Mimeograph Report AN64-7
THE INFLUENCE OF PROTEIN LEVEL ON FEEDLOT
PERFORMANCE AND CARCASS CHARACTERISTICS OF BARROWS AND GILTS
H. D. Wallace, M. E. Palmer,
A. Z. Palmer, J. W. Carpenter and G. E. Combs I/
Protein level has long been an important subject for investigation
in swine research. Since protein represents a very critical nutrient
and also a very costly ingredient of the feed mixture it is necessary
to know how to use it wisely. Most feeding experiments involving pro-
tein levels have been concerned largely with effects on daily gain and
feed conversion. Based on these two important criteria the fortified
corn-soybean meal ration, widely used at present, has permitted.a signif-
icant reduction in protein level recommendations. However, very little
emphasis has been placed on carcass value as influenced by dietary protein.
A few recent reports have provided limited data in this regard. Invari-
ably pigs fed the lower levels of protein have produced inferior carcasses
when measured in terms of lean pork produced. Differences have not been
great and research workers have not stressed the differences. If the hog
market in this country would encourage greater carcass va!Ns differentia-
tion in pork production, these differences could have great meaning.
The present experiment was undertaken to study protein level in grow-
ing-finishing rations primarily as it influences carcass quality and
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 borrows and two lots
con it.d of gi Its. The expe;-iient was conducted on co:-cr-tc c;:d was
initia-oed January 9, 1963. Thie feed mixtures used are ,.senir.jd in Table
I. Ore lot of barrows and onr; lot of gilts were startI-' on 2
level of 17 percent crude protein. Similarly one lot of barrc:;s and
one lot of gilts were started on 13 percent crude protoin~. t.::n the
average weight of the pigs in each lot reached approximately 100 pounds,
the level of protein was reduced as indicated in Table 2.
I/ Wallace, Animal Nutritionist; M. E. Palmer, Laboratory Assistant;
A. Z. Palmer, Associate Meat Scientist; Carpenter, Assistant Meat
Scientist; 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 Richard Newman
and Mrs. Barbara Sullivan, Laboratory Assistants is gratefully
Table I._ COMPOSITION OF RATIONS
Crude Protein Levels (g)_ 17 15 13 11
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 1/ 0.05 0.05 0.05 0.05
Vitamin premix 2/ 0.10 0.10 0.10 0.10
Vitamin BI2 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), 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/ Phizer's B12 supplement, contains 20+ mg./lb.
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.
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 verte-
bral 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).
Results 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 protein (17-15%) gained 1.77 pounds per head per day compared to 1.54
pounds for pigs in lots 3 and 4 fed the lower protein level (13-11). This
difference was highly significant (P<.01).
Table 7. THE INFLUENCE OF PROTEIN LEVEL ON
FEEDLOT PERFORMANCE AND CARCASS CHARACTERISTICS OF BARROWS AND GILTS
Protein Level I
Protein Sex Interaction
Number of pigs
Initial wt. Ib.
Slaughter wt. lb.
Daily gain, lb.
Feed/Ib. gain, lb.
Percent liver I/
Carcass length, in.
Backfat thickness, in.
Carcass firmness 2/
Firmness of lean 2/
Percent 4 lean cuts 3/
Loin eye area, sq. in.
Loin eye marbling score 4/
Color of lean 5/
I/ Based on slaughter wt.
2/ Hard I, medium hard 2, medium soft 3, soft 4, oily 5
3/ Based on chilled carcass wt.
4/ Marbling scores coded from 0-21, 0 = devoid, 21 = extremely abundant
5/ Color of lean coded from 1-5, I = very dark, 2 = dark, 3 = greyish pink (ideal color) 4 =
slightly light, 5 = very light (chicken meated)
-I- -- --
- .. ----
There was not a significant interaction between sex and protein level.
Although gilts gained much slower than barrows the two sexes responded
similarly to level of protein.
Pigs fed the higher level of protein required an average of 3.08
pounds of feed per pound gain while those fed the lower level of protein
required 3.34 pounds of feed. These data were not analyzed statistically,
but the magnitude of the difference suggests a significant advantage in
feed conversion for the pigs fed on the higher level of protein.
Dressing percent was significantly higher for the lower protein pigs
(P<.05) and the interaction of protein and sex was significant (P/.O0).
Gilts fed the higher level of protein dressed higher'while gilts fed the
lower level of protein dressed lower.
Liver percentage was significantly higher (P4.01) for pigs fed the
higher protein ration and again the interaction of sex and protein was
Carcass length.was not affected significantly by protein level.
Backfat thickness was significantly higher (P<.01) for pigs fed the
lower protein level. The magnitude of this difference was approximately
0.1 of an inch.
Carcasses from pigs fed the low protein level were significantly
firmer (P<.05), probably reflecting the greater degree of fat deposition.
No significant differences in firmness of lean were ascertained. Pigs
fed the higher protein rations yielded considerably greater lean cut-out
(52.78 vs. 50.46). This difference was highly significant (P<.01).
The higher protein level also produced significantly larger loin eye
area measurements (3.75 vs.'3.44).
One of the most interesting observations concerned the degree of
marbling or fat deposition in the loin eye muscle. Chemical determi-
nations have not been made as yet but gross observations recorded indicate
that the lower level of protein induced extensive marbling compared to the
higher level of protein. In some cases the fat infiltration appeared to
be objectionably extensive.
The color of lean was not measurably influenced by level of protein.
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 (Animal Science
Mimeo Series Nos. 60-13, 63-16 and AN64-5).
In the present study barrows gained much faster than gilts and made
more efficient gains. The magnitude of the difference in gains was rather
Also, in previous tests gilts have often gained more efficiently than
Gilts yielded longer carcasses (P<.01) which carried less backfat
(P<.05). Gilt carcasses were leaner as measured by the percent of four
lean cuts (P<.OI) and loin eye area measurements were greater (Pc.05).
Less marbling was evident in the loins of gilt carcasses.
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 extensive marbling and in
several cases the fat infiltration seemed excessive.
Barrows gained faster-and more efficiently than gilts, but carcasses
from gilts yieded a much higher percentage of lean cut out. There
appeared to be no important interaction effects between protein level and