1.  Field of the Invention
The present invention relates generally to livestock feeding devices and, more particularly, to a pig feeder having a hopper for storing feed and a trough in communication with the hopper for permitting pigs to reach the feed. 
2.  Description of the Prior Art
The science of raising pigs has become highly developed since the days when pigs roamed free in mud filled yards eating slop fed to them in open troughs.  Today, it is common to see pigs raised in very clean confinement units having separate pens for pigs of similar sizes.  These separate pens are employed to segregate pigs by size so that different feed formulas may be fed to different sized pigs thus enabling the farmer to bring the pigs to market size much more quickly than has been possible in the past. 
A concern in the design of feeders used with modern day confinement units is to conserve feed by attempting to prevent feeding pigs from rooting or raking feed from the troughs and onto the ground surrounding the feeder.  This concern is especially important where the floors of a unit are grated or otherwise incapable of containing feed that falls from the feeder such that feed falling from the feeder is wasted by passing beneath the floor out of reach of the feeding pigs. 
In order to conserve as much feed as possible, and in light of the fact that pigs in confinement units are frequently segregated by size, feeders provided in each of the units of a conventional hog confinement structure are commonly customized for the size of pig to be confined therein.  For example, a known feeder construction has a hopper communicating with a trough through an adjustable slot in the hopper, and the trough is provided with a top cover having circular openings through which pigs may feed.  When a feeder of this construction is employed in a unit in which pigs of less than sixty pounds are to be confined, the feeder may be provided with a cover having openings which are smaller in diameter than a similarly constructed feeder in a unit for use with pigs nearing market size. 
In addition to allowing feeding by pigs of a predetermined size, the circular holes are intended to serve the purpose of preventing feed from being rooted up out of the trough during feeding.  The premise on which the circular hole design is based, is that by surrounding the head of the pig as it enters the trough, none of the feed therein will escape through the hole during feeding and the pig will not be able to push the feed to the end of the feeder and up out of the trough.  However, several problems have been encountered in troughs of this known construction.  For example, if the pigs in a given confinement unit are not moved at the proper time to a unit adapted to enclose larger pigs, they will outgrow the feeder in the unit and will develop sores around their ears by attempting to get to the feed through the now undersized holes in the trough.  Thus, the holes restrict the feeder to use only with pigs of a narrow size range. 
Further, even when the feeder openings are of the proper size, pigs feeding from the trough are able to work feed therefrom by raking the feed up along the underside of their chins and out the lower part of the opening.  It would be desirable to provide a feeder which overcomes these problems encountered with feeders provided with circular holes and which prevents feed from being rooted from the feeder trough by feeding pigs.