GROWTH A N D CARCASS TRAITS AT 135 KG FOR PROGENY OF
SWINE SELECTED FOR GROWTH A N D BACKFAT 1
Daryl L. Kuhlers, Steve B. Jungst, Dale L. Huffman,
Joseph C. Cordray and Peter M. Brown
Auburn University 2, AL 36849
Summary
I ntroduction
Age and carcass composition recorded for
250 barrows that were the offspring of parents
selected one generation for either low
or high number of days to reach 105 or 135 kg
or for low or high ultrasonically-measured backfat thickness at 105 or 135 kg, were studied.
Selection of the parents had a significant effect
on ultrasonically-measured backfat thickness,
carcass length, average and 10th-rib backfat
thickness, loin eye area, specific gravity, estimated kilograms of muscle and lean tissue
growth/day of age of their offspring. The
weight at which the parents were selected did
not significantly affect growth and carcass
composition of the barrows. Progeny of parents
selected for low-backfat had longer and leaner
carcasses with larger loin eye areas than progeny of parents selected for low days. Pigs that
were from parents selected for high-backfat or
low days were fatter than pigs from high-days
or low-fat selected parents, respectively. Estimated kilograms of muscle at a constant carcass weight was higher in the offspring of
parents selected for low-backfat than in the offspring of low-days selected parents, but was less
in offspring of high-backfat selected parents
than in offspring of high-days selected parents.
Lean tissue growth/day of age was approximately equal for the offspring from low-backfat
or low-day selected parents and these progeny
produced significantly more lean tissue growth/
day than did progeny of high-backfat or highday selected parents.
(Key Words: Swine, Selection, Growth, Ultrasonically Measured Backfat, Carcass Traits.)
Interest in marketing pigs at weights heavier
than the usual 95 to 110 kg resulted in initiation of a number of studies examining the effect of weight on the performance of pigs (Carr
et at., 1978; Neely et al., 1979; Christian et al.,
1980; Martin et al., 1980; Sather et al., 1980).
As weight increased, gains continued to increase in some studies while in other studies
gains slowed during the later stages of the test
period, carcasses became fatter and longer, loin
eye area increased, but percentage of lean
decreased.
Limited information is available on the effects of genetic differences on performance and
carcass traits at heavy weights. Christian et al.
(1980) studied the performance and carcass
traits in two breeds with differing fat thicknesses.
Neely et al. (1979) examined differences in performance after dividing the pigs into fat and
lean litters at 68 kg. Bereskin et al. (1975),
Bereskin and Davey (1976) and Bereskin et al.
(1976) examined differences in performance of
pigs at 100 kg from a long-term selection experiment for and against live-animal-probe
backfat at 79.4 kg.
We know little about the effects of different
selection schemes at different weights on
growth and carcass traits in swine. Therefore,
the objective of this study was to determine
the effects of four different single-trait selection schemes each at two different weights on
growth and carcass traits of progeny grown to
135 kg.
Materials and Methods
The 250 crossbred FI barrows used in this
study were the offspring of 52 purebred Duroc
or Landrace boars and out of 75 purebred
1Contribution from the Alabama Agr. Exp. Duroc or Landrace sows all of which were preSta., Journal Ser. No. 4-82272.
viously selected for one generation for either
2 Dept. of Anita. and Dairy Science.
lowest (LD) or highest (HD) number of days reReceived August 3, 1982.
quired to reach 105 or 135 kg or low (LF) or
Accepted July 11, 1983.
275
JOURNAL OF ANIMAL SCIENCE, Vol. 58, No. 2, 1984
276
KUHLERS ET AL.
high (HF) ultrasonically measured backfat
thickness at 105 or 135 kg (table 1). Selection
differentials for each line were calculated by
deviating each of the selected animals from its
breed-sex-farrowing group subclass mean. These
deviations were then weighted by the number
of progeny completing the test at 135 kg (table
2). Pigs were farrowed in a central farrowing
house at the swine breeding farm in three
groups (year-season) and moved to an openfronted sow-pig nursery at 10 to 14 d of age.
All pigs were vaccinated with a Bordatella
bronchiseptica and Pasteurella multocidavaccine
at 7 and 21 d of age and with an erysipelas
bacterin at about 90 d of age. Boars were castrated at 21 d and litters were weaned at 35 d
of age. Pigs were allowed ad libitum consumption of commercial, pelleted, corn-soybean
meal diets (18% CP to 18 kg, 16% CP from 18
to 36 kg and 14% CP from 36 to 135 kg)
fortified with vitamins, minerals and antibiotics.
