Published November 24, 2014
Association of pro-melanin concentrating
hormone genotype with beef carcass quality and yield1
L. J. Walter,* C. A. Gasch,* T. J. McEvers,*
J. P. Hutcheson,† P. DeFoor,‡ F. L. S. Marquess,§ and T. E. Lawrence*2
*Beef Carcass Research Center, Department of Agricultural Sciences, West Texas A&M University, Canyon 79016; †Merck Animal
Health, Summit, NJ 07901; ‡Cactus Feeders, Ltd., Cactus, TX 79013; and §Quantum Genetix Canada Inc., Saskatoon, SK S7N 3R3
ABSTRACT: Beef cattle from 3 independent studies
conducted in the Texas Panhandle (Exp. 1: n = 3,906 and
Exp. 2: n = 4,000) and southern Idaho (Exp. 3; n = 542)
were used to investigate the association of pro-melanin
concentrating hormone (PMCH) genotype with beef
carcass quality and yield attributes. Tissue samples were
collected from each animal to determine which PMCH
allele they expressed (Trial 1: AA, 62.60%; AT, 32.05%;
and TT, 5.35%; Trial 2: AA, 64.33%; AT, 31.07%; and
TT, 4.60%; Trial 3: AA, 65.87%; AT, 29.34%; and TT,
4.80%). Twenty-four hours after harvest, carcass attributes were evaluated for all carcasses and longissimus
dorsi steak samples were allocated from a subset of carcasses in Exp. 2 (n = 352; AA, 49.43%; AT, 28.98%;
and TT, 21.59%) and each carcass in Exp. 3. Warner–
Bratzler shear force measurements were determined
for each steak after aging for 7, 14, or 21 d postmortem. Carcasses from Exp. 1 and 2 expressing the AA
genotype had greater (P < 0.01) 12th rib subcutaneous
(s.c.) fat depth and marbling scores, concurrent with
smaller (P < 0.01) LM area than carcasses of AT and
TT genotypes. Subsequently, carcasses expressing the
AA genotype were represented by a greater (P < 0.02)
proportion achieving Prime and Premium Choice quality grades, and a lesser (P < 0.01) proportion grading
Select or Standard. In all trials, carcasses of the AA
genotype had greater (P < 0.04) calculated yield grades
than carcasses of the TT genotype. Carcass composition
was associated with PMCH genotype evident by calculated empty body fat differences (P < 0.04) between
AA and TT cattle in Exp. 1 and 3, and differences (P <
0.01) among all 3 genotypes in Trial 2. Shear force data
on 7-d postmortem aging tended (P = 0.06) to favor cattle of the AA genotype in Exp. 2. However, additional
aging to 14 or 21 d minimized any tenderness differences. These data illustrate the potential relationship
that may exist among PMCH genotypes and indicators
of carcass composition.
Key words: beef, pro-melanin concentrating hormone, quality, yield
© 2014 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2014.91:325–331
doi:10.2527/jas2013-6931
INTRODUCTION
Pro-melanin concentrating hormone has been reported to play a role in the regulation of appetite and metabolism in mice and humans (Shimada et al., 1998; Elliott et
al., 2004; Gavrila et al., 2005), and has been associated
with beef tenderness (Helgeson, 2007). Helgeson and
Schmutz (2008) mapped the pro-melanin concentrating
hormone (PMCH) gene in Bos taurus cattle and dis-
1Supported by funding from Merck Animal Health,
2Corresponding author: [email protected]
Summit, NJ.
Received July 18, 2013.
Accepted October 23, 2013.
325
covered that cattle of the AA genotype had significantly
more carcass subcutaneous fat than TT cattle in 2 separate populations (n = 122 and 382), indicating that PMCH
genotype may influence carcass composition. In addition
to an effect on carcass composition, PMCH genotype was
associated with Warner–Bratzler shear force (WBSF) in
longissimus dorsi steaks with AA genotypes exhibiting
lower WBSF than AT and TT genotypes in steaks cooked
to medium, whereas in steaks cooked to well done AA
genotypes had a lower WBSF than AT cattle. Thus, based
on previous literature, PMCH has been associated with
beef carcass subcutaneous fat depth and tenderness.
