INFO SHEET
Breast Meat Yield in
Commercial Turkeys:
Environmental Impact on
Breast Meat Yield
[email protected]
www.hybridturkeys.com
This is the third in the series of Hybrid Info Sheets devoted
to the topic of breast meat yield. Previously, we discussed
the importance of understanding the physiology and
growth of breast muscle and how this information might be
used to develop strategies for optimizing turkey operations.
This Info Sheet addresses specific environmental factors
affecting growth rate and breast meat yield.
As with most performance traits, the expression of
breast meat yield is controlled by three main
sources of variation:
The term allometry, refers to the study of change in the
proportion of various parts of an organism as it grows.
Dissection of turkey carcasses at various ages shows that
the allometric growth of leg and thigh muscle is quite
different from breast muscle (Figure 1). We presume that
precocial bird species like the turkey need to walk and run in
order to feed and evade predators before they are required
to fly. In altricial species, where the fledgling must literally
fly from the nest, the reverse is true, with breast meat
growth earlier in development. As the growth rate of the
breast muscle (primarily pectoralis superficialis) begins to
accelerate around 12 weeks of age, the allometric growth
relationship between the leg-thigh muscle and breast
muscles begins to diverge. This relationship is obviously
inherent in the species, but has been augmented by primary
turkey breeders over many generations of genetic selection
for exaggerated breast conformation. The difference in the
allometric growth of the lower limbs versus breast muscle
has significant ramifications when attempting to develop the
optimum strategy for growing commercial turkeys.
3) the interaction between the two.
The change in morphology of the commercial turey carcass
over the years has been dramatic. During the early years of
the commercial turkey industry, extreme emphasis was
placed on the morphology or appearance of the turkey
breast. Customers came to associate the broad, dimpled
breast of the turkey with “quality” and “more white meat”.
Today, with many turkey carcasses being cut up, the
appearance of the turkey breast “in the bag” – or on the
plate – may be of less importance in some operations. In the
North American market for example, where consumers have
shown a preference for white meat products, the value of
breast muscle can often be four times that of the leg-thigh
muscles. As a consequence, North American turkey
operations are constantly evaluating and developing new
strategies that will optimize white meat production.
Body weight (lb)
BREAST MEAT YIELD IN COMMERCIAL TURKEYS: Environmental Impact
1) genetic variation,
2) environmental variation,
The following equation is often used to represent
this relationship:
(P) = G + E + (G x E)
P = Performance, G = Genotype; E = Environment;
G x E =Genotype by Environment Interaction
Figure 1: Allometry of the turkey showing the growth
curve and the change body composition due to the
variation in size of the breast and thigh muscles relative to
body weight.
35%
40
(18.2)
30
(13.6)
20
(9.1)
Growth
(commercial tom turkeys)
30%
% Breast muscle
25%
% Drum and thigh
10
(4.5)
(kg)
15%
0
5
10
15
20
25
Weeks of Age
INFO SHEET | BREAST MEAT YIELD IN COMMERCIAL TURKEYS: Environmental Impact | 2
Percent Breast of CWOG
Adjusted 18 week body weight (pounds)
0
20%
As percent of body weight
50
(22.7)
1
2
3
BREAST MEAT YIELD IN COMMERCIAL TURKEYS: Environmental Impact
Genotype
Temperature
The genotypic influence on performance is largely fixed with
the purchase of parent stock. Yet even this source of
variation can be modified, by the type and level of selection
pressure placed on parent stock breeder toms and the
methods used in artificial insemination systems. (See Hybrid
Info Sheet, “Advantages of Increased Selection Pressure in
Breeder Males” at www.hybridturkeys.com, in the Library,
Management section.) However, the only trait with
sufficient heritability that can be efficiently selected for in
parent stock toms is body weight. The genetic impact at the
parent stock level can be significant, but is often overlooked
or under-utilized in many integrated turkey operations.
One of the most influential management components
affecting performance is environmental temperature. The
physiology of day-old turkey poults is more like that of
amphibians and reptiles than mature birds and mammals.
For several days post hatching, the poult’s homeostatic
mechanism is not fully competent, and its metabolism
generates insufficient heat to maintain homeostasis. Turkey
poults regulate their body temperature best when provided
the opportunity to move toward or away from an external
heat source. By the time the poult is 6 to 8 weeks of age,
and contour feathers have completely replaced down
feathers, an external heat source is less important. In fact,
as the turkey grows, heat dissipation becomes a more
significant problem for the turkey. After 8 weeks of age,
environmental temperatures above about 55°F (13°C) begin
to negatively affect performance.
Figure 2: Seasonal variation in body weight and
breast meat
35.0
30.5
34.5
30.0
34.0
29.5
33.5
29.0
33.0
28.5
32.5
28.0
32.0
1
2
3
4
5 6 7 8 9
Slaughter Month
18 wk wt
INFO SHEET | BREAST MEAT YIELD IN COMMERCIAL TURKEYS: Environmental Impact | 3
10 11 12
Percent breast of CWOG
27.5
Percent Breast of CWOG
Experimental estimates suggest that 80% of the
improvement seen in commercial turkey performance over
the last 30 years can be explained by genetic selection.
However, as performance improves, environmental factors
are becoming more important, especially for optimization.
