Aside from the divider fence/wire issue Fenceman brings up, I would be concerned about the waste on 15" rows.

What I notice is that when ever I open up a new patch of fresh standing corn, the cattle almost immediately dive in, not just eat the outside rows.

Cattle being cattle, they walk along pulling an ear off here, walking down the row a bit then taking another... until the ears are all gone then they go back for the rest of the plant.

Dr Temple Grandin uses a magic number of exactly 30" for the inside width of cattle handling facilities like chutes, ramps etc. I built my loading ramp at exactly 30" clear inside and it works. I would not want any more or less for most commercial cattle.

I have actually been thinking the old 36" row width would be even better between standing corn rows for grazing.

On 15" I am concerned that they would just knock over a lot of rows getting inside the patch rather than working from the outside in. There might be a lot more waste than on 30" or wider. Again cattle will not readily eat anything that's been trampled.

 I don't have any hard data, just a feeling from watching them. Here's one of the photos from last fall with them entering between the rows. Personally I would take the Black Machine and open it up to 30".

Jim at Dawn

on edit: by the way this is about the way you want the corn to look when grazing. If it is much greener or higher moisture than this you may have problems. 

You can sure see my guess row on this sideslopein the second photo. Definitely not rtk guidance here! But you can imagine the cows do not fit down that guess row without damaging a lot of corn.

These two photos were also a few days before weaning the calves off of these cows - they had started coming back since they's been on corn about 3 weeks when the photo taken but not really up to their winter condition yet.

(Grazing Strip Tilled Standing High Moisture Corn_Cattle Entering New Front_10-27-08_IMG_3107_1.jpg)

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Grazing Strip Tilled Standing High Moisture Corn_Cattle Entering New Front_10-27-08_IMG_3107_1.jpg (78KB - 178 downloads)

Grazing Strip Tilled Standing High Moisture Corn_Cattle Entering New Front_10-27-08_IMG_3110_2.JPG (109KB - 180 downloads)