Feather retention force in broilers ante-, peri-, and post-mortem as influenced by electrical and carbon dioxide stunning

Feather Retention Force in Broilers Ante-, Peri-, and Post-Mortem as Influenced by Electrical and Carbon Dioxide Stunning R. J. BUHR,*,1 J. A. CASON,† and G. N. ROWLAND* *Department of Avian Medicine, College of Veterinary Medicine, The University of Georgia, Athens, Georgia 30602-4875, and †USDA, Agricultural Research Service, Richard B. Russell Agricultural Research Center, P. O. Box 5633, Athens, Georgia 30604-5677 methods for the pectoral and femoral feather tracts. Small changes in FRF values occurred from ante-mortem to peri-mortem (–1 to +12%), and from ante-mortem to post-mortem (–2 to +8%) across stunning methods. A significant increase was determined for only the pectoral tract (7%) from ante- to peri-mortem across stunning methods. Electrically stunned broilers that were not bled gained weight in excess of the 36 feathers removed (0.16%), apparently due to body surface water pickup during the brine-stunning process, whereas CO2stunned broilers lost weight due to excretion of cloacal contents (–0.31 to –0.98%). The change in body weight among stunning methods was significant (P < 0.0233). Peri- and post-mortem FRF, in addition to bleed-out body weight loss, were not substantially influenced by electrical or CO2 stunning methods, and, therefore, carcass defeathering efficiency may not differ after scalding.

(Key words: feather retention force, electrical stunning, carbon dioxide stunning, broiler, post-mortem) 1997 Poultry Science 76:1602–1606

INTRODUCTION Feather retention force (FRF), the force required to remove a feather from the feather follicle, can be modified in conscious (ante-mortem) and unconscious (peri-mortem, after stunning) birds, but substantial carryover after slaughter (post-mortem), either an increase or decrease in force, has not been observed (Buhr et al., 1997). Peri-mortem sampling of broilers at 20 or 120 s after electrical stunning (without bleeding) resulted in a lower FRF of 16 to 18% compared to prestunning ante-mortem values (Dickens and Shackleford, 1988). Following stunning (50 V alternating current) and bleeding (90 s) Kuenzel et al. (1986) reported that post-mortem FRF was reduced 10%, or in conjunction with an additional secondary post-bleeding stunner was reduced by as much as 28%. However,

Received for publication November 12, 1996. Accepted for publication June 9, 1997. 1To whom correspondence should be addressed.

Mahoney et al. (1971) found no significant differences in carcass picking scores, following scalding and picking, among electrically stunned (whole body, head, or back), debrained, or semi-Kosher slaughtered broilers. These reports indicate that electrical stunning induces minor reductions in FRF as compared to the 81 to 99% reduction after immersion scalding (Klose et al., 1962; Dickens and Shackleford, 1988; Walker and Griffis, 1994). Although administration of anesthetics or tranquilizers has been shown to reduce ante-mortem FRF >80%, approaching postscalding values (Klose et al., 1961; Ostmann et al., 1963), carryover post-mortem has not been found. Spinal cord transection in anesthetized White Leghorn hens further reduced FRF (66%) in feather tracts innervated by spinal nerves located caudally to the lesion, beyond the 22% decrease associated with the light anesthesia measured from feather tracts innervated by spinal nerves located cranial to the lesion (Ostmann et al., 1964). When death was induced in anesthetized and spinal cord transected hens

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ABSTRACT Stunning and slaughter trials were conducted to evaluate the influence of stunning method (electrical 50 V alternating current, CO2 gas: 0 to 40% for 90 s or 40 to 60% for 30 s) on feather retention force (FRF) in commercial broilers. Feathers from the pectoral, sternal, and femoral feather tracts were sampled with a force gauge before stunning (ante-mortem) and contralaterally either after stunning (peri-mortem from 0.5 to 4 min) or after stunning and bleeding (post-mortem from 2 to 6 min). Prior to stunning, ante-mortem FRF values varied among assigned stunning methods only for the pectoral (7%) feather tract. After stunning, perimortem FRF values were higher only for the sternal tract (11% for 40 to 60% CO2 for 30 s); whereas after stunning and bleeding, post-mortem FRF values were lower than ante- or peri-mortem only for the sternal tract (10% lower for 40 to 60% CO2 for 30 s). Peri- and post-mortem FRF values did not differ among stunning

