens (n = 16). A potential modification of intracellular mediators involved in the regulation of cell growth and survival in small follicles that were overrecruited in SA compared with SR was also investigated in SA and SR hens at 32 wk. There was no effect of food restriction in phospho-Akt, Akt, phospho-ERK, and phospho-S6 in the small white ovarian follicles (n = 6) in the basal state and after 30 min of refeeding. In conclusion, the present study does not demonstrate any evidence of glucose intolerance during the prebreeding period, specific change in the ovarian small follicle insulin signalling pathway, or both, in laying broiler breeders fed ad libitum compared with feed-restricted hens.

The level and source of free-methionine affect body composition and breast muscle traits in growing broilers.

Although dietary Met, as the first limiting amino acid (AA), has been extensively studied for poultry, little is known about how the supply and source of free Met affect tissue composition. The purpose of this study was to investigate the effect of feeding young broiler chickens with a deficient or sufficient TSAA (Met+Cys) supply, using either dl-Met (dl-Met+ and dl-Met-, for respectively diets sufficient and deficient in TSAA) or dl-2-hydroxy-4-methylthiobutyric acid (HMTBA+ and HMTBA-, for respectively diets sufficient and deficient in TSAA) as a Met source on tissue composition and breast muscle traits. For both Met sources, the deficient diets were formulated to provide true digestible Met:Lys and TSAA:Lys respectively 45% and 30% below that of the sufficient diets. Performance and tissue weights were affected by the Met supply but not by the Met source. In TSAA-deficient chickens, ADG and FCR, and protein content in empty body and pectoralis major muscles (PM) were lower than in TSAA-sufficient chickens (P < 0.05). Reducing the Met content of the diet increased the redness value of PM (a*) and the hue angle (H°; P < 0.01). The source of Met affected body AA composition and the partitioning of body Cys among tissues (P < 0.05). In TSAA-deficient birds, body Cys mass decreased in the commercial carcass and PM, but increased in the rest of the body (P < 0.01). The Met source also had an impact on the Cys mass, which was reduced in the commercial carcass and PM of dl-Met birds, but higher in the rest, especially in the feathers of TSAA-deficient birds (P < 0.05). The Met source, supply, or both altered the AA composition of the empty body, mostly in the commercial carcass. In conclusion, a dietary TSAA deficiency altered performance, tissue composition and quality traits of PM of broilers. There was no impact between dietary dl-Met and dl-HMTBA on performance or muscle weight, although the Met source affected the partitioning of Cys among tissues.

Cyclic variations in incubation conditions induce adaptive responses to later heat exposure in chickens: a review.

Selection programs have enabled broiler chickens to gain muscle mass without similar enlargement of the cardiovascular and respiratory systems that are essential for thermoregulatory efficiency. Meat-type chickens cope with high ambient temperature by reducing feed intake and growth during chronic and moderate heat exposure. In case of acute heat exposure, a dramatic increase in morbidity and mortality can occur. In order to alleviate heat stress in the long term, research has recently focused on early thermal manipulation. Aimed at stimulation of long-term thermotolerance, the thermal manipulation of embryos is a method based on fine tuning of incubation conditions, taking into account the level and duration of increases in temperature and relative humidity during a critical period of embryogenesis. The consequences of thermal manipulation on the performance and meat quality of broiler chickens have been explored to ensure the potential application of this strategy. The physiological basis of the method is the induction of epigenetic and metabolic mechanisms that control body temperature in the long term. Early thermal manipulation can enhance poultry resistance to environmental changes without much effect on growth performance. This review presents the main strategies of early heat exposure and the physiological concepts on which these methods were based. The cellular mechanisms potentially underlying the adaptive response are discussed as well as the potential interest of thermal manipulation of embryos for poultry production.

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.

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.

Effects of delayed feed intake on body, intestine, and muscle development in neonate broilers.

The short-term effects of delayed feeding (DF) for 2 d posthatching were measured in neonate chicks and compared to early feeding (EF). Chicks from 10 independent families were used in this study to determine whether genetic background control of growth may be influenced by EF and DF. Early feeding maintained significant interfamily body weight variations from hatch to 4 d of age, whereas there were no significant differences from 1 d of age when feeding was delayed to 48 h posthatching. These results suggest that posthatching feeding delay may distort genetic selection by masking the expression of genetic potential and disturbing the estimation of chick breeder value. In DF chicks, overall body growth was delayed until the beginning of feeding and body weight at 6 d of age was 25% lower than EF chicks. Availability of feed after the fasting period was not sufficient to compensate for the retardation of weight gain in either body weight or in intestine and breast muscle weight. However, initiation of intestine growth in DF chicks occurred from 1 d of age despite the lack of feeding, whereas feed intake was essential to enhance muscle growth. The potential for protein synthesis was lower in DF than in EF chicks during the first 2 d posthatching (P < 0.001) and then reached similar values after feed intake. These results confirm that initiation of growth in neonate chicks is improved by earlier feeding after hatching. Awareness of changes in overall body weight caused by posthatching food deprivation, especially in the intestine and muscle might help in the development of new diets which could minimize retardation of body weight gain in chicks.

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.

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.

Response of broilers selected on carcass quality to dietary protein supply: live performance, muscle development, and circulating insulin-like growth factors (IGF-I and -II).

