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.

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.

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.

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.

Expression profile of hypothalamic neuropeptides in chicken lines selected for high or low residual feed intake.

The R(+) and R(-) chicken lines have been divergently selected for high (R(+)) or low (R(-)) residual feed intake. For the same body weight and egg production, the R(+) chickens consume 40% more food than their counterparts R(-) lines. In the present study we sought to determine the hypothalamic expression profile of feeding-related neuropeptides in these lines maintained under fed or food-deprived conditions. In the fed condition, the suppressor of cytokine signaling 3 (SOCS3) was 17-fold lower (P<0.05) and the ghrelin receptor was 7-fold higher (P<0.05) in R(+) compared to R(-) chicken lines. The hypothalamic expression of the other studied genes remained unchanged between the two lines. In the fasted state, orexigenic neuropeptide Y and agouti-related peptide were more responsive, with higher significant levels in the R(+) compared to R(-) chickens, while no significant differences were seen for the anorexigenic neuropeptides pro-opiomelanocortin and corticotropin releasing hormone. Interestingly, C-reactive protein, adiponectin receptor 1 and ghrelin receptor gene expression were significantly higher (12-, 2- and 3-folds, respectively), however ghrelin and melanocortin 5 receptor mRNA levels were lower (4- and 2-folds, P=0.05 and P=0.03, respectively) in R(+) compared to R(-) animals. We identified several key feeding-related genes that are differently expressed in the hypothalamus of R(+) and R(-) chickens and that might explain the difference in feed intake observed between the two lines.

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.

Thermal manipulation of the embryo modifies the physiology and body composition of broiler chickens reared in floor pens without affecting breast meat processing quality.

Selection in broiler chickens has increased muscle mass without similar development of the cardiovascular and respiratory systems, resulting in limited ability to sustain high ambient temperatures. The aim of this study was to determine the long-lasting effects of heat manipulation of the embryo on the physiology, body temperature (Tb), growth rate and meat processing quality of broiler chickens reared in floor pens. Broiler chicken eggs were incubated in control conditions (37.8°C, 56% relative humidity; RH) or exposed to thermal manipulation (TM; 12 h/d, 39.5°C, 65% RH) from d 7 to 16 of embryogenesis. This study was planned in a pedigree design to identify possible heritable characters for further selection of broiler chickens to improve thermotolerance. Thermal manipulation did not affect hatchability but resulted in lower Tb at hatching and until d 28 post-hatch, with associated changes in plasma thyroid hormone concentrations. At d 34, chickens were exposed to a moderate heat challenge (5 h, 32°C). Greater O2 saturation and reduced CO2 partial pressure were observed (P < 0.05) in the venous blood of TM than in that of control chickens, suggesting long-term respiratory adaptation. At slaughter age, TM chickens were 1.4% lighter and exhibited 8% less relative abdominal fat pad than controls. Breast muscle yield was enhanced by TM, especially in females, but without significant change in breast meat characteristics (pH, color, drip loss). Plasma glucose/insulin balance was affected (P < 0.05) by thermal treatments. The heat challenge increased the heterophil/lymphocyte ratio in controls (P < 0.05) but not in TM birds, possibly reflecting a lower stress status in TM chickens. Interestingly, broiler chickens had moderate heritability estimates for the plasma triiodothyronine/thyroxine concentration ratio at d 28 and comb temperature during the heat challenge on d 34 (h(2) > 0.17). In conclusion, TM of the embryo modified the physiology of broilers in the long term as a possible adaptation for heat tolerance, without affecting breast meat quality. This study highlights the value of 2 new heritable characters involved in thermoregulation for further broiler selection.

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.

Modulation of glycogen and breast meat processing ability by nutrition in chickens: effect of crude protein level in 2 chicken genotypes.

