Animal Science Florida Agricultural
Mimeograph Report AN65-3 Experiment Station
July, 1964 Gainesville, Florida
THE INFLUENCE OF PROTEIN LEVEL ON FEEDLOT PERFORMANCE
AND CARCASS CHARACTERISTICS OF BARROWS AND GILTS
R. C. Crum, Jr., H. D. Wallace, A. Z. Palmer,
J. W. Carpenter and G. E. Combs I/
The importance of ration influences on carcass quality are often not adequate-
ly emphasized in the evaluation of experimental feeding results. Two recent exper-
iments conducted at this station have demonstrated very clearly the need for an
adequate level of good quality protein if efficient production of lean pork is to
be expected (1) (2).
The experiment summarized here was undertaken to further study this problem
and to determine more precisely the minimum protein levels essential for optimum
lean pork production.
Ninety-six crossbred pigs (Duroc-Landrace X Hampshire) were allotted to four
pens from outcome groups formed on the basis of weight, sex and litter. Each pen
included 12 gilts and 12 barrows.
The feed mixtures used are presented in Table I. As indicated in Table 2,
Lot I pigs were fed the mixture containing 17 percent protein throughout the feed-
ing trial; Lot 2 pigs were started on 17 percent and when they reached an average
weight of 100 lb. the protein level was reduced to 15 percent; Lot 3 pigs were fed
the mixture containing 13 percent protein throughout the feeding trial and Lot 4
pigs were started on 13 percent and when they reached an average weight of 100 lb.
the protein level was reduced to II percent.
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 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,
I/ Crum, Research Assistant; Wallace, Animal Nutritionist; Palmer, Associate Meat
Scientist; Carpenter, Assistant Meat Scientist; and Combs, Associate Animal
Nutritionist, Animal Science Department. The assistance of Billy Ray Cannon
and L. S. Taylor, Swine Herdsmen; Jeff Jeter, Meats Laboratory Manager; and
Mrs. Barbara Sullivan, Laboratory Assistant is gratefully acknowledged.
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
Iodized salt 0.50 0.50 0.50 0.50
Trace minerals J/ 0.05 0.05 0.05 0.05
Vitamin premix 2/ 0.10 0.10 0.10 0.10
Vitamin B12 Supplement 3/ 0.05 0.05 0.05 0.05
Total 100.05 100.05 100.05 100.05
I/ Adds in p.p.m.: manganese (29.6),
zinc (42.0) and potassium (3.9).
iron (36.5), copper (2.5), cobalt (0.83),
./ Merck vitamin Supplement No. 1231. Contains 8000 mg. riboflavin, 14,720 mg.
d-pantothenic acid, 36,000 mg. niacin and 40,000 mg. choline chloride per lb.
3/ Commercial Solvents Corporation Proferm-12. Contains not less than 12 mg.
vitamin 812 activity per lb.
Results and Discussion
A summary of performance and carcass data is presented in Tables 2 and 3.
Protein level effects (Table 2). Pigs fed the higher levels of protein (Lots
I and 2) gained significantly faster (P (.01) then pigs fed the lower levels of
protein (Lots 3 and 4). When protein levels were reduced (Lot 2 and Lot 4) gains
were slowed as compared to the lots maintained on the initial levels of protein.
Feed conversion was considerably better for pigs fed the higher protein levels
(Lots I and 2). A marked depression of feed conversion was apparent in Lot 4 where
the protein level was reduced to II percent during the finishing phase of the ex-
No significant differences in dressing percentage, carcass length or carcass
firmness due to protein level were observed. Backfat thickness tended to average
somewhat more for pigs on the low protein levels which agrees with results obtained
in previous experiments.
Pigs from Lots I and 2 which were fed the higher levels of protein yielded
carcasses with significantly higher percent of lean cuts (P<.01), larger loin
eyes (P <.01) and less marbling in the loin eye muscle (P<.01). A. more critical
analysis of the data indicated that reduction of the protein level from 17 to
Table 2. The influence of protein
of barrows and gilts.
level on feedlot performance and carcass quality
Lot Number I 2 3 4 Statistical Significance
Protein Level ($) 17-17 17-15 13-13 13-11 Protein-.kevels ..