The pigs were weighed and measured ultrasonically for backfat thickness at 2- to 4-wk
intervals during the growing-finishing period
and were removed from test in the interval they
attained 132 kg. Live animal traits studied were
days required to weigh 105 and 135 kg and
10th
rib
ultrasonically-measured backfat
thickness at 105 and 135 kg. Ages at each of
the weights were estimated by fitting cubic regression equations for each pig, while backfat
thickness was estimated by fitting a quadratic
equation for each pig at each weight. The
equations used were selected because preliminary analyses indicated that these explained
a significant portion of the variation in ages and
backfat thicknesses of each pig. All the available measurements from birth that included the
105 kg weight were used in the predictions for
105 kg, whereas all the available measurements
were used for the 135 kg predictions. For carcass data, pigs were moved to the Auburn
University Meat Science Laboratory in late
afternoon for slaughter the following morning.
Carcasses were chilled at 2 C for 24 h, at which
time the following data were collected: carcass
length, average backfat thickness (average of
first rib, last rib and last lumbar vertebra), loin
eye area at the 10th rib, subjective marbling
and color scores (scale of 1 to 5, where 1 was
devoid of marbling or pale color), backfat
thickness at the 10th rib at a point threefourths of the distance down the loin eye
towards the belly and specific gravity of the
right side of the carcass. Kilograms of muscle
were estimated using the following formula
(L. L. Christian, unpublished data):
Estimated kg muscle
= 4.377
+
.46 (hot carcass weight, kg)
- 2.44 (10th rib backfat thickness, cm)
+ .1301 (loin eye area, cm2).
Lean tissue growth/day of age was calculated
by dividing the estimated kilograms of muscle
by the number of days required to reach
135 kg.
The carcass traits, except color and marbling
scores, were analyzed with the following model
using the REGR procedure of the Statistical
Analysis System (Barr and Goodnight, 1972):
Yijklmn =/2 + t i + bj + Sk + Pl + -bsjk
+ bPil + Spk1 + bsPikI + Cm:ijkl
+ z(w--95) + eijklmn ,
TABLE1. DISTRIBUTION OF PIGS BY
SELECTION LINE OF PARENTS
Line
No. of
litters
Low days to 105 kg
High days to 105 kg
Low fat at 105 kg
High fat at 105 kg
Low days to 135 kg
High days to 135 kg
Low fat at 135 kg
High fat at 135 kg
Total
10
8
9
10
8
11
10
9
75
No. of
pigs
32
29
24
41
27
40
22
35
250
where t, b, s, p, c, z and w are the effects of
year-season, (farrowed August 1980; March
1981 and July 1981), breeding of pig (Duroc C~
X Landrace 9 or Landrace c~ • Duroc 9), selection line, selection weight, litter, regression coefficient of the trait on carcass weight and
carcass weight, respectively. No nonlinear forms
of the regression coefficients were considered
because the carcass weight range was small and
due only to scheduling through the slaughter
facility. Litter was considered a random effect
and therefore, was used as the error term in the
test of significance for year-season, breeding of
pig, selection line, selection weight and the
interactions. Live animal traits and color and
EFFECTS OF SELECTION ON SWINE CARCASS TRAITS
277
TABLE 2. PARENTAL MEANS AND WEIGHTED SELECTION DIFFERENTIALS
FOR THE FOUR TRAITS STUDIED
Weighted selection differentials
Trait
Days to
Days to
Backfat
Backfat
105 kg
135 kg
at 105 kg, cm
at 135 kg, cm
Parental
mean
High
line
Low
line
203.4
249.4
1.61
1.98
24.3
27.9
.36
.50
-21.4
-31.2
-.36
-.45
m a r b l i n g scores were a n a l y z e d using t h e same
m o d e l w i t h t h e e x c e p t i o n t h a t t h e covariate
for carcass w e i g h t was e x c l u d e d . T h r e e ort h o g o n a l c o n t r a s t s o f t h e line m e a n s were calc u l a t e d t o d e t e r m i n e t h e significance o f t h e
d i f f e r e n c e s o f (1) low days vs low fat, (2) high
days vs high f a t a n d (3) low days a n d low fat
vs high days a n d high fat.
Results and Discussion
S e l e c t i o n o f p a r e n t s h a d a h i g h l y significant
effect on ultrasonically measured backfat thicknesses a t 105 or 135 kg, b u t less so f o r d a y s t o
r e a c h 135 kg a n d n o significant effect f o r d a y s
t o r e a c h 105 kg ( t a b l e 3). This was e x p e c t e d
b e c a u s e t h e h e r i t a b i l i t y f o r g r o w t h is less t h a n
t h a t f o r b a c k f a t t h i c k n e s s (Craft, 1 9 5 8 ) . Backf a t t h i c k n e s s at 105 a n d 135 kg was t h i n n e r
in t h o s e pigs f r o m p a r e n t s selected f o r L F t h a n
it was in t h e pigs f r o m p a r e n t s selected f o r LD.
