Jerry D. Volesky

Effects of Grazing Pressure on Efficiency of Grazing on North American Great Plains Rangelands

Abstract Comparisons of stocking rates across sites can be facilitated by calculating grazing pressure. We used peak standing crop and stocking rates from six studies in the North American Great Plains (Cheyenne, Wyoming; Cottonwood, South Dakota; Hays, Kansas; Nunn, Colorado; Streeter, North Dakota; and Woodward, Oklahoma) to calculate a grazing pressure index and develop relationships for harvest efficiency, utilization, grazing efficiency, and animal performance and production. Average grazing pressures for heavy, moderate, and light stocking across the study sites were 40, 24, and 14 animal unit days · Mg−1, respectively. These grazing pressures resulted in average harvest efficiency values of 38%, 24%, and 14% and grazing efficiencies of 61%, 49%, and 39% for heavy, moderate, and light stocking rates, respectively. Utilization increased quadratically as grazing pressure index increased, whereas grazing and harvest efficiencies exhibited a linear increase with grazing pressure. The latter indicates that nonlivestock forage losses (e.g., weathering, senescence, wildlife, insects) were disproportional across stocking rates. Average daily gain of livestock decreased linearly as grazing pressure index increased across study sites. Prediction equations reaffirm assumptions of 50% grazing efficiency and 25% harvest efficiency associated with moderate stocking. Novel here, however, is that harvest and grazing efficiencies increased at high grazing pressures and decreased at low grazing pressures. Use of grazing pressure index to “standardize” stocking rates across rangeland ecosystems in the North American Great Plains should improve communication among scientists, resource managers, and the public, and thus better achieve both production and conservation goals on these lands.

Effects of mechanical treatments and climatic factors on the productivity of Northern Great Plains rangelands.

Impacts of 7 range treatments and climate on late spring herbage standing crops (SC) were measured in rangelands near Miles City, Mont., from 1983 to 1990. Treatments, established in 8 pastures at 2 sites, were: (1) untreated control + season long grazing (SL); (2) soil tillage (ST) + SL; (3) ST + drill seeding legumes (DS) + SL; (4) brush control (BC) + ST + DS + switchback grazing (utilizing 2 pastures); (5) BC + ST + DS + SL; (6) ST + nitrogen fertilization + SL; and (7) contour furrowing (CF) + aerial seeding legumes + SL. Data were analyzed using years as a repeated measure. Treatments increased (p less than or equal to 0.05) total SC 320 kg/ha over controls, but did not affect species/species group composition. Treated pastures produced similar (p greater than or equal to 0.10) SC of 881 kg/ha. Total SC averaged 490 kg/ha more (p less than or equal to 0.05) in 1983, 1986, 1987, 1989, and 1990 than in 1984, 1985, and 1988. Perennial cool-season grass SC was greatest in 1986 (651 kg/ha). Peak annual grass SC (337-506 kg/ha) occurred in 1983 and 1984, the 2 years following ST or CF, and 1989 and 1990, the 2 years following severe drought. Although regression analyses showed fall, winter, and spring precipitation and temperature were closely related to spring SC, less than 50% of the variation in SC was accounted for when precipitation and temperature were summed on a 1-month, 2-month, or 3-month basis. Above-average fall and spring precipitation (September and April) resulted in the greatest total SC. Species composition varied temporally with changing weather conditions and management strategies.

Stocking rate and grazing frequency effects on Nebraska Sandhills meadows

Abstract Nearly one-half million ha of the Nebraska Sandhills is comprised of highly productive wet meadows. A study was conducted from 1998 to 2001 to evaluate the effects of stocking rate and grazing frequency on herbage dynamics, disappearance, and composition of a wet meadow dominated by cool-season vegetation. Defoliation characteristics were measured on 2 key species. Stocking rates were 148, 296, and 444 AUD ha−1 combined with a grazing frequency of 3 (F3) or 5 (F5) times. Cumulative standing crop disappearance and height reduction increased linearly with increasing stocking rate. Disappearance was 1,920, 2,700, and 3,090 kg ha−1 for the 148, 296, and 444 AUD ha−1 stocking rates, respectively. Greater disappearance at the highest stocking rate was expected based on calculated intake estimates for that stocking rate. Percentage of tillers grazed and percentage height reduction increased with stocking rate for both key species. Percentage of tillers grazed was greater under F3 compared to F5. This li...

