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Key messageWe investigate the genetic basis of panicle architecture in switchgrass in two mapping populations across a latitudinal gradient, and find many stable, repeatable genetic effects and limited genetic interactions with the environment.AbstractGrass species exhibit large diversity in panicle architecture influenced by genes, the environment, and their interaction. The genetic study of panicle architecture in perennial grasses is limited. In this study, we evaluate the genetic basis of panicle architecture including panicle length, primary branching number, and secondary branching number in an outcrossed switchgrass QTL population grown across ten field sites in the central USA through multi-environment mixed QTL analysis. We also evaluate genetic effects in a diversity panel of switchgrass grown at three of the ten field sites using genome-wide association (GWAS) and multivariate adaptive shrinkage. Furthermore, we search for candidate genes underlying panicle traits in both of these independent mapping populations. Overall, 18 QTL were detected in the QTL mapping population for the three panicle traits, and 146 unlinked genomic regions in the diversity panel affected one or more panicle trait. Twelve of the QTL exhibited consistent effects (i.e., no QTL by environment interactions or no QTL × E), and most (four of six) of the effects with QTL × E exhibited site-specific effects. Most (59.3%) significant partially linked diversity panel SNPs had significant effects in all panicle traits and all field sites and showed pervasive pleiotropy and limited environment interactions. Panicle QTL co-localized with significant SNPs found using GWAS, providing additional power to distinguish between true and false associations in the diversity panel.

Objective The objective of this study was to determine the influence of varying levels of dried distillers grains with solubles (DDGS) supplemented daily on the performance of beef stocker cattle grazing Coastal bermudagrass [Cynodon dactylon (L.) Pers.] pastures. Materials and Methods Steers (n = 127, 342 ± 5.6 kg of BW) were stratified by BW and breed type and randomly allocated to 9 pastures (1.3 ± 0.17 ha) during each summer of 2 yr (2014, 2015). Pastures were allocated randomly to 1 of 3 treatments, including 2 daily levels of a DDGS supplement (SUPP; 0.25 or 1% BW) and a nonsupplemented control (PAS) for 96 d in 2014 and 92 d in 2015. Steers were shipped approximately 700 km to a commercial feedlot for the finishing phase. Finally, animals were transported less than 100 km for slaughter at a commercial abattoir. Results and Discussion Steer ADG on pasture tended to increase quadratically (P = 0.06) from 0.67 kg/d from PAS to 1.01 kg/d from 1% BW SUPP. Gain per hectare increased linearly (P 0.36). Implications and Applications Supplementation of steers with 1% BW DDGS resulted in the most efficient management strategy.

Objective Our objective was to develop models to estimate the CP, NDF, lignin, and ash concentrations of bermudagrass [Cynodondactylon (L.) Pers.] forage daily throughout the grazing season and use them to estimate TDN daily. We hypothesized that the CP, NDF, lignin, ash, and TDN concentrations might change daily. Materials and Methods Coastal bermudagrass forage CP, NDF, lignin, and ash concentrations spanning several years were obtained from Overton, Texas. The forage samples used comprised hand-plucked plant parts intended to estimate animal-selected diets. We developed an empirical model for each nutritive variable with the day of the year (DOY) as a predictor. By incorporating these models into a pre-existing summative equation, we estimated the daily values of TDN. These nutritive value models were evaluated using the Willmott index, modeling efficiency, root mean squared error, and R2 as the measures of fit. Results and Discussion Bermudagrass CP concentration had a negative, curvilinear association with DOY, whereas lignin and NDF concentrations were positively, curvilinearly related to DOY. The ash concentration had a negative, linear association with DOY. The likely causal factors for these relationships were plant maturity and weather conditions, especially temperature. The Willmott index, modeling efficiency, and R2 values were greater than 0.87, 0.64, and 0.65, respectively. The root mean squared error and percent error values were less than 3.1 and 11%, respectively. These values indicated that the nutritive value models were reliable. Implications and Applications We showed that the CP, NDF, lignin, ash, and TDN values of bermudagrass forage changed daily. By incorporating these trends into a nutritive value prediction system, accurate estimates of daily TDN could be made. These nutritive value models could be a valuable asset in forage-animal modeling for more accurately studying the effects of various management strategies and environmental factors on forage nutritive value and animal performance.

Polyploidy results from whole-genome duplication and is a unique form of heritable variation with pronounced evolutionary implications. Different ploidy levels, or cytotypes, can exist within a single species, and such systems provide an opportunity to assess how ploidy variation alters phenotypic novelty, adaptability, and fitness, which can, in turn, drive the development of unique ecological niches that promote the coexistence of multiple cytotypes. Switchgrass, Panicum virgatum, is a widespread, perennial C4 grass in North America with multiple naturally occurring cytotypes, primarily tetraploids (4×) and octoploids (8×). Using a combination of genomic, quantitative genetic, landscape, and niche modeling approaches, we detect divergent levels of genetic admixture, evidence of niche differentiation, and differential environmental sensitivity between switchgrass cytotypes. Taken together, these findings support a generalist (8×)–specialist (4×) trade-off. Our results indicate that the 8× represent a unique combination of genetic variation that has allowed the expansion of switchgrass’ ecological niche and thus putatively represents a valuable breeding resource.

Objective The objective of this study was to determine the influence of varying rates of dried distillers grains with solubles (DDGS) supplemented daily on performance of beef stocker cattle grazing Tifton 85 (Cynodon dactylon [L.] Pers. × Cynodon nlemfuensis Vanderyst) bermudagrass pastures. Materials and Methods Steers (n = 112, 379 ± 35.5 kg of BW) were stratified by BW and randomly allocated to 16 pastures (0.7 ± 0.01 ha) during each summer of 2 yr (2014, 2015). Pastures were allocated randomly to 3 daily rates of a DDGS supplement (SUPP; 0.25, 0.5, or 1% BW) and a nonsupplemented control (PAS) for 110 d in 2014 and 112 d in 2015. Results and Discussion Steer ADG increased linearly (P Implications and Applications Supplementation of beef stocker cattle with DDGS while grazing Tifton 85 bermudagrass may be a viable management strategy to enhance gain per animal or land area.