Pigs f r o m H D p a r e n t s were l e a n e r t h a n t h o s e
f r o m H F p a r e n t s , w h i l e t h e pigs f r o m LD a n d
L F selected p a r e n t s were leaner t h a n t h e
o f f s p r i n g f r o m H D a n d H F selected p a r e n t s .
Pigs f r o m LD a n d L F s e l e c t e d p a r e n t s t o o k
f e w e r days t o r e a c h 105 a n d 135 kg t h a n did
pigs f r o m HD or H F s e l e c t e d p a r e n t s . H o w e v e r ,
n o significant d i f f e r e n c e s in t h e days r e q u i r e d
to r e a c h 105 a n d 135 kg were n o t e d b e t w e e n
LD a n d L F o f f s p r i n g n o r b e t w e e n H D a n d H F
TABLE 3. TESTS OF SIGNIFICANCE AND SELECTED LEAST-SQUARES MEANS
FOR THE LIVE ANIMAL TRAITS
Source
Year-season
Breeding
Line
Low days (LD)
High days (HD)
Low fat (LF)
High fat (HF)
LD vs LF
HD vs HF
LD+LF vs HD+HF
Selection weight
105 kg
135 kg
Litters mean square
Residual mean square
aNS = Not significant.
tp<.lO.
*P<.05.
**P<.01.
df
2
1
3
1
1
1
1
32
200
Days to
105 kg
Backfat at
105 kg, cm
Days to
135 kg
Backfat at
135 kg, cm
NS a
NS
NS
176.6
187.1
182.1
182.1
NS
NS
t
NS
182.0
181.9
523.0" *
266.0
**
NS
**
2.03
1.85
1.62
2.13
**
**
**
NS
1.94
1.88
.14" *
.05
NS
NS
t
215.2
229.0
220.9
224.9
NS
NS
*
NS
224.2
220.8
729.9* *
353.2
*
NS
**
2.50
2.22
1.93
2.63
**
**
**
NS
2.35
2.29
.18* *
.10
278
KUHLERS ET AL.
TABLE 4. PARTIAL REGRESSION
COEFFICIENTS OF CARCASS TRAITS
ON CARCASS WEIGHT (KG)
Trait
b + SE
Length, em
Average backfat, cm
10th rib backfat, cm
Loin eye area, cm 2
Specific gravity
Estimated muscle, kg
Ltmn tissue growth/day of age, kg/d
.12
.027
.038
.327
-.226 a
.41
2.06 a
+ .04
+ .006
+ .009
+- .079
+ .lOOa
+ .03
+ .34 a
aMultiply b and its standard error • 10 -3.
offspring. Weight a t s e l e c t i o n did n o t have a
significant e f f e c t o n a n y o f t h e live a n i m a l traits
studied.
Partial regression c o e f f i c i e n t s o f t h e carcass
traits o n carcass w e i g h t are given in t a b l e 4. All
were significantly d i f f e r e n t f r o m zero. L e n g t h ,
average a n d 1 0 t h - r i b b a c k f a t , loin eye area,
e s t i m a t e d k i l o g r a m s o f m u s c l e a n d lean tissue
g r o w t h / d a y o f age increased as carcass w e i g h t
increased. H o w e v e r , specific gravity d e c r e a s e d
as carcass w e i g h t increased.
L e n g t h , average a n d 1 0 t h - r i b b a c k f a t , loin
eye area, specific gravity a n d e s t i m a t e d kilog r a m s of m u s c l e all were a f f e c t e d b y s e l e c t i o n
line o f t h e p a r e n t s , b u t o n l y average b a c k f a t
was a f f e c t e d b y w e i g h t at w h i c h s e l e c t i o n t o o k
place ( t a b l e 5). In all o f t h e traits s t u d i e d , n o n e
of t h e i n t e r a c t i o n s in t h e m o d e l were significant. T h e r e f o r e , t h e effects o f s e l e c t i o n line or
weight at selection would not be different for
t h e t w o k i n d s o f c r o s s b r e d pigs p r o d u c e d . Offspring o f L F selected p a r e n t s h a d longer carcasses c o m p a r e d w i t h o f f s p r i n g of p a r e n t s
selected for LD. Carcass l e n g t h was also longer
f r o m o f f s p r i n g o f HD selected p a r e n t s c o m p a r e d w i t h o f f s p r i n g o f H F selected p a r e n t s .
