Ralston, S. L. (1984). Controls of feeding in horses. J. Anim Sci., 59(5), 1354–1361.
Abstract: Members of the genus Equus are large, nonruminant herbivores. These animals utilize the products of both enzymatic digestion in the small intestine and bacterial fermentation (volatile fatty acids) in the cecum and large colon as sources of metabolizable energy. Equine animals rely primarily upon oropharyngeal and external stimuli to control the size and duration of an isolated meal. Meal frequency, however, is regulated by stimuli generated by the presence and (or) absorption of nutrients (sugars, fatty acids, protein) in both the large and small intestine plus metabolic cues reflecting body energy stores. The control of feeding in this species reflects its evolutionary development in an environment which selected for consumption of small, frequent meals of a variety of forages.
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Robinson, T. A., Foster, T. M., Temple, W., & Poling, A. (1995). Performance of domestic hens under progressive-ratio schedules of food delivery. Behav. Process., 34(3), 233–239.
Abstract: Domestic hens were exposed to progressive-ratio 2 and progressive-ratio 10 schedules of food delivery with different initial ratios (2, 10, 20, 30, and 40). Breaking points, defined as the largest ratios completed before responding ceased for 600 consecutive seconds, were recorded under all conditions. In general, breaking points were higher under the PR 10 schedule than under the PR 2 schedule, and the value of the initial ratio did not systematically affect the breaking point. The former finding suggests that relative satiation affected breaking points in the present study, but the latter finding suggests that the primary determinant was the `price' of the reinforcer, defined in terms of the number of responses required to produce it. Breaking points were similar under conditions where initial ratios changed from session to session and under more conventional conditions, where initial ratios remained unchanged over several sessions.
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Harlow, H. F. (1950). Learning and satiation of response in intrinsically motivated complex puzzle performance by monkeys. J Comp Physiol Psychol, 43(4), 289–294.
Abstract: Two rhesus monkeys, given 60 two-hour sessions with a six-device mechanical puzzle showed clear evidence of learning, the curve showing ratio of incorrect to correct responses appearing quite comparable to similar curves obtained during externally rewarded situations. When, on the thirteenth day of tests, the subjects were presented with the puzzle 100 times at 6-minute intervals, the number of devices manipulated decreased regularly throughout the day, although there was no significant change in the number of times the problem assembly was attacked.
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