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Theses

DETERMINANTS DE L'UTILISATION DES RESSOURCES ALIMENTAIRES PAR LE CHEVAL : INFLUENCE DE LA QUALITE ET DE LA HAUTEUR DE LA VEGETATION SUR L'INGESTION ET LES CHOIX DE SITES D'ALIMENTATION

Abstract : The characteristics of resources are important determinants of intake and patch selection by herbivores, whatever the time scale considered. In this thesis we have used horses to explore the adaptations of a large herbivore faced with variations in their resource quantity and/or quality, using an experimental approach.
From the meta-analysis of individual measures of intake on a large range of hay quality, we have shown that the horses were able to compensate for the low nutritional value of their food by eating more. However, the animals expressed different responses to a decrease in forage quality and we discuss this individual variability in terms of behavioural strategies. In choice situations at pasture, when the animals could adjust their feeding behaviour between alternative patches differing in height only or in height and quality simultaneously, intake levels were maintained (13gDDM/kgLW/day), whatever the amount of grass offered. Instantaneous intake rates increased with grass height but the average daily intake rates achieved on the different swards types on a daily basis were constant, perhaps because depletion over the day levelled the instantaneous intake rates. From both studies at trough and at pasture, the horses were able to maintain their intake levels when energy and nitrogen content of the resource declined in order to satisfy their nutritional requirements. In a choice situation between feeding patches that did not differ much in quality, the horses selected the taller swards where they achieved higher DM and digestible DM intake rates (as predicted by optimal foraging theory). When the preferred sward matured, and a trade-off between sward height and quality was deepened, the horses increased their feeding time on the shorter good quality alternative, even though digestible DM intake rates were still higher on the reproductive sward. We demonstrate that, in both studies at pasture, the maximisation of their digestible crude protein intake rate explains the selection of their feeding sites. As protein supplies on the mature swards became limiting, the animals favoured the quality of their diet and selected the patches that met their nutritional requirements. The horses expressed partial preferences leading to sub-optimal choices: they did not graze the most profitable sward only. They may have done so to re-evaluate sward value regularly, as nutrient intake rate varies due to depletion by the animals. In the last study at pasture, when grass height and quality differed simultaneously, the sward maximising protein content was not the one that maximised energy content, and we propose that by feeding on both sward types they probably balanced their protein and energy intake.
By modulating their feeding time between the different feeding sites, the horses adapted their behaviour to the heterogeneity of their environment and achieved a high-quality, balanced diet that met their nutritional requirements. Some prospects for further research are proposed in order to improve the management of horses and their pastures. Finally, the contributions of this work to the understanding of the relationships between large herbivores and their resources are discussed.
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https://tel.archives-ouvertes.fr/tel-00365057
Contributor : Martine Lacalle <>
Submitted on : Monday, March 2, 2009 - 10:33:08 AM
Last modification on : Friday, October 23, 2020 - 4:52:09 PM
Long-term archiving on: : Tuesday, June 8, 2010 - 11:02:39 PM

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Nadège Edouard. DETERMINANTS DE L'UTILISATION DES RESSOURCES ALIMENTAIRES PAR LE CHEVAL : INFLUENCE DE LA QUALITE ET DE LA HAUTEUR DE LA VEGETATION SUR L'INGESTION ET LES CHOIX DE SITES D'ALIMENTATION. domain_other. Université de Limoges, 2008. Français. ⟨tel-00365057⟩

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