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1.
In a 3-yr study, 135 crossbred steers (330 ± 10 kg) were used in a randomized complete block design to evaluate corn dried distillers grains plus solubles (DDGS) fed to yearling steers as a substitute for forage and N fertilizer and its effect on N use efficiency in yearling steers grazing smooth bromegrass pastures. Steers were initially stocked at 6.8 animal unit months (AUM)/ha on nonfertilized smooth bromegrass pastures (CONT), at 9.9 AUM/ha on smooth bromegrass pastures fertilized with 90 kg of N/ha (FERT), or at 9.9 AUM/ha on nonfertilized smooth bromegrass pastures with 2.3 kg (DM) of DDGS supplemented daily per steer (SUPP). Paddock was the experimental unit, with 3 replications per treatment per year for 3 yr. Paddocks were strip-grazed, and put-and-take cattle were used to maintain similar grazing pressure among treatment paddocks during the 160-d grazing season. Steers consumed less forage (P < 0.01), but total N intake for SUPP was greater (P < 0.01) per steer and per hectare than for FERT, and both were greater (P < 0.01) than for CONT. Nitrogen retention for steers in the SUPP treatment was increased (P < 0.01) by 31% compared with N retention in the CONT and FERT treatments. Nitrogen retention per hectare for SUPP was 30 and 98% greater (P < 0.01) than N retention per hectare for FERT and CONT, respectively. Nitrogen excretion per steer and per hectare were also greater (P < 0.01) for SUPP than FERT, and both were increased (P < 0.01) compared with CONT. Animal N use efficiency was similar (P = 0.29) for steers in the CONT, FERT, and SUPP treatments. However, system-based N use improved (P < 0.01) by 144% for SUPP compared with FERT. The DDGS increased N intake and N excretion in yearling steers. However, because of improvements in BW gain and increases in stocking rate of pastures, DDGS can be a useful tool to increase the efficiency of N use in smooth bromegrass grazing systems.  相似文献   

2.
Tall fescue (Festuca arundinacea Schreb.) infected with the endophyte Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin) causes fescue toxicosis in cattle grazing the forage, but effects of the endophyte were considered to be abated soon after removal of the animals from pastures. Tasco-Forage, a proprietary extract from the brown seaweed Ascophyllum nodosum, is a known source of cytokinins and has increased antioxidant activity in both plants and the animals that graze the forage. Tasco was applied at 0 and 3.4 kg/ha to infected and uninfected tall fescue pastures in Virginia and Mississippi. Forty-eight steers grazed the pastures at each location during each of 2 yr (n = 192) before being transported to Texas for feedlot finishing. On arrival at the feedlot, steers from Tasco-treated pastures had higher (P < 0.01) monocyte phagocytic activity and tended (P < 0.07) to have higher major histocompatibility complex class II expression than steers that grazed the untreated pastures. A depression (P < 0.05) in monocyte immune cell function due to grazing infected fescue was detected throughout the feedlot finishing period but was reversed by Tasco. Rectal temperatures were elevated (P < 0.07) in steers that had grazed the infected tall fescue when they arrived in Texas, but by d 14 no difference was detected. However, by d 28 the temperature effects of infected tall fescue were reversed. Steers that had grazed infected fescue had lower (P < 0.01) rectal temperatures on d 112 of the feedlot period, demonstrating a much longer-lasting effect of the endophyte on thermoregulatory mechanisms than previously thought. Steers that had grazed Tasco-treated pastures had higher (P < 0.01) rectal temperatures on d 56 than steers that had grazed untreated fescue. Steers that had grazed the Tasco-treated pastures had higher marbling scores (P < 0.05) regardless of the endophyte, but no effect of Tasco or endophyte on gain was measured. Our data suggest that Tasco application to tall fescue pastures alleviated some of the negative effects of tall fescue toxicity.  相似文献   