The environmental component covers, by default,
everything that is non-genetic. Nutrition, health and
management are the broad environmental categories and
each of these has many subcomponents. In most turkey
operations, the environmental factors that affect
performance are well known, and every attempt is made to
provide an environment that will allow the animal to express
its full genetic potential. Perhaps the most thoroughly
researched environmental factor affecting growth rate and
breast meat yield is nutrition. Since feed represents 60% to
70% of the cost of production, it is no surprise that many
integrated companies have dedicated research facilities for
conducting nutritional research and employ full-time
nutritionists. The nutritional requirements for growth and
performance in turkeys have been reported in the literature;
however, the nutritional requirements for optimum breast
meat yield have received less attention. As growth of the
turkey’s breast muscle is accelerated during the latter weeks
of the growing cycle, careful attention must be given to the
nutritional requirements during this period. Determining the
optimum nutritional plane and slaughter age for turkeys is
an ongoing challenge that requires constant re-evaluation.
For more information, refer to the Hybrid Info Sheet,
“Feeding for Breast Meat Yield”, at www.hybridturkeys.
com, in the Library, Nutrition section.
Adjusted 18 week body weight (pounds)
Environment
BREAST MEAT YIELD IN COMMERCIAL TURKEYS: Environmental Impact
In hot weather, the turkey is at a particular disadvantage
compared to other livestock. Their extremity is covered with
feathers and the skin has significant subcutaneous fat
deposits, both with high insulative properties. To complicate
this further, the general morphology of the turkey’s body is
spherical, resulting in a low surface area to volume ratio,
and turkeys have no sweat glands. As the bird increases in
size, there is proportionally less surface area from which to
dissipate heat, not to mention that the normal deep core
body temperature of the turkey is 104°F (40°C)!
The seasonal change in environmental temperature
dramatically affects turkey growth rates and breast meat
yield. Figure 2 plots typical growth rate and percent breast
meat yield data by month of slaughter in North America.
This trend in weight for age and percent breast meat yield is
highly predictable and repeatable, north or south of the
equator during hot weather.
Figure 3 plots data for typical average monthly CDD for
Minneapolis, MN and Charlotte, NC (upper Midwest and
Southeastern US, respectively). It is easy to see how much
more heat turkey growers must contend with in the
Southeast as compared to the upper Midwest.
Figure 3: Cooling degree days for Minneapolis, MN &
Charlotte, NC.
300
Cooling degree days (CDD) per month
The turkey has four basic means of dissipating body heat:
radiation, convection, conduction and evaporation (respiratory
moisture loss). As environmental temperatures rise, turkeys
begin to drink more water and to pant (gular fluttering). They
take on a characteristic posture (feather covering opened up to
expose bare skin, wings held away from the body, blood
shunted to the extremities) to take advantage of any air
movement that will help remove body heat through the
convective process. At temperatures above about 85°F (29°C),
the turkey’s thermo regulatory mechanisms become only
marginally effective, especially in larger turkeys.
250
200
150
100
50
0
0
2
In an effort to better describe this seasonal relationship we
can take an example from the electric company. Power
companies use a term called cooling degree days (CDD) to
estimate their energy requirements for air conditioning and
refrigeration. Typically, CDD is expressed as the difference
between a standard temperature of 65°F (18°C) and the
mean temperature at a specific location on a given day. For
example, if a location experiences a mean temperature (high
plus low divided by 2) of 75°F (24°C) on a certain day, the
CDD value equals 10 that day, because 75 - 65 = 10.
INFO SHEET | BREAST MEAT YIELD IN COMMERCIAL TURKEYS: Environmental Impact | 4
4
6
8
10
Month of the Year
Charlotte, NC
Minneapolis, MN
12
BREAST MEAT YIELD IN COMMERCIAL TURKEYS: Environmental Impact
Genotype by Environment Interactions (G x E) As the
growth rate of turkeys continues to increase, the third
source of variation, genotype by environment interaction,
will become increasingly influential on performance. Larger
turkeys will likely be more sensitive to fluctuations in
nutrition, environmental insults, disease challenges, and
heat stress. The interactions between nutritional
requirements, seasonal temperature, and management
strategies such as stocking density, slaughter weight and
slaughter age, must be carefully considered in the
optimization process. Currently only about 50% of
commercial flocks achieve performance potential (weight for
age) during the cool seasons and only about 30% during
hot weather. Furthermore, flocks of similar strain, weight,
age, and slaughter age/date often demonstrate as much as
1.5% difference in average breast meat yield regardless of
the time of year marketed.
Figure 4: Linear regression of cooling degree days on
performance (body weight) for the South East and Midwest.
35.0
Avg 18 week wt (pounds)
A large commercial tom database was used to investigate
how the CDD statistic is related to commercial tom
performance at these two locations. The average flock
market weight by calendar month was calculated for each
location and then plotted against the accumulated CDD
statistic. suggests that perhaps 80% of the difference in
seasonal performance is simply related to differences in
environmental temperature.
34.5
y=-0.0046x+34.137
R2=0.9427
34.0
33.5
33.0
32.5
32.0
y=-0.0016x+32.883
R2=0.7678
31.5
31.0
30.5
30.0
0
200
400
600
800
1000
1200
1400
1600
Cumulative Cooling Degree Days
Southeast
Midwest
Linear (Southeast)
Linear (Midwest)
Environmental factors and genotype by environment
interactions are a major source of variation in most turkey
operations. A better understanding (knowledge) of these
will allow turkey production companies to develop strategies
leading to optimization and increased profits.
© Hybrid Turkeys
Unless otherwise specified, the information provided here is the property
of Hybrid Turkeys. Before reproducing or publishing this material in
any manner, please obtain approval by contacting the Hybrid Turkeys’
head office in Kitchener, Ontario, Canada.
[email protected]
www.hybridturkeys.com
INFO SHEET | BREAST MEAT YIELD IN COMMERCIAL TURKEYS: Environmental Impact | 5