Vegetation response to late growing-season wildfire on Nebraska Sandhills rangeland

This study examined the effects of late growing-season (September) wildfire on the subsequent production and species composition of upland Nebraska Sandhills prairie vegetation. Three paired-plots (burn and control), 0.5 ha in size were established in 1995 on sands range sites on each of 3 replications in west-central Nebraska. Soil temperature data were collected the following growing season and herbage standing crop and species composition data were collected for 3 growing seasons following the burn. During March through May of the 1996 growing season, soil temperature in the burn treatment was an average of 1.6 degrees C higher at both 15 and 30 cm depths compared to the control (P 0.05). Little bluestem [Schizchyrium scoparium (Michx.) Nash] was the species most adversely affected by burning. Percentage composition by weight of little bluestem in August 1996 averaged 8% under the burn treatment compared to 47% in the control. Other species and species groups, however, were more abundant in burned plots, thus offsetting the lesser amounts of little bluestem. Little bluestem exhibited a marked recovery during the second and third growing seasons after the burn. During the third growing season, percent composition of little bluestem averaged 46% and was not different between treatments (P > 0.05). Forbs were more abundant under the burn treatment compared to the control only during the first growing season following the burn (P < 0.05). DOI:10.2458/azu_jrm_v53i4_volesky

Supplementation and monensin effects on digesta kinetics. II. Cattle grazing winter range.

Sixteen ruminally cannulatcd beef steers grazing native summer range in the Northern Great PIains were assigned to Qtreatments in a 2 X 2 factorial arrangement. Main effects were barley grain and monensin. Rolled barley (RB) containing 7.5% molasses was fed at 0 and 1.36 kg l head”* day”. Steers received no monensin (M) or M released at 101 mg/d via a ruminal deiivery device. Forage intake and digestibiIity, ruminal fermentation, and ruminal passage rate were measured during trials in: (1) June, (2) July, and (3) August. Diet samples were collected from esophogeally fistuIated steers during each Mol. Dietary crude protein was greater (KO.05) during trials 1(15.2%)and 3 (14.3%) than in trial 2 (10.2%). In vivo organic matter (OM) digestibiiity, ruminal fluid passage rate, and fermentation variables varied by trial (PCO.01). Forage OM intake was reduced (P<O.lO) by RB, but was not influenced (-0.10) by M or the M and RB combination. In vivo OM digestibility was increased (PCO.05) by M, while RB had no effect. Particulate passage was not affected by M or RB but gastrointestimd tract fill was reduced by monensin (P<O.OS). Ruminal fluid passage rate was affected by the RB X M X Trial interaction (PCO.05). Within June and July, fluid passage rate was similar among treatments and ranged from 14.0 to 11.3 %/h, respectively. During trial 3, a RB X M interaction (PCO.05) increased fluid passage rate. Ruminai ammonia-N concentration was simiiar among treatments. Barley lowered (P<O.OS) ruminal pH and increased (PCO.10) totai volatile fatty acids. A RB X M X Trial interaction (P<O.OS) was noted for molar proportions of acetate, propionate, and butyrate. Within trials, RB, M, and their combination affected (P<O.Ol to PCO.10) acetate, propionafe, and butyrate. We conclude that barley, monensin, and forage quality infiuence ruminal fermentation, passage rate, and intake traits of steers grazing summer range.

Growth patterns of yearling steers determined from daily live weights.

Growth patterns for free-ranging yearling steers were quantified from daily live weights obtained with automatic scales which animals entered to obtain drinking water. Forty steers were monitored during each summer grazing period of 1986 and 1987. Frequency of watering and, thus, weighing on the automatic scales averaged 2.4 times/day. Significant (P & 0.01) quadratic relationships between live weight and Julian date were obtained. In 1986, predicted live weight of the steers peaked in late July to early August and then decreased through to the end of the grazing period in September. Live weight of the steers in 1987 followed a similar pattern although the late summer decrease was not as great as in 1986. When animals were periodically weighed using manual procedures, a lower rate of gain was measured in the second half than in the first half of the summer grazing period every year from 1983 through 1987. However, we were unable to specifically identify when these weight changes occurred until the automatic scales were used in 1996 and 1987. The automatic weighing equipment documented substantial within-day live weight variability among steers. This variability changed over the grazing period on a day-to-day basis. Within-day variability must be considered when establishing manual weighing schedules with conventional equipment. Live weight data in conjunction with other measurements will permit development of a more comprehensive animal-plant-climate model.

Steer performance on native and modified Northern Great Plains rangeland.

Research was conducted to quantify the effects of various range improvement treatments on diet quality and summer weight gain of steers grazing semiarid rangeland from 1983 through 1988. Treatments were: no treatment (i.e., control), contour furrowing, intertilling with a prototype range improvement machine and combinations of the range improvement machine, nitrogen fertilization, legume interseeding, or brush control. Diet quality was measured in 1987 and 1988. Data were analyzed using vitrious repeated measures analysis of variance models. Various relationships between the animal performance data and previously published herbage standing crop data were examined using standard correlation procedures. There were no significant treatment (P > 0.17) or year by treatment (P > 0.82) interaction effects relative to average daily gains, total gain steer-1, and gain ha-1. However, all year effects were significant (P < 0.05) for these variables with years accounting for about 67% of the observed variation in weight gains. Percentage crude protein in diet samples was greater in 1987 compared to the severe drought year of 1988 and was greater at the beginning than at the end of each grazing season (P < 0.05). However, in vitro dry matter digestibility of diets was greater in 1988 than 1987 primarily because digestibility of diets increased in 1988 from the beginning to the end of the trial. Significant correlations between gain steer-1 and gain ha-1 and early season total and perennial cool-season grass standing crop estimates indicated some rudimentary information is available at the beginning of each grazing season for predicting season-long weight gains. Because average daily gains during late spring and early summer were several fold greater than late season gains in all years except one, it is hypothesized that intensive early stocking strategies may be appropriate for stocker cattle grazing in the Northern Great Plains.