FEATHER RETENTION FORCE AFTER STUNNING

MATERIALS AND METHODS The procedures used in these experiments were similar to those described by Buhr et al. (1997). The following description indicates differences in procedures and includes an abbreviated overview. On each of 4 processing d, 18 live male broiler chickens were obtained from a commercial processing plant, cooped, and transported in a covered vehicle to the pilot processing facility. Broilers were removed from transport coops, individually weighed, assigned a stunning method, and the initial ante-mortem feather samples were pulled from conscious broilers. The second weighing occurred after pulling the peri- or post-mortem set of feathers. Body weight loss was determined by the difference between ante-mortem and peri- or postmortem weights. Body weight was measured to assure uniformity in broiler size and feather development

2Shimpo America 3Liquid Carbonic,

Corp., Lincolnwood, IL 60659. Industrial Gases, Oak Brook, IL 60521-2216.

among assigned stunning methods. Body weight loss during bleeding was calculated to compare blood loss among stunning methods. Broilers were assigned the three stunning methods sequentially (forward and reverse, i.e., 1st, 6th, 7th, 12th, 13th, and 18th) resulting in first and last broiler sampled each day being assigned to the same stunning method. In addition, ante-mortem sampling side (left or right) was alternated for each successive broiler as was the feather tract sampled (pectoral, sternal, or femoral) to minimize bias between initial ante-mortem and final peri- or post-mortem feather samples. These three feather tracts were chosen as representative of covert feathers varying in size from different regions of the body.

Measuring Feather Retention Force A maximum indicating force gauge2 was used to record the force (grams) required to remove a late-immature feather from the feather follicle. Individual feathers were clamped above the follicle umbilicus with a hemostatic tissue forceps, the forceps attached to the force gauge, and the forceps-gauge moved away from the carcass. During feather removal, broilers were suspended in shackles (inverted) and feathers were extracted from the carcass at an angle parallel to the median plane of the carcass, and perpendicular to the floor. This orientation required a correction of 75 g, (the combined weight of the internal components of the force gauge and the hemostat used to grasp the feather), prior to analysis. Prestunning feather samples pulled from conscious broilers were considered ante-mortem. Ante-mortem values were collected to enable determination of the relative depression or elevation in FRF peri- or postmortem. Feather removal initiated at 0.5 min after stunning was considered as peri-mortem and these broilers were not bled. Feather extraction initiated at 2 min after stunning and during completion of bleed-out was considered as post-mortem. Peri- and post-mortem samples were taken to determine the relative depression or elevation in FRF following stunning and after death. Sampling rate was approximately four broilers per hour, requiring 4 min to pull six feathers unilaterally from each of the three feather tracts. Six feathers were pulled in sequence from the pectoral, sternal, and femoral feather tracts for each sampling period. Feather retention force was averaged for each feather tract, individual broiler, and sampling period. The difference between antemortem and peri- or post-mortem contralateral samples was expressed as percentage change in FRF.

Stunning and Slaughter Electrical stunning was applied using a brine stunner (saturated salt solution) with voltage set at 50 V alternating current for 10 s, with an average current draw of 30 mA per bird. Broilers were stunned individually head to shanks. Controlled atmosphere CO2 stun was applied in a test stunning cabinet3 (60.5 ×

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by an overdose of anesthetic (sodium pentobarbital, Ostmann et al., 1964) an immediate additional postmortem decrease (37%) in FRF occurred. After 5 min post-mortem, FRF had increased by 94% above the anesthetized and spinal cord transected value to approximately 31% less than the unanesthetized value. When death was induced by exsanguination and clonic convulsions occurred, there was an immediate increase in FRF of 160% above the anesthetized and spinal cord transected value to approximately 5% lower than the unanesthetized value (Ostmann et al., 1964). These results indicate the lack of any significant carryover effects post-mortem from ante-mortem anesthesia or spinal cord transection, and suggest that the occurrence of clonic convulsions are associated with rapid return of FRF post-mortem for anesthetized hens. Gas stunning is an effective immobilizing agent for poultry (Kotula et al., 1957, 1961; Poole and Fletcher, 1995) and some sources suggest that carbon dioxide stunning lowers post-mortem FRF. For instance, Liquid Carbonic literature (1995) concerning its CO2 Controlled Atmosphere Stunning System lists as a benefit “facilitates loosening cover feathers”, and Lindholst (1991:29) states that with CO2 stunning “The shorter bleeding time makes it possible to have a quicker scalding, which allows for an easier plucking.” Reports measuring FRF or carcass picking scores following CO2 stunning are not available in the literature. It is possible, however, that the clonic convulsions experienced by broilers killed with CO2 (Mohan Raj et al., 1990) may influence FRF similar to the increases associated with clonic convulsions following exsanguination reported by Ostmann et al. (1964). The objective of this study was to quantify the effects of CO2 stunning on FRF in commercial broilers and to compare these with those for electrical stunning.

