The valve is selectively opened to allow a measured amount of feed material, for example water, to fill {TAIL ~ the trough}, from which {HEAD ~ the animal} is then free to drink 
The valve is selectively opened to allow a measured amount of feed material , for example water , to fill { TAIL ~ the trough } , from which { HEAD ~ the animal } is then free to drink
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH REL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH