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