Further research to explore the association of
PMCH and carcass composition could elucidate
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Walter et al.
differences with respect to marbling score, yield grade,
and HCW. This information could be used as a prediction
tool for certain PMCH genotypes to be marketed sooner
or marketed under different value-based grids to maximize producer financial returns. Furthermore, as tenderness is considered to be the single most important factor
influencing consumers’ perceptions of taste (Savell et
al., 1987, 1989), specific PMCH genotypes may serve
to derive a premium for the association with tenderness
and subsequent consumer palatability. Multiple DNA
tests (e.g., GeneSTAR® and HD 50K, Zoetis, Florham
Park, NJ; Igenity®, Neogen, Lincoln, NE) have been developed linking DNA SNP to tenderness. However, few
reports have investigated the PMCH alleles. Therefore,
the objectives of this study were to assess the association
of PMCH genotypes with attributes of carcass quality
and yield and to confirm the association of PMCH genotypes with longissimus dorsi tenderness.
MATERIALS AND METHODS
Live Cattle Procedures
The feeding portions of this experiment were conducted at Cactus Research Ltd. (Exp. 1 and 2; Cactus,
TX) and Johnson Research (Exp. 3; Parma, ID). All experimental procedures followed the guidelines described
in the Guide for the Care and Use of Agricultural Animals
in Agricultural Research and Teaching (FASS, Savoy, IL).
Cattle Processing and Trial Design
Experiments 1 and 2: The initial experiments were
designed to explore interactions between leptin genotypes (TT, CT, and CC) and zilpaterol hydrochloride
(ZH; Exp. 1: Kononoff et al., 2013; and Exp. 2: McEvers
et al., 2013). At arrival, all candidate steers (~7,200
British × Continental crossbreed steers for both Exp. 1
and 2) were uniquely identified, using duplicate visual
ear tags, tissue sampled with a modified Y-Tex ear tagger for subsequent leptin, and PMCH genotyping by
Quantum Genetix (Saskatoon, SK, Canada), and vaccinated with Vista 3 (Merck Animal Health, Summit, NJ)
for infectious bovine rhinotracheitis (IBR) and bovine
viral diarrhea virus (BVD) Type 1 and 2. Candidate steers
in Exp. 1 were implanted with Revalor-S (Merck Animal
Health) and given an anthelmintic treatment with Ivomec
(Merial, Duluth, GA), whereas candidate steers in Exp. 2
were implanted with Revalor-XS (Merck Animal Health)
and given an anthelmintic treatment via a combination of
Safeguard drench (Merck Animal Health) and Dectomax
injectable (Zoetis, Florham Park, NJ).
Within each experiment, cattle were randomized to
pens and fed by leptin genotype allele in 48 pens de-
signed to contain no more than 100 animals each. Cattle
were allowed to consume water on an ad libitum basis.
Initially, cattle were fed a starter diet and then allowed
to transition onto a finishing ration that met or exceeded
NRC (1996) requirements 3 times daily. Dietary information is listed in Kononoff et al. (2013) and McEvers
et al. (2013). Within each experiment, half of the pens
(n = 24) were supplemented ZH at a rate of 8.33 mg/kg
of dietary DM for a period of 21 d, followed by a 3-d
withdrawal before slaughter.
Experiment 3: Trial 3 sought to investigate the implications of sorting fed steers into groups based on the
IGENITY Profile score for tenderness and supplementing ZH (McEvers et al., 2012). At processing, 1,040 candidate steers were implanted with Revalor-XS (Merck
Animal Health), vaccinated with Vision 8 with SPUR
(Merck Animal Health) and for IBR and BVD using
Titanium 3 (AgriLabs, St. Joseph, MO), and administered anthelmintic treatments with oral fenbendazole
(Safe-guard; Merck Animal Health), along with injectable moxidectin (Cydectin; Boehringer Ingelheim, St.
