Beef cattle responses to pre-grazing sward height and low level of energy supplementation on tropical pastures

The objective of this study was to investigate the effects of energy supplementation and pre-grazing sward height on grazing behavior, nutrient intake, digestion, and metabolism of cattle in tropical pastures managed as a rotational grazing system. Eight rumen-cannulated Nellore steers (24 mo of age; 300 ± 6.0 kg body weight [BW]) were used in a replicated 4 × 4 Latin square design. Treatments consisted of two levels of energy supplementation (0% [none] or 0.3% of BW of ground corn on an as-fed basis) and two pre-grazing sward heights (25 cm [defined by 95% light interception (LI)] or 35 cm [defined by ≥ 97.5% LI]) constituting four treatments. Steers grazed Marandu Palisadegrass [Brachiaria brizantha Stapf. cv. Marandu] and post-grazing sward height was 15 cm for all treatments. Forage dry matter intake (DMI) was increased (P = 0.01) when sward height was 25 cm (1.86% vs. 1.32% BW) and decreased (P = 0.04) when 0.3% BW supplement was fed (1.79% vs. 1.38% BW). Total and digestible DMI were not affected by energy supplementation (P = 0.57) but were increased when sward height was 25 cm (P = 0.01). Steers grazing the 25-cm sward height treatment spent less time grazing and more time resting, took fewer steps between feeding stations, and had a greater bite rate compared with 35-cm height treatment (P < 0.05). Energy supplementation reduced grazing time (P = 0.02) but did not affect any other grazing behavior parameter (P = 0.11). Energy supplementation increased (P < 0.01) diet dry matter digestibility but had no effect on crude protein and neutral detergent fiber digestibilities (P = 0.13). Compared with 35-cm pre-grazing sward height, steers at 25 cm presented lower rumen pH (6.39 vs. 6.52) and greater rumen ammonia nitrogen (11.22 vs. 9.77 mg/dL) and N retention (49.7% vs. 20.8%, P < 0.05). The pre-grazing sward height of 25 cm improved harvesting efficiency and energy intake by cattle, while feeding 0.3% of BW energy supplement did not increase the energy intake of cattle on tropical pasture under rotational grazing.

Evaluation of warm season annual forages for forage yield and quality in the north-central United States

Grazing-based dairy operations require productive, high-quality forages capable of supporting the nutritional needs of mid-lactation dairy cows. Our objectives were to evaluate primary and regrowth harvests of two cultivars of sudangrass (SU), sorghum-sudangrass (S×SU), and pearl millet (PM) forages for growth and nutritive characteristics within the specific context of suitability for grazing by dairy cows. Three harvest cycles, including primary and regrowth cycles in 2016, and a single harvest cycle of primary growth in 2017, were evaluated at two locations (Prairie du Sac and Marshfield, WI). Within each cycle, sampling was initiated when canopy height was about 41 cm and continued thereafter on weekly intervals for 5 weeks, resulting in six equally spaced sampling dates per harvest cycle. Data were analyzed as a split-plot design with cultivars (6) as whole-plots arranged in randomized complete blocks and weekly harvest dates (6) as subplots. Yields of dry matter (DM) were less consistent at the more northern location (Marshfield), which is known for its heavier, poorly drained soils. Despite locational differences, the taller-growing cultivar within each forage type frequently exhibited yield advantages over dwarf or shorter-growing cultivars; this occurred for 7 of 9 intra-forage-type comparisons (P ≤ 0.021) across three harvest cycles at Prairie du Sac, and for 6 of 9 similar comparisons (P ≤ 0.032) at Marshfield. In 2016, shorter-growing cultivars had greater percentages of leaf in 4 of 6 intra-forage-type comparisons at both locations (P ≤ 0.004), which is especially relevant for grazing. Similarly, PM cultivars exhibited shorter canopy heights (P ≤ 0.002), but greater percentages of leaf (P < 0.001), than all other cultivars during all harvest cycles at both locations. However, the greater leaf percentages exhibited by PM cultivars did not translate into reduced percentages of structural plant fiber (asNDFom) on a whole-plant basis during any harvest cycle at either location; furthermore, asNDFom concentrations for PM cultivars were greater (P ≤ 0.047) than observed for other cultivars within 3 of 6 harvest cycles across both locations. Ruminal in-situ degradation of asNDFom for whole-plant forages based on a 48-h incubation was significantly greater (P ≤ 0.006) for PM compared with other cultivars in 4 of 6 harvest cycles. Pearl millet cultivars generally exhibited more suitable characteristics for grazing livestock than SU or S×SU cultivars.