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BUHR ET AL. TABLE 1. Ante-mortem, peri-mortem, and post-mortem feather retention force influenced by stunning method for the pectoral, sternal, and femoral feather tracts

Stunning method

Feather retention force Pectoral

Sternal

Femoral

349 361 351 354 24

Ante-mortem 336 681 361 648 347 663 348 664 23 31 Probability

Pectoral

Percentage change Sternal

Femoral

Pectoral

Sternal

(g) Trials 1 and 3 Electrical 0 to 40% CO2 40 to 60% CO2 Mean Pooled SEM

Source of variation Stunning method Ante-mortem to post-mortem Combined trials 1 to 4 Electrical 0 to 40% CO2 0 to 60% CO2 Mean Pooled SEM Source of variation Stunning method Ante-mortem to perior post-mortem

0.6724 0.0013 380a 372a 334b 362 23

0.0012 0.0510 365a 366a 342b 358 23

0.1820 0.1741 0.4077 0.2788 Ante-mortem 346 685 328 680 351 671 342 679 23 33 Probability 0.1857 0.7748 0.1137 0.7911 Ante-mortem 341 683 344 664 349 667 345 671 23 32 Probability

0.0214

0.6487

0.2959

0.0003

0.0949

0.5856

(%) Peri-mortem1 345b 672 381a 682 339b 672 355 675 26 32 Probability

390 376 370 379 23

0.3208

0.1060

0.0127

0.8910

–1 5 1 2

1 6 8 4

5 1 4 3

–2 –2 3 0

5 5 7 6

4 4 1 3

–2 1 2 1

0.3759

Peri- or Post-mortem 354 672 357 673 352 682 354 676 24 33 Probability

0.1058

3 6 –2 2

0.8096

Post-mortem2 362a 673 332b 664 365a 691 353 676 21 34 Probability

379 394 362 378 26

384 385 366 378 24

0.0108

12 4 5 7

0.7375

a,bMeans

within a column and sample period with no common superscript differ significantly (P < 0.05); n = 12 broilers per stunning method. 0.5 to 4.5 min after stunning and not bled. 2Post-mortem 2 to 6 min after stunning and initiation of bleeding. 1Peri-mortem

60.5 × 132 cm). Shackled broilers were suspended in the cabinet and CO2 injected at a precalibrated4 rate to provide an increasing concentration (0 to 40%) of CO2 within 90 s. Alternatively the cabinet was preloaded to 40% CO2, the shackled broiler placed into the cabinet, and then the CO2 concentration increased from 40 to 60% within 30 s. Air mixing within the cabinet was obtained by a continuous updraft created by top mounted exhaust fans that drew air into the cabinet from below the CO2 injector. Carbon dioxide gas was vaporized from liquid CO2 by passing through a copper tubing submerged in a hot waterbath. The resulting cabinet supply gas pressure was 2,068 kPa (300 psi), which was reduced by a regulator to an operating pressure of 552 kPa (80 psi). All broilers were removed from the stunning shackle and transferred to a bleed-out

4CO Gas Analyzer, Model 20-600, Gow-Mac Instrument Co., 2 Bridgewater, NJ 08807.

shackle, and those bled had both carotid arteries and at least one jugular vein severed within 10 s after completion of stunning.

Statistical Analysis Feather retention force was determined from broilers subjected to different stunning methods (electrical, CO2 0 to 40% or 40 to 60% CO2), at sample periods representing ante-, peri-, and post-mortem. All stunning and slaughter methods were replicated on 2 processing d (Trials 1 and 3 compared ante- and peri-mortem FRF values, and Trials 2 and 4 compared ante- and post-mortem FRF values) resulting in n = 24 broilers for ante-mortem and n = 12 broilers per stunning method and sample period. Mean FRF for the six feathers per feather tract per broiler was analyzed using the General Linear Models procedure of SAS, and the means separated using the Tukey’s Studentized range (HSD) Test (SAS Institute, 1994). For all analyses, significance was determined at P < 0.05 level. Feather tracts consistently differed in FRF; therefore, the

