Why is Magnesium Sulfate Heptahydrate (7H2O) 99.5% DM in the CNCPS library? Calculated on a molecular weight basis it’s about 51% water. MgSO4 anhydrous is also 99.5% DM.
The answer probably is that using our standard methods of measuring DM (moisture) by oven drying ‘bound’ water would not be liberated, as least not completely. But it’s probably not 99.5% dry either.
Jim, you’ve sparked me to do the deep dive on Mag Sulfate. Take a look at Mag Sulfate 7H2O in the RUM&N feed library. Totally different than the CNCPS values. 49.2%DM but with the same Mg and S specs on a DMB. That makes them vastly different on an ASIS basis. Next I looked at the US-Canadian Tables of Feed Composition. Two listings…one at 99%DM and the other at 98% !
I don’t get it but is sure seems that we should all be working from the same specifications.
Eastern Minerals has a published spec sheet for their Mag Sulfate and they show (for the same product, not two different products):
MgSO4 (as MgSO4 7H20), minimum % …………………………………………………………..………………….…….……99.00
MgSO4, minimum % ……………………………………… ………………………………………………….……………….……..…..48.00
Still confused. Hopefully someone that aced chemistry can sort this out.
Do we want to invite a “Guest” to look at this? I can reach out to MIke VA and set him up a Guest account if this is OK with everyone.
On a weight basis – here is the breakdown:
Mg = 9.86%
S = 13.01%
(H2O = 51.17%)
NRC 2001 Table 15-4 list MgSO4 fg (feed grade) as 98% DM 9.8% Mg and 13.31% S.
CNCPS (from AMTS) 99.5% DM 9.85% Mg and 13.0% S
So % Mg and S are correct in model library, because it is listed at 99.5% DM ash is listed at 100%. So other than the ash being overestimated (presumable the water would be driven off by ashing) in a mix with MgSO4, the amount of Mg and S provided would be correct.
I’m also curious which is correct. I use Mag Sulfate in all my close up mixes and never noticed this before. Thanks Jim!!!
So AMTS/CNCPS use 9.80% AF for Mg and 12.94% AF for S but NDS uses 4.84% AF for Mg and 6.39% AF for S?
In NDS library MgSO4 7 H20 is 95% DM, 9.84% Mg, 12.98% S, and 22.84% ash (DM basis). So using any of the libraries (CNCPS, NDS, or NRC) you will supply about the the same level of Mg, S, and DCAD per X amount fed. Ash will vary if however.
MgSO4 anhydrous and monohydrate sources are also on the market and may be lower cost per unit of mineral than heptahydrate. And obviously are more concentrated so lower feeding levels can be used. (if you do chose one of these to formulate with, make sure the mill knows this and has it available). A question is: is the Mg (and S) as bioavailable in these sources as it is in heptahydrate?
Another MgSO4 factoid: Tebbe et al. (Effects of magnesium source and monensin on nutrient digestibility and mineral balance in lactating dairy cows A.W. Tebbe, D.J. Wyatt, W.P. Weiss. J. Dairy Sci. 2018. 101:1152) did a study comparing MgO and MgSO4 with and without monensin and found some interesting interactions (a few summarized here):
“Feeding MgSO4 with monensin decreased NDF digestibility compared with other treatments (46.7 vs. 50.2%). That diet also had decreased apparent absorption of Mg compared with diets without monensin (15.6 vs. 19.2%), whereas MgO with monensin had greater apparent absorption of Mg (23.0%) than other treatments. “
Jim, I couldn’t figure out how to post an image directly in a reply but uploaded a screenshot of the specs from the NDS RUM&N feed bank.