E. T. Moran, Jr and J. Galobart
Poultry Science Department,
Auburn University, AL 36849
USA
Broilers received either "normal" preslaughter stress or avoided carrying-transport. Resultant carcasses were slush-ice chilled either 6 or 30 hours then breast meat removed. Similar yields of carcass and abdominal fat occurred between preslaughter treatments, but extended chilling increased carcass weight. Carrying-transport decreased P. major yield and increased blood appearance (?), whereas extended chilling-deboning also decreased P. major yield but had no effect on blood appearance. Reduced lightness (L) and increased redness (a) occurred with carrying¬transport while extended chilling-deboning increased redness and yellowness (b). P. minor yield was not affected by carrying-transport but myopathy increased, whereas extending chilling-deboning reduced yield without altering myopathy.
Introduction
Yield and quality of broiler breast meat are known to suffer from the stresses associated with bird transfer from farm to processing plant. Breast meat decreases more than any other tissue with transport (Moran and Bilgili, 1995). Vibration with movement has been shown to elevate body temperature and predispose a decrease in the pH of breast meat (Warris et al., 1997). Such excitement appears to accentuate redness of the final product that is not related to blood (Ngoka and Froning, 1982). Hemorrhaging into meat is multifaceted with physical handling being the primary culprit (Kranen et al., 2000). Handling that encourages wing movement is also known to facilitate the occurrence of deep pectoral myopathy (Siller et al., 1978). Processing and associate post mortem changes may also alter breast meat yield and quality. Tenderness of breast meat substantially improves through the first several hours post mortem (Lyon et al.1992; Young, 1997); however, color and cooking loss are not perceptibly altered (Papinaho et al., 1996). Wing activity from post-stun electrical stimulation to enhance post mortem glycolysis and tenderness also decreases muscle pH at the time, but differences ultimately equalize as the duration of chilling is extended (Gault et al., 2000). Mechanized catching and improved environment during transport can substantially decrease the stress perceived by broilers (Duncan et al., 1986; Nicol and Scott, 1990). Present experimentation examined the significance of the omission of carrying after catching and motion of transport on breast meat from heavy broilers, and whether modifications of these effects would occur after processing from an extended chill and duration before its removal from the carcass.
Materials and Methods
A total of 1600 male chicks (Ross x Hubbard HiY) obtained from a commercial hatchery were randomly distributed to 32 floor pens (4.2 sq m /pen) having pine shaving litter. All birds received common corn soybean meal feeds to 8 weeks of age (21.8% CP & 3.03 kcal ME/g, 0-17 days; 20.0 & 3.10, 17-38; 19.2 & 3.16, 38-45; and 18.4 & 3.17, 45-56, respectively).
At 56 days of age, birds were either carried approximately 25 m by one leg in groups of three from pen to coops on a truck or cooped directly at the pen and coop carried to the truck. Birds that had been carried were subsequently transported in coops for one hour then held stationary until processing, whereas those cooped the pen were directly transferred for holding at the processing plant. A total of 12 hours from catching until slaughter occurred with both preslaughter treatments.
On-line processing involved a 9-minute kill line followed by a 7-minute evisceration line until chilling. Warm carcasses from each preslaughter treatment were divided and subsequently static submersion slush-ice chilled either 6 or 30 hours. Immediate to chilling, fat was removed from the abdominal cavity followed by carcass deboning by experienced commercial personnel using stationary cones. Blood contaminating the P. major and P. minor indicating myopathy were ascertained concurrent with removal of breast meats from the carcass. Light reflectance was measured at the center on the skin side of all P. major muscles at 48 hours post-mortem using the Hunter scale with a Minolta hand-held spectrophotometer. Analysis of variance based on a factorial arrangement of the two preslaughter treatments and two chilling durations were the basis of statistical evaluation.
Results and Discussion
The feeding regimen and environment provided to broiler males used in present experimentation led to a favorable final performance at 56 days of age (live weight= 3665 g; F/G= 1.96; total mortality= 10.4%). Omitting both carrying and actual transportation during the 12 hours preslaughter was intended to simulate optimization of advantages using mechanical catching and improved conditions possible from optimal truck design; thereby, enabling a defined comparison to stresses existing under present circumstances. Moran and Bilgili (1995) imposed 6 hours of transport to broilers and observed a significant loss in body weight that was particularly apparent with breast meat compared to those kept stationary. Imposing carrying together with one hour of transportation failed to adversely affect loss in either abdominal fat or yield of the resultant carcasses in present experimentation (Table 1), but a decrease in the P. major was perceptible (Table 2).
Extending submersion chilling from 6 to 30 hours increased carcass weight; however, subsequent removal of the P. major indicated a substantial loss in yield that could largely be attributed to the associated improved tenderness and adherence of portions to the skeletal frame (Table 1).
The P. major from broilers that had received carrying-transport exhibited additional blood attributable to vascular rupture that was not altered by extended chilling-deboning. Measurements conducted 48 hours post mortem indicated a reduction in lightness (L) when additional preslaughter stress had been applied as well as increased redness (a). Areas of blood contamination and reflectance measurements differed; thus, the influence of one on the other seemed unlikely. Although extended chilling-deboning did not alter lightness, redness and yellowness (b) increased independent of preslaughter stress.
The P. minor responded to carrying-transport and chilling in a different manner than the P. major (Table 3). Carrying-transport did not perceptibly alter yield, whereas the improved tenderness arising from the delay from 6 to 30 hours post mortem led to a loss in its recovery from the carcass. The incidence of deep pectoral myopathy was extensive with these broilers, and an increased incidence with carry-transport was apparent. Wing flapping facilitates an ischemia that may affect all or part of the muscle (Martindale et al., 1979). Reddening appears with affected areas prior to the traditional gangrenous appearance. Its reduced incidence with extended chilling¬ delayed deboning occurs independently and probably relates to muscle changes that decrease detection. Overall results indicate that minimizing preslaughter stresses to improve bird welfare will benefit both breast muscles as will extended post mortem duration, but the basis of theses changes are different and independent of one another.
References
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From Proceedings of the "XVI European Symposium on the Quality of Poultry Meat" and the "X European Symposium on the Quality of Eggs and Egg Products", Saint-Brieuc Ploufragan, France.