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Source of variation Stunning method Ante-mortem to peri-mortem Trials 2 and 4 Electrical 0 to 40% CO2 40 to 60% CO2 Mean Pooled SEM

Femoral

FEATHER RETENTION FORCE AFTER STUNNING TABLE 2. Body weight and weight loss during feather sampling with and without bleeding1 Body weight Stunning method

Ante-mortem

Peri- or post-mortem

(kg)

(%)

1.873 1.945 1.948 1.922 0.041 0.3576

1.876 1.939 1.929 1.914 0.041 0.5209

+0.16a –0.31b –0.98b –0.42 0.27 0.0233

1.949 1.905 1.946 1.933 0.055 0.8241

1.881 1.837 1.870 1.863 0.054 0.8330

–3.50 –3.57 –3.91 –3.65 0.24 0.5225

a,bMeans within a column and stunning method with no common superscript differ significantly (P < 0.05). 1n = 12 broilers per stunning method.

data were reanalyzed and are reported by feather tracts. Sources of variation in this model included main effects: stunning method (electrical, 0 to 40% or 40 to 60% CO2) and sample period (ante-, peri-, and post-mortem). Interaction terms for main effects were tested by residual error. Interactions between trials and main effects were not significant, and therefore Trials 1 and 3 and Trials 2 and 4 were combined.

RESULTS AND DISCUSSION Consistent with previous reports (Dickens and Shackleford, 1988; Buhr et al., 1997), FRF for all trials and sample periods was greater in the femoral area (648 to 691 g) than the pectoral area (334 to 394 g), which was slightly greater than the sternal tract (328 to 381 g, Table 1). The data are reported for each discrete feather tract, stunning method, and sampling period. In Table 1, FRF values within a row represent ante-mortem and peri- or post-mortem contralateral samples collected from the same group of broilers. Ante-mortem FRF values collected prior to stunning did not differ among broilers assigned to each stunning method for all three feather tracts for Trials 1 and 3. Following stunning, peri-mortem FRF values changed minimally (–1 to +12%) from ante-mortem values. However, in the sternal tract 0 to 40% CO2 stunned broilers had a higher peri-mortem FRF value (11%) than electrical or 40 to 60% CO2 stunned broilers. This higher peri-mortem FRF value represents a 6% increase above the ante-mortem value for 0 to 40% CO2 stunned broilers. Only for the pectoral feather tract did FRF significantly increase (7%) from ante- to peri-mortem for all three stunning methods (P = 0.0013). Ante-mortem FRF values prior to stunning were lower for broilers assigned 40 to 60% CO2 stunning for

only the pectoral (13%) tract for Trials 2 and 4 (Table 1). Post-mortem, 2 min after stunning and bleeding, minimal changes in FRF (–2 to +8%) had occurred and FRF values did not differ among stunning methods for the pectoral and femoral feather tracts. For the sternal tract, FRF was significantly lower (10%) for broilers stunned with 0 to 40% CO2, opposite of the peri-mortem increase (11%). The significantly higher peri-mortem and lower post-mortem FRF values for only the sternal feather tract for broilers stunned with 0 to 40% CO2 may have been associated with corresponding relatively higher and lower ante-mortem FRF values of broilers assigned this stunning method. It was also noted that sternal feather tract was most variable in feather size of the three feather tracts at broiler market age. For all three feather tracts, the percentage change in FRF from ante- to post-mortem was not significant. To determine whether stunning method resulted in elevated or depressed FRF peri- or post-mortem values compared to ante-mortem values, data for Trials 1 to 4 were combined and analyzed by sampling period (antemortem and combined peri- and post-mortem). The rationale for combining peri- and post-mortem values was based on the 92% mortality rate for broilers stunned with either CO2 method without bleeding. Analysis detected that only the pectoral tract had significant increases (P < 0.0003) in FRF from ante- to peri- or postmortem values (6%). These results demonstrate that both CO2 stunning procedures, similar to electrical stunning, did not substantially alter FRF with or without bleeding (perimortem 0.5 to 4 min after stunning, or post-mortem 2 to 6 min after stunning and bleeding). These results indicate that broilers stunned with either CO2 method may not differ in defeathering efficiency compared to electrically stunned broilers. It is important to emphasize that the percentage change in FRF in this study is relatively small (–2 to +12%) compared to those reported following scalding and deep anesthesia (>80%).