The aim of the study was to evaluate the impact of 2 isoenergetic growing diets with different CP (17 vs. 23%) on the performance and breast meat quality of 2 lines of chicken divergently selected for abdominal fatness [i.e., fat and lean (LL) lines]. Growth performance, breast and abdominal fat yields, breast meat quality parameters (pH, color, drip loss), and muscle glycogen storage at death were measured. Increased dietary CP resulted in increased BW, increased breast meat yield, and reduced abdominal fatness at slaughter regardless of genotype (P < 0.001). By contrast, dietary CP affected glycogen storage and the related meat quality parameters only in the LL chickens. Giving LL chickens the low-CP diet led to reduced concentration of muscle glycogen (P < 0.01), and as a result, breast meat with a higher (P < 0.001) ultimate pH, decreased (P < 0.001) lightness, and reduced (P < 0.001) drip loss during storage. The decreased muscle glycogen content observed in LL receiving the low-CP diet compared with the high-CP diet occurred concomitantly with greater phosphorylation amount for the α-catalytic subunit of adenosine monophosphate-activated protein kinase and glycogen synthase. This was consistent with the reduced muscle glycogen content observed in LL fed the low-CP diet because adenosine monophosphate-activated protein kinase inhibits glycogen synthesis through its action on glycogen synthase. Our results demonstrated that nutrition is an effective means of modulating breast meat properties in the chicken. The results also highlighted the need to take into account interaction with the genetic background of the animal to select nutritional strategies to improve meat quality traits in poultry.

Effects of heat exposure on Akt/S6K1 signaling and expression of genes related to protein and energy metabolism in chicken (Gallus gallus) pectoralis major muscle.

In order to improve understanding of the heat-induced changes in muscle growth, we determined the expression of genes related to protein and energy metabolism in the pectoralis major muscle of chickens. We also explored the protein kinase B (PKB also called Akt)/p70 S6 kinase (S6K1)/S6 pathway that mediates anabolic signals thereby regulating metabolism and hypertrophic/atrophic balance. Four-week-old chickens were exposed to 32 or 22 degrees C for 1 week. Chickens from both groups were then fasted for 16 h or left fed, and submitted to an oral administration of glucose-arginine to induce an anabolic response (30-min treatment) or left untreated. High ambient temperature and the associated decrease in feed intake modified the expression of certain energy-related genes (e.g. -40% for PGC-1alpha) and protein metabolism (e.g. about +80% for atrogin-1), but the expression of several muscle metabolism-related genes considered here was unchanged. The capacity for muscle protein synthesis, i.e. RNA/protein ratio, was reduced in warm conditions (approximately -20%). Slightly lower activation of S6 induced by glucose-arginine treatment was found at 32 degrees C compared to 22 degrees C, which might indicate somewhat lower efficiency of mRNA translation. Analysis of glucose/insulin balance suggested changes in glucose metabolism under heat exposure. However, this remains to be characterized.

The beta-adrenergic system is involved in the regulation of the expression of avian uncoupling protein in the chicken.

Avian uncoupling protein (avUCP) is orthologous to UCP3, which is suggested to be involved in fatty acid metabolism and to limit the mitochondrial production of reactive oxygen species in mammals. In the chicken, the role and regulation of avUCP remain to be clarified. The aim of this study was to explore the control of avUCP expression by the beta-adrenergic system, known to be involved in avian thermoregulation and lipid utilization, and in UCP expression in mammals. Therefore, we measured the expression of avUCP mRNA and protein in the Pectoralis major muscle of chickens injected with the beta(2) agonist isoproterenol, and we investigated the potential pathways involved in the regulation of avUCP mRNA expression. Avian UCP mRNA expression was increased 7-fold 4h after isoproterenol injection, leading to a tendency to a 40% increase in avUCP protein 24h post-injection. This increase was preceded, 30 min after isoproterenol injection, by changes in the chicken thyroid status and in the muscular expression of PPARalpha, PPARbeta/delta, and PPARgamma coactivator-1alpha (PGC-1alpha). Moreover, the analysis of the avUCP promoter sequence suggested potential binding sites for PPARs and for thyroid hormone receptors. We also detected the activation of AMP-activated protein kinase, which has recently been reported to be involved in UCP3 regulation in mammals. This study presents for the first time evidence of beta-adrenergic control on avUCP messenger expression in chicken muscle and suggests the potential involvement of AMPK and several transcription factors in this regulation.

