ARS | Publication request: Relationship of bite mass of cattle to sward structure of four temperate grasses in short-term foraging sessions

Submitted to: Grass and Forage Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 2009
Publication Date: December 1, 2009
Repository URL: http://www3.interscience.wiley.com/journal/122683642/issue
Citation: Soder, K.J., Sanderson, M.A., Gregorini, P., Orr, R.J., Rubano, M.D., Rook, A.J. 2009. Relationship of bite mass of cattle to sward structure of four temperate grasses in short-term foraging sessions. Grass and Forage Science. 64(4):421-431.

Interpretive Summary: The amount of pasture forage harvested per bite (bite mass) is a fundamental element of ingestive behavior of grazing cattle. A study was designed to compare the sward structure and forage species effects of four cool-season grasses found in northeastern USA pastures on bite mass of grazing cattle. Four grasses were each sown separately in plastic boxes to create micro-swards that were offered to Holstein cows in short-term foraging tests in two consecutive years. Forage species did not affect bite mass and therefore had little influence on the decision-making process of bite placement in this study. However, bite mass did differ between years, primarily due to differences in sward structure between the years. Therefore, generic sward features (independent of forage species) such as sward height, bulk density and herbage mass had greater influence on bite mass between years than did forage species. In practice, sward height is frequently used as an empirical tool to evaluate intake potential of herbage. Current grazing management studies may need to evaluate factors other than sward height, such as green leaf availability, bulk density, and herbage mass that influence bite features of grazing cattle.

Technical Abstract: Bite mass is a fundamental element of ruminant ingestive behavior and is highly influenced by sward structure. We compared the sward structure of four grasses and related structure to the bite mass of cattle grazing the grasses. Reed canarygrass (RCG; Phalaris arundinacea L), quackgrass (QG; Elytrigia repens,) orchardgrass (ORG; Dactylis glomerata, L.), and meadow fescue (MF; , Festuca pratensis Hud.) were each sown separately in plastic boxes (79 cm x 47 cm x 11.5 cm) to create micro-swards in two consecutive years. Seeding rates were 8,000 and 500 seeds m**-2 in Year 1 and Year 2, respectively. Once established, micro-swards were defoliated at 21-day intervals before being offered to non-lactating, non-pregnant multiparous Holstein cows in short-term foraging tests. The boxes were weighed (+/- 0.1 g) before and after each foraging session during which the cows were allowed to take approximately 50 bites. Herbage mass was greatest (P is less than 0.05) for RCG in both years (342.5 and 227.8 g m**-2 for Years 1 and 2, respectively) while in Year 1 QG also had the highest (P is less than 0.05) herbage mass (365.5 g**-2). Sward surface height (SSH) was greatest (P is less than 0.05) for RCG (31.7 and 20.3 cm for Years 1 and 2, respectively) in both years and also for ORG in Year 2 (20.9 cm). Bulk density was not affected (P is greater than 0.05) by treatment in Year 1, but was greatest (P is less than 0.05) for MF and RCG in Year 2 (1140.3 and 1151.0 g m**-3, respectively). Tiller length was greatest (P is less than 0.05) for ORG in both years (averaging 36.2 and 25.2 cm in Years 1 and 2, respectively), and also for RCG in Year 2 (23.1 cm). Tiller density was greatest (P is less than 0.05) for MF and QG in both years (averaging 94.5 and 84.5 100 cm**2 for Years 1 and 2, respectively). Mean dry matter (DM) bite mass was not affected (P is greater than 0.05) by forage species in either year (averaging 0.95 and 0.50 g/bite for Years 1 and 2, respectively). The DM bite mass was not significantly correlated (P is greater than 0.05) with any sward factor. Despite differences in sward structure between the two years, the lack of difference in bite mass between grass species indicates that grass species had little influence on this decision-making process of foraging behavior of cattle.