ENVIRONMENT, WELL-BEING, AND BEHAVIOR Growth, livability, feed consumption, and carcass composition of the Athens Canadian Random Bred 1955 meat-type chicken versus the 2012 high-yielding Cobb 500 broiler K. E. Collins, B. H. Kiepper, C. W. Ritz, B. L. McLendon, and J. L. Wilson1 Poultry Science Department, The University of Georgia, Athens 30602 heavier feet, wings, internal organs, and feathers. The modern Cobb broiler had double the breast and larger leg muscles and had a significantly greater fat pad. Despite the larger muscle mass, the supply organs, the heart and lungs, were significantly smaller in the Cobb broiler than the ACRB as a percentage of BW. Relative size of supply and other vital organs should be given consideration for genetic selection of the future broiler. Comparisons of ACRB weights and organ percentages with past published data indicates that the ACRB remains a consistent control strain.
Key words: broiler, Athens Canadian Random Bred, process, heart, lung 2014 Poultry Science 93:2953–2962 http://dx.doi.org/10.3382/ps.2014-04224
INTRODUCTION The Athens Canadian Random Bred (ACRB) is a white-plumaged meat-type chicken control strain that has been maintained by the University of Georgia (Athens) since 1958 (Hess, 1962). This strain is a replication of the Ottawa Meat Control strain, which was developed from commercial meat-type chickens in 1955 (Hess, 1962; Merritt, 1968). Today the ACRB is the oldest known pedigree mated meat-type chicken control strain still in existence (Somes, 1988). Previous studies have compared selected modern broiler strains (1991 Arbor Acres feather-sexable broiler and the 2001 Ross 308 broiler) to the ACRB (Havenstein et al., 1994a,b, 2003a,b; Qureshi and Havenstein, 1994; Cheema et al., 2003). Results from these studies show that modern broilers continue to show increased mean BW over shorter periods of time, while achieving lower feed conversion ratios compared with the ACRB. These modern broiler strains also have been shown to devote approximately 20% of their BW to breast muscles (Havenstein et al., 1994a,b, 2003a,b), which is approximately 10% greater breast muscle than ©2014 Poultry Science Association Inc. Received June 2, 2014. Accepted September 26, 2014. 1 Corresponding author:
[email protected]
the ACRB. With the increase in breast muscle development, other organs have decreased in relative size compared with the ACRB. As an example, modern broiler strains were found to have significantly smaller relative heart and lung weights (Havenstein et al., 1994a,b, 2003a,b). These modern broiler strains also had significantly greater mortality and percentage fat (Havenstein et al., 1994a,b, 2003a,b). A more recent study compared a Ross 708 broiler and to a heritage broiler (Schmidt et al., 2009). This heritage broiler is stated to be a cross of New Hampshire males and Columbian Plymouth Rock females with both lines recorded as inbred lines starting in the 1940s (Schmidt et al., 2009); however, these male and female lines from the University of Illinois (Urbana) are not listed as an inbred line in the International Registry of Poultry Genetic Stocks (Somes et al., 1988). Although the BW of these heritage birds are 2.3 times the weight of ACRB birds when comparing mean 3 wk BW data between Schmidt et al. (2009) and Havenstein et al. (2003b) ACRB data on a 2001 diet, similar conclusions were drawn as in past studies with the ACRB (Havenstein et al., 1994a,b, 2003a,b). Additionally, Schmidt et al. (2009) found no difference in relative liver percentages between the heritage and modern broiler strain. The studies by Havenstein et al. (1994a,b, 2003a,b) show that emerging modern broiler strains continue to
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ABSTRACT A flock of the Athens Canadian Random Bred (ACRB), a 1955 meat-type chicken control strain, was raised alongside a flock of 2012 Cobb 500 fast feathering high-yielding broilers to determine selection changes over the past 57 yr. All birds were reared under management practices appropriate for the Cobb 500. Birds were weighed weekly and processed at 6, 8, and 10 wk. Whole carcass, carcass parts, and organs were weighed. Modern broilers outweighed ACRB at every age, ranging from 3.7 to 4.7 times the size of the ACRB. All parts and organs were compared as a percentage of live fasted BW. The ACRB had significantly
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increase in body size but devote a greater percentage of BW to breast muscle, and as a result continue to sacrifice or contribute less to the increase of other organs. The 1994 study showed 4.4% greater breast muscles in the Arbor Acres compared with the ACRB, whereas the 2003 study found almost 10% greater breast muscles in the Ross 308 than the ACRB. Havenstein et al. (2003a) attributed the increase in breast muscle between the 2 studies to the continuing development of high-yielding modern broiler strains. No known research has compared performance of the ACRB to a modern broiler since the 2001 study of Havenstein et al. (2003a,b). This study continues the next segment of information concerning the changes in modern broilers over the past 57 yr. The Cobb 500, one of the most commonly raised modern high-yielding broilers, is compared with the ACRB and evaluates additional relative organ weights in addition to those examined in past studies.
