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.
The study was conducted in 2010 and 2011 at the South Dakota State University Cow-Calf Unit near Volga, SD, (44 degrees 22’ 46.32” N latitude, 96 degrees 58’ 12.60” W longitude, 516 m elevation) and in 2010 only at the South Dakota State University Cow Camp Experiment Station near Miller, SD (44 degrees 27’ 41.39” N latitude, 98° 58’ 43.16” W longitude, 506 m elevation). The continental climate of the area is characterized by wide seasonal variations. The average maximum daily temperatures in Volga, SD, range from -5.1 C in January to 27.9 C in July. The long-term (1928 to 2010) annual precipitation in Volga averages 606 mm and about 75% of the precipitation falls during the growing season (April through September). The average maximum daily temperatures in Miller, SD, ranged from -3.7 C in January to 30.7 C in July. The long-term (1902 to 2010) annual precipitation in Miller averages 481 mm, and about 77% of the precipitation falls during the growing season (April through September) (HPRCC 2011). The topography at the study site near Volga varies from nearly level terrain to slopes of less than 15%. The prominent soil in the area was a Poinsett-Buse-Waubay complex. The topography at the study site near Miller was nearly level with the prominent soil being Dudley-Houdek loams (Web Soil Survey 2011). Vegetation at both experiment sites were dominated by invasive cool-season plants, primarily Kentucky bluegrass and smooth bromegrass.
The experimental design of this study was a completely randomized design with three replications. In 2010, two sets of pastures were located at the Volga and Miller study sites. The Volga location consisted of two side-by-side 8.14 ha paddocks, with an IES paddock and a SL paddock. The Miller location consisted of two side-by-side 12.14 ha paddocks, with an IES trial paddock and a SL paddock. In 2010, all of the paddocks were stocked with feeder steers weighing approximately 317.5 kg. The Miller site was stocked with Angus cross cattle and the Volga site was stocked with Limousin cross cattle. The grazing period for the IES was approximately 60 days and the SL was approximately 120 days at both locations. The grazing trial at the Miller site in 2010 was from May 5 to July 13 for IES and from May 5 to August 31 for the SL. The grazing trial at Volga in 2010 was from May 19 to July 22 for IES and from May 19 to September 23 for SL. The grazing trial at Volga in 2011 was from June 1 to July 28 for IES and from June 1 to October 4 for SL. Cattle were stocked at 2.51 AUM ha-1 at the Miller location and 2.65 AUM ha-1 at the Volga location. In 2011, only the Volga site was used in the study and it was stocked with Angus cross heifers weighing approximately 394.6 kg. The grazing period stayed the same with 60 days for the IES and 120 days for SL; however, the heifers were stocked at 4.28 AUM ha-1. A complete list of treatment information is listed in Table 1.
The weights of all animals in all trials were collected at turnout, at IES trial end, and at SL trial end to determine gain of each grazing system. The livestock in the SL trial were weighed when IES trial was over as well as at the end of the SL trial. This allowed documentation of gain in the first half and the second half of the growing season. Animals in both treatments were locked away from food and water for a 12 hour period prior to weighing.
Standing crop biomass was collected throughout the trial in order to monitor forage disappearance. Standing crop biomass was determined using a drop disc which correlates forage height to pasture yield (Rayburn, 2003). Drop disc samples were taken at a density of 6 samples per ha. Ten random samples were clipped, dried at 60°C for 72 hours, and weighed following the drop disc measurement in order to develop a regression relationship between height and weight (Table 2).
A sub-sample of these clipped samples was analyzed using Near-Infrared Reflectance Spectroscopy (NIRS) to determine crude protein (CP) content, acid detergent fiber (ADF), and neutral detergent fiber (NDF). Four samples collected at Volga in May, 2011, failed to pass quality assurance requirements of NIRS and were analyzed by chemical methods (AOAC 2007). Also, all of the samples collected in September and October of 2011 were analyzed by chemical methods because of a required change in laboratories. Standing biomass was collected in all pastures immediately prior to turnout in the spring and at 4 week intervals until the conclusion of the season long trial.
