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Arkansas Animal Science Department Report 2001
Statistical analysis. Total collection data were analyzed
by least squares analysis of variance as a randomized design
with three treatments. The effect of ionophore was examined.
All data were analyzed using the Fit Least Squares procedures
of JMP (SAS Inst. Inc., Cary, NC). Orthogonal contrasts
were used to compare control versus monensin and
control versus lasalocid. Each lamb represented an experimental
unit resulting in six replications per dietary treatment.
An additional orthogonal contrast was used to compare
changes in tissue mineral concentration between the lambs
that were initially harvested versus lambs that continued on
the study and were fed the high P hay.
Results and Discussion
Phosphorus. There was no difference (P > 0.10) in P
metabolism (Table 3) between the monensin-fed lambs and
the control lambs. Lasalocid supplementation tended to
increase (P < 0.10) the fecal excretion of P when compared to
control lambs (2.58 vs. 2.34 g/d). Monensin or lasalocid did
not alter (P > 0.10) the apparent absorption or retention of P
in this experiment. Kirk et al. (1994) also found no differences
in the apparent absorption and retention of P in wether
lambs fed monensin or lasalocid. Starnes et al. (1984) and
Kirk et al. (1985b), however, found that monensin and lasalocid
did increase the apparent absorption and retention of P.
While those studies involved ruminants fed high-concentrate
diets, Spears et al. (1989) found that monensin and lysocellin
increased the apparent absorption of P in steers fed greenchop
fescue diets.
There were no differences (P > 0.10) in heart or rumen
P concentrations (Table 4). Initially harvested lambs had
lower liver (P < 0.01), kidney (P < 0.05), and muscle (P <
0.10) P concentrations than the average of lambs that were
fed the three dietary treatments. Monensin supplementation
increased (P < 0.05) spleen and muscle concentrations of P
and decreased (P < 0.05) bone concentrations of P when compared
to control lambs. Kirk et al. (1985b) examined heart,
muscle, duodenum, ileum, liver, kidney, brain, and bone
samples and found no differences in tissue P concentrations
of lambs supplemented with and without monensin.
Calcium. There were no effects (P > 0.10) of ionophore
supplementation on the apparent absorption or retention of
Ca (Table 3). There was a tendency (P < 0.10) for lambs supplemented
with lasalocid to have a higher intake of Ca when
compared to the control treatment. This was due to an
increased intake of hay by the lasalocid-supplemented lambs.
There were no differences (P > 0.10) in concentrations of Ca
in heart, liver, kidney, spleen, and muscle (Table 4). Initially
harvested lambs had higher (P < 0.05) concentrations of
rumen Ca compared to lambs harvested following dietary
treatment. Lasalocid-supplemented lambs had a tendency to
have lower (P < 0.10) rumen concentrations of Ca than the
control lambs, but there were no differences (P > 0.10) due to
monensin. Lambs fed monensin had lower (P < 0.05) concentrations
of Ca in the bone when compared to control
lambs.
Magnesium. Lambs supplemented with monensin tended
(P < 0.10) to have a lower fecal excretion of Mg when
compared to the control animals (Table 3). Yet, monensinsupplemented
lambs also had a greater (P < 0.01) urinary
excretion of Mg than the controls. Lambs fed monensin had
greater apparent absorption of Mg when expressed as grams
per day (P < 0.10) and expressed as a percentage of intake (P
< 0.05) when compared to lambs fed no ionophore. There
were no differences (P > 0.10) observed in the retention of
Mg expressed as grams per day and as a percentage of intake.
Control lambs, however, had a greater (P < 0.01) retention of
Mg when expressed as a percentage of absorbed Mg compared
to monensin-supplemented lambs.
Greene et al. (1986) and Kirk et al. (1994) also
observed a decrease in fecal Mg excretion when monensin
was fed to sheep. Greene et al. (1986) also reported that monensin
supplementation increased both the apparent absorption
and retention of Mg in concentrate-fed lambs.
There were no differences (P > 0.10) in rumen Mg concentrations
due to treatment observed in this study (Table 4).
Initially harvested lambs had lower liver (P < 0.05) and kidney
(P < 0.10) concentrations of Mg than the average of
lambs fed the three supplements. When compared to control
lambs, monensin increased concentrations of Mg in the heart
(P < 0.05), spleen (P < 0.05), and muscle (P < 0.01), but tended
to lower concentrations of Mg in bone (P < 0.10).
Implications
Although there were no effects of ionophore supplementation
on the retention of phosphorus, calcium, or magnesium,
monensin did increase the apparent absorption of
magnesium. There were significant effects of ionophore supplementation
on tissue mineral concentrations suggesting that
ionophores did have a physiological effect on mineral metabolism.
Research should continue to explore the variability of
ionophore effects on mineral metabolism.
Literature Cited
Greene, L. W., et al. 1986. J. Anim. Sci. 63:1960.
Kirk, D. J., et al. 1994. J. Anim. Sci. 72:1029.
Kirk, D. J., et al. 1985a. J. Anim. Sci. 60:1479.
Kirk, D. J., et al. 1985b. J. Anim. Sci. 60:1485.
Spears, J. W., et al. 1989. J. Anim. Sci. 67:2140.
Starnes, S. R., et al. 1984. J. Nutr. 114:518.
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