Sward structural resistance and biting effort in grazing ruminants

Abstract

-Grazing ruminants face complex decisions in searching for and harvesting adequate forage to meet their requirements in the face of heterogeneity in the abundance, nutritive value and distribution of resources. Some of the major decisions which affect the bite mass and therefore, forage intake adjustments in bite depth, bite area and exerted bite force, are made in relation to heterogeneity in sward structure. A number of relationships have been established linking the adjustment of bite mechanics in response to variations in sward height and bulk density on temperate forages for animals of a range of body sizes. However, there is less consistency in the response of the bite mechanics to the greater variations in structural resistance that arise from the vertical and horizontal arrangements of the plant morphological organs of leaf, pseudostem and stem. Furthermore, only limited progress has been made in quantifying the biting forces involved in grazing, the linkages between the plant morphological organs and their effect on bite force and, the interaction with body mass. In this paper, we discuss the different hypotheses that have been proposed to explain the regulation of bite depth and provide evidence for their acceptance or rejection. We comment on the knowledge gap in understanding biting force mechanisms across animal species of contrasting body mass, and stress the need for differentiation between the concepts of biting force and biting effort.bite / effort / force / ruminants / structure Résumé -Résistance de structure du couvert végétal et effort de prélèvement des bouchées chez les ruminants au pâturage. Face à l'hétérogénéité de la ressource en abondance, en valeur nutritive et en répartition, les ruminants au pâturage doivent prendre des décisions complexes pour rechercher et récolter les fourrages nécessaires à leurs besoins. Certaines de ces décisions affectent la masse de la bouchée et donc, l'ajustement de l'ingestion en terme de profondeur et de surface de la bouchée, ainsi que de force de prélèvement. Ces décisions sont prises en relation avec l'hétérogénéité de la structure du couvert végétal. Nombre de relations ont été mises en évidence liant l'adaptation de la mécanique de la bouchée aux variations de la hauteur et de la densité du couvert végétal de fourrages tempérés pour des animaux de différentes tailles corporelles. En revanche, les grandes variations de résistance des végétaux, qui résultent des arrangements verticaux et horizontaux des organes morphologiques de la plante (feuille, gaine et tige), ont des effets variables sur la mécanique de la bouchée. De plus, seuls des progrès limités ont été accomplis pour quantifier les forces de prélève-ment des bouchées impliquées au pâturage, les liens entre les organes morphologiques de la plante et leurs effets sur les forces de prélèvement, ainsi que l'interaction avec le format des animaux. Dans cet article, nous discutons les différentes hypothèses qui ont été proposées pour expliquer la régulation de la profondeur des bouchées,...

The horizontal barrier effect of stems on the foraging behaviour of cattle grazing five tropical grasses

“…We did not find any evidence to support the 'summit maximum bite force hypothesis' (Griffiths and Gordon, 2003) in vegetative swards of tropical pasture grass species. Hughes et al (1991) and Laca et al (1993) also found that bite area decreased in response to the increase in grazing resistance of the swards but a maximum bite force was not detected.…”

“…Previous studies on temperate species did not find evidence to support the 'submit maximum bite force hypothesis' either (Griffiths and Gordon, 2003). Benvenutti et al (2008b) found that bite area and bite force decreased with increasing stem tensile resistance in animals confronted with a horizontal barrier of stems despite the fact that they were able to apply a higher bite force and avoid such a reduction in bite area.…”

“…The output of the force plate was used to measure grazing time and showed the three dimensional forces applied by the animal on the swards at 200 samples/s. By examining the force pattern, it was possible to identify when the animal was pushing the herbage around during the grasping of the bite, tugging the bites or masticating the herbage (Griffiths and Gordon, 2003). Grazing time, which was measured with a precision of 0.005 s, started with the prehension of the first bite, finished with the tugging of the last bite and included only the period of active grazing where mastication time was excluded.…”

The effect of the density and physical properties of grass stems on the foraging behaviour and instantaneous intake rate by cattle grazing an artificial reproductive tropical sward

“…, 1995). However, this holistic approach lacks empirical support (Griffiths and Gordon, 2003). A related approach, which has produced clear results, is based on the mechanical properties of the herbage in the vertical and horizontal dimensions (Flores et al.…”

Grass Yield and Quality Affect Potential Stocking Rate and Milk Production

“…Other studies suggest that additional factors influence dry matter intake. These include sward height and density (2,7), cell wall or neutral detergent fiber concentration (11), the digestibility of the cell wall (15), and factors related to animal preference for a feed (3). Factors other than the quantity of available pasture may have influenced results in a study by Casler et al (6), who found that apparent intake of orchardgrass and meadow fescue by dairy cows often exceeded that of tall fescue despite having lower available forage.…”