Species composition was also collected prior to turnout in 2010. It also was collected in the fall of 2010, and spring and fall in 2011. Species composition was determined by randomly selecting three permanent 15 m2 areas in each paddock. These areas where sampled throughout the study by taking ten randomly selected 0.25 m2 quadrates from within the 15 m2 area. The percent cover was visually estimated for native warm-season grasses, native cool-season grasses, introduced cool-season grasses, native forbs, introduced forbs, litter and bare ground.
Precipitation data was collected from the closest official weather stations. Precipitation in 2010 was collected from SDSU weather stations located at Highmore for the Miller site and at Brookings for the Volga site. The Highmore weather station is located approximately 25 miles west of the Miller site. The Brookings weather station is located approximately 10 miles east of the Volga site. In 2011, a weather station was placed on the Volga study site and precipitation data was obtained from this weather station.
Data for this experiment were analyzed as a completely randomized design. Analysis of variance was conducted to compare treatments for average daily gain (ADG), gain per ha, and species composition using PROC GLM (SAS, 2008). Means were separated using the least squares means and were significant at P < 0.05. Source of variation in the model included treatment, location x treatment, collection, treatment x collection, and location x treatment x collection to test effects for CP, ADF, and NDF, and standing crop biomass using PROC GLM (SAS, 2008). Means were separated using the least squares means and were significant at P < 0.05.
This study was conducted on an above average rainfall year in 2010 at both locations. The total precipitation for the entire grazing season (May 5 through August 31) at the 2010 Miller location was 308 mm or 108% of normal. During the IES grazing treatment, when the livestock where on the pasture from May 5 through July 13, the total precipitation was 272 mm or 149% of normal. The latter half of the grazing season, from July 13 through August 31, when just the SL livestock were on the pasture, the total precipitation was 36 mm or 35% of normal.
The total precipitation for the entire grazing season (May 19 through September 23) at the 2010 Volga location was 666 mm or 192% of normal. During the IES grazing treatment, when the livestock where on the pasture from May 19 through July 22, the total precipitation was 335 mm or 166% of normal. The latter half of the grazing season, from July 22 through September 23, when only the SL livestock were on the pasture, the total precipitation was 331 mm or 228% of normal (SDOC, 2011)
In 2011, the Volga study site received below normal precipitation during the study period. The total precipitation for the entire grazing season (June 1 through October 4) at the 2011 Volga location was 230 mm or 74% of normal. During the IES grazing treatment, when the livestock where on the pasture from June 1 through July 28, the total precipitation was 194 mm or 123% of normal. The latter half of the grazing season, from July 28 through October 4, when only the SL livestock were on the pasture, the total precipitation was 36 mm or 23% of normal.
Total residual standing crop for the IES treatment, averaged across locations at each sampling date, dramatically decreased from the turnout date until the completion of the treatment, and then came back quickly due to the lack of grazing pressure in the latter half of the grazing season (Figure 1). The total residual standing crop for the SL treatment increased slightly after turnout, and then gradually decreased throughout the rest of the growing season (Figure 1).
Midsummer, when the IES livestock were removed, the standing crop on the IES pastures was 23% less than the SL pastures. However, at growing season’s end, the standing crop on the IES pastures was 1.4 times greater than the SL pastures. Smith and Owensby (1978) found similar results on Flint Hills Range in Kansas. The lesser standing crop remaining on the IES pasture at mid-season reflected the higher stock density early in the season; whereas, the rest period in the second half of the grazing season gave plants time to produce regrowth.
These changes in the residual standing crop can be attributed to the stock density of each treatment and the cumulative grazing pressure associated with each treatment (Figure 2). Smart et al. (2010) defined cumulative grazing pressure as stocking rate divided by peak standing crop.