The effect of dietary protein supply on muscle development and circulating concentrations of insulin-like growth factors (IGF)-I and -II was examined in chickens selected for increased breast yield and decreased fatness (quality, QL) and in its control line (CL). CL and QL chickens were fed isoenergetic diets containing 121.5 or 215.8 g CP/kg during a 12-d period; comparisons were performed at 33 d of age. Birds given the high protein diet grew faster, ate less feed, had lower feed conversion ratio (FCR), and higher muscle weights than their counterparts given the low protein diet. The muscle weight response to protein supply differed between muscles in both lines, with pectoralis major appearing more sensitive than sartorius. The response of the gastrocnemius muscle depended on the line. Selection for carcass quality increased (P < 0.01) body weight, growth rate, feed intake, pectoralis major and sartorius muscle weights, and pectoralis major muscle proportion. There was, however, no line difference in FCR or in sartorius muscle proportion. The weight and proportion of the gastrocnemius muscle were higher (P < 0.05) in the QL than the CL chickens on the high protein diet, but there was no line difference for the low protein diet. Plasma levels of IGF-I, and to a lesser extent IGF-II, were lower (P < 0.01) in protein-restricted chickens. No difference in circulating IGF-II was observed between the lines. Concentrations of IGF-I were higher (P < 0.05) in QL than CL chickens, which may contribute to improved body composition for this genotype.

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.

Sequential feeding programs for broiler chickens: twenty-four- and forty-eight-hour cycles.

Sequential feeding programs (Seq) of 2 feeds, 1 protein rich-energy poor and 1 energy rich-protein poor, during the same day or every other day were compared with a control complete diet for male broiler growth and body composition from 15 d to market weight. In experiment 1, BW gain and breast meat yield were significantly lower than those of controls for 24-h-cycle Seq with extreme protein content difference between the 2 feeds. BW gain and breast meat yield were higher than those of controls when feeds with moderate differences [feed moderately rich in protein (PM) = 26% CP; feed moderately rich in energy (EM) = 16% CP] were fed. Feeding periods that were half as long but changed twice as frequently gave less favorable results. In experiment 2, effects of allowing access to feed for different lengths of time were measured. The treatments in a 24-h cycle were a constant control diet, 50% PM-50% EM, 40% PM-60% EM, or 80% PM-20% EM decreasing to 40% PM-60% EM. Chickens fed 40% PM-60% EM had a 6% lower BW gain and a 3% higher feed/gain ratio and were fatter than those from other treatments. In experiment 3, male chickens fed a 48-h-cycle Seq of EM and PM every other day had the same BW gain, feed intake, and feed/gain ratio as controls. In experiment 4, five 48-h-cycle Seq with varying differences of energy and protein contents between EM and PM gave similar or slight reduction of performances compared with controls. A field trial with 8 flocks of broilers confirmed that feeding high and low protein feeds on alternate days resulted in performance similar to that from feeding a complete feed despite large day-to-day variations in lysine intake. Converse to shorter phases, Seq for 48-h cycles offers new opportunities for practical application and also for studies of short-term regulation of protein and lipid metabolism in chickens.

The amino acid composition of tissue protein is affected by the total sulfur amino acid supply in growing pigs.

The factorial approach to assess the amino acid (AA) requirements of pigs is based on the assumption that the AA composition of body protein is constant. However, there are indications that this assumption may not be valid because the AA composition of body protein can be affected by the AA supply. The extent to which different tissues are affected by an AA deficiency is unknown. The objective of this study was to investigate the effect of feeding pig diets with a deficient or sufficient total sulfur AA supply (TSAA; Met+Cys) from 6 to 23 weeks of age on tissue composition and meat quality. The deficient diet (TSAA-) provided 24% Met : Lys and 51% TSAA : Lys on a standardized ileal digestible basis, which are 19% and 16% below the recommended requirements, respectively. The sufficient diet (TSAA+) provided 33% Met : Lys and 60% TSAA : Lys. Diets were offered slightly below the ad libitum feed intake capacity of the pigs. Pigs offered diet TSAA- had a lower average daily gain, lower weights of the longissimus dorsi (LM) and rhomboideus muscles (RM), and of selected skin sections (P<0.05). The weight of different sections of the small intestine and the liver was not affected by the diet. The protein content of the LM and RM decreased in pigs offered diet TSAA- (P<0.05), whereas the protein content of other tissues was not affected. The TSAA supply affected the AA composition (g/16 g N) of protein in all tissues, but the Met content was changed only in the liver (P<0.05). Pigs receiving diet TSAA- had a lower Cys content in the RM and in the distal jejunum and ileum (P<0.01). The deficient TSAA supply resulted in a lower carcass weight and higher muscle glycogen stores (P<0.05), but did not affect other meat quality traits. The results of this study indicate that the muscles, jejunum and ileum respond more to a prolonged AA deficiency than the liver. In addition, the observed changes in AA composition of tissue protein question the use of a constant AA profile of retained protein to assess AA requirements.

N-3 fatty acids improve body composition and insulin sensitivity during energy restriction in the rat.

The hypothesis that n-3 polyunsaturated fatty acids (PUFA) could contribute to maintain muscle mass during energy restriction aiming to weight loss was tested in the rat, with special attention paid to insulin signalling. After 10 weeks on a diet rich in lipids and sucrose, male rats were energy restricted and fed diets rich in 18:1 n-9 (OLE), 18:3 n-3 (ALA) or n-3 long-chain (LC, >18 carbons) PUFA. After 4 weeks, they were killed after an insulin injection. Red blood cells, liver, and Gastrocnemius muscle were enriched in ALA in the ALA group, and in LC-PUFA in the ALA and LC groups. The LC diet resulted in a higher weight loss, without negative impact on the muscle weight. In parallel, hepatic phosphorylation of insulin receptor and IRS1 was the highest in this group. This suggests that the trend we observed in the preservation of protein homeostasis in the LC group is mediated, at least partly, by an enhancement of the early steps of insulin signalling resulting from cell membrane enrichment in n-3 PUFA.