Joseph, MO). From the original candidate population,
582 steers (initial BW = 420 ± 26 kg) were selected
based on their IGENITY Profile score, weighed, transported to Johnson Research, LLC, Parma, ID, and randomized to 10 animal pens.
Cattle were allowed to consume water ad libitum
and fed a total mixed ration that met or exceeded NRC
(1996) requirements (McEvers et al., 2012). Cattle were
fed ad libitum and transitioned using a step-up diet, followed by a traditional finishing diet. Half of the pens
received a ration containing ZH (Merck Animal Health)
at 8.33 mg/kg of dietary DM for 20 d, with a 3-d withdrawal before slaughter.
Tissue samples were obtained postmortem and
shipped to Quantum Genetix for subsequent PMCH
genotyping.
Pro-melanin Concentrating Hormone Determination
The DNA samples (Exp. 1, n = 3,906; Exp. 2, n =
4,000, and southern Idaho, n = 542) were evaluated
(Quantum Genetix) to determine which PMCH allele
(AA, AT, TT) each animal expressed. Texas samples
were collected as a 1-mm ear tissue biopsy via a modified Y-Tex ear tagger (Cody, WY) used to capture a DNA
collection tag. Samples were stored at –20°C until the
collection tag was cut open and tissue was removed and
placed in individually labeled, 1.5-mL microcentrifuge
tubes for further analysis.
Idaho samples were taken as muscle tissue samples and placed in individually labeled Whirl-Pak bags
(Nasco, Fort Atkinson, WI). Samples were shipped,
frozen, to Quantum Genetix for PMCH genotype anal-
PMCH and carcass quality and yield
ysis. Again, samples were stored at –20°C until they
were opened and prepared for DNA extraction. To extract DNA from the muscle biopsy, ~ 20 mg (3- × 3-mm
piece of muscle tissue) of tissue was isolated from the
test sample and placed in a 1.5-mL microcentrifuge
tube for further processing.
The DNA extraction was performed by adding
75 μL of fresh 0.2 M NaOH solution to each microcentrifuge tube. Samples were vortexed for 10 s and
then incubated for 15 min at 65°C. Samples were then
neutralized with 125 μL of a solution containing 1.6%
(vol/vol) concentrated HCl and 0.1 M Tris. Samples
were mixed by briefly vortexing and diluted with sterile dH2O at a 1:10 ratio while transferring into a 96well microplate. Low yielding samples from the previously described extraction method were purified in the
MagNA Pure LC instrument (Roche Applied Science,
Mannheim, Germany) with MagNA Pure LC DNA
Isolation Kit I (Roche Applied Science).
Genotyping was performed in the LightCycler
2.0 (Roche Applied Science) real-time capillary PCR
instrument. The forward and reverse primers were
manufactured by Integrated DNA Technologies,
Coralville, IA, and the probes were manufactured
by IT Biochem, Salt Lake City, UT. The oligonucleotide sequences were as follows: forward primer 5’
CACTTAAACAATATGCCACT 3’, reverse primer
5’ CTTTGTAAATGATTCTTGCCT 3’, anchor probe
sequence 5’ GGTTGGTTTCTATCTGATGAGTCATFluorescein 3’, and sensor probe sequence was 5’ LC
Red640-TCTAAAATGATGTAAGTTTTTCA-C3
3’. Each 10 μL reaction contained 4.5 μL Fermentas
PyroStart Fast PCR Master Mix (2X; Fisher Scientific,
Pittsburg, PA), 0.5 µM of each primer, 0.15 µM of
each probe, 2.5 mM MgCl2, 200 ng/μL Human HDL
(Biomedical Technologies Inc., Stoughton, MA), and
3% (vol/vol) DMSO (Sigma-Alrich, St. Louis, MO).
For each reaction, 1.0 μL of extracted sample was used
as template DNA. The PCR conditions consisted of an
initial denaturation at 95°C for 5 min, followed by an
amplification program of 45 cycles of 95°C for 2 s (denaturation), 58°C for 10 s (annealing), and 72°C for 10 s
(extension). A melting program consisted of 95°C for 0 s
and then cooling to 40°C for 2 min, with a ramp rate
of 0.2°C/s until a temperature of 75°C was reached, after which the temperature was returned to 40°C. Melting
curve analysis was performed using LightCycler 2.0
software version 4.0 (Roche Applied Science).