Body Weight Measurements Prestun broiler body weight did not differ among slaughter methods for any processing trial, P = 0.8241 (Table 2). Therefore, similar body size and degree of feather maturity among stunning methods can be assumed. After removal of 36 feathers, peri-mortem body weight loss (without bleeding) significantly differed for broilers stunned electrically compared to those stunned with CO2 (P = 0.0233). Broilers electrically stunned had gained weight (+0.17%), whereas body weight loss occurred following stunning with 0 to 40% CO2 (–0.34%) or 40 to 60% CO2 (–0.95%). Carcass weight for electrically stunned broilers increased greater than the loss from 36 feathers, presumably due to body surface water pickup during the brine-stunning process. The greater perimortem body weight loss that occurred in broilers stunned with CO2 was due most likely to excretion of cloaca content. These findings demonstrate that water

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Stunned not bled Electric 0 to 40% CO2 40 to 50% CO2 Mean Pooled SEM Probability Stunned and bled Electric 0 to 40% CO2 40 to 60% CO2 Mean Pooled SEM Probability

Percentage change

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BUHR ET AL.

pick-up and cloacal discharge should be determined and accounted for in comparing bleed-out blood loss among different stunning methods. However, in Trials 2 and 4, post-mortem body weight loss following stunning, bleeding, and feather extraction did not significantly differ (P = 0.5225) among stunning methods, electrical (3.5%), 0 to 40% CO2 (3.57%), or 40 to 60% CO2 (3.91%). The results of this study indicate that peri- and post-mortem FRF values for the pectoral, sternal and femoral feather tracts are not substantially altered (–2 to +12%) by electrical or CO2 stunning methods.

ACKNOWLEDGMENT The authors thank V. Allan Savage for technical support and assistance with data collection.

Buhr, R. J., J. A. Cason, and G. N. Rowland, 1997. Feather retention force in broilers ante-, peri-, and post-mortem as influenced by carcass orientation, angle of extraction, and slaughter method. Poultry Sci. 76:1591–1601. Dickens, J. A., and A. D. Shackleford, 1988. Feather-releasing force related to stunning, scalding time, and scalding temperature. Poultry Sci. 67:1069–1074. Klose, A. A., E. P. Mecchi, and M. F. Pool, 1961. Observations on factors influencing feather release. Poultry Sci. 40: 1029–1036. Klose, A. A., E. P. Mecchi, and M. F. Pool, 1962. Feather release by scalding and other factors. Poultry Sci. 41:1277–1282. Kotula, A. W., E. E. Drewniak, and L. L. Davis, 1957. Effect of carbon dioxide immobilization on the bleeding of chickens. Poultry Sci. 36:585–589.

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REFERENCES

Kotula, A. W., E. E. Drewniak, and L. L. Davis, 1961. Experimentation with in-line carbon dioxide immobilization of chickens prior to slaughter. Poultry Sci. 40:213–216. Kuenzel, W. J., J. Walther, and W. Collins, 1986. The effect of pre- and post-stunning on bleed-out and feather release in processed broilers. Pages 62–66 in: Proceedings 21st National Meeting Poultry Health Condemnations, Ocean City, MD. Lindholst, S., 1991. Gas stunning has positive effect on meat quality. World Poult. 7(6):29. Liquid Carbonic, 1995. Controlled atmosphere stunning system. Form No. 6917R. Liquid Carbonic, Industrial Gases, Oak Brook, IL. Mahoney, W. A., G. W. Newell, and G. Olson, 1971. Feather release as related to stunning methods. ASAE Paper No. 71-865. American Society of Agricultural Engineers, St. Joseph, MI. Mohan Raj, A. B., N. G. Gregory, and S. B. Wooton, 1990. Effect of carbon dioxide stunning on somatosensory evoked potentials in hens. Res. Vet. Sci. 49:355–359. Ostmann, O. W., R. A. Peterson, and R. K. Ringer, 1964. Effect of spinal cord transection and stimulation on feather release. Poultry Sci. 43:648–654. Ostmann, O. W., R. K. Ringer, and M. Tetzlaff, 1963. The effect of various neuromimetic, anesthetic and tranquilizing drugs on feather release. Poultry Sci. 42:969–973. Poole, G. H., and D. L. Fletcher, 1995. A comparison of argon, carbon dioxide, and nitrogen in a broiler killing system. Poultry Sci. 74:1218–1223. SAS Institute, 1994. SAS/STAT Guide for personal computers. Version 7 edition. SAS Institute Inc., Cary, NC. Walker, J. T., and C. L. Griffis, 1994. Effects of electrical stimulation on feather pulling force. Trans. ASAE 37: 541–544.