Harvesting forages and frost

As was predicted, temperatures dropped below freezing and much of Richland County (and probably much of Eastern Montana) did receive frost last night (9-11).  While it definitely did frost, it probably should not be labeled as a killing frost as I don't believe it got cold and stayed cold for an extended period of time.

NITRATES
With that being said however, it definitely did frost and any time that happens and there is still forages to be cut, there is always some justified concern in regards to the threat of elevated levels of nitrates in forages that are cut after a frost.  So I did some searching and found an excellent paper on the very subject, that can be found by following this link (http://www.agriculture.gov.sk.ca/Default.aspx?DN=1bd24bc2-167e-4b02-9f21-2b7f9217312e).

The take home message from this document is that, forage quality should be a bigger concern right now than nitrate levels.  Once the forage is hayed, test can be done on it to determine the nitrate levels and if the levels are high, then steps can be taken (such as blending) to mitigate the nitrate issue.  However, if quality starts to deteriorate, there is nothing that can be done to re-gain the loss.

 WHAT ABOUT PRUSSIC ACID POISONING?
Another concern with forages and an early frost is prussic acid poisoning.  For those with pastures containing sorghums and/or sorghum-sudangrass species, prussic acid poisoning of livestock is a legitimate concern.  When animals feed on these grass species after a frost, or if they are very young or stunted, the prussic acid concentration can potentially kill them.

For more information about prussic acid and considerations to take before feeding these grasses, visit this site (http://www.agry.purdue.edu/ext/forages/publications/ay196.htm) 

The take home message here is that it is generally safe to allow animals to pasture these grasses 5 to 6 days after a killing frost.  If the frost was sever enough (which I don't believe last night's was) that it actually killed plants and new shoots are emerging from the rootstock, these shoots should not be grazed until the new growth is at least 2 ft. high.  In regards to hay, according to the site listed above from Purdue University, "the prussic acid content of sorghum hay decreases as much as 75 percent while curing and is rarely hazardous when fed to livestock."