Average a n d 1 0 t h - r i b b a c k f a t t h i c k n e s s foll o w e d t h e live a n i m a l u l t r a s o n i c a l l y - m e a s u r e d
b a c k f a t m e a s u r e m e n t s closely; pigs o f p a r e n t s
selected for L F were leaner t h a n pigs f r o m
p a r e n t s selected f o r LD, t h e r e was less b a c k f a t
in pigs o f H D s e l e c t e d p a r e n t s t h a n in pigs f r o m
H F selected p a r e n t s a n d pigs f r o m LD a n d L F
selected p a r e n t s were leaner t h a n pigs f r o m
HD a n d H F selected p a r e n t s . L o i n e y e areas
were t h e largest in pigs f r o m L F a n d L D
TABLE 5. TESTS OF SIGNIFICANCE AND SELECTED LEAST-SQUARES MEANS
FOR THE QUANTITATIVE CARCASS TRAITS
Source
Year-season
Breeding
Line
Low days (LD)
High days (HD)
Low fat (LF)
High fat (HF)
LD vs LF
HD vs HF
LD+LF vs HD+HF
Selection weight
105 kg
135 kg
Litters mean square
Residual mean square
df
2
1
3
1
1
1
1
32
200
Length,
cm
Backfat (cm)
Average
10th rib
Loin eye
area, cm*
Specific
gravity
Estimated
muscle,
kg
*
**
**
87.0
89.1
90.0
87.0
**
**
NS
NS
88.2
88.3
7.5**
4.1
NS a
NS
**
3.46
3.25
t
**
*
35.8
34.4
36.8
33.9
NS
NS
**
NS
35.5
34.9
21.3 t
14.9
NS
NS
**
1.039
1.044
1.049
1.039
**
**
**
NS
1.042
1.043
.307 b
.238 b
NS
*
**
44.2
44.7
45.8
43.5
**
**
**
NS
44.5
44.5
3.3*
2.0
aNS = Not significant.
bThese values should be multiplied X 10 -4.
tP<.lO.
*P<.05.
**P<.01.
2.97
3.57
**
**
**
*
3.37
3.25
.19"*
.10
NS
NS
**
3.51
3.23
2.89
3.70
**
**
**
NS
3.36
3.31
.36*
.21
279
EFFECTS OF SELECTION ON SWINE CARCASS TRAITS
T A B L E 6. TESTS OF SIGNIFICANCE A N D SELECTED LEAST-SQUARES MEANS F O R THE
Q U A L I T A T I V E CARCASS TRAITS A N D LEAN TISSUE GROWTH PER DAY OF A G E
Color
Marbling
Lean tissue
growth/day
of age, kg/d
NS a
NS
NS
2.43
2.45
2.40
2.63
NS
NS
NS
NS
2.45
2.50
.542*
.348
*
NS
NS
2.02
1.82
1.98
2.25
NS
*
NS
NS
2.07
1.97
.938*
.576
NS
NS
**
.208
.196
.209
.195
NS
NS
**
NS
.200
.203
.526 b**
.282
Score
Source
Year-season
Breeding
Line
Low days (LD)
High days (HD)
Low fat (LF)
High fat (HF)
LD vs LF
HD vs HF
LD + LF vs HD + HF
Selection weight
105 kg
135 kg
Litters m e a n square
Residual m e a n square
df
2
1
3
1
1
1
1
32
200
aNS = Not significant.
bThis value should be multiplied • 10 -3.
*P<.05.
**P<.01.
selected parents and smallest in pigs from HD
and HF selected parents. Specific gravity was
higher in offspring o f LF selected parents
than offspring of LD selected parents, lower in
offspring of HF selected parents than offspring
of HD parents with offspring of LD and LF
parents having a higher specific gravity than offspring of HD and HF selected parents. Estimated kilograms of muscle was higher in the
offspring of LF selected parents than of LD
selected parents and less in offspring of HF
selected parents than in
offspring of HD
selected parents.
Subjective color scores were not significantly affected by the line of selection or the
weight at which selection was practiced (table
6); however, marbling scores were higher in HF
offspring than HD offspring.
Lean tissue growth/day of age combines
carcass composition with growth rate. This
combined trait shows that offspring of LF
and LD selected parents were not significantly
different from each other in the daily deposition of lean tissue (table 6). But these two
groups deposited significantly more muscle/day
than did the offspring of HD and HF selected
parents which did not differ significantly from
each other. Facilities available did not allow
easy collection of feed consumption data,
t h e r e f o r e , it w a s n o t p o s s i b l e t o d e t e r m i n e l e a n
tissue efficiency. However, additional research
is n e e d e d t o d e t e r m i n e l e a n t i s s u e a n d r e p r o ductive efficiencies of single-trait-selected lines
to determine the economic benefits of such
lines.
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