Animal Science Department Florida Agricultural
Mimeograph Report AN64-3 Experiment Station
THE INFLUENCE OF AGE AT CASTRATION ON FEEDLOT
PERFORMANCE AND CARCASS CHARACTERISTICS OF MALE SWINE
H. D. Wallace, A. Z. Palmer,
J. W. Carpenter, G. E. Combs, T. H. Berry and R. C. Crum I/
It is common practice in commercial swine herds to castrate male pigs
very early In life, usually before eight weeks of age. Pigs are easier to
handle and are subjected to less stress during this period. However, very
little research has been undertaken to determine if there Is a best age
at which to castrate to attain optimum efficiency in the production of lean
pork. Boars are known to gain faster, more efficiently and also hang
leaner carcasses than barrows. Nevertheless the objectionable sex odor
imparted to boar meat has necessitated early castration.
This study was undertaken to determine the influence of age at
castration on the overall production efficiency of male market pigs as
measured by rate of gain, feed conversion and carcass characteristics. It
was also of interest to determine the degree of boar odor in the pork pro-
duced as influenced by castration age.
Three separate feeding trials were conducted during 1962. For each
trial 24 two-week old male pigs were divided into 4 lots of six pigs each
by outcome groups formed on the basis of litter and weight. One pig in
each outcome group had been castrated at one week of age in order to form
Lot I. The pigs in all groups were self fed in concrete confinement the
feed mixtures shown In Table 1. At eight weeks of age the pigs in Lot 2
were castrated. At this time all pigs in the trial were weighed and feed
intakes rare determined. This procedure was repeated when the pigs reached
12 and 16 weeks of age at which time pigs in Lots 3 and 4 respectively
were castrated. All animals were slaughtered individually at a final live
weight of 200 + 5 pounds.
]/ Wallace, Animal Nutritionist; Palmer, Associate Meat Scientist;
Carpenter, Assistant Meat Scientist; Combs, Associate Animal
Nutritionist; Berry and Crum, Research Assistants, Animal Science
Department. The assistance of W. E. Collins and L. S. Taylor,
Swine Herdsmen, Jeff Jeter, Meats Laboratory Manager and Richard
Newman and Mrs. Barbara Sullivan, Laboratory Assistants is
The pigs were slaughtered and dressed packer style for carcass study.
Carcass weights and measurements were taken after the carcasses had been
chilled for 48 hours at 34 36 degrees F. Length of carcass was obtained
by a measurement from the anterior edge of the aitch bone (pelvis) to the
anterior edge of the first rib. Backfat thickness was calculated as an
average of measurements taken at the first rib, last rib and last lumbar
vertebra. A tracing was made of the perimeter of the lonqissimus dorsi
muscle (loin eye), exposed by cutting the loin perpendicular to the
vertebral column equidistant between the-tenth and eleventh ribs. The
area of the loin eye muscle was then determined by use of a compensating
polar planimeter. The carcasses were broken down by a standard procedure
(Reciprocal Meat Conference, 1951).
TABLE I. BASAL FEED MIXTURES FED
TO ALL LOTS
INGREDIENT 2-6 WKS. 6-8 WKS. 8 WKS.- SLAUGHTER
GROUND YELLOW CORN 54.35 65.85 78.35
SOYBEAN OILMEAL (50%) 8.50 11.50 19.00
DRIED SKIM MILK .20.00 10.00 --
CANE SUGAR. 10.00 5.00
STABILIZED LARD 3.00 3.00 --
STEAMED BONEMEAL 1.00 1.50 1.00
GROUND LIMESTONE -- -- 1.00
IODIZED SALT 0.50 0.50 0.50
TRACE MINERALS I/ 0.10 0.10 0.05
VITAMIN BI2 SUPPLEMENT 2/ 0.10 0.10 --
B-VITAMIN SUPPLEMENT 3/ 0.15 .0.15 0.10
VITAMIN A AND D SUPPLEMENT 4/ 2.00 2.00 --
ANTIBIOTIC SUPPLEMENT 5/ 0.30 .0.30 -
100.00 100.00 100.00
J/ Adds the following to
(36.5), copper (2.5),
ration (p.p.m.): manganese (29.6), iron
cobalt (.83), zinc (42.0) and potassium
2/ Contained 9.0 mg. B12 per pound.
3/ Contained 2000 mg. riboflavin, 4000 mg. pantothenic acid, 9000
mg. niacin, and 10,000 mg. choline chloride per pound.
4/ Contained 20 gm, vitamin A (10,000 I.U./gm.), 4.44 gm. vitamin
D (9,000 I.U/gm.), and 883.56 gm. soybean meal.
5/ Contained 10 gm. aureomycin per pound.
Backfat and leaf fat samples were removed from the chilled carcasses,
finely diced and covered with boiling water. Aroma was then scored by a
trained panel on a I to 4 scale with I being no boar odor, 2 slight, 3 -
moderate and 4 strong boar odor.
Loins were wrapped, frozen; later, I-inch thick chops were cut.from
the 10th rib area. Two chops from each animal were defrosted at 36 'F.
for 24 hours; the L, dorsi muscle was removed and cooked in covered
petri dishes in.a preheated 350"' F. oven for 30 minutes. A one-half inch
core was taken from each chop for Warner-Bratzler shear testing. Two
shear readings were taken per core. Each chop was divided in half thus
providing four samples for the four-member taste panel. The chops were
evaluated as to tenderness on a I to 7 scale with 2 designating "extremely
tough", 5 average tenderness and 7 very tender.
Results and Discussion
Significant differences in gains and backfat thicknesses were
observed between trials. However, age at castration effects were similar
in the three trials, so for the sake of brevity the data from the three
trials were combined and are presented in this form in Table 2.
