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Zolovick, A., Upson, D. W., & Eleftheriou, B. E. (1966). Diurnal Variation In Plasma Glucocorticosteroid Levels In The Horse (Equus Caballus). J. Endocrinol., 35(3), 249–253.
Abstract: Thin-layer chromatography, acetylation of reference and unidentified glucocorticosteroids, u.v. absorption and fluorescence induced in sulphuric acid were used to identify cortisol as the major free plasma glucocorticosteroid in the horse (Equus caballus), with cortisone and corticosterone as minor glucocorticosteroids. Deoxycorticosterone was also identified. The plasma ratio for free cortisol: cortisone: corticosterone was 16:8:0·5.The diurnal variation was determined for all three glucocorticosteroids. The highest levels of cortisol and corticosterone were found at 10.00 hr. (260 and 10·3 μg./100 ml., respectively) and the lowest concentration of cortisol at 02.00 hr. The highest level of cortisone occurred at 02.00 hr. (140 μg./100 ml.), and the lowest appeared at 16.00 hr. (65 μg./100 ml.). The maximum plasma concentration of the combined glucocorticosteroids was found at 10.00 hr. (395·3 μg./100 ml.), and the minimum at 20.00 hr. (219 μg./100 ml.).
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Irvine, C. H. G., & Alexander, S. L. (1994). Factors affecting the circadian rhythm in plasma cortisol concentrations in the horse. Domest. Anim. Endocrinol., 11(2), 227–238.
Abstract: In horses, a circadian rhythm in plasma cortisol concentrations has been reported in some but not all studies. When a rhythm occurred, horses were accustomed to a management routine, comprising stabling, feeding and sometimes exercise, which may entrain a circadian pattern. In this work, we monitored plasma cortisol by collecting jugular blood through indwelling cannulae from four groups: 1): 10 untrained, unperturbed mares grazing excess pasture, bled hourly for 26 hr; 2) 4 mares housed in a barn for 48 hr before sampling every 15 min for 20–24 hr; 3) 5 mares placed in an outdoor yard for sampling every 30 min from 0930–2100 hr; and 4) 4 stabled racehorses in training, bled every 30 min from 0730–2000 hr and once the following morning at 0830 hr. Plasma cortisol showed a similarly-timed circadian rhythm (P<0.0001) in all Group 1 horses, with a peak at 0600–0900 hr, and a nadir at 1800–2100 hr. By contrast, cortisol concentrations did not vary with time in either Group 2 or 3. Neither daily mean nor peak cortisol values differed in Group 1 and 2 (i.e. bled for >= 20 hr); however nadir values were higher (P<0.05) in Group 2. In Group 4, cortisol declined (P=0.004) during the sampling period but had returned to initial concentrations the next morning. Values did not differ from those for Group 1, except between 1000 and 1300 hr when cortisol in Group 4 was lower (P<0.05). We conclude that a circadian cortisol rhythm exists in horses in the absence of any known cues imposed by humans. However, this rhythm can be obliterated by the minor perturbation of removing the horse from its accustomed environment. By contrast, the rhythm occurs in trained racehorses, suggesting either that they have adapted to their environment thereby allowing an endogenous rhythm to emerge, or that the rhythm is entrained by their daily routine. These observations highlight the difficulties in determining the cortisol status of a horse, since measurements will be affected by time of day, the occurrence of short-term fluctuations, and how accustomed the horse is to its environment.
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Ventolini, N., Ferrero, E. A., Sponza, S., Della Chiesa, A., Zucca, P., & Vallortigara, G. (2005). Laterality in the wild: preferential hemifield use during predatory and sexual behaviour in the black-winged stilt. Anim. Behav., 69(5), 1077–1084.
Abstract: We recorded preferential use of the left and right monocular visual field in black-winged stilts, Himantopus himantopus, during predatory pecking and during courtship and mating behaviour in a naturalistic setting. The stilts had a population-level preference for using their right monocular visual field before predatory pecking; pecks that followed right-hemifield detection were more likely to be successful than pecks that followed left-hemifield detection, as evinced by the occurrence of swallowing and shaking head movements after pecking. In contrast, shaking behaviour, a component of courtship displays, and copulatory attempts by males were more likely to occur when females were seen with the left monocular visual field. Asymmetric hemifield use observed in natural conditions raises interesting issues as to the costs and benefits of population-level behavioural lateralization in wild animals.
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Güntürkün, O., & Kesch, S. (1987). Visual lateralization during feeding in pigeons. Behav. Neurosci., 101(3), 433–435.
Abstract: In a quasi-natural feeding situation, adult pigeons had to detect and consume 30 food grains out of about 1,000 pebbles of similar shape, size, and color within 30 s under monocular conditions. With the right eye seeing, the animals achieved a significantly higher discrimination accuracy and, consequently, a significantly higher proportion of grains grasped than with the left eye seeing. This result supports previous demonstrations of a left-hemisphere dominance for visually guided behavior in birds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)
Keywords: use of right vs left eye, amount & accuracy of pecking in food discrimination task, homing pigeons, implications for lateralization of cerebral function
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Rogers, L. J. (1997). Early Experiential Effects on Laterality: Research on Chicks has Relevance to Other Species. Laterality, 2(3-4), 199–219.
Abstract: The influence of early experience on the development of lateralisation of hemispheric function was further investigated, using the chick as a model. A range of functions are lateralised in the chick and these correlate with asymmetry in the organisation of the visual projections. Chicks using the right eye and, therefore, primarily the left hemisphere are able to switch from pecking randomly at grain and pebbles to pecking mainly at grain, whereas those using the left eye and primarily the right hemisphere continue to peck at random. Exposure to light during the last days of incubation establishes this lateralisation in males, as a consequence of the embryo being oriented in the egg so that the left eye only is occluded. Males incubated in the dark peck at random when using either the right or left eye. Irrespective of light experience, females perform the same as darkincubated males: they are not influenced by light exposure. Monocular performance of the pebble-grain task is compared to binocular performance, and the sensitive period for the influence of light is delineated. The interactive effects of sex hormone levels on the differentiation of lateralisation are discussed and also the relevance of the results to other species, including humans.
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