Eggs from the Athens Canadian Random Bred (ACRB) birds from the University of Georgia’s breeding stock and from a similar aged (48 wk old) commercial Cobb 500 broiler breeder flock where incubated together in a single Natureform NMC2000 incubator at a constant 37.7°C (temperature more appropriate for the ACRB) and 53% RH and transferred at 18 d to a 36.9°C and 53% RH Natureform hatcher. The ACRB eggs were oriented in the upper half of the incubator and the Cobb eggs were placed in the lower half of the incubator. Air temperatures were monitored during incubation and a hatch pattern was recorded every 6 h starting at 468 h of incubation. Further details of the incubation of these birds are described in a thesis (Collins, 2013). Chicks (n = 108) from both strains were randomly selected and reared in three 1.5 m × 1.5 m pens of 36 birds per pen (of the same strain) for a stocking density of 0.07 m2 per bird. Daily mortality was recorded. During the first week of rearing, 1 h of dark was provided per day followed by 4 h of dark per day for the rest of the growout period. Light intensity was maintained throughout the growout period (54 lx). All chicks were fed a mash starter diet (23% CP and 3,100 kcal/kg of ME) and a single crumbled grower diet (20.5% CP and 3,150 kcal/kg of ME) ad libitum until slaughter. Cobb 500 chicks were kept on the starter diet from 0 to 11 d based on the Cobb 500 Broiler Performance and Nutrition Supplement recommendation (Cobb-Vantress Inc., 2012). The ACRB chicks were kept on the starter diet 10 d longer from 0 to 21 d. This differential feeding was an effort to provide the ACRB an appropriate amount of starter feed while not overfeeding the Cobb 500. Feed was weighed weekly. Birds were weighed as a total batch weight per pen at placement and at 4 and 14 d. Birds were individually weighed at 3, 4, 5, 6, 8, and 10 wk. Birds were slaughtered at 6, 8, and 10 wk of age.
RESULTS AND DISCUSSION Growth, Feed Consumption, and Mortality From the time of hatch through 10 wk of rearing, the Cobb 500 weekly measured mean BW were signifi-
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MATERIALS AND METHODS
On each slaughter date, an effort was made to select 13 of each sex per strain based on secondary sex characteristics (comb size, shank shape, and vocal sounds). Selected birds were moved to 4 holding pens (each 1.5 m × 1.5 m) separated by strain and sex the day before slaughter. The birds selected for slaughter were chosen to be representative of the population range of BW of each strain at each slaughter age. Feed was withdrawn from selected birds 10 h before slaughter and water was withdrawn 4 h before slaughter. Thus, bird density decreased after each processing date, which allowed for maximum ventilation and less stress in anticipation of the Cobb birds expected large size at the processing ages older than today’s typical industry processing age of 6 wk. Each bird was individually weighed and electrically stunned (25 V DC, 25 V AC); one side of the neck was manually cut and bled out for 120 s. The bird was then weighed again after bleedout. Each carcass was hard scalded at 60°C for 120 s, feathers removed by an automatic picker, and weighed again as a New York-dressed bird. Evisceration was done by hand. The head separated at the highest point on the neck, the neck with skin separated at the body, feet, preen gland, heart, liver, gizzard, lungs, and remaining viscera including intestines, pancreas, gall bladder, and spleen were removed and weighed separately. Sex was verified by examining the gonads. The eviscerated carcass was washed inside and outside, allowed to drip for 10 s, and weighed as a hot carcass weight without giblets. The carcasses were placed in a static chiller for 3 h, removed and then were hung for 10 min before weighing for a cold carcass weight without giblets. The fat pad was removed and weighed, and the carcass was cut into parts and weighed. The weighed parts included the front half, breast quarters, split breasts, pectoralis major muscles, pectoralis minor muscles, wings, drumettes, wing flats, the back half, leg quarters, drumsticks, thighs, and deboned thighs. Duplicate parts were each weighed individually. The data were analyzed with the GLM procedure of SAS (version 9.2, SAS Institute Inc., Cary, NC) to determine differences between strains and the sexes. Differences were examined using Fisher’s least significant difference. Broilers were handled in accordance with the principles and specific guidelines presented in the Guide for the Care and Use of Agricultural Animals in Research and Teaching (FASS, 2010), and an experimental protocol was reviewed and approved by the University of Georgia Animal Care and Use Committee.
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ATHENS CANADIAN RANDOM BRED 1955 VERSUS COBB 500
Table 1. Weekly mean BW (g) comparison of Athens Canadian Random Bred meat-type control chickens and Cobb 500 high-yielding broilers reared to 10 wk of age Males Age (wk) 0 1 2 3 4 5 6 8 10
Females
Strain average
Probability
ACRB1
Cobb2
ACRB
Cobb
ACRB
Cobb
Pooled SEM
NA3
NA NA NA 981.0 1,632 2,297 2,950 3,815 4,285
NA NA NA 227.7 316.8 422.5 540.9 783.5 1,038
NA NA NA 914.8 1,464 2,001 2,518 3,297 3,887
35.09 75.00 141.0 238.7 345.3 459.1 594.3 871.9 1,153
44.07 175.3 470.7 1,151 1,548 2,149 2,734 3,556 4,086
2.02 22.65 73.84 25.61 43.32 61.08 77.80 115.9 168.1
NA NA 249.6 373.7 495.8 647.7 960.4 1,269
Strain
Sex
Strain × sex