3.
We evaluated elk (Cervus elaphus), mule deer (Odocoileus hemionus), cattle (Bos taurus), and domestic sheep (Ovis aries) diet composition, diet overlap, and forage selection on aspen (Populus tremuloides Michaux)–sagebrush (Artemisia spp. L.) summer range in northeastern Nevada to understand potential for forage competition to provide better information for managing these communities. Diets were determined through microhistological fecal analysis from 1998 to 2000, and forage selection was evaluated at feeding sites in aspen and sagebrush communities in 1999 and 2000. Elk spring diets were the most diverse in composition; summer elk diets were dominated by forbs (59%–78%); deer consumed mostly woody browse (64%–72%); and cattle and sheep ate mostly graminoids. Lupines (Lupinus spp. L.) constituted ≥ 11% of elk, deer, and sheep diets in summer. Spurred lupine (Lupinus caudatus Kellogg) was the lupine typically selected in feeding sites and greatest consumption occurred in summer when total alkaloid levels were lowest. Highest diet overlap was between cattle and sheep in 1999 (68%) and lowest between deer and cattle in 2000 (3%). Summer elk and deer diets overlapped moderately (45%–59%). Diets did not differ between elk in spring with sheep, elk in summer with deer and sheep, or cattle with sheep. Cattle foraged selectively on forbs in aspen communities (68%) and on graminoids in sagebrush communities (88%), reflecting relative forage availabilities. We detected no differences among elk, cattle, and sheep for forage selection in aspen communities. Electivity indices indicated elk preferred forbs in aspen and sagebrush communities; cattle preferred graminoids in sagebrush; and foraging sheep preferred forbs in aspen. Our results suggest potential for forage competition among ungulates on aspen–sagebrush summer range is highest for forbs in aspen communities. Monitoring productivity and use of key forage species, particularly forbs in aspen communities, should complement management objectives on shared aspen–sagebrush summer range.  相似文献   

4.
To evaluate the effects of balancing total diet degradable intake protein with dietary total digestible nutrients (TDN), we conducted two studies during 2 yr with 100 (302 +/- 8 kg initial BW) mixed-breed yearling steers and 12 ruminally cannulated steers (526 +/- 28 kg). Steers individually received one of four supplements 5 d/wk while grazing dormant native tallgrass prairie. Supplements included: 1) corn and soybean meal, balanced for total diet degradable intake protein in relation to total diet TDN (CRSBM), 2) corn and soybean hulls, equal in supplemental TDN to CRSBM (CORN), 3) soybean meal, equal in supplemental degradable intake protein to CRSBM (SBM), or 4) a cottonseed hull-based control supplement (CONT). At each feeding (5 d/wk), steers consumed 13.6, 13.6, or 4.2 g of dry matter/kg of body weight, or 178 g of DM, respectively, of supplement. Steers fed CRSBM had greater (P < 0.01) average daily gain than cattle fed CORN or SBM. Feeding soybean meal (CRSBM, SBM) resulted in improved (P < 0.01) efficiency of supplement. Grazing time, intensity, and harvesting efficiency were reduced (P < 0.05) by corn supplementation (CRSBM and CORN), whereas the number of grazing bouts per day was increased (P < 0.08). Intake and digestibility of forage organic matter were reduced (P < 0.01) for steers supplemented with corn (CORN and CRSBM) vs cattle not fed corn (SBM and CONT). Total diet digestibility (P < 0.12) and digestible organic matter intake (P < 0.01) were greater for CRSBM-fed steers than for cattle fed either CORN or SBM. Steers fed CRSBM had greater (P < 0.01) fecal nitrogen and serum insulin than cattle fed CORN or SBM. Corn-fed cattle had lesser (P < 0.01) fecal pH and ADF concentrations than steers not consuming grain. Cattle fed supplements with soybean meal (CRSBM and SBM) had greater (P < 0.01) serum urea nitrogen than steers fed supplements without soybean meal (CORN, CONT). Supplemented steers grazing dormant tallgrass prairie had a greater rate of gain, with the greatest response in animal performance occurring when grain supplements were balanced for total diet degradable intake protein in relation to total diet TDN. These results lead us to suggest that grain-supplemented cattle grazing dormant tallgrass prairie require a balance of total diet degradable intake protein in relation to total diet TDN to optimize animal performance.  相似文献   

