Effect of Feed Delivery Management on Yearling Steer Performance

Gain efficiency by cattle fed high grain diets can be affected by feed delivery management (FDM). Restricted or limit feeding improves feed efficiency but can reduce ADG. This experiment was designed to evaluate if feeding near ad libitum intake while reducing the amount of variation between daily feed deliveries could provide feed efficiency advantages over unrestricted access to feed without restricting ADG. The FDM strategies for the 121-day feeding period included prescription intakes (PI) where variability between day to day feed deliveries were minimized or ad libitum intake (ALI) where feed was always available. Crossbred yearling steers (n = 76, initial BW 866 Ib ± 6.72) of mixed origin were stratified by BW and randomly assigned to one of two treatments then to one of five pens within a treatment. The 92% concentrate, 63 Mcal NE,/cwt diet, was fed to the PI group throughout the 121 –day study. Four step-up diets were fed over 12 days to adapt the ALI group to the 92% concentrate diet. Feed was delivered daily at 0730 and 1630. The bunks were slick for the PI treatment at 0700 69% of the days on feed and 40% for the ALI treatment (P\u3c .01). The PI fed steers consumed less DM (P\u3c .001) during interim periods days 1 to 29 and 58 to 85 (P\u3c.05). The PI steers were more efficient days 1 to 29 (P\u3c .03) and overall (P\u3c.10). Carcass variables associated with yield grade were not affected (P\u3e.10) by FDM and PI caused higher marbling scores (5.67 vs 5.31; P\u3c .085), while percent choice did not differ, 74 vs 79% for the PI and ALI treatments, respectively. The PI treatment lowered (P\u3c .05) feed cost $5.30/cwt gain. This experiment indicated that FDM can influence DM1 and feed efficiency without compromising ADG

A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years

Climate models show that ice-sheet melt will dominate sea-level rise over the coming centuries, but our understanding of ice-sheet variations before the last interglacial 125,000 years ago remains fragmentary. This is because terrestrial deposits of ancient glacial and interglacial periods1,2,3 are overrun and eroded by more recent glacial advances, and are therefore usually rare, isolated and poorly dated4. In contrast, material shed almost continuously from continents is preserved as marine sediment that can be analysed to infer the time-varying state of major ice sheets. Here we show that the East Greenland Ice Sheet existed over the past 7.5 million years, as indicated by beryllium and aluminium isotopes (10Be and 26Al) in quartz sand removed by deep, ongoing glacial erosion on land and deposited offshore in the marine sedimentary record5,6. During the early Pleistocene epoch, ice cover in East Greenland was dynamic; in contrast, East Greenland was mostly ice-covered during the mid-to-late Pleistocene. The isotope record we present is consistent with distinct signatures of changes in ice sheet behaviour coincident with major climate transitions. Although our data are continuous, they are from low-deposition-rate sites and sourced only from East Greenland. Consequently, the signal of extensive deglaciation during short, intense interglacials could be missed or blurred, and we cannot distinguish between a remnant ice sheet in the East Greenland highlands and a diminished continent-wide ice sheet. A clearer constraint on the behaviour of the ice sheet during past and, ultimately, future interglacial warmth could be produced by 10Be and 26Al records from a coring site with a higher deposition rate. Nonetheless, our analysis challenges the possibility of complete and extended deglaciation over the past several million years

Human and natural controls on erosion in the Lower Jinsha River, China

The lower Jinsha River has the highest sediment yield rates of the entire Yangtze watershed; these high yields have previously been attributed to a mix of the local geologic setting as well as intensive human land use, particularly agriculture. Prior studies have not quantified long-term background rates of sediment generation, making it difficult to know if modern sediment yield is elevated relative to the long-term rate of sediment generation. Using in situ 10Be in detrital river sediments, we measured sediment generation rates for tributaries to the lower Jinsha River. We find that the ratio of modern sediment yield to long-term sediment generation rate is 5.9 ± 2.8 (mean, 1 SD, n = 5), which is significantly higher than that elsewhere in western China and implies contemporary rates of sediment export far exceed long-term rates of sediment generation by weathering on hillslopes (1.9 ± 1.6 [median, 1 SD, n = 20]; [Schmidt et al., 2017]). Long-term (thousand year) rates of sediment generation correlate best with the steepness of the upstream watershed, a result found around the world. In contrast, modern sediment yield and the ratio of sediment yield to sediment generation rates correlate best with agricultural land use and distance to the nearest dam. Modern (1950s–1980s) sediment yield and the ratio of sediment yield to sediment generation rate also correlate well with percent of the watershed containing landslides observable today. The significantly higher modern sediment yield, lack of correlation between percent of the basin with landslides and long-term rates of sediment generation, and widespread deforestation and agriculture in the region suggest that landslide scars observable today are at least in part a result of human-induced land use change. Thus, we conclude that a mix of geologic setting and human activity control high contemporary sediment yield rates in the region

