- Animals: bovine
- Animal Production: grazing management
- Education and Training: extension
- Farm Business Management: budgets/cost and returns
- Natural Resources/Environment: biodiversity
Cow-calf producers in eastern South Dakota often over-winter calves to take advantage of the low cost gain associated with lightweight cattle on grass to improve profit margins. Producers will typically use a season-long stocking (SL) grazing system to manage these cattle on grass the following year. Season-long stocking, however, has converted the majority of native grassland to a mix of introduced cool-season species which has reduced production efficiency and biodiversity. The use of Intensive Early Stocking (IES) may address both of these issues by improving production and economic efficiency through improved gain per acre and reducing biological resource competition for native warm-season species. The objective of this study is to determine the effect of IES on livestock production, biomass disappearance, and plant species composition of cool-season dominated pastures. Study sites were established in Miller, SD, and Volga, SD, and data was collected from Miller in 2010 and Volga in 2010 and 2011. Study sites were predominately introduced cool-season grass pastures. At each study site, two side-by-side paddocks were established and stocked for SL stocking and IES (2 x normal stocking rate) with yearling cattle. The SL trial lasted 120 days while the IES trial lasted 60 days. All cattle were weighed prior to grazing, at 60 days (end of IES), and at 120 days (end of SL). Forage yield was measured weekly throughout the grazing season. Samples collected for forage yield were analyzed for forage quality using Near-Infrared Reflectance Spectroscopy (NIRS). Gain per hectare (ha) was calculated following the end of the trial. Species composition was sampled in May and September. Gain per ha was similar between the IES and SL treatments. Available forage in the IES trial was 23% less than SL at midsummer; however, at the end of the growing season available forage on IES was 1.4 times that of SL. There was also a significant increase in native warm-season grass composition on the IES trial.
In the tallgrass prairie ecosystem, introduced species often displace native species and reduce diversity (Wilson, 1988; Drake et al., 1989; Wilson and Belcher, 1989; Billings, 1990; D’Antonio and Vitousek, 1992; Burke et al., 1997). In most cases these introduced species are cool-season perennial plants and are able to out-compete native species by growing earlier in the season and reducing the amount of light, soil moisture, and soil nutrients available. Smooth bromegrass (Bromus inermis Leyss.) and Kentucky bluegrass (Poa pratensis L.) are two species that have invaded much of the tallgrass prairie and the northern Great Plains in general. Pastures that are cool-season grass dominated produce most of their growth in the spring and early summer (Nelson and Moser, 1994).
Stocking rates can have an effect on the vegetation of a pasture as well as the performance of the animals that are grazing the pasture (Vallentine, 2001). Intensive early stocking (IES) uses the same stocking rate as season-long stocking (SL), but the grazing pressure is distributed differently throughout the year. IES employs a high stock density during the first half of the summer, and removes cattle from range in midsummer. IES has been used in central and southern Great Plains to effectively utilize early season forage for the production of growing cattle (Smith and Owensby, 1978; McCollum et al., 1990; Olson et al., 1993). Drier, hotter conditions in late summer result in lowered forage quality and quantity with an associated decreased rate of gain of steers grazing these forages. Steer gains during the latter half of the growing season on Kansas Flint Hills range are barely one-half those of the first half of the season because forage quality declines with grass maturation and translocation of nutrients to reserve pools (Anderson et al., 1970). Olson et al. (1993) conducted a grazing trial to compare short grass vegetation response under IES at 2 stocking rates to SL. By concentrating the grazing pressure during the first half of the growing season they were able to increase the warm-season composition of the pasture (Olson et al., 1993).
The objective of this study is to determine the effect of IES vs SL of cool-season dominated pastures on livestock production, biomass disappearance, and plant species composition. This study will establish whether similar results can be obtained as have been seen in the southern Great Plains, whereby there is an increase in gain per ha of beef production and an increase in composition of warm-season native plant species. Results of this study should guide the development of an optimum summer grazing program for cool-season dominated pastures.