5.
Fall-weaned crossbred steer calves (n = 300; 184 +/- 2.9 kg) received either no implant (Control) or were implanted with Synovex-C (SC = 10 mg estradiol benzoate + 100 mg progesterone), Synovex-S (SS = 20 mg estradiol benzoate + 200 mg progesterone), or Revalor-G (RG = 8 mg estradiol-17beta + 40 mg trenbolone acetate) to determine the effects of implants on weight gain during winter grazing on dormant tallgrass prairie, subsequent grazing and finishing performance, and carcass characteristics. Steers grazed two dormant tallgrass prairie pastures from October 16, 1996, until March 29, 1997 (164 d), and received 1.36 kg/d of a 25% CP supplement that supplied 100 mg of monensin/steer. Following winter grazing, all steers were implanted with Ralgro (36 mg zeranol) and grazed a common tallgrass prairie pasture until July 17 (110 d). After summer grazing, all steers were implanted with Revalor-S (24 mg estradiol-17beta + 120 mg trenbolone acetate), and winter implant treatment groups were equally allotted to four feedlot pens. Steers were harvested November 17, 1997, after a 123-d finishing period. Daily gains during the winter grazing phase averaged .28, .32, .32, or .35 kg/d, respectively, for Control, SC, SS, or RG steers and were greater (P < .01) for implanted steers than for Controls. Summer daily gains were similar (1.05 +/- .016 kg/d; P > or = .61) for all treatment groups. Feedlot daily gains were also similar (1.67 +/- .034 kg/d; P > or = .21), with implanted steers weighing 14 kg more than Control steers (P = .05) at harvest, despite similar management during summer grazing and feedlot phases. Control steers tended (P = .06) to have lower yield grades. There were no differences (P = .99) in marbling between implanted and nonimplanted steers. Steers implanted during the wintering phase had increased skeletal and overall (P < .01) carcass maturities compared with nonimplanted steers, which resulted in more "B" and "C" maturity carcasses. Because carcass maturity score affects quality grade, the increased maturities of implanted steers resulted in a $9.04 decrease in carcass value/100 kg (P < .01) compared with Controls. The results of this study indicate that growth-promoting implants are efficacious for cattle wintered on dormant native range despite low daily gains. This increased weight is maintained through the summer grazing and feedlot phases; however, the benefit of the increased weight may be offset by decreased carcass quality grade and value due to increased carcass maturity.  相似文献   

6.
Five studies (trials I to V) were conducted on ranches located in the intermountain west to determine the effect of sustained-release parasite control (Ivomec SR Bolus®, Merial Limited, Rahway, NJ) on cattle performance and fecal nematode egg counts. Cattle in trials I to IV grazed irrigated meadows for 156 d (n=250 yearling heifers), 117 d (n=250 yearling steers), 85 d (n=150 yearling heifers), and 85 d (n=60 calves), respectively. In trial V, yearling steers (n=200) grazed dry high-desert range for 190 d. Weights and fecal samples were taken initially and at the end of each trial. Cattle were paired by weight and randomly assigned to treatment 1) Control: no deworming for the grazing period or 2) SRI: sustained-release ivermectin. For trials I to V, total gain difference (SRI minus Control) and ADG difference were 10.0 kg and 0.064 kg/d (P<0.001), 13.9 kg and 0.119 kg/d (P<0.001), 6.9 kg and 0.082 kg/d (P<0.01), 8.0 kg and 0.095 kg/d (P=0.05), and −0.48 kg and −0.003 kg/d (P=0.86), respectively. For trials I to V, mean initial, final Control, and final SRI fecal egg counts in eggs per gram were 0.4, 15.2, and 0.1; 6.0, 8.3, and 0.0; 75.8, 57.0, and 16.6; 76.0, 39.1, and 0.0; and 1.8, 2.0, and 0.0; respectively. Treatment of cattle grazing irrigated meadows with sustained-release ivermectin resulted in improved weight gain and fecal egg counts that were diminished to near zero. No differences (P>0.05) in weight gains were detected for cattle administered sustained-release ivermectin that grazed dry high desert range.  相似文献   

