Variations in chicken breast meat quality: implications of struggle and muscle glycogen content at death

1. Pectoralis major (P. major) muscle pH and meat quality traits were studied in relation to bird response to ante-mortem stress in three chicken lines: a fast-growing standard line (FGL), a slow-growing French 'Label Rouge' line (SGL) and a heavy line (HL). Ninety-nine birds of the three genetic types were slaughtered at their usual marketing age (6, 12 and 6 weeks for FGL, SGL and HL birds, respectively) on the same day. The birds of each line were divided into three different ante-mortem treatment groups: minimum stress (shackling for 10 s) (C), shackling for 2 min (SH) and acute heat plus shackling stress (exposure to 35 degrees C for 3.5 h and shackling for 2 min before stunning) (H + SH). 2. Regardless of chicken line, wing flapping duration (WFD) between hanging and stunning was strongly negatively related to P. major muscle pH at 15 min post-mortem. It was also moderately negatively related to P. major muscle glycolytic potential (GP), which represents glycogen level at death. Increasing WFD induced an increased ultimate pH (pHu) only in HL. The consequences of increased WFD for breast meat traits were dependent on the chicken line: it induced lower L* and b* and higher a* and drip loss in SGL while it only increased breast a* in HL birds. By contrast, WFD variations did not alter breast meat quality traits of FGL birds. Regardless of the chicken line, increased GP was associated with lower pHu and higher L* and drip loss. In SGL, it also increased b* and decreased curing-cooking yield of breast meat. 3. Struggling activity on the shackle line and muscle glycogen content at death could partly explain line and pre-slaughter variations in breast meat pH and quality traits. The water holding capacity of the raw and cooked meat was impaired by long shackling in the case of SGL birds while it was barely affected by ante-mortem conditions in the two standard lines. In conditions which minimised bird struggling (C), SGL and FGL birds had meat with a better water holding ability than that of broilers from the heavy line. However, when broilers were subjected to SH or H + SH conditions, the breast meat water holding capacity of SGL birds was lowered to the same level as that of the heavy line birds.     

Behavioural and physiological responses of three chicken breeds to pre-slaughter shackling and acute heat stress

1. The aim of this study was to compare the behavioural and physiological responses to hanging and acute heat stress in three different chicken breeds. Chicks were obtained from a slow-growing French 'Label Rouge' line (SGL), a fast-growing standard line (FGL) and a heavy line (HL). The SGL, FGL and HL birds were slaughtered at their respective market ages of 12, 6 and 6 weeks, in an attempt to achieve similar body weights. Before stunning, birds were either shackled by their legs on the moving line for 2 min (shackling stress: SH) or placed in a room at 35 degrees C and 60% of humidity for 3.5 h and then shackled for 2 min (acute heat stress plus shackling: H + SH) or subjected to minimal stress by shackling for 10 s before stunning (control group: C). 2. Bird physiological responses to the three pre-slaughter treatments were estimated by measuring blood corticosterone, glycaemia, creatine kinase activity, acid-base status and electrolyte concentration as well as lactate content and glycolytic potential in the breast (Pectoralis major) and thigh (Ilio tibialis) muscles. Behavioural responses to shackling stress were evaluated by measuring wing flapping duration, straightening up attempts and vocalisations. 3. Blood corticosterone was higher in SH and H+SH groups than in the C group, regardless of genotype. The struggling activity on the shackle line differed among chicken breeds. It was more intense and occurred more rapidly after hanging in the SGL birds than in both other breeds. Furthermore, SGL struggling activity was not affected by hanging duration while it increased with hanging duration in FGL and HL birds. 4. Wing flapping duration was negatively correlated with blood pH, bicarbonate concentration and positively correlated with breast muscle lactate content, indicating that struggling stimulated antemortem glycolysis activity in breast muscle. Acute heat stress affected blood Ca2+ and Na+ concentration and increased glycaemia and glycolytic potential of thigh muscle. 5. Both acute heat stress and shackling before slaughter were experienced as stressful events by all types of birds.     

