The first three essential amino acids (EAA) for broilers including methionine (Met), lysine (Lys) and threonine (Thr) may greatly influence the growth of chick muscles at early stages of life. In order to survey the potential effects of those EAA on growth muscles, a rotatable three-variable central composite design (CCD) was conducted to track the interrelationships of dietary digestible Met (dMet), Lys (dLys) and Thr (dThr) for optimization of processing yields in broiler chicks using response surface methodology. A total of 60 floor pens of six birds each were assigned to 15 dietary treatments based on CCD containing five levels of dMet (0.416% to 0.584% of diet), dLys (0.881% to 1.319% of diet) and dThr (0.532% to 0.868% of diet) from 3 to 16 days of age. Experimental treatments significantly affected breast mass (BM) and leg mass (LM) of the birds (P<0.05) in which the main effect of dLys on BM was threefold higher than the main effect of dThr, and interaction effect between dMet and dLys was observed on BM (P<0.05). However, in the case of LM, the main effect of dThr was higher than the main effects of dMet and dLys and highest interaction effect exist between dThr and dMet (P<0.05). The second-order models for BM and LM were fitted by least squares regression. Canonical analysis revealed that the stationary points for carcass components were saddle points, thus ridge analysis was performed for getting optimal values of each EAA. Ridge analyses of BM and LM models showed that the maximum BM point may be obtained with 0.58%, 1.05% and 0.76% of dMet, dLys and dThr, respectively, in diet, and maximum LM point may be achieved with 0.58%, 1.09% and 0.70% of dMet, dLys and dThr, respectively, in diet. The resultant ideal ratios of dMet and dThr to dLys were 55% and 72% for BM; 53% and 64% for LM. Moreover, sensitivity analysis showed that the most important amino acids in BM and LM models were Lys and Thr, respectively. In conclusion, providing these three amino acid for BM optimization may warrant LM optimization and higher ideal ratios of dMet and dThr for breast muscle may indicate the higher importance of these EAA in this muscle than those in thigh muscle.

The present study aimed to investigate the responses of broilers with different hatching weights (HW) to dietary methionine (Met). A total of 192 1-d-old Arbor Acres broiler chicks with different HW (heavy: 48·3 (sem 0·1) g and light: 41·7 (sem 0·1) g) were allocated to a 2 (HW) × 2 (Met) factorial arrangement with six replicates of eight chicks. Control starter (1–21 d) and finisher (22–42 d) diets contained 0·50 and 0·43 % Met, respectively. Corresponding values for a high-Met treatment were 0·60 and 0·53 %. Light chicks had poorer (P< 0·05) growth performance and breast muscle weight and lower (P< 0·05) insulin-like growth factor-I (IGF-I) concentration and mRNA level in breast muscle than heavy chicks when both were fed the control diets. High-Met diets improved performance and promoted breast muscle growth and IGF-I concentration in light chicks (P< 0·05). Increased IGF-I and target of rapamycin (TOR) mRNA levels as well as decreased eIF4E-binding protein 1 (4EBP1), atrogin-1 and forkhead box O 4 (FOXO4) mRNA levels were induced by high-Met diets in light chicks (P< 0·05). In conclusion, the Met requirement of broilers might depend on their HW and Met levels used in the control diets in the present study were adequate for heavy chicks but inadequate for light chicks, resulting in poorer performance and breast muscle growth, which were improved by increasing dietary Met supply presumably through alterations in IGF-I synthesis and gene expression of the TOR/4EBP1 and FOXO4/atrogin-1 pathway.

