Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2008
Publication Date: 7/1/2008
Citation: Gregorini, P., Gunter, S.A., Beck, P.A., Soder, K.J., Tamminga, S. 2008. The interaction of diurnal grazing pattern, ruminal metabolism, nutrient supply and management in cattle. Professional Animal Scientist. 24:308-318. Interpretive Summary: The amount of pasture a cow eats is dependent upon many factors that influence the beginning and ending of grazing ‘meals’. Ruminal fill, or how ‘hungry’ a cow is, may play an important role in short-term pasture intake at the individual meal level, while daily energy demand of the animal may play a significant role at the larger scale, such as total daily pasture intake. When first introduced to a new pasture, cattle select the most desirable plant parts first (usually leaves and young shoots), leaving less desirable plant parts (stems and dead material). However, as they make successive passes over the same areas, they must then decide whether to consume the less desirable plant parts, or whether to continue searching for more desirable plants. This selective grazing pattern may result in decreased pasture intake as they spend more time searching and less time eating, which in turn can impact animal productivity. Therefore, studying grazing patterns throughout the day from an internal (ruminal) standpoint can increase our understanding of how cattle respond to a dynamic feeding environment such as pasture. This paper summarizes previous and current research that evaluates the impact of ruminal metabolism, pasture nutrient supply, and management of grazing cattle on grazing behavior and ultimately animal productivity. This advance in knowledge will help pasture-based dairy and livestock farms improve pasture utilization, carrying capacity of their land, and animal productivity.
Technical Abstract: Daily herbage intake depends on several factors that govern the initiation and cessation of successive grazing bouts. Ruminal fill, which regulates grazing bout-eating behavior, is one such factor. Under grazing conditions, nutrient supply varies among grazing bouts, not only in amount, but also in balance. Also, there is evidence suggesting differential energy expenditures in herbage harvesting and ingestive mastication among grazing bouts. The animal internal state plays an important role in shaping grazing pattern, although rumen microflora demands may be at times more important. It may well be that perception of ruminal conditions dominates the short-term intake rate during a complete grazing bout, while at a larger spatio-temporal scale, the animal may operate within a framework of daily level of energy demand. Simultaneously, cattle might be dealing with pasture progressive defoliation as the grazing event progresses. This leads to selective behaviors and herbage intake rate reductions. From this work emerges that integrating different ingestive and digestive behaviors across foraging spatio-temporal scales would provide greater comprehension of factors driving the diurnal grazing patterns of cattle, thereby aiding in the design of better grazing methods.