In this post Captain Craig speaks of "thinning the field":
In this one he speaks of "thinning the ranks":
Ranks, field, herd.. really he's just talking about a group. In this thread the group is women. He's sorting through people that are attractive and picking the ones he thinks are most attractive. The actual purpose of this thread. He is quite on topic. It has nothing to do with cows.
I've read some crass things in these threads but thinning the herd isn't one of them.