High-performance short-duration and repeated-seasonal grazing systems: effect on diets and performance of calves and lambs

Diet composition, performance, and production of calves and lambs grazing in combination were contrasted between a repeatedseasonal (RSG) (May-Sep.) and a 16-subunit, 1-herd high-performance short-duration grazing (HPSDG) system during 1983 and 1984. Animal numbers were adjusted with put-and-take sets of livestock to attain planned forage use levels for each cycle in HPSDG and comparable end-of-season use levels in both treatments. Diet quality, as estimated from fecal nitrogen (N), was better (P<0.05) for the RSG livestock especially during the first 2 grazing periods. Similarity indices of lamb and calf diet composition indicated compatibility of the lamb and calf mix in both grazing systems treatments. Calves primarily selected western wheatgrass (Agropyron smithii Rydb.) and annual grasses and lambs selected buffalograss (Buchloe dactyloides [Nutt.] Engelm.) and blue grama (Bouteloua gracilis [H.B.K.J Lag. ex Griffiths). Average daily gain (ADG) of RSG calves was greater in both 1983 and 1984 (0.52 and 0.68 kg/d) compared to HPSDG calves (0.39 and 0.62 kg/d,P<0.05). RSG lamb ADG (72.6 g/d) was greater in 1983 compared to HPSDG (45.4 g/d, P<0.05). Attained stocking rates were 35 and 25% higher in HPSDG during 1983 and 1984, respectively. Gain/ha, however, was greater for the HPSDG calves and combined livestock (calves + lambs) only during 1984 (P<0.05).

TECHNICAl NOTE: Estimating beef-cattle forage demand: Evaluating the animal unit concept

The objective of this experiment was to evaluate the effect of BW and physiological status of a beef animal on forage intake. The experiment was repeated over 2 yr with 6 replications of 3 treatments per year: cow-calf pair (CCP, BW = 629 kg), nonlactating cow (NLC, BW = 503 kg), and yearling steer (YS, BW = 305 kg). The CCP was treated as one unit, with the sum of cow BW and calf BW comprising CCP BW. Calves averaged 42 d of age and 73 kg at the start of the experiment each year. Animals were housed in individual pens and fed grass hay harvested from subirrigated meadow (11% CP) in quantities sufficient for ad libitum intake. Intake of DM, OM, DM that disappeared in vitro, and NDF were greatest (P 0.05) from each other. When expressed as a percentage of metabolic BW (BW0.75), intake of DM, OM, DM that disappeared in vitro, and NDF were greatest (P < 0.01) for CCP, intermediate for NLC, and least for YS. Results indicate that intake differences among cattle of different physiological states should be considered when calculating forage demand for stocking rate or feeding purposes.

Diet Composition of Cattle Grazing Sandhills Range During Spring

Abstract The grazing season on upland Sandhills range traditionally begins in mid-May when the dominant warm-season grasses have initiated growth. Initiating grazing earlier would improve efficiency of use of cool-season plants and reduce the time period during which hay is fed. A 2-year study was conducted to determine nutrient and botanical composition of cattle diets when grazing upland Sandhills range during spring. Diets were collected from esophageally-fistulated cows on 10 April, 1 May, and 22 May each year. Concurrently, current-year, and residual herbage was clipped to determine pasture composition and calculate preference indices for the primary plant species and groups. Averaged across dates, needleandthread (Stipa comata Trin. & Rupr.), bluegrasses (Poa spp.), and sedges (Carex spp.) accounted for 19% of the total herbage and 68% of the current-year herbage yield. These species constituted an average of 74% of cow diets. Diet composition of sedges was less on 10 April than on 22 May (P < 0.05), whereas similar amounts of needleandthread and bluegrasses were present on all dates. Preference indices indicated strong selection for species with abundant current-year growth and avoidance of residual herbage. Crude protein content of diets was less on 10 April (10.7%) than on 1 May or 22 May (13.9%, P < 0.05), likely because of a greater amount of residual herbage present in 10 April diets. Overall quality of diets would meet requirements of average spring-calving cows; however, grazing management strategies would need to account for the limited availability of current-year growth during spring, particularly April, to ensure that cattle are meeting their nutrient needs.