Carcass Evaluation
At slaughter, individual ear tag, assigned beef processor identification number, and hot carcass weights were
recorded. Twenty-four hour postharvest, a detailed car-
327
cass evaluation was conducted by personnel from the Beef
Carcass Research Center (West Texas A&M University,
Canyon, TX), which included marbling score (10 = practically devoid, 20 = traces, 30 = slight, 40 = small, 50 = modest, 60 = moderate, 70 = slightly abundant, 80 = moderately
abundant, 90 = abundant), 12th ribsubcutaneous (s.c.) fat
depth (cm), LM area (cm2), and estimated percentage of
kidney, pelvic, and heart fat. A final quality grade and calculated yield grade was determined (USDA, 1997). Also,
percentage of empty body fat and empty body weight were
calculated for each animal (Guiroy et al., 2001).
Warner–Bratzler Shear Force Determination
A subset of carcasses from Exp. 2 and all carcasses
from Exp. 3 were used for WBSF determination. For
Exp. 2, within a pen, all cattle expressing TT alleles
were selected and cattle expressing AA and AT alleles
were randomly sampled to achieve a sampling rate of
10 animals per pen. This was done to increase the sampling rate of TT alleles due to low population frequency.
Twenty-four hour postharvest, the boneless rib (IMPS
#112A-Exp. 2) or loin (IMPS # 180-Exp. 3) subprimal
(Institutional Meat Purchase Specifications, USDA,
Agricultural Marketing Service, 2010), from 1 side of
each carcass was removed. Three, 2.54-cm-thick steaks
were cut from the posterior end of each rib subprimal or
the anterior end of each loin subprimal, and randomly
assigned to an aging period of 7, 14, or 21 d. After aging,
steaks were individually vacuum packaged and frozen at
–20°C until ready for shear force determinations.
Steaks were thawed at 1°C for 24 h before cooking and then cooked in a forced-air convection oven
(model CTB/R; G.S. Blodgett Co., Burlington, VT) set
at 177°C until an internal endpoint temperature of 71°C
was reached. The internal temperature of each steak was
monitored through a copper-constantan thermocouple
wire (Omega Engineering, Stamford, VT), positioned
in the geometric center, and connected to a temperature
monitoring device (Omega Engineering). After cooking, steaks were cooled for 10 min, wrapped in cellophane, and chilled for 24 h at 1°C. After chilling, six,
1.27-cm cores were randomly removed, parallel to the
muscle fiber direction, from each steak. The cores were
immediately sheared using a V-shaped blade on a WBSF
machine (G-R Manufacturing, Manhattan, KS). The
peak shear force value was displayed on a Mecmesin
BNG-500 Shear Force Gauge (Newton House, United
Kingdom) and manually recorded.
Statistical Analysis
For every trial, each individual carcass was considered an experimental unit. The MIXED Procedure
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Walter et al.
of SAS (SAS Inst. Inc., Cary, NC) was used to test for
PMCH allele effects, with PMCH allele as the fixed effect and ZH (presence or absence), pen (leptin genotype
in Exp. 1 and 2; IGENITY Profile score in Exp. 3), and
block as random effects. The GLIMMIX Procedure
(SAS Inst. Inc.) was used to test for distributions of
quality and yield grades with fixed and random effects,
as previously detailed. Because cell sizes were unbalanced, the KENWARDROGER option was used to
generate new denomination degrees of freedom. A least
squares means statement generated means and a PDIFF
statement was used to determine where the differences
(α = 0.05) occurred between PMCH alleles.