Duration of wing flapping in chickens shackled before slaughter

Shackling can induce wing flapping in chickens. In this survey of 30 chicken processing plants the proportion of birds flapping their wings had usually subsided to less than 0.5 per cent after the birds had been conveyed 2 m away from the shackling area. Thereafter, there were many causes of wing flapping, of which the following were thought to be important; tight fitting shackles on the birds' shanks, electric shocks at the water bath stunner before stunning, sudden bright sunlight, bends in the line, temporary loss of visual contact between neighbouring birds, and unevenness in the line which jolted the birds. If it is decided that legislation is required to prescribe a minimum 'hang-on' period before stunning it is suggested that birds should not be put through the stunner less than 12 seconds after shackling because after this time 99.7 per cent of the birds had stopped flapping.     

Shackling of broilers: Effects on stress responses and breast meat quality

1. Experiments were conducted to study the welfare and meat quality effects of shackling. In experiment 1, broilers with or without leg problems were shackled (S) for 4 min on a moving line and blood sampled; or handled (H), returned to the crate and sampled after 4 min; or sampled immediately after removal from the crate (control, C).

2. Plasma corticosterone (CORT) concentrations, as measured by radioimmunoassay, were highest in S and lowest in C, while the H group was intermediate. Leg problems had no effect on CORT.

3. In experiment 2, tonic immobility (TI) was induced in broilers after 2 min inverted handling to determine fear responses. One week later, the birds were fasted, transported and then shackled on a moving shackle line for 0, 1, 3 or 4 min, then unshackled and blood sampled. Wing flapping during shackling was also quantified.

4. Shackling time did not influence CORT concentrations. There was a negative correlation (r= ? 0.714) between CORT and wing flapping duration in the 1 min shackling treatment. There was no relationship between TI and wing flapping or CORT.

5. In experiment 3, broilers were exposed to two food withdrawal (FW) times (food withdrawn overnight or during crating only) and held for 4 h prior to processing, shackled (0, 2 or 4 min shackling time, ST), and then killed by exsanguination. Blood samples were collected during the neck‐cut. Pectoralis superficialis and Supracoracoideus samples were either collected after 15 min and individually quick frozen (IQF) in liquid nitrogen or collected at 4 h post mortem from carcases chilled on slush ice (COI).

6. CORT increased significantly with increased ST. There was a FW × ST interaction effect on the initial pH of fillets. ST influenced the b*, chroma and Hue values of the COI fillets. FW influenced the L* and Hue values of both IQF and COI fillets as well as the a* value of the COI fillets.

7. In summary, CORT increased with shackling time when birds were held after transport. FW and ST also influenced the colour of fillets, although it is not clear whether these changes are perceptible to the consumer. The duration of wing flapping during shackling did not appear to be related to fearfulness, although it was influenced by properties of the shackle line. We suggest that there be a maximum time lapse between shackling and stunning or killing of 2 min to minimise stress and meat quality changes.     

Effects of salinity and the use of shackle/leg sprays on the electrical conductivity of a commercial waterbath stunner for broilers

The effect of salinity and temperature on the electrical conductivity of a waterbath stunner was assessed in a commercial broiler processing plant. During a break in production, the waterbath was emptied and filled with either cold water, cold water plus sodium chloride, warm water, or warm water plus sodium chloride. Different concentrations of sodium chloride in distilled water at different temperatures were prepared in the laboratory and their conductivities were compared with the results obtained in the processing plant. No significant increase in conductivity was achieved through an increase in water temperature in either the laboratory or the processing plant, but there was an increase in conductivity after the addition of sodium chloride. However, the increase in conductivity was lost after 20 to 30 minutes of birds passing through the waterbath. The effects of the use, the location and the water temperature of the shackle/leg sprays on electrical conductivity were also studied, but under the conditions of the experiment none of these factors increased the electrical conductivity.     

