Residual Sward Height Effects on Growth and Nutritive Value of Grazed Temperate Perennial Grasses

Abstract

ABSTRACTResidual 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 {Festuca pratensis Huds. subsp. pratensis [syn. 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 (Bos taurus) 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 2 yr. 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.