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Three studies were conducted to evaluate late summer protein supplementation for growing steers on Northern Great Plains rangeland. In Experiment 1, crossbred yearling steers (N = 80 per year, mean initial live-weight = 275 kg) were allotted to 1 of 2 treatments replicated in 3 pastures in each of 3 years. Treatments were summer-long grazing with or without protein supplementation in late summer. Protein supplement (26% crude protein) was fed at a rate of 1.68 kg (dry matter basis) every third day. In 1995, a third treatment was added to additional pastures consisting of 1.62 kg (dry matter basis) of a 40% crude protein supplement fed every third day. There was no weight gain response to protein supplementation. In Experiment 2, yearling steers grazing rangeland from May to September were fed either no supplement, 1.5 kg of a 22% crude protein safflower meal-based supplement, 1.2 kg of 26% soybean meal-based supplement or 1.2 kg of a 26% safflower and soybean meal-based supplement every third day in late summer. Live-weight gain, forage intake, and digestibility were not affected by supplementation. A third experiment using ruminally cannulated steers fed grass hay and the 3 protein supplements based on safflower and soybean meals showed an increase in ruminal ammonia concentrations but no other appreciable change in ruminal fermentation with protein supplementation. Supplementation with as much as 648 grams of protein every third day was not a viable means to increase gains of steers grazing Northern Great Plains rangelands during late summer under the conditions of this experiment.

A 3-year study was conducted to evaluate grazing strategies for production of growing cattle during summer on Northern Great Plains rangeland. Crossbred yearling steers (N = 123 per year, avg initial weight = 275 kg) were allotted to 1 of 2 treatments replicated in 3 pastures. Treatments were season-long grazing of pastures at recommended stocking rates assuming a 4-month grazing period or intensive-early grazing of pastures stocked at the same rate assuming only a 2-month grazing season. Precipitation in 1993 was 169% of normal resulting in greater forage quality than in other years and no differences were observed in weight gains between treatments during 1993. In 1994 and 1995, steers in the intensive-early stocked pastures gained less weight during the 2 months of grazing than did those in the season-long stocked pastures; however, gain per hectare was greater in the intensive-early stocked pastures. Intensive-early stocking with growing steers may be a viable means to overcome limited forage quality during late summer in the Northern Great Plains and to maximize forage utilization in years of abundant forage. DOI:10.2458/azu_jrm_v55i2_grings

An understanding of the impacts of grazing during and following drought on rangeland ecosystems is critical for developing effective drought management strategies. This study was designed to examine the effects of drought and grazing on blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] and western wheatgrass [Pascopyrum smithii Rydb. (Love)] tiller growth dynamics. Research was conducted from 1993 to 1996 at the Fort Keogh Livestock and Range Research Laboratory located near Miles City, Mont. An automated rainout shelter was used during 1994 to impose a severe late spring to early fall (May to October) drought on 6 of twelve, 5- x 10-m non-weighing lysimeters. Twice replicated grazing treatments were: 1) grazed both the year of (1994) and the year after (1995) drought; 2) grazed the year of and rested the year after drought; and 3) no grazing either year. Drought had minimal impact on tiller relative growth rates of plants grazed twice, although it reduced (P less than or equal to 0.01) rates of axillary tiller emergence for blue grama (79%) and western wheatgrass (91%), respectively. Defoliation periodically increased relative growth rates (P less than or equal to 0.05) and tiller emergence (P less than or equal to 0.01) of both species. Neither drought nor grazing affected tiller densities or tiller replacement rates of either species nor did they affect productivity of blue grama. Drought, however, reduced (P less than or equal to 0.01) productivity of western wheatgrass 50% in 1994 whereas grazing reduced productivity (P less than or equal to 0.01) by 46% in 1994 and 69% in 1995. Moderate stocking levels (40-50% utilization) during and after drought did not adversely affect the sustainability of these dominant native grasses. DOI:10.2458/azu_jrm_v55i1_eneboe

Presence of invading annual bromes (Bromus spp.) can alter seasonal patterns of forage production and quality and require management changes for efficient use of infested rangelands in the Northern Great Plains. We studied biological impacts of the presence of brome by comparing brome infested rangeland to similar sites in which brome had been suppressed with autumn applications of atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)- 1,3,5-triazine-2,4-diamine] at 0.56 kg ha(-1) in 1992 and 1993. Each treatment was randomly assigned to three, 12-ha pastures. Vegetation was measured for 5 months (May to September) each year from 1993 to 1995. Each pasture was stocked with 8 cross-bred steers (Bos taurus) from mid-May to mid-September 1993 and 1995 and to mid-August 1994. The forage base varied temporally by date and year, but generally was not less than 800 kg ha(-1). Brome suppression increased (P less than or equal to 0.05) crude protein concentration for western wheatgrass (Pascopyrum smithii Rydb. [Love]) in July (7.1 vs. 9.1%) and August (6.0 vs. 7.1%). With the variation in annual brome stands among years, as influenced by growing conditions, this experiment demonstrated that improvement in forage nutritional quality can be expected from suppression of annual bromes on semiarid rangelands. DOI:10.2458/azu_jrm_v54i6_haferkamp

