|Jackson, Randall -|
|Alber, Nadia -|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 23, 2013
Publication Date: May 1, 2013
Citation: Brink, G.E., Jackson, R.D., Alber, N.B. 2013. Residual sward height effects on growth and nutritive value of grazed temperate perennial grasses. Crop Science. DOI: 10.2135/cropsci2013.01.0068. Interpretive Summary: The effects of grazing intensity on cool-season grasses have been studied extensively using mechanical clipping to impose differences in stubble height, but rarely under actual grazing conditions. We conducted a study to determine how the grazing stubble height of immature and mature grasses influences annual productivity, the distribution of yield produced during the grazing season, grass digestibility, and persistence of the grass. We found that annual yield generally increased as stubble height decreased, but the time interval between each grazing event increased and the number of grazing events decreased, which concentrated grass production in a smaller proportion of the grazing season. The quality of the grass consumed by cattle was not influenced by stubble height. Persistence of the four grasses was not consistently influenced by stubble height. When grasses were grazed extremely short (less than one inch), however, the first grazing event of the following spring was delayed two weeks. Pasture-based livestock producers must consider the trade-off that occurs between annual pasture production and the time period over which pastures can be grazed – grazing pastures short may result in more grass being grazed but reduce the length of the grazing season.
Technical Abstract: Residual sward height (RSH) has a significant impact on temperate perennial grass growth, but its effect is rarely studied under grazing. We determined RSH effects on forage harvested (FH), seasonal yield distribution, nutritive value, and persistence of meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.], orchardgrass (Dactylis glomerata L.), quackgrass [Elymus repens (L.) Gould], and reed canarygrass (Phalaris arundinacea L.). Grasses were rotationally stocked with dairy heifers at vegetative stage (32-cm height) to a 16-, 8-, or 2-cm RSH or at mature stage (48-cm height) to a 24-, 12-, or 4-cm RSH in each of two years. Grass FH and nutritive value were measured for each grazing event. Annual FH of grasses grazed at vegetative stage to a 2- or 8-cm RSH was greater than that grazed to a 16-cm RSH when precipitation was limiting, but few differences existed when precipitation was abundant. Annual FH of grasses grazed at mature stage increased as RSH decreased. As RSH increased, the mean grazing interval decreased, which increased the number of seasonal grazing events of vegetative- but not of mature-stage grasses. There was no apparent relationship between forage nutritive value and RSH. The primary risks incurred by grazing vegetative-stage grasses to a shorter RSH (< 8 cm) were reduced persistence in a dry year and delayed date of first grazing event the following spring. Little or no advantage in growth was gained by intentionally leaving a tall RSH when grazing mature-stage grasses.