My experience with cattle says if the cattle want in, they will get in. The hotwire will deter them better than the barbed wire. My question to you woud be: assuming you are at some point going to remove the fencing and the cattle in the said field, will you be allowing enough time for the deer to get used to coming to the food plot? The said fencing will also deter the deer from getting in, (barbed or hot wire). If they learn to stay away from the plot, will they learn to come back to it in time for it to do you any good? Is there any timber on the property, that the cattle cannot get to that you could clear an area for your foodplot and not have to fence it off from the cattle? Hence, allowing the deer to come freely to the plot uninhibited by any fence.