The premaxilla of the fowl contains both mechano-receptors and pain receptors, and this series of experiments was carried out to determine what effect removing either one-third or one-half of the upper mandible would have on the hen's food intake, feeding behaviour and body weight. Beak trimming in adult hens caused a temporary fall in food intake which was not followed by a compensatory hyperphagia, and body weight was reduced for at least 6 weeks. Removal of half the beak had more effect than removing one-third, and the consequences were greater when the hens were fed pellets rather than mash. Beak trimming reduced feeding efficiency (number of pecks per gram of pellets ingested) to only 20% of its preoperative value. Frame-by-frame analysis of cine film showed that the bird was either failing to grasp the pellet in its beak, or not transferring it to the pharynx where it could be swallowed. It could not adapt its stereotyped behaviour pattern to compensate for the altered beak shape. Pecking rate rose sharply after beak trimming, then declined to the pre-operative value after 3 weeks, indicating no decline in feeding motivation. © 1982.
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