Winter wheat (Triticum aestivum L.) grown as a dual‐purpose crop is a unique and economically important resource, especially in the southern Great Plains. Since the last major review of grazing effects on grain yield, in 1956, wheat cultivars have been developed that may affect the productivity of the grazing‐grain enterprise. Thus, we decided to review current research on grazing winter wheat and the effects on grain yield in light of earlier information. During a year of favorable precipitation and adequate to excess soil fertility, tall winter wheat cultivars grazed prior to jointing experienced increased grain yield relative to nongrazed wheat, because of reduced lodging. Current research suggests that the grain yield of semidwarf wheat cultivars is more sensitive to forage removal than for tall cultivars. Grazing termination dates necessary to prevent grain yield reduction of semidwarf cultivars also appear to be much earlier than for taller wheat cultivars. The reason for the difference in grazing tolerance is not clear; however, research suggests that semidwarf cultivars require maximum leaf area at anthesis for maximum grain yield. Tall wheat cultivars are not affected in the same manner, and decreased leaf area due to later grazing does not reduce grain yield of taller wheat cultivars to the same extent as for the semidwarf cultivars. Thus, taller wheat cultivars have the potential for extending the grazing period for livestock producers while producing grain yield similar to that of semidwarf wheat cultivars (which generally produce more grain in a nongrazed situation).

The economic impact of timing of grazing termination in the wheat (Triticum aestivum L.) grain‐stocker cattle (Bos sp.) enterprise has not been elucidated. A 4‐yr study used the first hollow stem stage of growth in ungrazed wheat as a grazing termination indicator and the subsequent effect on net return. First hollow stem is the stage at which hollow stem can first be identified above the crown; it occurs prior to the growing point reaching the soil surface. Net return was maximized when grazing was terminated at first hollow stem. Grain yield decreased (P< 0.05) 83 kg ha−1 d−1 as cattle grazed past first hollow stem. Increased weight gain by cattle was not sufficient to offset grain yield losses. Since hollow stem formation was delayed in grazed wheat, producers who use semidwarf wheat as a dual‐purpose crop should monitor the morphological stage in ungrazed areas of the field to determine the optimum time to terminate grazing.

One in vitro and one in vivo metabolism experiment were conducted to examine the effects of supplemental Zn on ruminal parameters, digestion, and DMI by heifers fed low-quality prairie hay supplemented with urea. In Exp. 1, prairie hay was incubated in vitro for 24 h with five different concentrations of supplemental Zn (0, 5, 10, 15, and 20 ppm) and two concentrations of supplemental Mn (0 and 100 ppm), both provided as chloride salts. Added Mn increased (P < 0.02) IVDMD, but added Zn linearly decreased (P < 0.03) IVDMD. Added Zn tended to increase the amount of residual urea linearly (P < 0.06) at 120 min and quadratically (P < 0.02) at 180 min of incubation, although added Mn counteracted these effects of added Zn. Six 363-kg heifers in two simultaneous 3 x 3 Latin squares were fed prairie hay and dosed once daily via ruminal cannulas with urea (45 or 90 g/d) and with Zn chloride to provide the equivalent of an additional 30 (the dietary requirement), 250, or 470 ppm of dietary Zn. After a 7-d adaptation period, ruminal contents were sampled 2, 4, 6, 12, 18, 21, and 24 h after the supplement was dosed. Supplemental Zn did not alter prairie hay DMI (mean = 4.9 kg/d) or digestibility, although 470 ppm added Zn tended to decrease (P < 0.06) intake of digestible DM, primarily due to a trend for reduced digestibility with 470 ppm supplemental Zn. Zinc x time interactions were detected for both pH (P = 0.06) and NH3 (P = 0.06). At 2 h after dosing, ruminal pH and ruminal ammonia were linearly decreased (P < 0.05; P < 0.01) by added Zn. At 5 h after feeding, ruminal pH was linearly increased (P < 0.05) by added Zn, suggesting that added Zn delayed ammonia release from urea. The molar proportion of propionate in ruminal fluid was linearly and quadratically increased (P < 0.02; P < 0.01) whereas the acetate:propionate ratio was linearly and quadratically decreased (P = 0.02; P < 0.05) by added Zn. Through retarding ammonia release from urea and increasing the proportion of propionate in ruminal VFA, Zn supplementation at a concentration of 250 ppm may decrease the likelihood of urea toxicity and increase energetic efficiency of ruminal fermentation.

