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Arkansas Animal Science Department Report 2001
(Table 3). Moreover, carcasses of Nn pigs had considerably
less (P < 0.01) fat at the tenth rib (0.87 vs. 1.28 in.), and
greater (P < 0.01) LM depth (2.35 vs. 2.00 in.) than carcasses
from NN pigs.
Eikelenboom et al. (1980) reported that carcasses from
Nn pigs had less average backfat than carcasses from NN
pigs. Other studies, however, have shown that carcasses from
NN and Nn pigs had similar midline backfat measurements
and tenth rib fat depths (Leach et al., 1996; Sather and Jones,
1996). Moreover, Simpson and Webb (1989) and Jones et al.
(1988) found that carcasses from Nn pigs were actually fatter
than carcasses from NN pigs.
As for carcass muscling, results from the present study
are comparable to those of Sather and Jones (1996) and Jones
et al. (1988), who reported that carcasses from Nn pigs had
greater LM depth and a higher percentage muscle than carcasses
from NN pigs. In contrast, Leach et al. (1996) failed
to denote differences in LM area or depth and carcass muscle
percentage among carcasses from NN and Nn pigs.
Supplementation of swine diets with MM had no effect
(P > 0.10) on midline backfat measurements, tenth rib fat
depth, LM depth, or percentage muscle (Table 3). These
results are consistent with those of Schaefer et al. (1993) and
D’Souza et al. (1998; 1999), who failed to note an effect of
supplemental Mg on any fat or muscle measurement of pork
carcasses; however, these authors fed Mg aspartate for a brief
5-day period before harvest. In the first experiment, Apple et
al. (2000) reported no effect of long-term supplementation of
MM on pork carcass composition, but, in the second experiment,
they reported a 0.07 to 0.17 in. reduction in tenth rib fat
depth, and a 0.89 to 1.44% increase in percentage muscle of
carcasses from pigs fed 2.50 and 1.25% MM, respectively.
Although LM pH was not affected (P > 0.81) by
halothane genotype, drip loss percentages were higher (P <
0.01), and LM moisture content was lower (P < 0.01), in pork
from Nn pigs compared to NN pigs (Table 4). The LM from
Nn pigs received lower (P ≤ 0.02) marbling, firmness, and
color scores than the LM from NN pigs. Moreover, pork
from Nn pigs was lighter (P < 0.01), less (P < 0.01) red, and
less (P < 0.01) yellow compared to that from NN pigs, and a
higher proportion of carcasses from Nn pigs received
American and Japanese color scores indicating PSE pork
(Table 5).
Our results are in agreement with those of Sather and
Jones (1996) and Leach et al. (1996), who found that Nn pigs
produced lighter, less desirable colored pork with greater drip
loss than pork from NN pigs. Moreover, Simpson and Webb
(1989) reported a higher percentage of pork carcasses from
Nn pigs were PSE than carcasses from NN pigs, which is
consistent with results from the present study.
The pH of the LM was not affected (P > 0.10) by inclusion
of MM in the diets of growing finishing pigs (Table 4).
Moreover, dietary MM had no effect (P > 0.10) on drip loss
percentages or moisture contents of the LM. Results of the
present study confirm previously published information from
our laboratory that long-term supplementation of swine diets
with MM did not affect LM pH, drip loss, or moisture content.
However, several authors have reported that feeding
diets fortified with Mg shortly before harvest increased initial
and/or ultimate muscle pH (D’Souza et al., 1999; 1998;
Schaefer et al., 1993) and reduced drip loss percentages
(D’Souza et al., 1999; 1998; Schaefer et al., 1993).
Both subjective color scores and objective color measurements
of the LM were similar (P > 0.10) among carcasses
from pigs fed 0.0, 1.25 and 2.50% MM (Table 4). Moreover,
dietary MM had no effect (P > 0.49) on the percentage of carcasses
with color scores characteristic of PSE pork (Table 5).
Neither O’Quinn et al. (2000) or D’Souza et al. (1999) found
a difference in pork color among pigs fed diets containing
supplemental Mg. On the other hand, D’Souza et al. (1998)
reported lower L* values, and Schaefer et al. (1993) reported
higher a* values, for LM chops from pigs supplemented with
Mg aspartate 5 days before slaughter. Similarly, the percentage
of PSE, or PSE-like, carcasses was greatly reduced by
short-term (D’Souza et al., 1998) or long-term (Apple et al.,
2000) Mg supplementation.
Implications
Results from this study indicated that homozygous negative
pigs had greater growth rates and superior pork quality
traits than their heterozygous contemporaries, yet carcasses
of the homozygotes were lighter muscled and fatter than the
heterozgyous pigs. Even though inclusion of magnesium
mica in the diets of growing-finishing pigs had no effect on
pork color or any other pork quality attribute, the economic
benefits realized from enhanced feed efficiency and lower
diet costs (Apple et al., 2000) makes magnesium mica supplementation
an attractive management decision for today’s
swine industry.
Literature Cited
Apple, J. K., et al. 2000. J. Anim. Sci. 78:2135.
D’Souza, D. N., et al. 1998. J. Anim. Sci. 76:104.
D’Souza, D. N., et al. 1999. Meat Sci. 51:221.
Eikelenboom, G., et al. 1980. Livest. Prod. Sci. 7:317.
Jones, S. D. M., et al. 1988. Can. J. Anim. Sci. 68:139.
Leach, L. M., et al. 1996. J. Anim. Sci. 74:934.
Nakai, H., et al. 1975. Bull. Natl. Inst. Anim. Industry (Chiba)
29:69.
NPPC. 1999. Official Color and Marbling Standards.
National Pork Producers Council, Des Moines, IA.
NPPC. 1991. Procedures to Evaluate Market Hogs (3rd
Edition). National Pork Producers Council, Des
Moines, IA.
NRC. 1998. Nutrient Requirements of Swine (10th Edition).
National Academy Press, Washington, DC.
O’Quinn, P. R., et al. 2000. Can. J. Anim. Sci. 80:443.
Sather, A. P., and S. D. M. Jones. 1996. Can. J. Anim. Sci.
76:507.
Schaefer, A. L., et al. 1993. Can. J. Anim. Sci. 73:231.
Simpson, S. P., and A. J. Webb, A. J. 1989. Anim. Prod.
49:503.
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