Growth performance and meat yield of commercial broilers and turkeys has improved linearly each year during the past four decades (Havenstein et al., 2003b; Havenstein et al., 2003a; Havenstein et al., 2007), and this trend is likely to continue in the future as new technologies in genetics, biotechnology and developmental biology are adopted by the poultry industry. As the time it takes meat birds to achieve market size decreases, the period of embryonic development becomes a greater proportion of a bird's productive life. Therefore, incubation and embryonic development towards hatch is of greater relative importance to the successful rearing of meat poultry than ever before (Hulet 2007; Foye et al., 2007b). Consequently, anything that supports or limits growth and development during the incubation period will have a marked effect on overall growth performance and health of modern strains of meat poultry. Many poultry researchers now realize that future gains in genetic and production potential of poultry will come from advancements made during the incubation period and embryogenesis (Elibol et al., 2002; Peebles et al., 2005; Christensen et al., 2007; Collin et al., 2007; Leksrisompong et al., 2007). The urgent need to explore and understand the biology of incubation has been emphasised by several symposia: two held at the annual conference of the U.S. Poultry Science Society (July 2006-Edmonton, Alberta, Canada “Managing the embryo for performance”, and July 2007-San Antonio, TX Informal Nutrition Meeting “The impact of imprinting on biological and economical performance in animals”), and one held by the European Federation of World Poultry Science Society (October 2007-Berlin, Germany “Fundamental physiology and perinatal development in poultry), which were specifically devoted to demonstrating the importance of the embryonic period on poultry performance. This review will summarise the metabolic events and pathways in four of the most active tissues of embryos during the period just prior to hatch, and the hormonal control that coordinates the marked changes as the embryo prepares for its post-hatch life.

The effects of age (from 1 day post-hatch to 98 days of age) and feeding levels (feed restriction followed by overfeeding v. ad libitum feeding) on lipid deposition in breast muscle (quantity and quality, localisation) of mule ducks were determined in relation to muscle energy metabolism (glycolytic and oxidative), plasma levels of lipids, glucose and insulin, and muscle capacity for lipid uptake (characterised by lipoprotein lipase (LPL) activity). Two periods were defined for age effects on intramuscular lipids in breast muscle: − 1 to 42 days of age when lipids (mainly phospholipids and cholesterol provided by egg yolk) stored in the adipocytes during embryonic life were transferred to the muscle fibres and used for growth and energy requirements, − 42 to 98 days of age when the muscle again stored lipids (mainly triglycerides provided by liver lipogenesis), first in fibres and then in adipocytes.

Plasma glucose and insulin levels were not affected by age. Plasma levels of lipids and LPL activity in breast muscle were high at 1 and 14 days of age and then decreased, remaining stable until 98 days of age. Energy metabolism activity in the breast muscle (mainly glycolytic activity) increased with age.

Feed restriction, corresponding to 79% of ad libitum intake, applied between 42 and 75 days of age only resulted in decreases in plasma insulin concentration and total lipid content of breast muscle, mainly affecting triglyceride and mono-unsaturated fatty acid (MUFA) levels. Overfeeding increased plasma levels of insulin and lipids while glycaemia remained stable. LPL activity and total lipid levels increased in breast muscle, mainly induced by deposition of triglycerides and MUFA occurring particularly during the 2nd week of this period. Glycolytic energy metabolism decreased.

In response to age or feeding levels, muscle lipid levels and composition reflect plasma lipid levels and composition and high muscle lipid levels stimulate oxidative energy metabolism.

The objective of this work was to evaluate the ultrasound method as a tool for in-vivo breast and abdominal fat prediction on Campero-INTA broilers. Breast length (mm), width (mm), surface (mm2; ultrasound) and depth (mm; ultrasound), and abdominal fat depth (mm; ultrasound) were measured at 65-66 and 72-73 days of age on 96 males. At 79 days of age, the broilers were weighed and slaughtered. Breast and abdominal fat weights (g) were obtained. Multiple regression equations were fitted using live weight (g) and in-vivo measurements to predict breast and abdominal fat weights and proportions (g/g). The best model for each case was selected by the Stepwise procedure. Equations fitted were verified using another set of data. Breast weight prediction using live weight and breast length in the model was as accurate as using live weight and breast depth. The former is recommended for breeding work. Abdominal fat weight prediction using ultrasound measurements of fat was less accurate than breast weight prediction. Repeatabilities for ultrasound breast measurements were higher (0·72 to 0·73) than those for abdominal fat (0·51 to 0·52). Operator effect may be important when training levels are different.