Presence of annual bromes (Bromus spp.), introduced annual weedy grasses, can alter seasonal patterns of forage production and quality and require management changes for efficient use of infested rangelands. We determined biological impacts of the presence of brome by comparing livestock performance on brome infested rangeland to similar sites on which brome had been suppressed by autumn application of atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)- 1,3,5-triazine-2,4-diamine] at 0.56 kg ha(-1) in 1992 and 1993. Each treatment was randomly assigned to three, 12-ha pastures. Vegetation was measured for 5 months (May to September) each year from 1993 to 1995. Each pasture was stocked with 8 crossbred steers of British breed origin (Bos taurus) from mid-May to mid-September 1993 and 1995 and to mid-August 1994. Initial body weights averaged 329 kg SD = 31 in 1993, 273 kg SD = 14 in 1994, and 272 kg SD = 21 in 1995. Brome suppression and environment influenced plant species in diets, diet quality, and livestock performance. Brome suppression reduced percentage of annual grasses in diets from 14% to 10%. Annual grasses were replaced in the diet by a variety of forb and grass species [western wheatgrass [Pascopyrum smithii Rydb. (Love)], and blue grama [Bouteloua gracilis [H.B.K.] Lag. ex Griffiths]], with specific replacement depending on year and month. Steer gains were increased from 0.92 to 1.04 +/- 0.02 kg head(-1) day(-1) (P < 0.02) and from 69 to 81 +/- 2.8 kg ha(-1) (P < 0.05) with brome suppression. This experiment demonstrated that improvement in livestock performance can be expected with the suppression of annual bromes on semiarid rangelands. DOI:10.2458/azu_jrm_v54i6_haferkamp2

Drought and herbivory frequently influence North American rangelands. While these influences may temporarily reduce vegetative cover, their mutual influence on the available seedbanks which might occupy new safe sites is unclear. We examine effects of drought and grazing upon pre- and post-drought plant root distribution and germinable seed bank to determine 1) if the response of root distributions to drought depends upon grazing use and 2) if the presence of germinable seeds is altered significantly by drought and grazing. Using twelve, 5 X 10 m non-weighing lysimeters with an automated rainout shelter, we documented root intercepts in situ using a minirhizotron from 1993-1996. Seed bank samples were incubated in a greenhouse to determine seedling emergence. Roots were fewer in shallow soil layers in grazed plots than ungrazed plots by the end of the study, irrespective of drought. Roots in deeper (Bw horizon) soil layers were fewer during drought, but were not influenced by grazing. Seed bank composition results suggest that perennial grasses were a small portion of the seed bank. Cool-season annual grass seeds accumulated after drought. Without drought, forb seed banks increased with grazing. Thus while shallow roots may decrease during drought, in the year following drought grazing may decrease aboveground net primary production, and allow large accumulations of cool-season annual grass seed in a northern mixed grass prairie. DOI:10.2458/azu_jrm_v54i3_hild

The effects of animal age and sex on chemical and botanical composition of diets of cattle grazing native rangelands were evaluated in a 2-year study. Samples were collected monthly from June through October using esophageally cannulated suckling calves, yearling heifers, mature cows, and mature steers. Dietary crude protein and digestibility differed among animal classes, but these differences varied over time. These 2 diet quality indicators did not vary in the same manner over time for all animal classes. Dietary crude protein varied from a low of 7.2% for steers in August 1994 to a high of 14.3% for heifers in June 1993. In vitro digestibility varied from a low of 50.7% for cows in October 1993 to a high of 74.3% for calves in June 1993. Botanical composition of diets varied with animal class and sampling date with interactions among these. Cool-season grasses accounted for an average of 70% of the diet with a range of 33 to 90%. Shrubs varied from 1 to 61% of the diet. Differences in chemical composition among age and sex classes of cattle grazing native rangeland during the growing season may be partially related to differences in botanical composition of diets. Animals used to obtain diet samples should, therefore, be of similar physiological state and age as animals being monitored for performance. DOI:10.2458/azu_jrm_v54i1_grings