ANIMAL SCIENCE FLORIDA AGRICULTURAL
MIMEOGRAPH REPORT AN64-16 EXPERIMENT STATION
THE INFLUENCE OF PROTEIN LEVEL ON FEEDLOT
PERFORMANCE AND CARCASS CHARACTERISTICS
OF BARROWS AND GILTS.
H. D. Wallace, A. Z. Palmer, J. W. Carpenter,
Ghazi Taki and G. E. Combs ./
Since protein represents a very critical nutrient and also a costly ingred-
ient it is necessary to know how to use it wisely. Most feeding experiments
involving protein levels have been concerned solely with effects on daily gain
and feed conversion. Based on these two important criteria the fortified corn-
soybean meal ration, widely used presently, has permitted significant reduction
in protein level recommendations. However, insufficient emphasis has been placed
on carcass value as influenced by dietary protein.
A recent report from this station (I) emphasized the importance of an ade-
quate level of dietary protein in order to obtain an optimum lean-fat ratio in
the carcass. It was also observed that meat-type hogs require a more liberal
level of good quality protein in the ration for top performance.
The present experiment was undertaken to further study protein level in the
growing-finishing ration primarily as it influences carcass quality and meat-
One hundred crossbred pigs (Duroc-Landrace x Hampshire) were allotted from
outcome groups formed on the basis of weight, sex and litter to four lots of
twenty-five pigs each. Two lots consisted of barrows and two lots consisted of
gilts. The experiment was conducted on concrete and was initiated May 21, 1963.
The feed mixtures used are presented in Table i. One lot of barrows and one lot
of gilts were started on a level of 17 percent crude protein. Similarly one lot
of barrows and one lot of gilts were started on 13 percent crude protein. When
the average weight of the pigs in each lot reached approximately 100 pounds, the
level of protein was reduced as indicated in Table 2.
The pigs were individually weighed off test for slaughter at 200 5 pounds.
The pigs were weighed on and off test in a "full" state of fill.
The pigs were slaughtered and dressed packer style for carcass study. Car-
cass 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
I/ Wallace, Animal Nutritionist; Palmer, Associate Meat Scientist; Carpenter,
Assistant Meat Scientist; Taki, Research Assistant and Combs, Associate
Animal Nutritionist, Animal Science Department. The assistance of W. E.
Collins and L. S. Taylor, Swine Herdsmen; Jeff Jeter, Meats Laboratory
Manager and Mrs. Barbara Sullivan, Laboratory Assistant is gratefully ack-
at the first rib, last rib and last lumbar vertebra. A tracing was made of the
perimeter of the lonoissimus 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 (Recip-
rocal Meat Conference, 1951.).
Table I. COMPOSITION OF RATIONS
Crude Protein Levels (%) 17 15 13 II
Yellow corn 77.35 81.75 86.65 91.55
Soybean meal (50%) 20.00 15.50 10.50 5.50
Steamed Bonemeal 1.50 1.60 1.70 1.80
Ground Limestone 0.50 0.50 0.50 0.50
lodized salt 0.50 0.50 0.50 0.50
Trace minerals JL/ 0.05 0.05 0.05 0.05
Vitamin premix 2/ 0.10 0.10 0.10 0.10
Vitamin B12 supplement ,/ 0.05 0.05 0.05 0.05
Total 100.05 100.05 100.05 100.05
J/ Adds in p.p.m.: Manganese (29.6), iron (36.5), copper (2.5), cobalt
(0.83), zinc (42.0) and potassium (3.9).
2/ Dawe's 2-4-9-10 Vitamin supplement, contained 2000 mg. riboflavin,
4000 mg. pantothenic acid, 9000 mg. niacin and 10,000 mg. choline
chloride per lb.
3/ Pfizer's BI2 supplement, contains 20+ mg./lb.
RF.SUI.TS AND DISCUSSION
A summary of the performance and carcass data is presented in Table 2.
Protein level effect The pigs in lots I and 2 fed the higher level of pro-
tein (17-15%) gained 1.68 pounds per head per day compared to 1.42 for pigs in lots
3 and.4 fed the lower protein level (13-11%). This difference was highly signifi-
cant (P <.01). As regards rate of gain there was not a significant interaction
between sex and protein level. Although gilts gained much slower than barrows the
two sexes responded similarly to dietary protein level.
All lots were somewhat less efficient in the utilization of feed than in the
previous experiment (I). This can be explained in part by the heavier initial
weights of the pigs in.this experiment. Pigs fed the higher level of protein re-
quired an average of 3.30 lb. of feed per 1'. gain while those on the lower level
of protein required 3.87 lb. of feed per lb. of gain. These data were not analyzed
statistically, but the magnitude of the difference suggests a significant advantage
in feed conversion for pigs fed the higher level of protein.
TABLE 2. THE INFLUENCE CF PROTEIN LEVEL CN FEEDLOT
PERFORMANCE AND CARCASS CHARACTERISTICS OF BARROWS AND GILTS
Lot Number I 2 3 4 Statistical Significance
Protein Level % 17-15 17-15 13-11 13-II Protein Sex Inter-
Sex Barrows Gilts Barrows Gilts
Number of Pigs 25 25 25 25
Initial wt. Ib. 59.3 59.3 58.9 59.2
Slaughter wt. lb. 203.9 200.8 202.8 200.0
Daily gain, Ib. 1.74 1.61 1.50 1.34 ** ** N.S.
