The effect of stage of maturity on the biological availability of magnesuim from wheat and orchardgrass fed to sheep
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Wheat, a tetany prone forage, and orchardgrass, a non-tetany prone forage, were cut at three stages of maturity to determine the magnesium availability in these forages for lambs. The forages were dried in forced air ovens and ground through a 2.5 cm screen. The nitrogen contents of the forages were not significantly different between forages but decreased quadratically with maturity in wheat (P < .Ol) and linearly in orchardgrass (P < .Ol). Nonprotein nitrogen was significantly higher in wheat than in orchardgrass. The magnesium content of the wheat was lower (P < .O1) than orchardgrass (.14 vs .21%). Magnesium content in wheat was similar at all maturities but decreased with maturity in orchardgrass. Potassium, calcium and phosphorous levels in the forages were similar between wheat and orchardgrass but decreased with advancing maturity in both forages.
In two metabolism trials with 18 wether lambs, the biological availability of magnesium was determined for the two forages cut at three stages of maturity. The biological availability of magnesium for lambs fed wheat was slightly lower than for those fed orchardgrass. It increased linearly with increasing maturity in wheat (P < .O1) and tended to decrease with maturity in orchardgrass. In the first two maturities of wheat, the biological availability of magnesium was approximately 22% and for the third maturity it approached 39%. In orchardgrass, it was 36, 34 and 28% for maturities l, 2 and 3, respectively.
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