Magnesium is an essential
nutrient for all animals. Mild deficiencies can result in reduced
feed intake, poor diet digestion, and bone abnormalities. More
severe deficiencies can cause a serious metabolic disorder
known as “Grass Tetany.” Providing a palatable magnesium
supplement with high biological availability is an effective
strategy for meeting magnesium requirements of grazing cattle.
MAGNESIUM TRIAL
An experiment was recently conducted at Kansas State
University to evaluate magnesium oxide as a supplemental
source of magnesium when fed in a dry supplement
or when added to SmartLic® NE-Mag 12 blocks.
Six steers averaging 675 lbs. were placed into metabolism crates equipped
with urine collection funnels. A total of three treatments were used:
CONTROL (no supplemental magnesium); MAGOX (magnesium oxide combined
with ground corn and molasses); NE-Mag 12 (Smartlic NE-Mag 12 block).
Two steers were allocated to each of the three treatment groups. The
study was repeated three times, exposing each animal to each of the
three dietary treatments.
The identical source of magnesium oxide was used to make NE-Mag 12
blocks and the MAGOX supplement. NE-Mag 12 blocks contained 12% crude
protein and 2% magnesium. The MAGOX supplement was a mixture of 15%
molasses, 26% magnesium oxide, and 59% ground corn, and contained 14.4%
magnesium. SmartLic NE-Mag 12 blocks were offered to cattle continuously.
The MAGOX supplement was fed in sufficient amounts to provide the identical
level of magnesium provided by the NE-Mag 12 blocks. All steers were
fed free-choice brome hay (10.0% crude protein; 0.14% magnesium) for
a 7-day adaptation period. Records of daily forage consumption, fecal
output and urine output were maintained throughout a 4-day collection
period. Total urine output was measured at 6-hour intervals, and a
sample of urine was retained from each interval for determination of
magnesium concentration. Total feed intake and fecal output were determined
at 24-hour intervals for the 4-day collection phase. Finally, a sample
of blood was taken from each animal daily for determination of blood
plasma magnesium concentrations.
RESULTS
Steers fed the SmartLic NE-Mag 12 blocks consumed an average of 1.03
pounds of block per head daily. Hay consumption was not impacted by
feeding either type of magnesium supplement, but dry matter digestibility
was slightly higher with MAGOX compared to the CONTROL, and about 6%
greater for steers fed the NE-Mag 12 block compared to CONTROL. (See
figure 1.)
Total magnesium intake was tripled by feeding either type of supplement
(19 grams/day for controls compared to 59 grams/day for supplemented
groups). Availability of the magnesium from either supplement was above
50%. Urinary excretion of magnesium was substantially greater for cattle
fed the MAGOX treatment than for the NE-Mag 12 block or the CONTROL
treatment. Additionally, urinary excretion of magnesium was more erratic
for cattle fed the MAGOX supplement compared to cattle consuming identical
levels in the form of a block.
Blood plasma concentrations of magnesium were significantly higher
for cattle fed the NE-Mag 12 block in comparison to CONTROL, and were
intermediate when cattle were fed the MAGOX treatment. (See figure
2.)
Higher plasma concentrations of magnesium combined with lower urinary
output and comparable fecal outputs of magnesium suggest that magnesium
oxide is utilized more effectively when incorporated into SmartLic
NE-Mag 12 blocks in comparison to feeding in a dry meal supplement.
(See figure 3.) This is attributed to the fact that cattle consume
blocks throughout the day, delivering small but uniform increments
of essential nutrients. Alternatively, meal supplements tend to be
consumed in a relatively short period of time, thereby causing nutrients
to be excreted through the urine when they are present in excess.
