Title: Linking pasture and animal processes. The effect of appetite on the way they graze Author
Submitted to: Extension Fact Sheets
Publication Type: Other
Publication Acceptance Date: April 1, 2008
Publication Date: April 20, 2008
Citation: Gregorini, P. 2008. Linking pasture and animal processes. The effect of appetite on the way they graze. Extension Fact Sheets. Interpretive Summary: An interpretive summary is not required.
Technical Abstract: Little is known regarding how foraging ruminants adjust bite dimensions and instantaneous herbage intake rate according to different ruminal fill levels, or if short-term temporal variations in ruminal fill reflect changes in the underlying endocrine physiology. Therefore, we determined the effect of ruminal fill on short-term foraging mechanisms (at bite scale), instantaneous herbage intake rate, and plasma ghrelin and serum insulin and glucose levels of cattle grazing a vegetative temperate micro-sward. The treatments compared were removal of 1.00, 0.66, 0.33 or 0 of total ruminal content before a short foraging session (15 bites). Eating time, intake rate, total jaw movements, and bite parameters (mass, depth, area and rate) data were collected. Plasma was analysed for ghrelin and serum for insulin and glucose. Short-term intake rate, bite mass and bite area decreased while bite depth increased as ruminal fill increased. The ruminal fill did not affect biting rate or total jaw movements. Increasing ruminal fill resulted in lower mean levels of circulating ghrelin, with no changes in mean levels of insulin and glucose. However, increasing ruminal fill decreased the incremental change in ghrelin, insulin and glucose levels from the time of treatment setting until the foraging sessions. This study showed that cattle may adjust bite mass and dimensions as a mechanism to increase instantaneous acquisition of energy in response to decreasing levels of “physical stimulation” coming from the rumen. In the progression of a grazing bout, these signals seem to be mediated by ghrelin and potentially by insulin-glucose metabolism. The present study elucidates some of the underlying endocrine physiology under short-term temporal variations of RF and its effect on foraging behavior.