Two experiments were conducted to examine the effect of previous BW gain during winter grazing on subsequent growth, carcass characteristics, and change in body composition during the feedlot finishing phase. In each experiment, 48 fall-weaned Angus x Angus-Hereford steer calves were assigned randomly to one of three treatments: 1) high rate of BW gain grazing winter wheat (HGW), 2) low rate of BW gain grazing winter wheat (LGW), or 3) grazing dormant tallgrass native range (NR) supplemented with 0.91 kg/d of cottonseed meal. Winter grazing ADG (kg/d) for HGW, LGW, and NR steers were, respectively, 1.31, 0.54, 0.16 (Exp. 1) and 1.10, 0.68, 0.15 (Exp. 2). At the end of winter grazing, four steers were selected randomly from each treatment to measure initial carcass characteristics and chemical composition of carcass, offal, and empty body. All remaining steers were fed a high-concentrate diet to a common backfat end point. Six steers were selected randomly from each treatment for final chemical composition, and carcass characteristics were measured on all steers. Initial fat mass and proportion in carcass, offal, and empty body were greatest (P < 0.001) for HGW, intermediate for LGW, and least for NR steers in both experiments. Live BW ADG and gain efficiency during the finishing phase did not differ (P = 0.24) among treatments, but DMI (% of mean BW) for NR and LGW was greater (P < 0.003) than for HGW steers. Final empty-body composition did not differ (P = 0.25) among treatments in Exp. 1. In Exp. 2, final carcass and empty-body fat proportion (g/kg) was greater (P < 0.03) for LGW and NR than for HGW steers. Accretion of carcass fat-free organic matter was greater (P < 0.004) for LGW than for HGW and NR steers in Exp. 1, but did not differ (P = 0.22) among treatments in Exp. 2. Fat accretion in carcass, offal, and empty body did not differ (P = 0.19) among treatments in Exp. 1, but was greater (P < 0.05) for LGW and NR than for HGW steers in Exp. 2. Heat production by NR steers during finishing was greater (P < 0.02) than by HGW steers in Exp. 1 and 2. Differences in ADG during winter grazing and initial body fat content did not affect rate of live BW gain or gain efficiency during finishing. Feeding steers to a common backfat thickness end point mitigated initial differences in carcass and empty-body fat content. However, maintenance energy requirements during finishing were increased for nutritionally restricted steers that were wintered on dormant native range.

W inter wheat (Triticum aestivum L.) production in the southern Great Plains is dominated by dual-purpose management schemes that provide a winter forage source for stocker cattle (Bos taurus L.) and grain production from the same crop. Relative emphasis on forage versus grain is highly impacted by a producer's personal preference, but factors intrinsic to a given crop season are also infl uential, such as forage availability before cattle turnout and the relative pricing of wheat versus beef. Wheat producers in the southern plains do not discriminate heavily among cultivars for dual-purpose capability, and most hard winter wheat breeding programs do not include dual-purpose adaptation as a selection criterion.A breeding-oriented emphasis is justifi ed, however, by the 40% lower rate of genetic gain observed for yield potential under dual-purpose (0.9% yr −1 ) versus grain-only (1.3% yr −1 ) production systems (Khalil et al., 2002). The yield difference between grain-only and dual-purpose systems (Winter and Thompson, 1990;Carver et al., 2001) can be attributed largely to the 4-wk earlier planting date essential to forage-biomass accumulation . Hence producers who choose a cultivar for dual-purpose production may prioritize early stand establishment with rapid canopy closure.The dual-purpose system provides an integral selection environment for the development and evaluation of experimental breeding lines (Thapa et al., 2010). Lines that reach candidate status are expected to excel in a grain-only system as well as they do in a dual-purpose system. The hard red winter (HRW) wheat cultivar 'Duster' (Reg. No. CV-1065,

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Two grazing trials were conducted in separate years on a 5.86 ha winter wheat (Triticum aestivum var. Chisholm) pasture divided into 10 experimental paddocks. Paddocks were differentially grazed with beef steers to produce an array of different herbage mass levels, espressed as kg dry matter @M)/ha. Each experimental paddock was then continuously stocked with 3 beef steers during each 7-day forage intake trial. Daily forage intake, expressed as kg organic matter (OM)/lOO kg body weight (BW), was estimated from fecal output (Cr,O, dilution) of the beef steers and in vitro organic matter disappearance of esophageal masticate collected from each paddock. Estimated daily gain was calculated from forage intake and net energy values calculated from organic matter disappearance data. Forage intake, organic matter disappearance, and estimated daily gain were related to daily herbage allowance, expressed as kg DM 100 kg BW day-l, and herbage mass utilizing a quadratic equation with a plateau function. As herbage allowance increased, organic matter disappearance improved (Y = 62.18 + 1.08 herbage allowance-.022 herbage allowance2; r2 = .64, MSE = 5.06) as did forage intake (Y = 1.3 + .12 herbage allowance-.003 herbage allowanced; r2 = .52, MSE = .07), and estimated daily gain (Y =-.059 + .12 herbage allowance-.003 herbage allowance2; r2 = .59, MSE = .07). Plateaus were achieved at herbage allowance between 20 to 24 kg DiU 100 kg BW* day-l. Results of this study indicate forage intake and estimated daily gain declined severely as herbage allowance fell below 20 to 24 kg DM 100 kg BW day-l. This data may provide a threshold herbage allowance for initiation of energ supplementation programs for growing cattle on wheat pasture.

Farmers in the southern Great Plains utilize wheat {Triticum aestivum L.) as a forage and grain crop (dual purpose). The objective of this study was to evaluate the impact of dual-purpose management on wheat grain yield using two multiyear data sets that included a diverse group of commercially released hard winter wheat cultivars and a limited number of advanced experimental breeding lines. Paired experiments were conducted from 1991 to 2010 at the Wheat Pasture Research Unit near Marshall, OK. Averaged across environments and years, grazing reduced wheat grain yield by 7% when both grazed and nongrazed plots were sown early to encourage lush forage growth. Regression analysis predicted an increase in wheat grain yield as a result of grazing in lower-yielding (<1100 kg ha"^) environments but a decrease when nongrazed yield potential exceeded this value. When planting was manipulated to allow comparison of dual-purpose and grain-only systems, dual-purpose management reduced grain yield by 14% as compared to grain-only management. Grazing increased grain volume weight in both experiments by approximately 1%. Our results indicate that yield reductions in dual-purpose wheat relative to grain-only wheat arise due to the combination of grazing and earlier-than-optimal planting date.