Effects of growth stage and growing degree day accumulations on triticale forages: 2. In vitro disappearance of neutral detergent fiber

The use of winter triticale (X Triticosecale Wittmack) in dairy-cropping systems has expanded greatly in recent years, partly because of its value as a forage crop but also to improve land stewardship by providing winter ground cover. Our objectives were to use 2-pool and 3-pool nonlinear models to characterize in vitro disappearance of neutral detergent fiber (NDF) and then describe the relationship between estimated parameters from those models with plant growth stage or growing degree days (GDD) >5°C for winter triticale forages harvested during 2016 and 2017 in Marshfield, Wisconsin. Forages were harvested from replicated field plots each year at growth stages ranging from stem elongation to soft dough. All NDF analyses included use of sodium sulfite and heat-stable α-amylase with residual fiber corrected for contaminant ash (asNDFom). Nonlinear 3-pool models for in vitro disappearance of asNDFom that included fast (Bfast) and slow (Bslow) disappearance pools as well as an associated disappearance rate for each (K_dfast and K_dslow, respectively) were easily fitted provided that a single discrete lag time was applied to both Bfast and Bslow pools to reduce the number of parameters to be estimated. An unresolved issue related to fitting 3-pool decay models was the incomplete recovery of asNDFom from immature triticale forages at 0 h, which was partially resolved with 2 approaches that produced similar estimates of K_dfast and K_dslow. Most parameters obtained from 2- and 3-pool decay models for asNDFom could be related to growth stage or GDD using polynomial regression techniques, often with high coefficients of determination (R²). For 3-pool models of asNDFom disappearance, Bslow increased with plant maturity, but the associated K_dslow ranged narrowly from 0.011 to 0.015/h and could not be related to growth stage or GDD by quartic, cubic, quadratic, or linear regression models. Despite different cultivars coupled with substantial differences in precipitation across years, single endpoint estimates of in vitro disappearance of asNDFom after 24, 30, or 48 h of incubation were closely related (R² ≥ 0.906) to growth stage and GDD by linear or quadratic regression models that were generally similar across production years. Typical recommendations for harvesting triticale at boot stage to facilitate the planting of a double crop are strongly supported by the extensive 30-h in vitro disappearance of asNDFom at that growth stage, which was 63.1 and 64.8% of asNDFom during 2016 and 2017, respectively.

Effects of growth stage and growing degree day accumulations on triticale forages: 1. Dry matter yield, nutritive value, and in vitro dry matter disappearance

The use of triticale (X Triticosecale Wittmack) in dairy-cropping systems has expanded greatly in recent years, partly to improve land stewardship by providing winter ground cover. Our objective was to establish relationships relating indices of nutritive value with growth stage or accumulated growing degree days >5°C for triticale forages grown in central Wisconsin. Replicated 3.7-m × 9.1-m plots were established following removal of corn for silage (fall 2015) and soybeans (fall 2016) and then harvested at various growth stages the following spring. Plants were assigned a numerical growth stage based on a linear staging system suitable for use as an independent regression variable. Response variables [e.g., dry matter (DM) yield, indices of nutritive value, and parameters from in vitro DM disappearance kinetics] were regressed on growth stage and growing degree days using linear, quadratic, cubic, or quartic models. For spring 2016, the mean DM yield at the boot stage (3,804 kg of DM/ha) was only 30% of that observed at the soft dough stage of growth (12,642 kg of DM/ha). Although yields were reduced during spring 2017, primarily due to spring flooding, the relationship between respective yields at these growth stages was similar (1,453 vs. 5,399 kg of DM/ha). Regressions of DM yield (kg/ha) on growth stage for 2016 were explained by a cubic model (Y = 0.0663x³ - 9.44x² + 595x - 9,810) compared with a simple linear response for 2017 (Y = 103x - 3,024); in both cases, coefficients of determination were very high (R² ≥ 0.934). Many nutritional and in vitro DM disappearance characteristics were affected by the juxtaposition and balance of 2 generally competing factors: (1) increased concentrations of structural plant fiber coupled with concurrent lignification as plants matured and (2) the accumulation of highly digestible carbohydrate during seed head development. A comparison of respective energy yields between the boot and soft dough stages of growth for 2016 (2,488 vs. 8,141 kg of total digestible nutrients/ha) and 2017 (1,033 vs. 3,520 kg of total digestible nutrients/ha) suggests that yields of energy are greater at soft dough stage and are mostly driven by DM yield. An informed harvest management decision for lactating cows may still favor a boot-stage harvest because of superior nutritional characteristics, a need to plant double-cropped corn expeditiously, or both. Harvest timing of triticale forages for other livestock classes would appear to be more flexible, but prioritizing a subsequent double crop may reduce the effects on DM yield to a secondary consideration.

