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Arkansas Animal Science Department Report 2001
lysine) from d 7 to 21 after weaning and a Phase 3 diet
(1.20% lysine) from d 21 to 35 after weaning (Table 1). Zinc
was maintained at 165 ppm in diets fed during Phase 3,
resulting in two dietary treatments (0 and 0.3% Bio-Mos ® )
during this phase of the experiment. Pig BW and feed intake
were determined at the initiation of the study, and weekly
thereafter to evaluate ADG, ADFI, and F/G.
Pigs were housed in an off-site nursery facility in pens
with two nipple waterers and a five-hole feeder. Pigs had ad
libitum access to feed and water. For the first week of the
trial, the nursery was maintained at 85°F and decreased 1°F
each week.
In vitro cellular immune response was measured using
a lymphocyte blastogenesis assay (Blecha et al., 1983). A
total of 72 pigs (18 pigs per treatment) were sampled across
four days of the experiment (d 21, 22, 26, and 27).
Phytohemagglutinin (PHA) and pokeweed mitogen (PWM)
were used as mitogens at a concentration of 50 and 25 mg/ml,
respectively to stimulate lymphocyte proliferation in vitro.
Uptake of [3]H-thymidine served as the measurement of cell
proliferation.
Data were analyzed as a randomized complete block
design with pen as the experimental unit and blocks based on
initial BW. Analysis of variance was performed using the
GLM procedure of SAS (SAS Inst. Inc., Cary, NC). The
effects of block, zinc, Bio-Mos ® , and the Bio-Mos ® x zinc
interaction were evaluated. When a significant interaction
was observed, least square means were generated and separated
using the PDIFF option. Main effect means were evaluated
when the interaction was not significant.
Results and Discussion
Main effect means in response to dietary supplementation
with Bio-Mos ® and zinc oxide are presented in Table 2.
There was no effect on ADG, ADFI, or F/G in response to
either Bio-Mos ® or zinc supplementation during the Phase 1
period.
During the first week of Phase 2 (d 7 to 14) and in the
overall Phase 2 period (d 7 to 21), ADG was greater (P <
0.05) when pigs were fed diets containing 2,465 ppm zinc
when compared to pigs fed diets containing 165 and 500 ppm
zinc, and ADFI was greater (P < 0.05) when pigs were fed
2,465 ppm zinc when compared to pigs fed 165 ppm zinc.
Also, F/G was improved (P < 0.05) when pigs were fed diets
containing 2,465 ppm zinc compared to pigs fed diets containing
500 ppm zinc. During the second week of Phase 2 (d
14 to 21) and in the overall Phase 2 period (d 7 to 21), F/G
improved when pigs were supplemented with Bio-Mos ®
when compared to those fed diets devoid of Bio-Mos ® .
During the first week of Phase 3 (d 21 to 28), pigs fed
Bio-Mos ® had greater (P = 0.02) ADG and improved (P =
0.009) F/G when compared to pigs fed diets without Bio-
Mos ® . Pigs previously fed diets containing 500 ppm zinc during
Phase 1 and 2 had greater (P < 0.05) ADG during the first
week of Phase 3 (d 21 to 28) than pigs previously fed 2,465
ppm zinc. During the second week of Phase 3 (d 28 to 35),
pigs fed 165 ppm zinc had greater (P < 0.05) ADG and
improved (P < 0.05) F/G when compared to pigs previously
fed 500 ppm zinc during Phase 1 and Phase 2. In the overall
experiment (d 0 to 35), pigs fed diets containing Bio-Mos ®
had improved (P = 0.03) F/G when compared to pigs fed diets
devoid of Bio-Mos ® .
Several studies evaluating the effects of zinc supplementation
have determined that pigs do not usually respond
to pharmacological levels of dietary zinc during the first
week of supplementation. However, as observed in this
experiment, supplementing zinc for 2 weeks following weaning
elicits an improvement in ADG, ADFI, and F/G during
the second week after weaning (Carlson et al., 1999;
Woodworth et al., 1999a, 1999b). There was no benefit to
supplementing 500 ppm zinc in the diet over providing zinc
to meet the pigs’ dietary requirement, as corroborated by
Kornegay et al. (1993) and Hill et al (2001), with or without
Bio-Mos ® supplementation. As observed in a previous experiment
(Davis et al., 2000), response to Bio-Mos ® was most
pronounced during Phase 2 and Phase 3 of the experiment.
When pharmacological levels of zinc were removed from the
diet during Phase 3, pig performance decreased when compared
to pigs fed the control diet. Contrary to the observations
in this experiment, Carlson and coworkers (1999) observed
either a similar response or an improvement in response when
pigs were previously fed pharmacological levels of zinc compared
to pigs fed a diet containing only enough zinc to meet
the pigs’ requirement.
Proliferation of lymphocytes in unstimulated cultures
was less (P = 0.03) when cells were isolated from pigs fed
Bio-Mos ® than when cells were isolated from pigs fed diets
without Bio-Mos ® (Table 2). A Bio-Mos ® x zinc oxide interaction
(P < 0.05) was observed for lymphocyte proliferation
in response to both PHA and PWM (Figures 1 and 2, respectively).
Lymphocyte proliferation in response to PHA and
PWM was greater (P < 0.05) when cells were isolated from
pigs fed 165 ppm zinc without Bio-Mos ® in the diet than
when cells were isolated from pigs fed the same level of zinc
with Bio-Mos ® supplementation. However, proliferation
responses did not differ regardless of Bio-Mos ® supplementation
when diets contained 500 and 2,465 ppm zinc. Bio-
Mos ® supplementation seems to suppress lymphocyte proliferation
response in unstimulated as well as stimulated cell
cultures. Since mounting an immune response is a metabolically
expensive process resulting in adverse effects on feed
intake and growth, the improvement in growth and efficiency
observed when pigs were fed Bio-Mos ® could be a result of
a suppression in immune responses that would otherwise be
amplified needlessly. In a study conducted by Dritz et al.
(1995), feeding dietary β-glucan (a feed additive similar to
Bio-Mos ® ) improved the gain and feed intake of weanling
pigs. However, mortality was greater when pigs were fed
diets containing β-glucan and administered a disease challenge,
indicating that the improved growth response may be
due to a suppression of the immune response. Similarly, the
mechanism by which Bio-Mos ® improves growth and efficiency
in weanling pigs may be a result of its suppressive
effect on the pigs’ cell mediated immune response.
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