Daily gain The age at which' pigs were castrated appeared to have
little influence on rate of gain. Pigs castrated at I week of age gained
slightly faster than pigs castrated at 8, 12 or 16 weeks of age. The
stress of castration did not cause a pronounced slowing in gains. However,
the pigs castrated at 8 and 12 weeks of age gained slightly slower than
the other groups during the ensuing four weeks following castration. The
fact-that this did not occur in the group castrated at 16 weeks probably
lessens the importance of this observation.
Feed efficiency Feed conversions were almost identical for the
four groups indicating that delayed castration did not reduce the amount
of feed required per unit of gain.
Dressing percent Pigs castrated at I, 8 and 12 weeks of age
dressed 70.56, 70.33, and 70.53 percent respectively. Pigs castrated at
16 weeks of age dressed 68.39 percent, significantly lower than the other
Carcass length Pigs castrated at 1, 8, or 12 weeks of age yielded
carcasses that averaged 30.25, 29.90 and 30.05 inches in length respec-
tively. These differences were not significant. The carcasses from pigs
castrated at 16 weeks of age were 30.65 inches in length which was'
significantly longer (P4.05) than the other groups.
STABLE 2. SUMMARY OF PERFORMANCE AND CARCASS
S DATA AS INFLUENCED BY AGE AT CASTRATION
LOT NUMBER 2 3 4 .OF AGE AT
AGE AT CASTRATION, WKS. CASTRATION
I 8 12 16 EFFECT
NUMBER OF PIGS 18 18 18 18 --
INITIAL WT., LB. 8.86 9.35 9.06 9.25
WT. AT CASTRATION, LB. 5.00 31.0 66.1 114.4
WT. AT SLAUGHTER, LB. 200.5 .198.8 198.9 201.7 .
DAILY GAIN, LB.
2 8 WKS. 0.60 0.58 0.59 0.53 N.S.
8 12 WKS. 1.36 1.22 1.25 1.23 N.S.
12 16 WKS. 1.74 1.76 1.64 1.80 N.S.
16 SLAUGHTER 1.96 1.98 1.96 1.95 -N.S.
.ENTIRE PERJDD0 1.42 1.39 1.38 1.39 N.S.
FEED PER LB. GAIN, LB.
ENTIRE PERIOD 2.93 2.89 2.91 2.87 N.S.
DRESSING PERCENT 70.56 70.33 70.53 68.39 .01
CARCASS LENGTH, IN. 30.25. 29.90 30.05 30.65 .05
BACKFAT THICKNESS, IN. 1.25 1.22 1.19 1.12 .05
LOIN EYE AREA, SQ. IN. 3.51 3.47 3.49 3.43 N.S.
PERCENT 4 LEAN CUTS 52.43 52.08 52.61 53.44 N.S.
CARCASS FIRMNESS SCORE 1/ 1.39 1.39 1.44 1.78 N.S.
DEGREE OF BOAR ODOR 2/
BACKFAT 1.02 1.07 1.07 1.06 N.S.
LEAF FAT 1.61 2.04 1.84 1.84 N.S.
TENDERNESS OF CHOPS 3/
TASTE PANEL 6.32 6..10 5.96 6.18 N.S.
SHEAR TEST 6.83 7.98 7.48 7.80 N.S.
LOIN EYE MARBLING SCORE 4/ 11.61 10.29 12.25 10.28 N.S.
I/ Hard I, medium hard 2, medium soft 3, soft 4, oily 5.
2/ None 1, slight 2, moderate 3, strong 4.
3/ Too tough to be edible I, extremely tough 2, very.tough 3,
bejow average 4, average tenderness 5, above average tender
6, very tender 7.
4/ Slight mimus 7, slight 8, slight plus 9, small minus 10,
small II, small plus 12, modest minus 13, modest 14,
modest plus 15 and etc. (Marbling scores coded from 0 21;
0 = devoid, 21 = extremely abundant)
Backfat thickness As age at castration increased backfat thickness
tended to decrease. Pigs castrated at 16 weeks of age carried 1.12 inches
of backfat compared to 1.25, 1.22 and 1.19 for pigs castrated at I, 8 and
12 weeks of age respectively.
Loin eye areas Age at castration did not exert a measurable influence
on the area of the loin eye.
Lean cut yield Pigs castrated at 16 weeks of age yielded the highest
percentage of the 4 lean cuts but differences were not statistically signif-
Boar odor Age at castration did not appear to be associated with the
degree of boar odor detected. Actually very little odor was detected.- Only a
slight odor was detected in leaf fat samples and practically none in back-
Tenderness Tenderness of chops as measured by taste panel and the
conventional mechanical shear test did not reveal any significant treat-
ment differences. All chops were acceptable from the standpoint of
Marbling Although wide variations existed between trials and
individuals within treatments of the three trials there was little evidence
to suggest that age at castration influenced the degree of marbling in
the loin eye muscle.
Three trials, involving a total of 72 male pigs, were conducted to
determine the effects of castration at I, 8, 12 or 16 weeks of age on
feedlot performance and carcass characteristics.
Gains and feed conversion were not significantly influenced by the
Dressing percent and backfat thickness were significantly decreased
by castration at 16 weeks of age compared to earlier castrations. Carcass
length was increased in this same group. Percent of four lean cuts was also
greater for pigs castrated at this age and carcass firmness appeared to
be adversely affected.
Only a slight boar odor was detected in a few carcasses and was not
clearly related to age at castration.
Tenderness measurements determined on chops suggested little, if any,
influence of age at castration. Marbling of the loin eye muscle was
quite variable, but again was not clearly associated with age at castration.