RESULTS AND DISCUSSION
Carcass Performance
Allelic frequencies for Exp. 1 (n = 3,906; Table 1)
were 62.60% (AA), 32.05% (AT), and 5.35% (TT); Exp. 2
(n = 4,000; Table 2) were 64.33% (AA), 31.07% (AT), and
4.60% (TT); and Exp. 3 (n = 542; Table 3) were 65.87%
(AA), 29.34% (AT), and 4.80% (TT). The subgroup (n =
352) in Exp. 2 used for further WBSF analysis had allelic
frequencies of 49.43% (AA), 28.98% (AT), and 21.59%
(TT; Table 2). The observed population frequencies for
PMCH alleles throughout all 3 trials do not exhibit typical
Mendelian frequencies of 25%, 50%, and 25% for heterozygote, homozygote, and heterozygote alleles, respectively.
A possible explanation for the discrepancy could be selection pressure against cattle exhibiting a TT genotype. In
mammals, PMCH encodes 3 neuropeptides, NE1, NGE,
and melanin-concentrating hormone (MCH; Pedeutour et
al., 1994). Melanin-concentrating hormone has been linked
to an increase in feed intake in mice (Shimada et al., 1998)
and humans (Gavrila et al., 2005). Therefore, producers
may have inherently selected against the TT PMCH allele,
likely due to a visually lower adipose content. Subsequently,
TT cows might also rebreed at a lower rate and potentially
might be culled from the herd at a greater rate.
There was no association between PMCH genotype
and HCW (P > 0.15) or calculated empty BW (P > 0.15)
for any of the experiments (Tables 1, 2, and 3). Cattle
in Exp. 1 and 2 expressing the AA genotype had greater
(P = 0.0001 and P = 0.0057; Tables 1 and 2, respectively) 12th rib s.c. fat depth and smaller (P = 0.0001
and P = 0.0080; Tables 1 and 2, respectively) LM areas than AT- and TT-expressed genotypes. Results from
Exp. 3 revealed a similar tendency for an association
between LM area and PMCH genotype, but the smaller
sample size of this trial lacked the statistical power to
clearly define the same significant results as Exp. 1 and
2. The increase in 12th rib s.c. fat thickness observed in
Exp. 1 and 2 is similar to results reported by Helgeson
Table 1. Carcass performance data by pro-melanin concentrating hormone (PMCH) genotype (n = 3,906) for Exp. 1.
Item
Population frequency, %
HCW, kg
Empty body fat,1 %
Empty BW,2 kg
12th rib subcutaneous (s.c.) fat
depth, cm
LM area,cm2
KPH, %
Calculated yield grade3
USDA yield grade (YG) 1, %
USDA YG2, %
USDA YG3, %
USDA YG4 and YG5, %
Marbling score4
PMCH genotype
AA
AT
TT
62.60
32.05
5.35
395
393
392
29.19a 28.52b 28.27b
552
550
548
1.26a
1.19b
1.15b
92.55b
1.93
2.85a
17.77b
42.09
33.69a
3.70a
42.06a
Prime and Premium Choice, % 11.36a
Low Choice, %
52.93
Standard and Select, %
33.25c
94.08a
1.93
2.69b
24.33a
43.57
94.35a
1.93
2.62b
26.75a
44.18
28.02b
1.89b
41.34b
8.32b
51.19
24.87b
1.82b
39.87c
3.24c
46.27
38.45b
49.51a
SEM P-value
8.5
0.593
11.2
0.028
0.1540
0.0001
0.1540
0.0001
4.061
0.021
0.182
-
0.0001
0.9669
0.0001
0.0001
0.6285
0.0004
0.0018
1.238
-
0.0001
0.0002
0.1726
0.0001
a–cMeans
without a common superscript differ (P < 0.05).
body fat, % = 17.76207 + (4.68142 × s.c. fat depth, cm) +
(0.01945 × HCW, kg) + (0.81855 × quality grade) – (0.06754 × LM area,
cm2). Numerical quality grade values were assigned based on the marbling
score derived quality grade, such that Standard = 3 to 4; Select = 4 to 5; Low
Choice = 5 to 6; Average Choice = 6 to 7; High Choice = 7 to 8; Low Prime =
8 to 9; and Average Prime = 9 to 10; Guiroy et al. (2001).
2Empty BW, kg = (1.316 × HCW, kg) + 32.29; Guiroy et al. (2001).