7.
From Nov 22, 1983 through May 15, 1984, 36 crossbred steers were allotted into 3 treatment groups (12/group) and were grazed on separate 3.4-hectare pastures. On Nov 22, 1983, the steers were administered a single morantel sustained-release bolus (MSRB), orally (group 1), or a single dose of thiabendazole (TBZ; 66 mg/kg of body weight, orally; group 2), or were left untreated (group 3; controls). Animal weights, nematode egg counts in fecal specimens, and plasma pepsinogen concentrations were monitored monthly. At the termination of the study, 4 steers from each treatment group were slaughtered and necropsied and worm counts were determined. A set of parasite-free tracer calves (3/treatment group) were grazed with each treatment group for 1 month, beginning on Nov 22, 1983; a second set of tracer calves (3/group) were grazed with each treatment group for 1 month, beginning Apr 3, 1984. At the end of their respective grazing periods, tracer calves were held for 3 weeks and then were slaughtered and necropsied and their worm counts were determined. Mean nematode egg counts in fecal specimens of group 1 (MSRB treated) were significantly lower (P less than 0.05) than that of the TBZ-treated or nontreated steers. Differences in worm counts were not found between treatment groups. Differences in worm counts of tracer calves were not found among the 3 groups for November 1983 nor for April 1984. Steers treated with the MSRB had a higher mean weight gain (P less than 0.06) than did the control or TBZ-treated steers.  相似文献   

8.
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9.
To evaluate effects of previous forage systems on feedlot performance, yearling Hereford steers (average initial weight of 249 kg) were grazed on tall fescue (TF), smooth bromegrass-red clover (BG-RC) or orchardgrass-red clover (OG-RC) pastures before finishing. Serial slaughter was utilized during the first 2 yr of this study to determine changes in carcass characteristics throughout finishing, while steers were slaughtered at approximately 29% body fat during the third year. Steers grazing TF entered the feedlot at lighter weights and maintained lighter weights throughout finishing (P less than .05) even though dry matter intakes and feed conversions were similar (P greater than .05) among treatments. Steers that previously grazed TF had less (P less than .05) body fat, body protein, fat thickness and marbling, smaller (P less than .05) ribeye areas and lower (P less than .05) USDA yield and quality grades than than those that grazed BG-RC and OG-RC. However, linear contrasts indicated that steers grazing TF were compensating in ribeye area, marbling and quality grade as days in feedlot increased. This was confirmed in the third-year study, since carcass characteristics were similar among all steers. During the third year, linear and quadratic contrasts indicated that steers that grazed TF partially compensated in body protein. As days in feedlot increased, live and hot carcass weights, body fat, fat thickness, kidney, pelvic and heart fat, marbling, and USDA yield and quality grades increased (P less than .05), while ribeye area and body protein plateaued. Although carcass characteristics were similar among treatments, steers backgrounded on TF entered the feedlot at lighter weights, and partially compensated in weight after 134 d of finishing.  相似文献   

10.
The spread of the invasive, Eurasian spotted knapweed (Centaurea maculosa Lam.) across the northwestern United States would be reduced if livestock regularly consumed it. We determined if white-face yearling ewes (n = 36) conditioned for 12 days to fresh-cut spotted knapweed, with or without molasses, would increase their use of it during a 5-day field trial and/or a 4-day drylot trial. Ewes were assigned to one of three treatments: ewes not conditioned to spotted knapweed or molasses (NC), ewes conditioned to spotted knapweed (SK), or ewes conditioned to spotted knapweed sprayed with liquid beet molasses (SKM). During conditioning, all groups consumed high amounts of their feed. Nonconditioned ewes (NC) consumed less than ewes conditioned to spotted knapweed (SK, SKM), indicating spotted knapweed did not inhibit initial consumption. In the field, SKM ewes spent more time grazing spotted knapweed and other forbs than SK ewes. In a drylot, time spent eating and intake of spotted knapweed and bromegrass (Bromus inermis Leyss.) varied through time. Conditioning yearling ewes to spotted knapweed, with or without molasses, did not increase consumption of this invasive plant, possibly because sheep inherently graze spotted knapweed only to a certain extent, or we did not use enough spotted knapweed during conditioning.  相似文献   

