Something I forgot last night - you really need 2 people besides the photographer in the picture pen. One person on either end to push the cattle up, and to stop them and get their heads and ears up. And yes, you really do need a picture pen, too. Something level,with good fences, clean, with neat uniformly short grass (green grass if possible) and preferably free of distractions like highways, railroad tracks, etc... And it needs to be big enough everyone isn't on top of the cattle, and small enough you don't get worn out trying to keep them in position. It's pretty much an accident to get a promotional quality picture out in the pasture by yourself - not to say it can't happen, but don't count on it. If it does, like Nesi said, it'll be 1 of 100 or more.
When we did online sales (I used to help with a bunch, but it's been a couple of years now), we figured on 5-6 people. A photographer, plus 2 more in the picture pen, and 2 or 3 to clean them up and do a little touch up clipping. Not saying all that is necessary for picturing a couple for an ad or a flyer, but it's just that a lot of people don't realize what all goes into most of the pictures they see.