Effects of cultivar and grazing initiation date on fall-grown oat for replacement dairy heifers

Fall-grown oat has shown promise for extending the grazing season in Wisconsin, but the optimum date for initiating grazing has not been evaluated. Our objectives for this project were (1) to assess the pasture productivity and nutritive value of 2 oat cultivars [Ogle and ForagePlus (OG and FP, respectively)] with late-September (EG) or mid-October (LG) grazing initiation dates; and (2) to evaluate growth performance by heifers grazing these oat forages compared with heifers reared in confinement (CON). A total of 160 gravid Holstein heifers (80 heifers/yr) were assigned to 10 research groups (8 heifers/group). Mean initial body weight was 509±40.5 kg in 2013 and 517±30.2 kg in 2014. Heifer groups were assigned to specific pastures arranged as a 2×2 factorial of oat cultivars and grazing initiation dates. Grazing heifer groups were allowed to strip-graze oat pastures for 6 h daily before returning to the barn, where they were offered a forage-based basal total mixed ration. Main effects of oat cultivar and sampling date interacted for forage characteristics in 2013, but not in 2014. During 2013, oat forage mass increased until early November before declining in response to freezing weather conditions, thereby exhibiting linear and quadratic effects of sampling date, regardless of oat cultivar. Similar trends over time were observed in 2014. For 2013, the maximum forage mass was 5,329 and 5,046 kg/ha for FP and OG, respectively, whereas the mean maximum forage mass for 2014 was 4,806 kg/ha. ForagePlus did not reach the boot stage of growth during either year of the trial; OG matured more rapidly, reaching the late-heading stage during 2013, but exhibited only minor maturity differences from FP in 2014. For 2013, average daily gain for CON did not differ from grazing heifer groups (overall mean=0.63 kg/d); however, average daily gain from FP was greater than OG (0.68 vs. 0.57 kg/d), and greater from EG compared with LG (0.82 vs. 0.43 kg/d). For 2013, advantages in average daily gain for heifers grazing FP pastures were likely related to the greater energy density of FP oat throughout the fall that reached a maximum of 68.8% total digestible nutrients on November 27 compared with only 63.7% for OG on October 10. During 2014, average daily gain from CON exceeded all grazing heifer groups (0.81 vs. 0.57 kg/d), and average daily gain from EG again exceeded LG (0.70 vs. 0.44 kg/d). These results suggest that delaying grazing until mid-October will consistently suppress heifer growth performance, particularly if rapidly maturing cultivars are used.

Total volatile fatty acid concentrations are unreliable estimators of treatment effects on ruminal fermentation in vivo

Volatile fatty acid concentrations ([VFA], mM) have long been used to assess the effect of dietary treatments on ruminal fermentation in vivo. However, discrepancies in statistical results between [VFA] and VFA pool size (VFAmol) possibly related to ruminal digesta liquid amount (LIQ, kg) indicate potential issues with the use of [VFA]. We investigated relationships among [VFA], VFAmol, and LIQ measured 2 h postfeeding using individual lactating cow data (n=175) from 7 separate feeding studies. Regression analyses were performed using mixed models with "study" as a discrete random variable. The mean across studies and average range of values within studies, respectively, were 151 and 75 for [VFA], 11.2 and 9.8 for VFAmol, 73.3 and 41.0 for LIQ, and 289 and 83 mmol/kg for rumen fluid osmolality. Liquid amount changed with VFAmol (3.76 VFAmol+31.2; average within-study R2=0.69), but the relationship was weak between [VFA] and LIQ (0.524 LIQ+112.8; average within-study R2=0.12). The relationship between LIQ and VFAmol was likely a function of the osmotic gradient between rumen liquid and blood. The VFA are a major ruminal solute; VFAmol amounts can affect water flux in the rumen as similar tonicities of rumen fluid and blood are maintained. This also has a damping effect on ruminal solute concentration, creating the weak relationship between [VFA] and LIQ. Within studies, similar [VFA] were found in LIQ differing by 30 kg or more. The difference between minimum and maximum LIQ within cow within study was 12.7 kg (standard deviation=7.1), so inclusion of "cow" in analyses did not correct for the variation in LIQ. To allow valid comparisons of experimental treatments, responses must be on an equivalent basis; concentrations in different LIQ are not on an equivalent basis and so are not valid to use for comparing treatment effects. The [VFA] changed with VFAmol (5.80 VFAmol+86.3; average within-study R2=0.56). However, the ratio of [VFA] to VFAmol ranged from 9.0 to 24.1 as a function of 1,000/LIQ; this reflects the inherent calculated relationship among the variables. The varying relationship of [VFA] to VFAmol further indicates that [VFA] is not an appropriate measure to evaluate the progress or effect of treatments on ruminal fermentation. Predictions of LIQ and VFAmol using cow and ruminal measures were insufficiently precise to be used in research. Previously drawn conclusions based on [VFA] need to be reevaluated, and alternate evaluations for in vivo ruminal fermentation are needed.