11.
Restoration of grasslands dominated by tall fescue (Schedonorus phoenix [Scop.] Holub) to native tallgrass prairie usually requires burning, herbicides, or reseeding. We tested seasonal grazing by livestock in winter, combined with cessation of fertilization, as a restoration tool for modifying the competitive dynamics among herbaceous plants to restore tallgrass prairie communities in southeastern Kansas. In 2004–2005, we compared responses of grassland plants and birds across a chronosequence of pastures that were winter-grazed from 1 yr to 5 yr. We compared winter-grazed pastures to pastures grazed year-round and to local native prairie remnants as starting and endpoints for restoration, respectively. Abundance of native warm-season grasses increased from 2% to 3% mean relative frequency in pastures grazed year-round to 18% to 30% in winter-grazed pastures, and increased with duration of winter-grazing. Native warm-season grasses accounted for 1–6% of total live aboveground biomass in pastures grazed year-round, 1–34% in winter-grazed pastures, and 31–34% in native prairie remnants. Tall fescue abundance and biomass were similar among grazing treatments, with a trend for tall fescue to be less dominant in winter-grazed pastures. Tall fescue made up 9–40% of total aboveground biomass in year-round grazed pastures and 10–25% in winter-grazed pastures. Grassland birds showed variable responses to winter-grazing. Dickcissels (Spiza americana) and Henslow’s sparrows (Ammodramus henslowii) were more abundant in winter-grazed pastures, whereas eastern meadowlarks (Sturnella magna) and grasshopper sparrows (A. savannarum) had similar abundance in pastures grazed year-round and during winter. Winter-grazing of pastures dominated by tall fescue combined with suspension of nitrogen fertilization could be an effective restoration technique that allows use of prairie rangeland while improving habitat for sensitive grassland birds.  相似文献   

12.
Two finishing trials and a metabolism trial were conducted to evaluate the effect of forage source and particle size in dry-rolled corn finishing diets. In Exp. 1, 224 crossbred yearling steers (BW = 342+/-11 kg) were used in a randomized complete block design consisting of seven treatments. Treatments were an all-concentrate diet or diets containing equal NDF levels provided by alfalfa hay or wheat straw (three treatments each) with each forage source ground to pass through a .95-, 7.6-, or 12.7-cm screen. Steers fed diets containing forage had greater (P < .05) DMI than steers fed an all-concentrate diet. Steers fed alfalfa diets gained faster (P < .05) with a greater (P < .05) concentrate efficiency than steers fed either all-concentrate or straw diets. In Exp. 2, 120 crossbred yearling steers (BW = 307+/-2 kg) were used in a completely randomized design and fed dry-rolled corn diets containing 10% alfalfa ground to pass through either a .95- or 7.6-cm screen. Alfalfa particle size had no effect on performance or carcass measurements. In Exp. 3, six ruminally fistulated steers (BW = 508+/-34 kg) were used in a 6 x 6 Latin square design and fed an all-concentrate diet or diets containing equal NDF levels provided by alfalfa hay, wheat straw, or ground corncobs with alfalfa and straw ground to pass through either a 2.54- or 12.7-cm screen. Steers fed straw diets spent more time (P < .10) chewing than those receiving the other diets. In conclusion, forage particle size had no effect on finishing cattle performance or ruminal metabolism data. However, cattle consuming different forage sources in dry-rolled corn finishing diets may not respond similarly in animal performance.  相似文献   

13.
Despite potential benefits, limitations of individual tropical legumes have restricted development of sustainable grass-legume pastures in tropical and subtropical regions. Sowing mixtures of complementary legumes may overcome limitations of individual species. Responses of yearling steers grazing a mixture of three tropical legumes with bahiagrass (Paspalum notatum Flugge) were evaluated at three stocking rates under continuous grazing. Carpon desmodium (Desmodium heterocarpon [L.] DC.), which is persistent under grazing but often difficult to establish, was combined with the short-lived legumes aeschynomene (Aeschynomene americana L.) and phasey bean (Macroptilium lathyroides [L.] Urb.). Diet composition, as determined by microhistological analysis of fecal samples, and animal performance were evaluated in three grazing periods: summer 1987 and spring 1988 (2.0, 3.5, and 5.0 steers/ha) and summer 1988 (3.0, 5.3, and 7.5 steers/ha). Stocking rate did not affect percentage of the selectively grazed legumes, aeschynomene and phasey bean, in the diet. Average daily gain decreased linearly (P less than .05) with increased stocking rate, as is typical for grass pastures. Aeschynomene and phasey bean contributed to diets during the first summer, and carpon desmodium contribution was greater in the second summer. These results indicate that this pasture mixture can provide legume herbage from aeschynomene and phasey bean in the year of sowing and from carpon desmodium thereafter. Over the range of grazing pressures obtained, legume responses were generally consistent; thus, optimizing stocking rate for gain per hectare or for economic returns can be targeted without additional constraints to maintain the contribution of these legumes to grazing livestock.  相似文献   

