Calculating Grazing Time on Cornstalks
Now that the corn is finally drying down, most producerers are getting cattle out to stalks.Here is a method of calculating the number of grazing days on a field of cornstalks. According to Dr. Rick Rasby at UNL, crop residue is related to grain yield. With high producing hybrids, there should be about 16 pounds of dry leaf and husk per bushel corn yield per acre.
Therefore, if a field produces 160 bushel/acre, then there should be about 2560 pounds of dry leaf and husk residue per acre. Now some of that residue disappears due to trampling and other factors so figure about 50% utilization, which leaves us with about 1280 pounds of grazable residue per acre.
Now we can convert our pounds of grazable residue to AUMs. An AUM (Animal Unit Month) is the amount of forage that is required to maintain a 1000-pound cow or equivalent for one month. It has been determined, that a 1000-pound cow will consume about 680 pounds of dry matter monthly. Therefore, this particular field will provide 1.88 AUMs/acre. If this field is 125 acres, then there is a total of 235 AUMs available for grazing in this field.
Now let’s assume we are planning on grazing 100 head of gestating cows on this field, we need to calculate the number of days that they can graze this field. Let’s assume the average weight of these cows is 1360. That means that each one of these cows requires 1.36 AUMs per month. Therefore, a total of 136 AUMs is required to feed this herd for a month. This field has 235 AUMs available for grazing so it should last about 1.72 months or 52 days.
Keep in mind that this calculation is just a starting point and is in no way a substitute for actual observation of residue disappearance. This calculation also does not figure in loss in stalk quality due to deteriorating weather conditions or just simply the natural deterioration that occurs over time.
There is also an Excel spreadsheet available for download online at http://agmanagerstools.com. Not only does this spreadsheet calculate the available grazing days using the same equation, but it also takes into account, the cost of the stalks, the cost of transporting the cattle to stalks, and the costs involved with checking the cattle and water. Kevin L. Cawthra, Animal Scientist, Twin Forks Clinic INC
Therefore, if a field produces 160 bushel/acre, then there should be about 2560 pounds of dry leaf and husk residue per acre. Now some of that residue disappears due to trampling and other factors so figure about 50% utilization, which leaves us with about 1280 pounds of grazable residue per acre.
Now we can convert our pounds of grazable residue to AUMs. An AUM (Animal Unit Month) is the amount of forage that is required to maintain a 1000-pound cow or equivalent for one month. It has been determined, that a 1000-pound cow will consume about 680 pounds of dry matter monthly. Therefore, this particular field will provide 1.88 AUMs/acre. If this field is 125 acres, then there is a total of 235 AUMs available for grazing in this field.
Now let’s assume we are planning on grazing 100 head of gestating cows on this field, we need to calculate the number of days that they can graze this field. Let’s assume the average weight of these cows is 1360. That means that each one of these cows requires 1.36 AUMs per month. Therefore, a total of 136 AUMs is required to feed this herd for a month. This field has 235 AUMs available for grazing so it should last about 1.72 months or 52 days.
Keep in mind that this calculation is just a starting point and is in no way a substitute for actual observation of residue disappearance. This calculation also does not figure in loss in stalk quality due to deteriorating weather conditions or just simply the natural deterioration that occurs over time.
There is also an Excel spreadsheet available for download online at http://agmanagerstools.com. Not only does this spreadsheet calculate the available grazing days using the same equation, but it also takes into account, the cost of the stalks, the cost of transporting the cattle to stalks, and the costs involved with checking the cattle and water. Kevin L. Cawthra, Animal Scientist, Twin Forks Clinic INC
posted by Kevin @ 11:17 AM
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