Feed/lb. gain, lb. 3.28 3.31 3.81 3.92
Dressing percent 69.82 70.21 70.30 70.24 N.S. N.S. N.S.
Percent liver 1/ 1.77 1.73 1.60 1.60 ** N.S. N.S.
Carcass length, in. 30.54 30.43 30.23 30.45 N.S. N.S. N.S.
Backfat thickness, in. 1.31 1.30 1.42 1.42 ** N.S. N.S.
Carcass firmness 2/ 1.60 1.96 1.24 1.56 ** ** N.S.
Firmness of lean 2/ 3.00 3.04 2.48 2.40 ** N.S. N.S.
Percent 4 lean cuts 3/ 51.34 52.71 48.23 48.81 ** ** N.S.
Percent ham 19.69 20.24 18.57 18.88 ** ** N.S.
Percent loin 15.38 15.88 13.73 14.01 ** N.S.
Loin eye area, sq. in. 3.41 3.88 2.95 3.14 ** ** N.S.
Loin eye marbling score A/
Left 8.72 8.36 19.16 14.80 ** N.S.
Right 8.16 7.84 18.44 13.16 ** *
Color of lean 5/ 3.88 3.56 3.40 3.12 ** N.S.
Based on slaughter wt.
Hard I, medium hard 2, medium
Based on chilled carcass wt.
soft 3, soft 4, oily 5
Marbling scores coded from 0-33, 0= devoid, 33= extremely abundant +.
Color of lean coded from 1-5, 1= very dark, 2= dark, 3= greyish pink (ideal color), 4= slightly
light, 5= very light (chicken meated).
Differences in dressing percent were not significant but tended to favor the
low protein pigs as was observed in the previous experiment (I).
Liver percentage was significantly higher (P(.O1) for pigs fed the higher
Carcass length was not significantly influenced by dietary protein level.
Backfat thickness wassignificantly greater (P<.0l) for pigs fed the lower
level of protein. The magnitude of this difference was approximately 0.1 of an
Carcasses from the lower protein groups were significantly firmer (P<.01),
probably reflecting the greater degree of fat deposition. Firmness of lean also
favored the low protein pigs (P<.01).
Pigds fed the higher level of protein yielded considerably greater percent
lean.cut-out (52.04 vs. .48.52). This difference was highly significant.
The higher protein level also produced significantly larger loin eye area
measurements (3.65 vs. 3.05).
One of the most interesting observations concerned the degree of marbling
or fat deposition in the loin eye muscle. Gross observations recorded indicated
that the low level or inadequate level of protein caused a greater degree of
marbling .as compared to the higher level of protein. In some cases the fat infil-
tration appeared to be objectionably extensive.
In this study the color of lean was significantly darker (P(.01) in the pigs
fed the low protein level.
Sex effect -.The differences in performance and carcass characteristics
between barrows and gilts is rather well documented in the literature. Previous
reports from this station have presented such data (I, 2, 3, 4).
In the present study barrows gained faster (P<.0l) and more efficiently
Carcass lengths and backfat thicknesses were not significantly different
between the sexes. Carcasses from barrows were firmer (P<.01). Gilt carcasses
were much leaner as measured by the percent of four lean cuts (P.O0I) and loin
eye area measurements (P <.01).
Less marbling was evident in the loins of gilt carcasses (P .05).
One hundred weanling pigs were used to study the relationship of dietary
protein level to feedlot performance and carcass characteristics. Twenty-five
barrows and twenty-five gilts were fed on each of two protein level regimes
(initially 17 and 13 percent protein, reduced respectively to 15 and II percent
at 100 pounds liveweight).
Pigs fed the higher level of protein gained significantly faster and more
efficiently and carcasses were significantly leaner in all respects. Carcasses
from the low protein groups showed a greater degree of marbling and in several
cases the fat infiltration seemed excessive.
Barrows gained faster and more efficiently than gilts, but carcasses from
gilts yielded a much higher percentage of lean cut out. There appeared to be no
important interaction effects between protein level and sex.
1. Wallace, H. D., M. E. Palmer, A. Z. Palmer, J. W. Carpenter and G. E. Combs.
1963. The Influence of Protein Level on Feedlot Performance and Carcass
Characteristics of Barrows and Gilts. Fla. An. Sci. Mimeo. AN64-7.
2. Wallace, H. D., G. E. McCabe, A. Z. Palmer, J. W. Carpenter, M. Koger, and
G. E. Combs. 1960. Feedlot Performance and Carcass Traits of Growing-Finishing
Swine as Influenced by Sex and Breed. Fla. An. Sci. Mimeo. 60-13.
3. Wallace, H. D., A. Z. Palmer, J. W. Carpenter, N. H. Anh and G. E. Combs.
1963. The Influence of Feed Restriction, High Level Copper Supplementation
and Sex on the Feedlot Performance and Carcass Characteristics of Swine.
Fla. An. Sci. Mimeo. Series. 63-16.
4. Wallace, H. D., A. Z. Palmer, J. W. Carpenter and G. E. Combs. 1963. The
Influence of Feeding a Constant Level of Feed From 100 pounds Liveweight to
Market Weight on Feedlot Performance and Carcass Characteristics of Swine.
Fla. An. Sci. Mimeo. AN64-5.