14.
Three experiments were conducted to determine the influence of both the concentration of endophytic fungus infestation in tall fescue pastures and calf genotype on the subsequent health and performance of steers in the feedlot. In Exp. 1 and 2, Angus steers grazed fescue pastures in Georgia containing low, moderate, or high endophyte infestations for 182 d (Exp. 1) or 78 d (Exp. 2) with 12 steers per treatment. Steers were transported 1,600 km to Texas in October (Exp. 1) and July (Exp. 2), were fed a 93% concentrate diet during the finishing period, and were harvested at an estimated backfat thickness of 12 mm. In both trials, DMI over the entire feeding period and carcass characteristics were not affected (P>0.05) by endophyte infestation. In both trials, pasture ADG decreased, and feedlot ADG and gain to feed ratio increased as the previous pasture endophyte infestation increased (P<0.05). Serum cholesterol concentrations tended (P<0.10) to decrease with increasing endophyte infestation during the first 14 d in the feedlot. In Exp. 3, Angus and Brahman × British crossbred steers grazed fescue pastures in Georgia containing low, moderate, or high endophyte in each of 2 yr. Six steers of each breed group were on each treatment each year. Steers were transported to Texas in late August of each year, were fed a 93% concentrate finishing diet, and were harvested at an estimated individual backfat thickness of 12 mm. As endophyte infestation increased, serum urea N concentrations and gain to feed ratios increased (P<0.05), whereas pasture ADG, initial BW, transit shrink, serum cholesterol concentrations, final BW, and carcass weights decreased (P<0.05) in Angus steers, but not in Brahman-cross steers. In these studies, the adverse effects of high endophyte infestations in fescue pastures appeared to carry over to the feedlot for ca. 14 d. However, steers from highly infested pastures can compensate for poor pasture performance with improved performance in the feedlot when no adverse health effects occur. Any impact of the endophyte seems to be similar in Brahman-cross and Angus steers.  相似文献   

15.
The effect of altering supplementation frequency on host N balance and key N transactions in the ruminal ecosystem were monitored. Four ruminally fistulated beef steers (BW = 513 kg; SEM = 6.5) were used in a 2 x 2 crossover design with two periods and two supplementation frequency treatments. Supplementation frequencies were 2 and 7 d/wk. Steers were fed tallgrass prairie hay (73.1% NDF, 5.3% CP) ad libitum. Supplement (42% CP; DM basis) was fed at 0.36% BW/d to steers supplemented 7 d/wk. Steers supplemented 2 d/wk received the same amount of supplement per week, but it was equally split among the two supplementation events. Steers supplemented 7 d/wk had higher forage (P < 0.02) and total digestible OM intake (P < 0.06), total N intake, fecal N excretion, and N retention. Although both supplementation frequencies were characterized by positive N balance, the decrease in N retention in the steers supplemented 2 d/wk was due to higher (P < 0.01) urinary N loss. Ruminal fluid was sampled at 0, 2, 4, 6, 12, 24, 48, and 72 h after supplementation beginning on a day when both treatments were supplemented. Frequency x hour interactions (P < 0.02) were observed for ruminal N metabolism criteria. Counts of peptide- and AA-fermenting bacteria peaked at 2 h and returned to nadir by 12 h for steers supplemented 7 d/wk. Steers supplemented 2 d/wk peaked at 6 h with a greater population and returned to nadir at 48 h. Ruminal ammonia concentrations followed a similar trend. Specific activity of ammonia production was lower (P < or = 0.05) immediately after supplementation for steers supplemented 2 d/wk, but by 12 h was the same as for 7 d/wk steers. Ruminal peptides and free AA peaked at 2 h for steers supplemented 2 d/wk and were generally higher (P < or = 0.05) during the first 6 h compared with steers supplemented 7 d/wk. Total VFA concentration was not different (P = 0.35) due to supplementation frequency. Frequency x hour interactions (P < 0.01) were observed for all molar proportions of VFA. The molar proportion of acetate and acetate:propionate ratio were lower (P < 0.01) and the molar proportions of propionate and butyrate were higher for steers supplemented 2 d/wk from 4 h to 24 h. In conclusion, forage use and N balance improved with supplementation 7 d/wk, but supplementation 2 d/wk was associated with some desirable shifts in select ruminal events that may contribute to moderating potential negative impacts of supplementing infrequently.  相似文献   