Broken bones in domestic fowl: handling and processing damage in end-of-lay battery hens

1. 3115 end-of-lay battery hens and carcases were sampled at set points in the sequence of events that occurred between depopulation of the battery cages at the layer farms and the end of the evisceration line in two processing plants. Live birds were killed in a convulsion-free manner and carcases were dissected to determine the incidence of broken bones. 2. Of the live battery birds 29% had broken bones by the time they reached the waterbath stunner, with on average 0.5 broken bones per bird. Removing birds from the battery cages and hanging them on the slaughter line were identified as causes of broken bones. 3. By the time birds left the end of the eviscerating line, 98% of carcases had broken bones, with on average 6 broken bones each. The stunning, plucking and eviscerating processes caused most of this damage. In particular, stunning broke the furculum, coracoid and scapula, plucking broke the ischium, pubis and ribs, and evisceration damaged the ischium and pubis.     

Effects of divergent selection for incidence of tibial dyschondroplasia (TD) on purebred and crossbred performance. 2. Processing yield

1. An experiment was conducted to determine the effect of selection for high (H) or low (L) incidence of tibial dyschondroplasia for 7 generations on processing performance of broilers. 2. Birds were obtained from diallel matings of the H and L lines (HH, HL, LH, and LL) and a randombred control (CC) line. Birds were reared to 7 weeks of age under standard management conditions. All birds were processed at 7 weeks of age. Body weight at 7 weeks, carcase weight, and carcase part weights were recorded on each bird. 3. An interaction between sire line and dam line was caused by lighter body and carcase weight at 7 weeks of age in HH birds than from the birds of the other crosses. 4. Birds by L line dams had heavier drumstick weights. The influences of sire line and dam line on weight of total breast muscle were not significant. Thigh weights and Pectoralis minor weights were lighter in HH line birds than those other matings. 5. Heterosis for body weight and for weights of carcases, drumstick and thigh was negative. Total breast muscle weight and P. major weight did not show significant heterosis. 6. It was concluded that selecting against TD does not reduce processing yield of broilers.     

Importance of bird traits for seed dispersal patterns of co‐fruiting trees in a patchy forest

Habitat fragmentation is globally one of the most important drivers of change in biodiversity. Seed dispersal by birds is crucial for tree regeneration in remnant patchy forests, yet how bird traits affect seed dispersal pattern is still poorly understood. We studied the extent to which bird traits affect seed‐removal networks and whether these traits affect seed deposition and seedling recruitment for 3 co‐fruiting tree species (Taxus chinensis, Cinnamomum bodinieri and Machilus thunbergii) in a patchy forest. A total of 17, 18 and 10 bird species were recorded foraging for seeds of T. chinensis, M. thunbergii and C. bodinieri, respectively. Frequency of bird visitation increased with tail length, wing length and body length. Furthermore, bird body length, bill length, body weight and wing length were important in the strength of the seed removal network. During foraging, 6 bird species exhibited different patterns of microhabitat utilization and their perching frequency increased with bird weight and tarsus length. As a consequence, frequency of habitat use, bird length and tarsus length were important in determining the number of deposited seeds. For seedling recruitment, seedling number increased with bird tarsus length and weight, but decreased with wing length. Overall, our results showed that various bird traits not only affected seed removal, but also influenced the subsequent processes of seed deposition and seedling distribution in a patchy forest. These results thus highlight the importance of large‐bodied birds for plant recruitment and point out the need to prioritize the protection and conservation of these birds in remnant patchy forests.     

Forced locomotor activity improves walking ability of male turkeys and modifies carcass characteristics

ABSTRACT

1. This trial investigated the effect of forced locomotor activity (training) on walking ability, leg posture, and growth performance, as well as carcass composition and meat quality in male fattening turkeys.

2. A flock of 744 commercial turkeys was divided into three experimental groups, either without any training period (control), training from weeks 2 to 8 (short-term), or training from weeks 2 to 21 (long-term). All birds were slaughtered at an age of 21 weeks. To study the effect of short vs. long time lapse between shackling and stunning (suspension time), each training group was split into two halves that were hooked on the shackle for either 15 s or 3 min prior to stunning.

3. Long-term physical training, compared to short-term or no training, resulted in better walking ability and in a lower percentage of leg malposition, as assessed at the end of fattening. No effect on final body weight was detected.