Lot Lot Lot
1,2 vs 3.4 I-vs 2 3'vs 4
Number of Pigs 24 24 24 24
Initial Wt. (lb.) 49.9 50.0 49.9 50.1
Slaughter Wt. (lb.) 199.9 201.0 201.4 197.9
Daily Gain (lb.) 1.70 1.63 1.59 1.43 ** **
Feed/lb. Gain 3.08 3.06 3.19 3.43 --
Dressing Percent 70.9 71.0 71.4 71.5 NS NS NS
Carcass Length (in.) 29.9 29.9 30.1 29.8 NS NS NS
Backfat Thickness (in.) 1.30 1.28 1.29 1.34 NS NS *
Carcass Firmness L/ 1.3 1.4 1.4 1.4 NS NS NS
Percent Lean Cuts 2/ 51.4 51.6 50.9 48.9 ** NS **
Percent Ham 19.7 19.8 19.5 18.8 NS **
Percent Loin 15.3 15.5 15.4 14.5 NS **
Loin Eye Area (in.) 4.02 3.97 3.84 3.59 ** NS *
Loin Eye Marbling Score 3/ NS NS NS
Left 15.0 14.9 18.0 19.7 ** NS NS
Right 15.5 15.0 18.6 19.9 ** NS NS
Color of Lean 4/ 3.0 3.1 3.3 3.1 NS NS NS
Firmness of Lean 1/ 2.3 2.5 2.4 2.2 NS NS NS
Hard I, medium hard 2, medium soft -
Based on chilled carcass wt.
3, soft 4, oily 5
scores coded from 0-33, 0 = devoid, 33 =extremely abundant.
lean coded from I 5, I = very dark, 2 = dark, 3 = greyish pink
= very light (chicken meated)
(ideal color) 4 = slightly
15 percent at IO lb. liveweight (Lot 2) did not affect carcass leanness. However,
a reduction from 13 to 1I percent (Lot 4) caused a significant drop in yield of
four lean cuts (P-.O0) and loin eye area (P<.05).
Protein levels did not influence color or firmness of lean significantly.
Sex effects (Table 3). The barrows in the experiment gained an average of
1.65 lb. per head per day.while the gilts averaged 1.53. This difference was
highly significant (P-<.01).
Differences in dressing percentage, carcass length, backfat thickness, carcass
firmness and percent 4 lean cuts due to sex were not statistically significant.
However, percent of 4 lean cuts were considerably greater for gilts in the two lots
fed the high level of protein (Lots I and 2). The data suggest that gilts require
more protein than barrows for optimum lean tissue development. Gilts yielded a
higher percentage of trimmed ham, exhibited less marbling in the loin eye muscle
and showed greater firmness in the lean than barrows (P<.01).
No significant interactions of protein level and sex were
observed in this
No. of Pigs
Initial Wt. (Ib.)
Slaughter Wt. (lb.)
Daily Gain (lb.)
Carcass length (in.)
Backfat thickness (in.)
Carcass firmness I/
Percent 4 lean cuts 2/
Loin eye area (in.)
Loin eye marbling score j/
i Color of lean A/
Firmness of lean I/
17, 2/, 2/, &/ same as Table 2.
An experiment, involving 96 growing-finishing pigs, has been conducted to study
the influence of various protein level sequences on feedlot performance and carcass
For optimum daily gain, a 17 percent protein ration fed continuously from an
initial weight of 50 Ib. to a final weight of 200 lb. proved most effective. How-
ever, when the protein level was dropped to 15 percent at 100 Ib. liveweight neither
feed conversion nor the several criteria used to measure carcass leanness were
adversely affected. Thus, this reduction in protein level appeared to be compatible
with good performance and optimum lean carcass development.
A level of 13 percent protein during the entire feeding period appeared to be
fairly adequate for barrows as measured in terms of gain and carcass leanness but
was inadequate for gilts. Gilts gained considerably slower on this protein level
and their carcasses yielded a lower percentage of lean cut out. When the 13 percent
level of protein was reduced to II percent at 100 lb. liveweight both sexes were
adversely affected in gains and carcass leanness.
These results emphasize the importance of maintaining an adequate dietary pro-
tein level for efficient production of lean pork. Not only will production costs be
less with adequate protein, but the pork produced will be leaner and more acceptable
to the consumer.
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. Rpt. AN64-7.
2. Wallace, H. D., A. Z. Palmer, J. W. Carpenter, Ghazi Taki and G. E. Combs.
1964. The influence of protein level on feedlot performance and carcass
characteristics of barrows and gilts. Fla. An. Sci. Mimeo. Rpt. AN64-16.