Interestingly, our year-end grazing pressures on both treatments were similar at 40 AUD/Mg, which indicates the grazing pressure was the same on both treatments but was obtained faster with the IES treatment. A grazing pressure of 40 AUD/Mg was considered heavy stocking in the studies analyzed by Smart et al. (2010) but it was calculated using peak standing crop. In this study we did not have any enclosures in place so grazing pressure was calculated based on production available at the time of collection. This artificially caused our grazing pressure to be higher because calculations were not made with a year-end production value.
There were no significant differences in crude protein (P = 0.56), ADF (P = 0.99), NDF (P = 0.99) for treatment by collection interactions. The data in this study showed that CP stayed relatively uniform throughout the growing season, with both treatments starting at approximately 10% and dropping to approximately 7% by the end of the season (Table 3).
This could be attributed to the above normal precipitation on the majority of the trials causing a slower decline in crude protein of cool-season grasses in the northern Great Plains. A slow decline in crude protein of cool-season grasses in the northern Great Plains has been documented in other research. Smart et al. (1995) saw the CP of Kentucky bluegrass in Wisconsin change from 21% to 14% from May to July. This slower decline may have had the biggest influence on the animal performance data and why IES may not be the best management practice for increasing gain in the northern tallgrass prairie. Research in the southern Great Plains has documented different changes in forage quality. In the 1981 Kansas State University Agriculture Experiment Station Bulletin, Smith (1981) monitored the CP for each month of the growing season on warm-season grass pastures on Kansas tallgrass prairie. Their results showed that CP started out high in May (17.7%) and then gradually decreased through the growing season (September, 4.3%).
Livestock production data was only analyzed from cattle weights collected in 2010. In 2011 the livestock were switched to breeding heifers and were not properly shrunk at the first weigh date resulting in a negative gain at the end of the IES trial. Average daily gains (P = 0.45) and gain per ha (P = 0.33) were not significantly different between IES and SL treatments (Table 4). Early season gains were comparable between both stocking rates with IES treatments gaining 0.56 kg/day and the SL treatment gaining 0.61 kg/day. Late season gains were only collected on the SL treatment and were 0.67 kg/day. Launchbaugh (1957) found similar results between light, moderate, and heavy use during the early season. However, Anderson et al. (1970) reported that steer gains during the latter half of the growing season on Kansas Flint Hills range were 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.
Declines in gain during the latter half of the growing season were not observed in this study, but drastic declines in forage quality were not observed either. Forage quality may have stayed uniform throughout the growing season due to above normal precipitation as discussed earlier. If this trial were conducted in the northern Great Plains on a year with below normal precipitation, gains could be higher on IES because moisture levels are typically high in the spring due to snow melt. Intensive early stocking would allow a producer to take advantage of all early season moisture before drought conditions set in towards the middle of the growing season.
Another possible explanation for poorer gains in the first part of the growing season may have been attributed to the livestock becoming acclimated to a grass diet. The livestock in this trial were not allowed to become acclimated to a grass diet, and the livestock used at the Volga location came directly out of a dry lot with a mixture of forage and grain diet. When cattle diets are changed dramatically, such as moving from a feedlot to a pasture with an all forage diet, bacteria in the rumen have to change to be able to cope with the new diet. The growth of stocker cattle will often “stall” for up to 30 days after being switched from drylot diets to pasture (Phillips et al., 2003). This would lead to animal performance being low early on in the grazing trail, while the rumen adjusts, and then improving later on in the grazing trial. It would have been beneficial to allow for an adjustment period prior to the beginning of this trial to allow rumens to adjust before the trial started.
Gain per ha also did not change between IES and SL treatments (P = 0.33). This is important because it means that either type of grazing system should lead to the same amount of beef produced per ha. This is where the true benefits of the IES are expressed because as discussed earlier, forage production at the end of the year was higher under the IES. This excess production could be saved for future use with dormant season grazing or left for wildlife habitat because it did not come with an added cost.