16.
A 2-yr study was conducted to confirm that managed pastures can provide Holstein steers adequate P to meet their daily requirement. Treatments offered were trace mineralized salt with or without additional P. In the first year, 80 Holstein steers (248 kg of BW) were assigned to 4 grazing groups. Treatments were trace mineralized salt only or a 67:33 mixture of trace mineralized salt and dicalcium phosphate. Steers rotationally grazed a cool-season grass/legume mixture for 137 d. Fecal bags were placed on 3 steers from each grazing group (n = 12) over a 4-d period for estimation of forage DMI and forage contribution to daily P intake twice during the grazing season. Analyzed pasture samples contained 3.28 mg of P/g of DM. During the second year, 72 Holstein steers (297 kg of BW) were blocked into 2 BW groups and subsequently assigned to 1 of 4 pasture groups. Steers rotationally grazed the same forage base as the first year for 126 d. Pasture samples contained 3.27 mg of P/g of DM. No significant differences (P > 0.10) were detected for BW, ADG, or free-choice supplemental mineral intake. Forage provided 126% of the recommended NRC P requirement. Thus, supplemental phosphorous was not required for Holstein steers grazing mixed, cool-season, grass/legume pastures.  相似文献   

17.
Finishing of dairy steers having grazed semi-natural grasslands   总被引：1，自引：1，他引：1  
The objective of this study was to determine the effects of initial live weight, level of grain feeding, and length of finishing period on weight gain and carcass traits of dairy steers that had grazed semi-natural grasslands. Steers were subdivided by initial live weight (low vs. high) and were fed two levels of grain (0.5% vs. 1.0% of live weight day− 1) during three different lengths of finishing period (3, 5 vs. 8 months). In total, 192 steers, initially 18 to 21 months of age, were fed grass–clover silage ad libitum. Steers fed high levels of grain had a higher dietary feed intake than steers fed low levels of grain (10.5 vs. 9.7 kg DM day− 1; P < 0.001). Carcass weight gain (630 g) was highest and feed conversion (169 MJ metabolizable energy per kg carcass gain) was best in steers with 5 months of finishing. Steers with low initial weights had a higher daily carcass weight gain than initially heavy steers (614 vs. 571 g, P = 0.013). A high initial weight and a long finishing period resulted in heavier and fatter carcasses with a higher conformation score and lower proportions of valuable retail cuts and bone. In conclusion, high-quality carcasses can be produced when finishing dairy steers that previously have grazed semi-natural grasslands. Performance and carcass traits were more effected by initial weight and length of finishing period than by level of grain feeding.  相似文献   

18.
OBJECTIVE: To measure the reduction in fecal nematode egg counts and productivity impact of treatment of yearling steers with doramectin at entry into the feedlot, compared with control steers treated only with fenthion. ANIMALS: 6,096 crossbred yearling steers with a mean (+/- SD) body weight of 377.0 (+/- 37) kg. PROCEDURE: Steers were implanted with zeranol and alternately separated to fill each of 24 pens. Groups of steers within 12 matched pairs of pens were randomly allocated to treatment with doramectin or no treatment with doramectin for internal nematodes. Fecal samples were collected from approximately every twentieth steer from each pen at day 0 and at reimplant (approx day 60). Each steer was weighed on day 0 and at reimplant and then mean body weights of steers per pen were determined at 120 to 140 days after trial initiation. RESULTS: Treatment steers had a significantly lower fecal egg count at reimplant than control steers. Treatment steers had a significantly greater mean daily gain during the study, significantly greater feed consumption, significantly lower feed-to-gain ratio, and significantly better quality carcass grades at slaughter. CONCLUSIONS AND CLINICAL RELEVANCE: Under the conditions of our trial, there was a significant fecal egg count reduction response to doramectin treatment, which resulted in significantly improved productivity. Results of economic analysis of return on investment indicated that even with low egg counts in heavy body weight cattle, nematode egg count reduction with doramectin significantly improved returns.  相似文献   