4. In a subsample, the composition of 80 carcasses was determined by dissection. Long-term training favoured the percentage of the drumstick over that of the breast cut in comparison to the group without any training.

5. Meat quality parameters were determined for breast muscle. The pH values 20 min post-mortem were reduced by long-term training, and the highest value was observed for a combination of no training with short suspension. After 24 h, pH values did not differ between experimental groups. The breast muscles were characterised as fast-glycolysing. Prolonged suspension time resulted in higher electrical conductivity after 24 h, and in higher a* values (redness).

6. In conclusion, the study revealed that a long-term training period improved walking ability and leg posture of heavy male turkeys. Thus, training can contribute to the improvement of animal welfare in turkey husbandry. Meat quality variables of breast muscles were partially influenced by locomotor activity and suspension time.     

Broiler carcass quality using head-only electrical stunning in a waterbath

1. The objective was to assess carcass quality of broilers when they were stunned by immersing their heads in a waterbath with an electric current flowing from one side of it to the other, while a second small current passed through the body to the waterbath to prevent involuntary wing flapping. 2. The prevalence of wing, shoulder and breast fillet haemorrhages and of broken bones in the pectoral region was not greater than that resulting from the normal stunning practice in that plant (63 mA, 610 Hz pDC). 3. These results imply that carcass damage using this technique will be significantly lower than that which will result from the application of higher stunning currents required by the new EU slaughter poultry slaughter regulations.     

Evaluation of EEG based determination of unconsciousness vs. loss of posture in broilers

Evaluation of the loss of consciousness in poultry is an essential component in evaluating bird welfare under a variety of situations and applications. Many current approaches to evaluating loss of consciousness are qualitative and require observation of the bird. This study outlines a quantitative method for determining the point at which a bird loses consciousness. In this study, commercial broilers were individually anesthetized and the brain activity recorded as the bird became unconscious. A wireless EEG transmitter was surgically implanted and the bird anesthetized after a 24-48 h recovery. Each bird was monitored during treatment with isoflurane anesthesia and EEG data was evaluated using a frequency based approach. The alpha/delta (A/D) ratio and loss of posture (LOP) were used to determine the point at which the birds went unconscious. There was no statistically significant difference between time to unconsciousness as measured by A/D ratio or LOP.     

Broiler chicken health, welfare and fluctuating asymmetry in organic versus conventional production systems

The aim of this study was to test three predictions: (1) that a combination of animal-based parameters indicates better health and welfare in broilers from organic versus conventional farms, (2) that broilers from organic farms show less fluctuating asymmetry (FA) than broilers from conventional farms, and (3) that, at the level of the individual bird, the relationship between FA and welfare is negative and strongest in conventional broilers. On 140 slaughter-age birds randomly selected from seven organic and seven conventional flocks in Belgium we measured standardised FA and five conventional animal-based welfare indicators (tonic immobility duration, latency-to-lie, and condition of the foot pad, hock, and breast). The caeca from the birds from four organic and four conventional flocks were removed for assessing the presence of two bacterial pathogens (Salmonella and Campylobacter) and the concentration of the health-promoting lactic acid bacteria. Finally, the blood serum concentration of the acute phase protein alpha-1-acid glycoprotein (AGP), a non-specific indicator of immunological stress, was determined. Salmonella was found in the caeca content of two (2.5%) birds only (both from the same conventional farm), whereas 44 (55.7%) birds were infected with Campylobacter. The prevalence of Campylobacter, the concentration of lactic acid bacteria, the duration of tonic immobility, and the condition of the breast and foot pad did not differ between both production systems. Apart from a higher concentration of AGP, organic birds had better scores for hock condition and a longer latency-to-lie indicating better leg health. In addition, organic birds scored better on the aggregated welfare index (i.e. the average of the five standardised welfare indicators). As both production systems differed in many aspects (e.g. slower-growing genotypes, slaughter age, feed, stocking density, group size) it is impossible to assign differences in welfare/health indicators to a single factor. Whatever the causes may be our findings suggest that, despite the potentially elevated risk of immunological challenge, broiler chicken welfare is generally superior in organic farms as compared with conventional farms in Belgium. Regarding the validity of FA as welfare indicator, the prediction of lower FA in the population with highest aggregated welfare score was confirmed but, at the level of the individual, no associations between FA and the aggregated welfare index were found irrespective of whether data from organic and conventional broilers were analysed separately or combined.     