3USDA calculated yield grade = 2.5 + (2.5 × FT) + (0.2 × KPH) + (0.0038 ×
HCW) – (0.32 × REA), where FT = 12th rib fat depth in cm, KPH = percentage of kidney, pelvic, and heart fat, HCW = hot carcass weight in kg, and
REA = longissimus muscle area in cm2.
4Marbling scores: 30 = slight; 40 = small; 50 = modest.
1Empty
and Schmutz (2008), in which average backfat levels
were significantly higher in AA cattle vs. TT cattle for 1
sample population, and significantly higher in AA cattle
vs. AT and TT cattle in a second sample population.
The resultant effect of PMCH genotype on USDA
yield grade resulted in carcasses of the AA genotype associated with a higher (P = 0.0001, P = 0.0001 and P =
0.0305; Tables 1, 2, and 3, respectively) calculated yield
grade than AT and TT cattle in Exp. 1 and 2, and TT
cattle in Exp. 3; AT cattle also exhibited a higher yield
grade than TT cattle in Exp. 2 (Table 2), whereas AT cattle were not significantly different than AA or TT cattle
in Exp. 3 (Table 3). The distribution of carcasses with
a yield grade of 1 (P = 0.0001 and P = 0.0001; Table 1
and 2, respectively) and yield grade of 3 (P = 0.0004
and P = 0.0072; Table 1 and 2, respectively) was associated with PMCH genotype for Exp. 1 and 2, with TT
and AA genotypes exhibiting the highest proportion of
yield grade 1 and 3 carcasses, respectively. Furthermore,
the percentage of yield grade 4 and 5 carcasses was associated with PMCH genotypes, as AA type cattle exhibited higher yield grade 4 and 5 carcasses in Exp. 1
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PMCH and carcass quality and yield
Table 2. Carcass performance data by pro-melanin concentrating hormone (PMCH) genotype for Exp. 2.
Item
Population frequency, %
HCW, kg
Empty body fat1, %
Empty BW2, kg
12th rib subcutaneous (s.c.) fat depth, cm
LM area,cm2
KPH, %
Calculated yield grade3
USDA yield grade (YG) 1, %
USDA YG2, %
USDA YG3, %
USDA YG4 and YG5, %
Marbling score4
Prime and Premium Choice, %
Low Choice, %
Standard and Select, %
Sample frequency, %
7d cook loss, %
7d shear force, kg
14d cook loss, %
14d shear force, kg
21d cook loss, %
21d shear force, kg
a–cMeans
n
4,000
4,000
4,000
4,000
4,000
4,000
4,000
4,000
4,000
4,000
4,000
4,000
AA
64.33
394
27.96a
551
1.09a
92.77b
1.92
2.66a
17.25c
49.51
27.79a
3.42
4,000
4,000
4,000
4,000
352
352
352
352
352
352
352
39.17a
7.17a
35.61a
56.94c
49.43
22.47
4.54
22.23
3.86
21.74
3.54
PMCH Genotype
AT
31.07
394
27.63b
550
1.06b
94.01a
1.92
2.56b
20.81b
51.30
TT
4.60
390
27.16c
545
1.01b
95.37a
1.92
2.41c
29.57a
45.87
23.32ab
2.71
21.91b
0.49
38.41b
5.25b
33.14ab
61.46b
28.98
22.85
4.75
20.98
3.98
21.58
3.65
37.35b
3.22b
27.46b
69.27a
21.59
23.32
4.78
21.42
3.99
21.04
3.68
SEM
-
P-value
-
3.6
0.346
10.9
0.038
4.182
0.023
0.166
-
0.2123
0.0001
0.2153
0.0057
0.0001
0.9639
0.0001
0.0001
0.3188
0.0072
0.0818
0.926
-
0.0001
0.0178
0.0453
0.0080
0.2204
0.1187
0.0639
0.3440
0.3470
0.2368
0.2204
0.01
0.57
0.01
0.44
0.01
0.33
0.01
without a common superscript differ (P < 0.05).