A cosmogenic view of erosion, relief generation, and the age of faulting in southern Africa

Southernmost Africa, with extensive upland geomorphic surfaces, deep canyons, and numerous faults, has long interested geoscientists. A paucity of dates and low rates of background seismicity make it challenging to quantify the pace of landscape change and determine the likelihood and timing of fault movement that could raise and lower parts of the landscape and create associated geohazards. To infer regional rates of denudation, we measured 10Be in river sediment samples and found that south-central South Africa is eroding ∼5 m m.y.-1, a slow erosion rate consistent with those measured in other non-tectonically active areas, including much of southern Africa. To estimate the rate at which extensive, fossil, upland, silcrete-mantled pediment surfaces erode, we measured 10Be and 26Al in exposed quartzite samples. Undeformed upland surfaces are little changed since the Pliocene; some have minimum exposure ages exceeding 2.5 m.y. (median, 1.3 m.y.) and maximum erosion rates of \u3c0.2 m m.y.-1 (median, 0.34 m m.y.-1), consistent with no Quaternary movement on faults that displace the underlying quartzite but not the silcrete cover. We directly dated a recent displacement event on the only recognized Quaternary-active fault in South Africa, a fault that displaces both silcrete and the underlying quartzite. The concentrations of 10Be in exposed fault scarp samples are consistent with a 1.5 m displacement occurring ca. 25 ka. Samples from this offset upland surface have lower minimum limiting exposure ages and higher maximum erosion rates than those from undeformed pediment surfaces, consistent with Pleistocene earthquakes and deformation reducing overall landscape stability proximal to the fault zone. Rates of landscape change on the extensive, stable, silcretized, upland pediment surfaces are an order of magnitude lower than basin-average erosion rates. As isostatic response to regional denudation uplifts the entire landscape at several meters per million years, valleys deepen, isolating stable upland surfaces and creating the spectacular relief for which the region is known

Characterizing landscape-scale erosion using 10Be in detrital fluvial sediment: Slope-based sampling strategy detects the effect of widespread dams

Concentrations of in situ 10Be measured in detrital fluvial sediment are frequently used to estimate long-term erosion rates of drainage basins. In many regions, basin-averaged erosion rates are positively correlated with basin average slope. The slope dependence of erosion allows model-based erosion rate estimation for unsampled basins and basins where human disturbance may have biased cosmogenic nuclide concentrations in sediment. Using samples collected from southeastern North America, we demonstrate an approach that explicitly considers the relationship between average basin slope and erosion rate. Because dams and reservoirs are ubiquitous on larger channels in the field area, we selected 36 undammed headwater subbasins (average area 10.6 km2) from which we collected river sand samples and measured 10Be concentrations. We used these data to train a predictive model that relates average basin slope and 10Be-inferred erosion rate. Applying our model to 28 basins in the same region previously studied with 10Be, we find that the model successfully predicts erosion rates for basins of different sizes if they are undammed or if samples were collected \u3e25 km downstream of dams. For samples collected closer to dams, measured erosion rates exceed modeled erosion rates for two-thirds of the samples. In three of four cases where paired samples were collected upstream of reservoirs and downstream of the impounding dam, 10Be concentrations were lower downstream. This finding has implications for detrital cosmogenic studies, whether or not samples were collected directly downstream of dams, because dams obstruct most major rivers around the world, effectively trapping sediment that originated upstream

Influence of topography and human activity on apparent in situ 10Be-derived erosion rates in Yunnan, SW China

