You cannot place the pig (or any farmer) on a farm with a barn.
That rule is of course valid even when you place a tile that connects the farm.
The pig needs to be on a farm first, before you connect it to a barn. Then you get the extra point for each city.
I disagree and believe this is incorrect.
According to the CAR (ver 4.1):
(page 42): It is only a farmer that
cannot be placed on a field containing a barn. The rule does
not actually apply to the pig, which is
not a farmer (page 23, footnote 44 (a farmer is a follower)).
(page 22): The pig
can be placed on fields that already have farmers or other pigs in them.
Since there is no prohibition of using the pig in a field containing a barn, and the farmer being joined to the field with the barn allows the use of the pig, I see no official rules problem with this...
However, in re-reading the rules on this point, there has been mistake in my original post, and which changes my thoughts slightly:
I believe Derek is correct, but in this case he would only score 2 points in connecting his farmer to the field with the barn in and then laying his pig.
Remember the order of play in normal circumstances is: lay tile, move 'wood' then score. So in this case laying the tile which joins Dereks farmer to the field containing the barn is legal. At this point (move 'wood') Derek has fulfilled the conditions to play his pig (having his farmer in the field). Now he scores (as farmers cannot remain in a field where there is a barn): for adjoining his farmer into a field containing a barn, he scores 1 point for every complete city contained in the field, but with the pig it is 2 points for every completed city within the field.
Knowlton is incorrect in saying that the pig must be already down to make the claim. The pig is laid down to the tile that adjoins his farmer into the field containing the barn, so in one sense it is already down before point scoring takes place..
So Derek is absolutely right, this is a legitimate move
The person who now has the farmer and his pig in the field actually gets
4 points per completed city (CAR, ver 4.1, page 42), and not 2 as I originally state.
Now this does present a problem. It does seem unfair to be able to do this. Although I believe the rules allow for the placing of a pig into such a field, I find it incredible that that person would be allowed to score 4 points in that situation (particularly if a pig has been laid to the tile that joins the field with a barn), instead of 2. It is indeed legitimate, but is it ethical? I would not have had a problem if it were 2 points.
The status of the pig is something that HiG definately needs to clarify for this situation. How do others see the rules?