Thermoregulatory capacity and muscle membrane integrity are compromised in broilers compared with layers at the same age or body weight

1. The effects of acute heat stress (2 h at 32 degrees C and 75% RH) on body temperature and indices of respiratory thermoregulation and skeletal muscle function were examined in two divergently selected male grandparent lines of broiler and layer-type chickens at two ages (35 and 63 d), or at a similar body weight (approximately 2.2 kg). 2. The two chicken lines exhibited markedly different baseline blood acid-base and skeletal muscle characteristics. At the same age or live weight, birds from the broiler line had significantly higher venous blood carbon dioxide tensions associated with lower blood pH. Plasma creatine kinase (CK) activities reflecting muscle membrane damage were also greatly elevated in the broiler line. 3. Exposure to acute heat stress caused an increase in deep body temperature, panting-induced acid-base disturbances and elevated plasma CK activity in both lines of chicken, an effect that increased with age. The extent of disturbances in acid-base regulation and heat-stress-induced myopathy were more pronounced in the broiler than the layer line at the same age or similar live weights. 4. It is suggested that genetic selection for high muscle growth in broiler lines has compromised their capacity to respond to an acute thermal challenge, leading to detrimental consequences for muscle function. This reduction in heat tolerance may have important implications for bird welfare and subsequent meat quality.     

Carcase and meat quality in ducks killed with either gas mixtures or an electric current under commercial processing conditions

1. The feasibility of killing 7-week old Peking ducks with gas mixtures and their effects on carcase and meat quality were evaluated and compared with killing in electrical waterbath under commercial conditions. 2. The prevalence of carcase appearance defects and broken bones in the carcases and haemorrhaging, pH, colour, cooking loss and texture of breast muscles were determined. 3. Ducks can be killed within 3 min by exposure to either 90% argon in air or a mixture of 30% carbon dioxide and 60% argon in air. 4. Gas or controlled-atmosphere killing of ducks, whilst they are still in their transport containers, would eliminate some of the welfare concerns associated with the conventional electrical waterbath stunning systems, without adversely affecting carcase and meat quality.     

Electrocorticogram spectral analysis and somatosensory evoked potentials as tools to assess electrical stunning efficiency in ducks

1. Fast Fourier transformations (FFTs) of electrocorticogram (ECoG) signals and averaging of somatosensory evoked potentials (SEPs) were used for assessing the impact of electrical stunning of ducks in a waterbath set to deliver a constant current of 150 mA, 600 Hz alternating current (AC) for 4 s. The effectiveness of stunning was determined on the basis of induction of epileptiform activity in the ECoG followed by a decrease in total power content to less than 10% of pre-stun values and abolition of SEPs. 2. One out of 10 birds was killed by the stun. FFT analysis of the ECoG signals of the remaining 9 birds showed that only one bird had a decrease of the total power to less than 10% of the pre-stun values for up to 70 s post-stun. The SEPs were retained in 6 out of 9 ducks and and 4 of them retained the evoked responses throughout the post-stun period. In the two birds showing abolition of SEPs, this was associated with a decrease in the total power content to below 10% of the pre-stun value. 3. The present experiment confirmed that the abolition of SEPs and the decrease of the total power below 10% of the pre-stun value for assessing unconsciousness after an electrical stunning in various species are also applicable to ducks. Based on this, it is concluded that electrical waterbath stunning of ducks using 150 mA of 600 Hz AC is ineffective.     

A survey of slaughter procedures used in chicken processing plants

Information was collected on the slaughter procedures used in 12 processing plants in Australia. The processing line speed varied from 25 to 125 birds/minute; the voltage in the electrified waterbath varied from 55 to 165 V; the duration of stunning was 2.0 to 7.5 seconds and the time allowed for exsanguination was 45 to 180 seconds. As a result of the variables, some birds were dead on leaving the stunner and prior to exsanguination, while it was probable that others were not dead before entering the scald tank.     

