Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/2/2009
Publication Date: 5/11/2009
Publication URL: http://hdl.handle.net/10113/30371
Citation: Gregorini, P., Soder, K.J., Kensinger, R.S. 2009. Effects of rumen fill on short-term ingestive behavior and circulating concentrations of ghrelin, insulin, and glucose of dairy cows foraging vegetative micro-swards. Journal of Dairy Science. 92(5):2095-2105. Interpretive Summary: Ruminal fill is related to hunger, with level of ruminal fill influencing pasture intake. However, little is known regarding how cattle adjust bite dimensions (bite depth and area) and pasture intake rate (amount of pasture consumed per second) according to different ruminal fill, or if variations in ruminal fill reflect changes in appetite-regulating hormonal levels. This work aimed to assess the impact of ruminal fill on grazing behavior, pasture intake rate and levels of glucose and the hormones ghrelin and insulin. Four lactating dairy cows grazed orchardgrass in micro-sward boxes. The treatments were 0, 33, 66 or 100 % of the total rumen capacity. The results indicate that the level of ruminal fill affects pasture intake rate, bite mass and bite dimensions. As ruminal fill increased, cows took smaller bites that were deeper but of smaller surface area, resulting in lower bite mass. This may explain the lower pasture intake rate. In addition, as ruminal fill increased, levels of ghrelin and insulin decreased, but glucose levels increased. The present study increased knowledge of some underlying endocrine physiology that affects of ruminal fill, which impacts foraging behavior. This information may lead to improved grazing management strategies to optimize pasture utilization.
Technical Abstract: The impact of ruminal fill (RF) on foraging behaviour, intake rate and the levels of circulating ghrelin, insulin and glucose was measured with four rumen-cannulated lactating dairy cows foraging micro-swards of vegetative orchardgrass. The treatments compared were removal of 1.00 (RF0), 0.66 (RF33), 0.33 (RF66) or 0 (RF100) of total ruminal content. Treatments were randomly applied in a 4 x 4 Latin-square design. Micro-swards were weighed before and after foraging sessions. Foraging sessions were time unlimited, but cows were allowed to take a maximum of 15 bites. Herbage was analysed by canopy strata for chemical composition, toughness and module of elasticity. 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 (P < 0.05) while bite depth increased as RF increased. The RF did not affect (P > 0.05) biting rate or total jaw movements. Increasing RF resulted in lower (P < 0.05) mean levels of circulating ghrelin, with no changes (P > 0.05) in mean levels of insulin and glucose. However, increasing RF decreased (P < 0.05) the incremental change in ghrelin, insulin and glucose levels from the time of treatment setting until the foraging sessions. The present study elucidates some of the underlying endocrine physiology under short-term temporal variations of RF and its effect on foraging behaviour.