Regulation of fatty acid oxidation in chicken (Gallus gallus): interactions between genotype and diet composition.

To explore the mechanisms leading to excessive adiposity in chicken, we investigated the regulation of fatty acid oxidation depending on genotype-related body fatness and diet composition. mRNA expression and/or activity of proteins involved in mitochondrial energy metabolism were measured in liver and gastrocnemius muscle of genetically lean or fat chickens reared on a low-fat/high-protein diet or an isoenergetic high-fat/low-protein diet (HF/LP). Muscle expressions of the muscle isoform of carnitine-palmitoyltransferase 1 (M-CPT1) and PPARbeta/delta were higher in fat than in lean chickens. This was also observed in liver, although only with the HF/LP diet for M-CPT1. This could stimulate mitochondrial fatty acid oxidation in fat chickens. Up-regulations of liver and muscle CPT-1 hepatic isoform, and muscle cytochrome-c-oxidase mRNA expressions, and of beta-hydroxyacyl-CoA-dehydrogenase activities suggest higher fatty acid utilization with the HF/LP diet. PPARbeta/delta and PGC-1alpha could control fatty acid oxidation in muscle and liver, respectively. Regulation of avian uncoupling protein (avUCP) mRNA was tissue-dependent. Predominantly expressed in muscle, it was stimulated in fat and in HF/LP-fed chickens, where it could be associated to the special need in muscle anti-oxidant pathways of fatter animals. In liver it was lower in fat than in lean chickens, and its potential function remains to be clarified.

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.

Adenosine monophosphate-activated protein kinase involved in variations of muscle glycogen and breast meat quality between lean and fat chickens.

The present study was aimed at evaluating the molecular mechanisms associated with the differences in muscle glycogen content and breast meat quality between 2 experimental lines of chicken divergently selected on abdominal fatness. The glycogen at death (estimated through the glycolytic potential) of the pectoralis major muscle and the quality of the resulting meat were estimated in the 2 lines. The fat chickens exhibited greater glycolytic potential, and in turn lower ultimate pH than the lean chickens. Consequently, the breast meat of fat birds was paler and less colored (i.e., less red and yellow), and exhibited greater drip loss compared with that of lean birds. In relation to these variations, transcription and activation levels of adenosine monophosphate-activated protein kinase (AMPK) were investigated. The main difference observed between lines was a 3-fold greater level of AMPK activation, evaluated through phosphorylation of AMPKalpha-(Thr(172)), in the muscle of lean birds. At the transcriptional level, data indicated concomitant down- and upregulation for the gamma1 and gamma2 AMPK subunit isoforms, respectively, in the muscle of lean chickens. Transcriptional levels of enzymes directly involved in glycogen turnover were also investigated. Data showed greater gene expression for glycogen synthase, glycogen phosphorylase, and the gamma subunit of phosphorylase kinase in lean birds. Together, these data indicate that selection on body fatness in chicken alters the muscle glycogen turnover and content and consequently the quality traits of the resulting meat. Alterations of AMPK activity could play a key role in these changes.

Tissue-specific regulation of S6K1 by insulin in chickens divergently selected for growth.