Effect of electrical stun/kill method, interval between killing and neck cutting and blood vessels cut on blood loss and meat quality in broilers

1. Broiler chickens were killed using either an electrical waterbath (WB system) delivering 120 mA per bird (50 Hz, alternating current, AC) for 4 s or an alternative stun/kill method (ASK system); where head-only stunning for 1 s was immediately followed by head-to-body (vent) application for 1 s (150 mA, 50 Hz sine wave AC). Within each stun/kill system, the neck was cut ventrally or unilaterally 20, 60, or 180 s after killing. In addition, a control group of broilers was stunned with 100 mA per bird in a waterbath using 1500 Hz AC for 4 s and were bled by a ventral neck cut within 20 s. 2. Blood leaving the neck cut was collected for 90 s in a bin placed on an electronic balance and blood loss (g/kg body weight) calculated. 3. Individually identified, unplucked and uneviscerated carcases were held at ambient temperature until the end of the experimental day and then stored overnight in an air chiller (5 degrees C). The carcases were dissected and the incidence of broken furculum and coracoid bones, haemorrhaging in P. minor and P. major muscles, and discolouration of P. major muscles were determined. 4. When neck cutting was performed in broilers 20 s after the stun or kill, the ASK and WB systems, in comparison with high frequency stunning, produced on average about 10 g per kg less bleed out. Within the stun/kill systems, broilers killed by ASK had a greater bleed out than in the WB system. Neck cutting at 20 s or 60 s post-kill resulted in a greater bleed out than when performed after a delay of 180 s. Ventral or unilateral neck cutting resulted in a similar bleed out. 5. Stunning broilers with 1500 Hz AC resulted in lower incidences of broken bones, haemorrhaging in breast muscles and muscle discolouration post mortem than the stun/kill systems. These defects were significantly lower in the ASK than in the WB system. Delayed neck cutting increased the severity of discolouration occurring Post mortem in the breast muscles. 6. It is suggested that broilers killed by ASK can be neck cut with a delay of up to 180 s without compromising bleed out. The incidence of broken bones and haemorrhaging in breast muscles are significantly less with ASK than WB. 7. Owing to the commercial benefits and potential for improved welfare at slaughter, ASK would appear to be a better method than WB.     

Breast blisters in groups of slow-growing broilers in relation to strain and the availability and use of perches

1. The relationship between perching behaviour, availability of perches and the incidence and severity of breast blisters in broilers was investigated together with a comparison between two slow-growing broiler strains. 2. Sixteen single strain groups (n = 60) of Labresse and i657 broilers were subjected throughout the experiment to one of three perch availabilities: 15 cm per bird (Labresse and i657), 7.5 cm per bird (i657 only), and 0 cm per bird (i657 only) with 4 replicates per treatment. The birds were housed indoors from one day old, and at 43 d of age 52 birds from each group were moved to outdoor housing facilities with access to grass-covered outdoor areas until slaughter at 84 d of age. 3. The use of perches was monitored via video recordings throughout the experimental period. The severity of breast blisters was recorded on a scale from 0 to 2 at slaughter. 4. Groups of i657 with 15 cm perch per bird used these more than groups with 7.5 cm perch per bird (19% vs 8% of birds perching at midnight). A positive association between access to perches and severe breast blisters (score 2) was found in the groups of i657, with odds ratios of 3.1 and 3.4 for 7.5 and 15.0 cm per bird, respectively, relative to the no-perch treatment. 5. Labresse were more likely to develop breast blisters than i657 (odds ratio 3.5), but used the perches less (0.1 vs 9.5 birds perching at midnight) and weighed less (2011 g vs 2246 g) than i657. 6. Males had a higher incidence of breast blisters than females (odds ratio 12.2), and this was most prominent in the Labresse strain (odds ratio 40.0). 7. In some broiler strains access to perches may be associated with an increase in the occurrence of severe breast blisters, but strain and sex of broiler chickens appear to have a much larger influence than access to perches on the incidence of breast blisters.     

