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Ruminant diversification as an adaptation to the physicomechanical characteristics of forage. a reevaluation of an old debate and a new hypothesis


Clauss, Marcus; Lechner-Doll, Matthias; Streich, W J (2003). Ruminant diversification as an adaptation to the physicomechanical characteristics of forage. a reevaluation of an old debate and a new hypothesis. Oikos, 102(2):253-262.

Abstract

The validity of Hofmann's classification of ruminants into browsers/"concentrate selectors", intermediate feeders and grazers/"grass and roughage eaters" and of his consecutive physiological postulates has repeatedly been questioned. In contrast to former concepts, which all focused on the chemical characteristics of the respective forages, we propose a new hypothesis on the main driving force of ruminant diversification, namely the physicomechanical characteristics of the respective forages. In contrast to browse, grass tends to stratify and form a "fibrous raft" in the reticulorumen. The significantly more capacious forestomachs of grazers, and the significantly thicker rumen pillars (indicating the strength of reticulorumen muscle equipment) of their forestomachs, are interpreted as particular adaptations to this forage characteristic. With these parameters, we present, for the first time, two single morphological measurements that allow the statistical reconstruction of Hofmann's classification. A small forestomach capacity and the lack of strong reticulorumen muscles in browsers would explain the observed exclusiveness with which browsers avoid grass forage under natural conditions, which we confirmed using two datasets on the composition of the natural diet. Both rumen pillar thickness and relative forestomach capacity were significantly correlated to the grass content of the natural diet, respectively. Our functional interpretation was also supported by a stepwise regression analysis with the proportion of grass in the natural diet as dependent variable and the rumen pillar thickness, the relative forestomach capacity, and the body weight as independent variables, which revealed significant equations.

The validity of Hofmann's classification of ruminants into browsers/"concentrate selectors", intermediate feeders and grazers/"grass and roughage eaters" and of his consecutive physiological postulates has repeatedly been questioned. In contrast to former concepts, which all focused on the chemical characteristics of the respective forages, we propose a new hypothesis on the main driving force of ruminant diversification, namely the physicomechanical characteristics of the respective forages. In contrast to browse, grass tends to stratify and form a "fibrous raft" in the reticulorumen. The significantly more capacious forestomachs of grazers, and the significantly thicker rumen pillars (indicating the strength of reticulorumen muscle equipment) of their forestomachs, are interpreted as particular adaptations to this forage characteristic. With these parameters, we present, for the first time, two single morphological measurements that allow the statistical reconstruction of Hofmann's classification. A small forestomach capacity and the lack of strong reticulorumen muscles in browsers would explain the observed exclusiveness with which browsers avoid grass forage under natural conditions, which we confirmed using two datasets on the composition of the natural diet. Both rumen pillar thickness and relative forestomach capacity were significantly correlated to the grass content of the natural diet, respectively. Our functional interpretation was also supported by a stepwise regression analysis with the proportion of grass in the natural diet as dependent variable and the rumen pillar thickness, the relative forestomach capacity, and the body weight as independent variables, which revealed significant equations.

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Additional indexing

Item Type:Journal Article, refereed, further contribution
Communities & Collections:05 Vetsuisse Faculty > Veterinary Clinic > Department of Small Animals
Dewey Decimal Classification:570 Life sciences; biology
630 Agriculture
Language:English
Date:2003
Deposited On:02 Dec 2008 11:09
Last Modified:25 Sep 2016 05:56
Publisher:Wiley-Blackwell
ISSN:0030-1299
Publisher DOI:10.1034/j.1600-0706.2003.12406.x
Permanent URL: http://doi.org/10.5167/uzh-3494

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