In chickens, insulin injection leads to the activation of the early steps of insulin receptor signaling in liver but not in muscles. Paradoxically, muscle p70 S6 kinase (S6K1), a kinase controlling protein synthesis and growth, was markedly activated in response to insulin. The aim of this study was to further investigate S6K1 regulation and activation using chickens divergently selected for growth, i.e. fast- (FGL) and slow- (SGL) growing lines. In the Pectoralis major muscle, insulin stimulated S6K1 phosphorylation on T389 in FGL and SGL chickens, whereas S6K1 phosphorylation on T421/S424 was increased by insulin only in FGL chickens. Moreover, insulin-related increase in muscle S6K1 activity was greater in FGL chickens than in SGL chickens. Surprisingly, liver S6K1 was insulin insensitive in the two genotypes. Such difference of regulation between tissues and between genotypes was not observed for the protein kinase B, which is involved in insulin signaling upstream of S6K1, or for eukaryotic initiation factor 4E-binding protein. Interestingly, insulin-activated a S6K1 downstream target, the ribosomal protein S6, irrespective of tissue, suggesting that a pathway different of the S6K1 cascade may be involved in S6 phosphorylation in chicken liver. In conclusion, the regulation of S6K1 differs between the liver and muscle and between chickens divergently selected for growth. Our results suggest a potential involvement of S6K1 in the control of muscle growth and an open issue concerning S6K1 function in chicken liver.

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.

Early lysine deficiency in young broiler chicks.

The carry-over effect of a pre-starter diet (0 to 3 days of age) deficient in lysine on subsequent growth and body composition (3 to 10 days) was examined in two experiments on male broiler chicks raised in cages. In experiment 1, lysine deficiency was applied from 3 to 10 days after providing a balanced pre-starter control feed (D+, 1.40% lysine) or a lysine deficient feed (D-) during the first 3 days. Three levels of deficiency (A = 0.63%, B = 0.72%, C = 0.82%) were tested. Growth and feed intake were higher in D+ than in D- chicks ( P < 0.001). However, the feed conversion ratio from 3 to 10 days of age was higher in D+ chicks ( P < 0.001); pre-starter and starter feeds interacted ( P < 0.04) with the feed conversion of treatment D+/A = 2.07 being better than treatment D+/A = 2.61 ( P < 0.05). This suggests that chicks deficient from hatching exhibit a relatively lower sensitivity to lysine deficiency than chicks started on a control diet. In experiment 2, performance, slaughter parameters and body composition were analysed at 3 and 10 days of age, in chicks having received a lysine deficient feed (D0, 0.72% lysine), a control feed (D+, 1.40% lysine) or having been pair fed with control feed adjusted to D0 intake (PF) from 0 to 3 days of age, and then fed D0 ad libitum from 3 to 10 days of age. At 3 days, PF chicks had a higher body weight ( P < 0.05) than D0, and thus a better feed conversion. Body composition in relative values was little or not affected by dietary treatments, but the breast muscle weight at 3 days was higher in D+ and PF chicks compared with D0 ( P < 0.05) and this effect was even accentuated at 10 days of age. The present work confirms that early nutrition can have subsequent consequences on the adjustment of fast growing broiler chicks to their nutritional conditions. It also suggests that breast muscle development is a more reactive parameter than whole body composition in this kind of experiments.

Responses to nutrients in farm animals: implications for production and quality.

It is well known that any quantitative (energy and protein levels) and qualitative (nature of the diet, nutrient dynamic) changes in the feeding of animals affect metabolism. Energy expenditure and feed efficiency at the whole-body level, nutrient partitioning between and within tissues and organs and, ultimately, tissue and organ characteristics are the major regulated traits with consequences on the quality of the meat and milk produced. Recent progress in biology has brought to light important biological mechanisms which explain these observations: for instance, regulation by the nutrients of gene expression or of key metabolic enzyme activity, interaction and sometimes cross-regulation or competition between nutrients to provide free energy (ATP) to living cells, indirect action of nutrients through a complex hormonal action, and, particularly in herbivores, interactions between trans-fatty acids produced in the rumen and tissue metabolism. One of the main targets of this nutritional regulation is a modification of tissue insulin sensitivity and hence of insulin action. In addition, the nutritional control of mitochondrial activity (and hence of nutrient catabolism) is another major mechanism by which nutrients may affect body composition and tissue characteristics. These regulations are of great importance in the most metabolically active tissues (the digestive tract and the liver) and may have undesirable (i.e. diabetes and obesity in humans) or desirable consequences (such as the production of fatty liver by ducks and geese, and the production of fatty and hence tasty meat or milk with an adapted fatty acid profile).