Composition of native warm-season grasses on IES pastures was significantly higher than that on the SL (P = 0.05) (Table 4). All other functional groups were not significantly different. Similar to Smith and Owensby’s (1978) results, these results indicated that IES tended to be beneficial to native warm-season grasses. This is due to the time of grazing. With IES cattle graze when the cool-season grasses are growing and then are removed from the pasture when the warm-season grasses begin to grow. IES was not detrimental to the undesirable components such as introduced cool-season grasses (Table 5). This could be attributed to the wetter than normal years allowing for these introduced cool-season grasses to stay more vegetative; however, complete control of species like smooth brome and Kentucky bluegrass with strictly grazing is unrealistic (Smith and Owensby, 1978; Owensby, 1988).
In order to get an increase in native warm-season grasses using IES systems, there has to be a component of native warm-season grasses within the pasture. The Miller location did have this component and this is where we saw the best results of warm-season grasses becoming more predominant. At the Volga location there was no native warm-season component within the pasture before the trial started and there was very little sign of any following the trial.
Educational & Outreach Activities
- Presented information in a seminar at SD Grazing School for US Fish and Wildlife Service at Huron, SD – June 2010
Presented information in seminar at SD Section SRM meeting in Watertown, SD – October 2010
Presented information in a poster at International SRM meeting in Billings, MT – February 2011
Presented information in a seminat at SD Grazing School for producers in Chamberlain, SD – September 2011
Presented information in a Thesis Defense Seminar to Animal and Range Science Department at Brookings, SD – December 2011
Will not publish in a Journal just yet. South Dakota State University Range Scientist’s plan to continue researching topic and publish at a future date.
Intensive-early stocking is a grazing system that has been used extensively in the southern Great Plains with much success. Smith and Owensby (1978) found IES to offer the following benefits on Kansas Flint Hills Range: grazing distribution was more uniform under IES than SL, desirable warm-season perennial grasses were favored more by IES than SL, Kentucky bluegrass and perennial forbs were favored more by SL than by IES, and daily gain and gain per ha by steers were increased by IES compared to SL.
In the northern Great Plains, IES has not been studied as intensely as in the south. The results from this study indicate that the gain per ha will not increase with IES because livestock gains do not decline in the latter half of the summer as they do in the south. This is because forage quality does not appear to decline through the summer as has been seen in the southern Great Plains. Although the exact reason why forage quality appears to be maintained over the summer in the northern Great Plains is not immediately clear, a number of assumptions can be made. Perhaps mean growing season temperatures in the northern Great Plains remain cool enough that forage quality is not adversely affected. Furthermore, the cooler growing season supports more cool-season plants in the northern Great Plains than in the south. Cool-season grasses tend to maintain forage quality much better through the growing season than warm-season grasses (Smart et al., 1995). Additionally, this trial was conducted in two years with above normal precipitation in the early part of the growing season causing the cool-season plants to be above normal in production. It is unclear of the effects of IES in drier years where the forage quality and quantity of the cool-season grasses may decrease as the growing season progresses.
These results indicated that gain per ha between IES and SL stocking were not significantly different. Therefore, opportunity may exist to use IES for other management objectives without having a negative impact on profitability. Grass production and species composition were affected by the two grazing systems. Intensive early stocking resulted in almost 1.5 times more grass production at the season’s end. There was also a trend for more warm-season grasses to occur in the IES. Intensive early stocking may have potential as a grazing system in the northern Great Plains because pasture restorations can be made without giving up animal production in the form of gain per acre. However, more research is needed to truly understand the benefits and disadvantages that may be associated with IES on the northern Great Plains.
Areas needing additional study
- Continued use of intensive early stocking on tallgrass prairie in Eastern South Dakota
Use of intensive early stocking on tallgrass prairie in dry years
Ability of tallgrass prairies to recover and produce more biomass by allowing a deferment following intensive early stocking.