Bacterial communities in the rumen of Holstein heifers differ when fed orchardgrass as pasture vs. hay

The rich and diverse microbiota of the rumen provides ruminant animals the capacity to utilize highly fibrous feedstuffs as their energy source, but there is surprisingly little information on the composition of the microbiome of ruminants fed all-forage diets, despite the importance of such agricultural production systems worldwide. In three 28-day periods, three ruminally-cannulated Holstein heifers sequentially grazed orchardgrass pasture (OP), then were fed orchardgrass hay (OH), then returned to OP. These heifers displayed greater shifts in ruminal bacterial community composition (determined by automated ribosomal intergenic spacer analysis and by pyrotag sequencing of 16S rRNA genes) than did two other heifers maintained 84 d on the same OP. Phyla Firmicutes and Bacteroidetes dominated all ruminal samples, and quantitative PCR indicated that members of the genus Prevotella averaged 23% of the 16S rRNA gene copies, well below levels previously reported with cows fed total mixed rations. Differences in bacterial community composition and ruminal volatile fatty acid (VFA) profiles were observed between the OP and OH despite similarities in gross chemical composition. Compared to OP, feeding OH increased the molar proportion of ruminal acetate (P = 0.02) and decreased the proportion of ruminal butyrate (P < 0.01), branched-chain VFA (P < 0.01) and the relative population size of the abundant genus Butyrivibrio (P < 0.001), as determined by pyrotag sequencing. Despite the low numbers of animals examined, the observed changes in VFA profile in the rumens of heifers on OP vs. OH are consistent with the shifts in Butyrivibrio abundance and its known physiology as a butyrate producer that ferments both carbohydrates and proteins.

Fall-grown oat to extend the fall grazing season for replacement dairy heifers

Our objective was to assess the pasture productivity and forage characteristics of 2 fall-grown oat (Avena sativa L.) cultivars, specifically for extending the grazing season and reducing reliance on harvested forages by replacement dairy heifers. A total of 160 gravid Holstein heifers (80 heifers/yr) were stratified by weight, and assigned to 1 of 10 identical research pens (8 heifers/pen). Initial body weights were 480 ± 43.5 kg in 2011 and 509 ± 39.4 kg in 2012. During both years of the trial, four 1.0-ha pasture replicates were seeded in August with Ogle oat (Schumitsch Seed Inc., Antigo, WI), and 4 separate, but similarly configured, pasture replicates were seeded with Forage Plus oat (Kratz Farms, Slinger, WI). Heifer groups were maintained as units, assigned to specific pastures, and then allowed to graze fall-oat pastures for 6h daily before returning to the barn, where they were offered a forage-based basal total mixed ration. Two heifer groups were retained in confinement (without grazing) as controls and offered the identical total mixed ration as pasture groups. During 2011, available forage mass increased with strong linear and quadratic effects for both cultivars, peaking at almost 9 Mg/ha on October 31. In contrast, forage mass was not affected by evaluation date in 2012, remaining ≤ 2,639 kg/ha across all dates because of droughty climatic conditions. During 2012, Ogle exhibited greater forage mass than Forage Plus across all sampling dates (2,678 vs. 1,856 kg/ha), largely because of its more rapid maturation rate and greater canopy height. Estimates of energy density for oat forage ranged from 59.6 to 69.1% during 2011, and ranged narrowly from 68.4 to 70.4% during 2012. For 2011, responses for both cultivars had strong quadratic character, in which the most energy-dense forages occurred in mid November, largely due to accumulation of water-soluble carbohydrates that reached maximum concentrations of 18.2 and 15.1% for Forage Plus and Ogle, respectively. Across the 2-yr trial, average daily gain for grazing heifer groups tended to be greater than heifers remaining in confinement (0.85 vs. 0.74 kg/d), but both management strategies produced weight gains within reasonable proximity to normal targets for heifers in this weight range. Fall-grown oat should be managed as stockpiled forage for deferred grazing, and good utilization of fall-oat forage can be accomplished by a one-time removal of standing forage, facilitated by a single lead wire advanced daily to prevent waste.