In order to understand better if and where erosion rates calculated using in situ 10Be are affected by contemporary changes in land use and attendant deep regolith erosion, we calculated erosion rates using measurements of in situ 10Be in quartz from 52 samples of river sediment collected from three tributaries of the Mekong River (median basin areaD46.5 km2). Erosion rates range from 12 to 209mm kyr-1 with an area-weighted mean of 117±49mm kyr-1 (1 standard deviation) and median of 74mm kyr-1.We observed a decrease in the relative influence of human activity from our steepest and least altered watershed in the north to the most heavily altered landscapes in the south. In the areas of the landscape least disturbed by humans, erosion rates correlate best with measures of topographic steepness. In the most heavily altered landscapes, measures of modern land use correlate with 10Be-estimated erosion rates but topographic steepness parameters cease to correlate with erosion rates. We conclude that, in some small watersheds with high rates and intensity of agricultural land use that we sampled, tillage and resultant erosion has excavated deeply enough into the regolith to deliver subsurface sediment to streams and thus raise apparent in situ 10Be-derived erosion rates by as much as 2.5 times over background rates had the watersheds not been disturbed

Nonlinear Semi-Analytic Methods for Trajectory Estimation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76298/1/AIAA-29106-621.pd

Influence of Dietary MP on the Production Rates and N Usage by Steers Fed High Grain Content Diets

An experiment was conducted to determine if dietary metabolizable protein (MP) could be manipulated to reduce N content of feedlot effluent without compromising production rates in yearling steers fed high grain content diets. Three feeding programs included: LO) 11 % CP fed throughout; HI) 13% CP fed throughout; and LHL) 11 % fed from d 1 to 35, 13% CP (HI) fed d 36 to 94 and 1 1 % CP (LO) fed from d 95 to 1 17. An estradiol-trenbalone acetate implant was administered on d 35. There were 5 pens of 8 steers (BW=7561b) assigned to each treatment. The MP allowed ADG for the diets were 3.3 and 4.0 Ib for the LO and HI diets respectively. Cumulative ADG and feed efficiency were improved (Pc.05) by feeding the HI diet. Fluctuations in interim growth rates obscured the determination of specifically when this effect occurred. The faster growth rate was associated with heavier and fatter carcasses. An evaluation of serum urea-N concentrations suggested that the influence of the growth promotant on N metabolism was beginning to diminish within 56d. The HI diet caused higher (P\u3c .05) serum urea-N levels at 63, 91 and 117d on feed. Total N intake was calculated by pen and increased (P\u3c .01) from 41.4 to 47.3 to 51.2 Ib/steer for treatments LO, LHL and HI respectively. The N intake1100 BW gained increased (P\u3c .01) from 9.89 to 10.90 to 11.33 Ib for LO, LHL and HI treatments respectively. These results indicate that increasing production efficiency by elevating the MP content of diets may not cause a concomitant improvement in the efficiency of N retention on the feedlot scale

Coupled-channels analysis of the 16^{{\bf 16}}O+208^{{\bf 208}}Pb fusion barrier distribution

Analyses using simplified coupled-channels models have been unable to describe the shape of the previously measured fusion barrier distribution for the doubly magic $^{16}$O+$^{208}$Pb system. This problem was investigated by re-measuring the fission excitation function for $^{16}$O+$^{208}$Pb with improved accuracy and performing more exact coupled-channels calculations, avoiding the constant-coupling and first-order coupling approximations often used in simplified analyses. Couplings to the single- and 2-phonon states of $^{208}$Pb, correctly taking into account the excitation energy and the phonon character of these states, particle transfers, and the effects of varying the diffuseness of the nuclear potential, were all explored. However, in contrast to other recent analyses of precise fusion data, no satisfactory simultaneous description of the shape of the experimental barrier distribution and the fusion cross-sections for $^{16}$O+$^{208}$Pb was obtained.Comment: RevTex, 29 pages, 7 postscript figures, to appear in PR

Cosmogenic \u3csup\u3e26\u3c/sup\u3eAl/\u3csup\u3e10\u3c/sup\u3eBe surface production ratio in Greenland

The assumed value for the cosmogenic 26Al/10Be surface production rate ratio in quartz is an important parameter for studies investigating the burial or subaerial erosion of long-lived surfaces and sediments. Recent models and data suggest that the production ratio is spatially variable and may be greater than originally thought. Here we present measured 26Al/10Be ratios for 24 continuously exposed bedrock and boulder surfaces spanning ~61–77°N in Greenland. Empirical measurements, such as ours, include nuclides produced predominately by neutron-induced spallation with percent-level contributions by muon interactions. The slope of a York regression line fit to our data is 7.3 ± 0.3 (1σ), suggesting that the 26Al/10Be surface production ratio exceeds the commonly used value of 6.75, at least in the Arctic. A higher 26Al/10Be production ratio has implications for multinuclide cosmogenic isotope studies because it results in greater modeled burial durations and erosion rates