ARS | Publication request: Short-term foraging dynamics of cattle grazing swards with different canopy structures

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 30, 2009
Publication Date: August 14, 2009
Repository URL: http://hdl.handle.net/10113/37642
Citation: Gregorini, P., Gunter, S.A., Beck, P.A., Caldwell, J., Bowman, M.T., Coblentz, W.K. 2009. Short-term foraging dynamics of cattle grazing swards with different canopy structures. Journal of Animal Science. 87:3817-3824.

Interpretive Summary: Planting methods for wheat affects the sward canopy structure and the main objective of the present experiment was to describe the sward canopy structure of 3 different wheat (Triticum aestivum L.) pastures and relate them to the short-term herbage intake rate and foraging dynamics by grazing steers. Differences in canopy structure were created by using 3 different tillage methods: conventional tillage, minimum tillage, and no-till. Pastures were sampled for leaf and stem fractions at the bottom, middle, and top canopy strata (thirds). Sward surface heights and tiller and bulk densities were measured. Herbage was separated into stem and leaf, leaves were then phenologically ranked. Three steers grazed (grazing sessions) the 3 different pastures using a Latin Square design. Ruminal contents were emptied and weighed before and after grazing sessions to assess herbage intake rate and bite mass. All grazing sessions were video recorded and analyzed for feeding stations, bites/feeding station, and feeding station/min. Bite depth and area, and area grazed/feeding station were calculated. Morphological components and tiller density did not differ (P > 0.05), but sward surface heights were taller (P < 0.05) in the pasture established with no-till seeding compared to the pasture established with conventional and minimum tillage, as well as the leaf proportion being greater (P < 0.05) in the middle and top canopy strata. The herbage intake rate, bite mass, and bite area increased (P < 0.05) as sward surface height increased. Steers grazing the tallest pasture with the greatest leaf accessibility ate faster, navigated slower, and grazed more efficiently (P < 0.05). The area grazed/feeding station differed between treatments (P < 0.05), being was 87 for the tallest pasture with the greatest leaf accessibility, and the lowest, 31%, for the pasture with the lowest leaf accessibility. Pastures with greater leaf accessibility may lead grazing cattle to reach the same herbage intake level in less time, while grazing more efficiently per unit area. Consequently, when grazing cattle in controlled grazing systems it may be logical to think of reducing the area and time allocation in pastures if taller swards with leafy upper canopy strata are present.

Technical Abstract: The main objective of the present experiment was to describe the sward canopy structure of 3 different wheat (Triticum aestivum L.) pastures and relate them to the short-term herbage intake rate and foraging dynamics by steers. Differences in canopy structure were created by using 3 different establishment methods (conventional tillage, minimum tillage, and direct seeding [no tillage]). Pastures were sampled for leaf and stem fractions at the bottom, middle, and top canopy strata. Sward surface heights and tiller and bulk densities were measured. Herbage was separated into stem and leaf, leaves were then phenologically ranked. Three steers grazed (grazing sessions) the 3 different pastures using a Latin Square design. Ruminal contents were emptied and weighed before and after grazing sessions to assess herbage intake rate and bite mass. All grazing sessions were video recorded and analyzed for feeding stations, bites/feeding station, and feeding station/min. Bite depth and area, and area grazed/feeding station were calculated. Morphological components and tiller density did not differ (P > 0.05), but sward surface heights were taller (P < 0.05) in the pasture established with direct seeding compared to the pasture established with conventional and minimum tillage, as well as the leaf proportion being greater (P < 0.05) in the middle and top canopy strata of direct seeding. The herbage intake rate, bite mass, and bite area increased (P < 0.05) as sward surface height increased. Steers grazing the tallest pasture with the greatest leaf accessibility ate faster, navigated slower, and grazed more efficiently (P < 0.05). The area grazed/feeding station differed between treatments (P < 0.05), being was 87 for the tallest pasture with the greatest leaf accessibility, and the lowest, 31%, for the pasture with the lowest leaf accessibility. Pastures with greater leaf accessibility may lead grazing cattle to reach the same herbage intake level in less time, while grazing more efficiently per unit area.