1Empty body fat, % = 17.76207 + (4.68142 × s.c. fat depth, cm) + (0.01945 × HCW, kg) + (0.81855 × quality grade) – (0.06754 × LM area, cm2). Numerical
quality grade values were assigned based on the marbling score derived quality grade such that Standard = 3 to 4; Select = 4 to 5; Low Choice = 5 to 6; Average
Choice = 6 to 7; High Choice = 7 to 8; Low Prime = 8 to 9; and Average Prime = 9 to 10; Guiroy et al. (2001).
2Empty BW, kg = (1.316 × HCW, kg) + 32.29; Guiroy et al. (2001).
3USDA calculated yield grade = 2.5 + (2.5 × FT) + (0.2 × KPH) + (0.0038 × HCW) – (0.32 × REA), where FT = 12th rib fat depth in cm, KPH = percentage
of kidney, pelvic, and heart fat, HCW = hot carcass weight in kg, and REA = longissimus muscle area in cm2.
4Marbling scores: 30 = slight; 40 = small; 50 = modest.
(P = 0.0018, Table 1) and tended to have more yield
grade 4 and 5 carcasses in Exp. 2 (P = 0.0818, Table 2).
Results from Exp. 1 and 2 also indicated an association of PMCH genotype with marbling score, with AA
genotype carcasses being higher (P = 0.0001; Tables 1
and 2) than AT and TT genotype cattle (Small21,
Small13, Slight99; Slight92, Slight84, Slight74 for AA,
AT, and TT genotypes in Trial 1 and 2, respectively).
Subsequently, cattle with an AA genotype expressed a
higher (P = 0.0001 and P = 0.0178; Table 1 and 2, respectively) percentage of carcasses grading Prime and
Premium Choice vs. cattle with AT and TT genotypes.
There was also an association of PMCH genotype (P =
0.0001 and P = 0.0080; Table 1 and 2, respectively)
to the percentage of carcasses grading Standard and
Select; carcasses with 2 T alleles were represented by
more Standard and Select grades than carcasses with 1
T allele, which had a greater percentage of those grades
than carcasses with a T allele.
Results from all trials indicate a strong association
of PMCH genotype to adipose tissue content in fin-
ished cattle (Tables 1, 2, and 3). Therefore, calculated
empty body fat (Guiroy et al., 2001) was associated
with PMCH alleles; AA genotyped cattle had greater
(P = 0.0001 and P = 0.0001; Table 1 and 2, respectively) calculated empty body fat percentage than AT
and TT genotypes in Trials 1 and 2, and greater (P =
0.0353; Table 3) calculated empty body fat percentage
than TT cattle in Trial 3. Albeit, HCW and calculated
empty BW (Guiroy et al., 2001) did not differ among
treatments. The dissimilarity in adipose tissue content
among cattle expressing differential PMCH allelic frequencies may allow for marketing end points based on
both weight and PMCH genotype.
Cook loss or shear force after 7, 14, and 21 d of aging
was not associated with PMCH genotype (Tables 2 and
3). Shear force had a tendency (P = 0.06) to be significant, favoring AA genotype cattle, at 7 d of aging for the
sample population in Exp. 2 (Table 2). As expected, aging time improved WBSF from an average of 4.54, 4.75
and 4.78 kg after 7 d of aging to 3.54, 3.65 and 3.68 kg
after 21 d of aging for AA, AT, and TT genotyped cattle,
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Walter et al.
Table 3. Carcass performance data by pro-melanin concentrating hormone (PMCH) genotype (n = 542) for Exp. 3.
PMCH Alleles
Item
AA
AT
TT
Population frequency, %
65.87
29.34
4.80
HCW, kg
418
419
412
Empty body fat,1 %
31.04a 30.79a 29.76b
Empty BW,2 kg
583
584
574
12th rib subcutaneous (s.c.)
