The present study was aimed at estimating the genetic variability between lines of breast and thigh meat quality (pH decline, color, drip loss, and curing-cooking yield) by comparing a slow-growing French label-type line (SGL) and a fast-growing standard line (FGL) of chickens exposed to different preslaughter stress conditions. The birds were slaughtered under optimal conditions or after exposure to 2 h of transport or acute-heat stress (2 h at 35 degrees C). Relationships between meat quality and stress sensitivity were investigated by measuring struggle during shackling and tonic immobility (TI) duration, 1 wk before slaughter, as an indicator of the basal level of fear of the birds. Although most of the meat quality indicators varied between the 2 lines, differences were muscle dependent. In concordance with a lower ultimate pH, curing-cooking yield of thigh meat was decreased for the FGL birds. In contrast, these birds had a higher curing-cooking yield and a lower drip loss of breast meat resulting from a less rapid pH decline in this muscle compared with SGL birds. Thigh meat characteristics were influenced by both preslaughter stresses, but no significant effects were detected for breast meat. The main effect of heat stress in thigh meat was a decrease of the ultimate pH and led to paler color and lower curing-cooking yield; opposite effects were obtained for transport. Breast meat was much more sensitive to physical activity of birds on the shackle line. Longer durations of wing flapping on the shackle line gave more rapid initial pH decline. Whatever the line, no relationship between TI duration and meat quality characteristics or activity was observed. The present study suggested that SGL birds could be at disadvantage due to more struggle during shackling and accelerated postmortem glycolysis, which is detrimental to the quality of breast meat.

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.

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.

A new enzyme immunometric assay of small haptens containing primary amino groups (thyroxine, MW 777; substance P, MW 1347; endothelin, MW 2492) is described. The procedure involves different sequential steps: (1) immunocapture of the haptens (standard or sample) by monoclonal anti-hapten antibodies coated on 96-well microtiter plates; (2) cross-linking of haptens via their amino groups to the wells using homobifunctional reagents (glutaraldehyde or disuccinimidyl suberate); (3) denaturing treatments (HCl or methanol); (4) measurement of linked epitope using the same monoclonal anti-hapten antibodies labeled with acetylcholinesterase. A minimal detectable concentration in the 4-10 fmoL/mL range was observed. Each assay appeared to be 70-200 times more sensitive than conventional competitive enzyme immunoassay using the same monoclonal antibody-coated plate technology and acetylcholinesterase-hapten conjugates as enzymatic tracers. Precision and specificity were very satisfying. Good correlation was noted between this assay and the competitive assays performed for different biological samples (plasma, tissues, or supernatant cell culture).

Soy proteins are used in products of pork butchery for their binding properties and/or their protein content. French legislation limits the addition of binding proteins to 2% in some meat products. Current detection methods are unable to quantify vegetable proteins in these products: the results differ according to the manufacturing process. We have developed a method to quantify these proteins by using immunohistochemical techniques associated with image analysis. This process is based on measuring the areas occupied by labeled soy proteins in sections mounted on slides, and not on estimating amounts of proteins in solution.