Influence of increasing slaughter age of chickens on meat quality, welfare, and technical and economic results

Because of the increasing demand for raw cuts and processed products, there is a trend to producing very heavy broilers. Breeds that are used for such kinds of production have been intensively selected for growth rate and breast meat yield, and birds are reared for a longer period than standard broilers. This study was to evaluate the effects of increasing slaughter age on technical and economic factors, including production efficiency and environmental costs, bird welfare, and breast meat quality in a modern heavy broiler line. Five groups of 300 male Ross 708 chickens were reared until slaughter ages of 35, 42, 49, 56, or 63 d. Increasing age at slaughter from 35 to 63 d resulted in a 7.4-fold increase (P < 0.01) in mortality rate (5.21 vs. 0.70%). It also increased (P < 0.001) the slaughter weight and ADFI of birds 2.5- and 1.4-fold, respectively, without affecting their G:F. Under our experimental conditions, economic profit evaluated through the net gain reached a maximum at 42 d. The moisture and ammonium content of litter increased (P < 0.05 and P < 0.01, respectively) rapidly during rearing concomitantly with increased (P < 0.05) occurrence and severity of contact dermatitis and decreased (P < 0.05) walking ability and activity of birds. Thermal comfort also decreased (P < 0.05) greatly as early as 42 d of age. Changes in carcass quality occurred mainly between 35 and 56 d of age, with a progressive increase (P < 0.001) in breast and leg yield, whereas body fatness was barely affected by age. Major changes in breast meat traits were observed between 35 and 49 d of age, with an increase in muscle pH at 15 min (P < 0.01) and 24 h (P < 0.001) postmortem and reduced (P < 0.001) lightness and drip loss. The protein and lipid content of raw breast meat also increased (P < 0.05 and P < 0.01, respectively) with age. Taking into account the main aspects of sustainability, we could recommend slaughtering chickens of heavy line at 42 d of age.     

Protein utilisation and turnover in lines of chickens selected for different aspects of body composition

1. Protein utilisation and turnover were measured in male chickens sampled from a line selected for high breast yield and a randombred control line (lines QL and CL, experiment 1) and in male chickens sampled from lines selected for either high or low abdominal fatness (lines FL and LL, experiment 2). In each experiment, 18 birds per line were given iso-energetic (12.9 MJME/kg) diets containing either 120 or 220 g CP/kg from 21 to 29 d (experiment 1) and 33 to 43 d (experiment 2). 2. Measurements were made of growth rate, food intake, body composition, excreta production and Ntau-methylhistidine excretion as a measure of myofibrillar protein breakdown, and fractional rates (%/d) of protein deposition, breakdown and synthesis were calculated. 3. In experiment 1, there were no significant differences between the line means for the fractional measures of protein turnover, but there was marked differential response in the two lines in the fractional rates of protein deposition, breakdown and synthesis, to increase in protein intake. The positive slope of the regressions of fractional (%/d) protein deposition and synthesis rates on protein intake (g/d/kg BW) were approximately 1.4- and 2.0-fold higher respectively in the QL than the CL line birds, and the negative slope of the regression of fractional breakdown rate on protein intake was approximately threefold greater in the CL than the QL line birds. 4. In experiment 2, fractional deposition rate was 6.2% lower, but fractional breakdown rate 9.4% higher in the LL than the FL birds, whilst there was essentially no difference in response of the FL and LL birds in the components of protein turnover to increase in protein intake. Line differences in deposition and breakdown rates were thus a reflection of the considerably higher (20%) food and hence protein intake in the FL than the LL birds. 5. The differential line responses in protein turnover in the two experiments suggest that selection for increased breast muscle yield and for reduced body fatness manipulate different physiological pathways in relation to protein turnover, but neither selection strategy results in an improvement in net protein utilisation at typical levels of protein intake by birds on commercial broiler diets, through a reduction in protein breakdown rate.