1.61
1.60
1.47
fat depth, cm
KPH, %
1.96
1.96
1.94
LM area, cm2
99.78 101.47 102.59
Calculated yield grade3
3.03a
2.94ab 2.69b
USDA yield grade (YG) 1, % 5.85
8.61
13.48
USDA YG2, %
42.85
44.25
46.56
USDA YG3, %
39.88
38.65
36.88
USDA YG4 and YG5, %
9.77
7.24
2.61
Marbling score4
47.73
46.85
44.77
Choice and Prime,5 %
89.25
85.95
85.93
Standard and Select, %
10.75
14.05
14.07
7d cook loss, %
18.75
18.77
19.65
7d shear force, kg
3.54
3.56
3.58
14d cook loss, %
18.16
18.31
19.32
14d shear force, kg
2.99
3.03
3.02
21d cook loss, %
17.74
17.54
17.63
21d shear force, kg
2.73
2.75
2.86
SEM
–
7.89
0.41
10.21
0.06
P-value
–
0.4418
0.0353
0.4421
0.2270
0.05
3.64
0.17
-
0.9014
0.0753
0.0305
0.2213
0.9040
0.9295
0.2931
0.1390
0.5328
0.5328
0.6424
0.9339
0.5991
0.7913
0.8781
0.4831
1.55
0.01
0.39
0.01
0.28
0.01
0.19
a– cMeans
without a common superscript differ (P < 0.05).
body fat, % = 17.76207 + (4.68142 × s.c. fat depth, cm) +
(0.01945 × HCW, kg) + (0.81855 × quality grade) – (0.06754 × LM area,
cm2). Numerical quality grade values were assigned based on the marbling
score derived quality grade such that Standard = 3 to 4; Select = 4 to 5; Low
Choice = 5 to 6; Average Choice = 6 to 7; High Choice = 7 to 8; Low Prime =
8 to 9; and Average Prime = 9 to 10; Guiroy et al. (2001).
2Empty BW, kg = (1.316 × HCW, kg) + 32.29; Guiroy et al. (2001).
3USDA calculated yield grade = 2.5 + (2.5 × FT) + (0.2 × KPH) + (0.0038 ×
HCW) – (0.32 × REA), where FT = 12th rib fat depth in cm, KPH = percentage of kidney, pelvic, and heart fat, HCW = hot carcass weight in kg, and
REA = longissimus muscle area in cm2.
4Marbling Scores: 30 = slight; 40 = small; 50 = modest.
5Due to limited data size, GLIMMIX model would not converge and Prime
and Premium Choice were combined with Low Choice.
1Empty
respectively, in the subpopulation in Exp. 2 (Table 2), and
from 3.54, 3.56, and 3.58 kg on 7 d of aging to 2.73, 2.75,
and 2.86 on 21 d of aging for AA, AT, and TT genotyped
cattle, respectively, in Exp. 3 (Table 3). Results reported by Helgeson (2007) indicated that longissimus dorsi
steaks from AA genotyped cattle had lower WBSF than
AT and TT cattle at 1 testing facility, whereas AA genotyped cattle had lower WBSF than AT cattle at another facility. The steaks used at both testing facilities (Helgeson,
2007) were from the same data set (n = 122), with allelic
frequencies of 51.64% (AA), 31.97% (AT), and 16.39%
(TT), similar to the sample population used for WBSF
analysis in Exp. 2. Aging time was not indicated, but overall shear force at both testing facilities was much higher
(Helgeson, 2007) than what was recorded in Exp. 2 and
3. Helgeson (2007) recorded shear force values of 6.41,
7.68, and 7.66 kg for steaks cooked to well done, and 8.05,
10.19, and 10.57 kg for steaks cooked to medium for AA,
AT, and TT genotyped cattle, respectively. Additionally,
the cattle reported by Helgeson (2007) were much leaner,
which may have allowed for cold shortening, particularly
for cattle of the TT genotype. Therefore, discrepancies of
tenderness outcomes with previous literature may be due,
in part, to differences in level of finish or length of postmortem aging.
These results suggest that PMCH is associated with
the composition of carcass gain. Future experiments designed to feed pens of cattle that are of specific PMCH
genotypes may elucidate any feeding efficiency differences among PMCH genotypes. Further feeding data
coupled to PMCH associations with carcass characteristics may encourage feeders to manage PMCH genotypes
differently, not only from a carcass marketing end point,
but also from a live feeding basis.
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