Swine effluent application timing and rate affect nitrogen use efficiency in common bermudagrass

Bermudagrass [Cynodon dactylon (L.) Pers.] hay production is integral to manure management on southeastern swine farms. But swine effluent timing must be synchronized with crop nitrogen (N) demands to decrease the potential for soil N accumulation and nitrate (NO(3)) leaching. Field studies were conducted on a Prentiss sandy loam (coarse-loamy, siliceous, semiactive, thermic Glossic Fragiudult) to determine N-use efficiency (NUE) and residual soil NO(3)-N. Two rates of 10 and 20 cm yr(- 1) ( approximately 260 and 480 kg ha(-1) N, respectively) were applied in four timing treatments: April to September (full season), April to May, June to July, and August to September. Plots were harvested every 7 to 9 wk beginning in June, and soil was sampled in fall after a killing frost and the following spring. Annual uptake of N and P were least in the August to September timing treatment. Doubling the effluent rate increased N uptake 112% in 2000 (from 130 to 276 kg ha(-1)) and 53% in 2001 (from 190 to 290 kg ha(-1)), suggesting 10-cm did not meet crop N demands. Due to low rainfall and decreased forage yield in 2000, doubling the effluent rate led to increased soil NO(3)-N to 30-cm depth in fall 2000 and spring 2001. Averaged across timing treatments, soil NO(3)-N at 5-cm depth ranged from 8.5 mg kg(-1) in non-irrigated controls to 39.6 mg kg(-1) with 20-cm effluent. Results indicate low NUE in the order of 30 to 38% for applications in August to September increase the risk to surface and ground water quality from excess N remaining in soil.

Managing broiler litter application rate and grazing to decrease watershed runoff losses

Pasture management and broiler litter application rate are critical factors influencing the magnitude of nutrients being transported by runoff from fields. We investigated the impact of pasture management and broiler litter application rate on nutrient runoff from bermudagrass (Cynodon dactylon) pastures. The experiment was conducted on a Ruston fine sandy loam with a factorial arrangement on 21 large paddocks. Runoff water was collected from natural rainfall events from 2001 to 2003. Runoff water and soil samples were analyzed for nutrients and sediments. Runoff was generally greater (29%) from grazed than hayed pastures regardless of the litter application rate. There was greater inorganic N in the runoff from grazed paddocks when litter rate was based on N rather than P. The mean total P loss per runoff event for all treatments ranged from 7 to 45 g ha(-1) and the grazed treatment with litter applied on N basis had the greatest total P loss. Total dissolved P was the dominant P fraction in the runoff, ranging from 85% to 93% of the total P. The soluble reactive P was greater for treatments with litter applied on N basis regardless of pasture management. Runoff total sediments were greater for N-based litter application compared to those which received litter on P basis. Our results indicate that litter may be applied on N basis if the pasture is hayed and the soil P is low. In contrast, litter rates should be based on a P-basis if pasture is grazed.

Characterization of broiler cake and broiler litter, the by-products of two management practices

The application of broiler manure and bedding (litter) on land has been a long-used disposal method that benefits plant and soil. For proper manure management, factors such as nutrient content, house cleaning management, application methods, and many land, crop, and climatic factors must be considered. A study was undertaken to characterize broiler cake and broiler litter as the by-products of two management systems in Mississippi. Broiler cake and litter productions were quantified and analyzed for four flocks during 1999 and 2000. The overall means for broiler cake production were 12.50, 13.90, and 10.30 kg m(-2) for producers 1, 2, and 3, respectively. Significantly greater quantities of litter, 27.50, 29.0, and 28.30 kg m(-2) than cake were determined for the same producers. The cake and litter moisture averaged 455 and 277 g kg(-1), respectively. No significant differences were observed between cake and litter total N, NH4-N, total C, total P, and water-soluble P (WP). However, cake had significantly greater Ca, Mg, K, Cu, Fe, Mn, and Zn than litter. Approximately 16.8% of the broiler cake and 15.2% of the broiler litter total P were in the form of water-soluble P. The NH4-N content of the cake and the litter were 12.5% and 11.5% of the cake and litter total nitrogen, respectively. The results also showed the advantage of the decaking practice with respect to the quantity of the manure generated for land application. Approximately 57% of the litter remains in the poultry house with decaking practice after each growth cycle compared to the 0% for total cleanout practice.