19.
Six ruminally cannulated Angus-cross steers (362 kg) were used in a replicated 3 x 3 Latin square design to determine effects of supplementing Maillard reaction products (MRP) on acid-resistant E. coli and coliform populations. Steers were fed roughage-based diets supplemented (DM basis) with either 10% soybean meal (SBM), 10% nonenzymatically browned SBM (NESBM), or 10% SBM top-dressed with 45 g of a lysine-dextrose Maillard reaction product (LD-MRP). Equal weights of dextrose, lysine hydrochloride, and deionized water were refluxed to produce the LD-MRP. The NESBM was manufactured by treating SBM with invertase enzyme, followed by heating to induce nonenzymatic browning. Steers were allowed slightly less than ad libitum access to diets fed twice daily and were adapted to their respective treatments within 10 d. On d 11, ruminal and fecal samples were collected at 0, 2, 4, 6, 8, and 12 h after feeding from each of the steers and transported to the laboratory for microbial analysis. Ruminal samples and feces were analyzed for pH and VFA, and both ruminal fluid and feces were tested for acid-resistant E. coli and total coliforms by incubating samples in tryptic soy broth adjusted to pH 2, 4, and 7. Ruminal pH and total VFA concentrations did not differ among treatments. The molar proportion of ruminal acetate was higher (P < 0.05) for steers receiving NESBM than for steers receiving SBM and LD-MRP. At pH 4, steers that received NESBM had lower (P < 0.05) ruminal populations of E. coli and total coliforms than steers that received SBM. No differences were observed for ruminal E. coli and total coliforms at pH 2 and 7. Fecal pH was lower (P < 0.05) for steers fed NESBM than for steers fed SBM or LD-MRP. Molar proportions of fecal acetate were lower (P < 0.05) and proportions of butyrate and isovalerate were higher (P < 0.05) for steers fed NESBM compared with steers fed SBM. Fecal E. coli at pH 4 was lower (P < 0.05) for steers fed NESBM than for steers fed LD-MRP. Fecal E. coli and total coliforms at pH 2 and 7 did not differ among treatments. Dietary MRP had limited effectiveness at decreasing acid-resistant coliforms in the rumen and feces of cattle. Acid resistance in coliforms may depend on protein availability.  相似文献   

20.
Urea recycling occurs in all mammalian species and represents an important source of ruminal nitrogen (N) for ruminants fed protein-restricted diets. However, its importance for cattle fed adequate amounts of protein and energy remains unclear. Six Nellore feedlot steers fed concentrate-based diets were used in a 6 × 6 Latin square design with a 3 × 2 factorial arrangement of treatments to evaluate ruminal fermentation, urea kinetics, and N excretion. Treatments consisted of 3 protein sources (PS: soybean meal plus urea [SU], corn gluten meal [CGM], and dry distillers grains [DDG]) and 2 inclusion levels (PL; 11% and 14%). Steers were adapted to the diets for 14 d followed by 8 d of sample collection. Feed intake, fecal output, and urine production were measured from day 18 to day 22 of each period. Blood samples were collected every 6 h on day 18. [15N-15N]-urea was infused into the jugular vein for 82 h over day 19 to day 22, and measurement of 15N in background (day 18) and enriched feces and urine (day 21) were used to evaluate urea kinetics. To evaluate the incorporation of recycled urea N into microbial protein (MICP), ruminal and duodenal fluid were collected on day 22. Steers fed SU diets had lower (P < 0.05) nitrogen use efficiency (NUE), greater (P < 0.05) urea-N entry rate (UER), and tended (P < 0.10) to have greater gastrointestinal entry rate of urea-N (GER) compared with those fed CGM or DDG. In addition, steers fed SU had greater (P < 0.05) urea-N returned to ornithine cycle (ROC) compared with those fed CGM or DDG. Increasing PL tended (P < 0.10) to increase UER. The proportion of total microbial N from recycled urea-N was greater (P < 0.05) for steers fed CGM compared with those fed SU and also greater for steers fed diets with 11% CP than for those fed with 14% CP. Diets with 11% CP can be used for Nellore feedlot cattle fed concentrate-based diets without negatively affecting intake, digestibility, and ruminal fermentation. Moreover, diets containing rumen undegradable protein (RUP) feed sources (CGM or DDG) compared with diets with SU markedly increased NUE, while maintaining microbial protein (MICP) synthesis. Results from this study suggest that the equation adopted by NASEM (NASEM. 2016. Nutrient requirements of beef cattle. 8th revised ed. Washington, DC: The National Academies Press) was not accurate in estimating the urea-N used for anabolism (UUA) in Nellore feedlot cattle fed concentrate-based diets.  相似文献   

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