Objective The objective of this study was to document the simulated effect of dried distillers grains with solubles (DDGS) supplementation of Coastal bermudagrass (COS; Cynodon dactylon [L.] Pers.) and Tifton 85 bermudagrass (TIF; C. dactylon [L.] Pers. × Cynodon nlemfuensis Vanderyst) forage on in vitro gas production, in vitro true digestibility (IVTD), in vitro NDF digestibility (IVNDFD), and methane production. Materials and Methods Forage and DDGS were combined to represent 3 levels of supplemental DDGS (0, 0.25, or 1% BW), which resulted in ratios of forage:DDGS of 100:0, 87.5:12.5, and 50:50. Samples were incubated using the in vitro gas production technique, and headspace was sampled for quantification of methane concentration. The residue was rinsed in neutral detergent solution for determination of IVTD and IVNDFD. Results and Discussion Discrete lag times of both the exponential and logistic equations decreased linearly (P Implications and Applications Results indicated that DDGS might be supplemented to cattle for increased diet digestibility with an additional potential benefit of reduced methane production. Efficacy of DDGS was dependent on forage nutritive value.

We investigate the genetic basis of panicle architecture in switchgrass in two mapping populations across a latitudinal gradient, and find many stable, repeatable genetic effects and limited genetic interactions with the environment. Grass species exhibit large diversity in panicle architecture influenced by genes, the environment, and their interaction. The genetic study of panicle architecture in perennial grasses is limited. In this study, we evaluate the genetic basis of panicle architecture including panicle length, primary branching number, and secondary branching number in an outcrossed switchgrass QTL population grown across ten field sites in the central USA through multi-environment mixed QTL analysis. We also evaluate genetic effects in a diversity panel of switchgrass grown at three of the ten field sites using genome-wide association (GWAS) and multivariate adaptive shrinkage. Furthermore, we search for candidate genes underlying panicle traits in both of these independent mapping populations. Overall, 18 QTL were detected in the QTL mapping population for the three panicle traits, and 146 unlinked genomic regions in the diversity panel affected one or more panicle trait. Twelve of the QTL exhibited consistent effects (i.e., no QTL by environment interactions or no QTL × E), and most (four of six) of the effects with QTL × E exhibited site-specific effects. Most (59.3%) significant partially linked diversity panel SNPs had significant effects in all panicle traits and all field sites and showed pervasive pleiotropy and limited environment interactions. Panicle QTL co-localized with significant SNPs found using GWAS, providing additional power to distinguish between true and false associations in the diversity panel.

Dried distillers grains with solubles (DDGS) is commonly used as supplemental feed in cattle rations. However, the systemic effects of overfeeding DDGS, especially to potential fertilizer benefits of pass-through nitrogen, are widely unknown. Therefore, our objective was to evaluate plant and soil response to fertilization with manure from steers supplemented with titrated levels of DDGS. Manure utilized was collected from steers supplemented with DDGS (0%, 0.25%, 0.5%, and 1% BW) during a 2-yr experiment. The experimental design was a randomized complete block design with an augmented factorial treatment structure wherein benches represented blocks. The factorial was made up of manure treatment (0, 0.25, 0.5, or 1% BW DDGS, chemical fertilizer, or none) soil type (Windthorst or Purves), and plant species (none, crimson clover, or rye). Pots were sown (5 seeds/pot) and grown in a greenhouse for 35 d. Water was applied daily at 90% evapotranspiration. After harvest, soils were sifted, dried for 72 h at 55°C, then assayed for C, N, NO3-N, P, K, Ca, Mg, Na, and S. There was an interaction of manure and soil type for soil C (P < 0.01). Purves soils amended with any manure had a greater (P < 0.05) concentration of C (1.8%) than did the negative control (1.3%). From Windthorst, soil C was greatest from 1% BW DDGS manure (1.9%), and least from 0% DDGS manure (1.5%), with 0.25 and 0.5% manures and the negative control intermediate. There was an interaction of manure, soil type, and forage for soil N (P < 0.01). Manures with higher levels of supplementation had greater (P < 0.05) soil N than lower levels of supplementation or the negative control. Legumes had greater soil N than grasses. Results are interpreted to mean that moderate supplementation of steers with DDGS may yield soil nutrient benefits through nutrient deposition.

Plant phenological timings are major fitness components affected by multiple environmental cues; thus, phenological traits can have important genotype-by-environment interactions (GxE). We use a flexible, data-driven method to characterize GxE in the timing of vegetative growth (‘green-up’) and flowering across eight environments and in two highly divergent switchgrass (Panicum virgatum) populations. We classified polygenic GxE patterns as suggestive of modulation of genetic effects via weather-based cues—or other, unknown modulators. >26% of Gulf population SNPs affecting flowering had effects that covaried with photoperiodicity and >34% of Midwest upland population SNPs affecting flowering had effects that covaried with cumulative growing degree days. 76% of SNP effects on green-up showed antagonistic pleiotropy, a change in effect sign, between environments native to Gulf plants (Texas) and environments native to Midwest plants (North). In contrast, 64%) showed no GxE. Top GxE-associated SNPs were highly enriched in the top associations from an independent pseudo-F2 cross of individuals from the same two populations. Breeding for particular alleles at GxE-associated loci could change flowering responsiveness to photoperiod cues in switchgrass. More broadly, this approach could be used to flexibly characterize patterns of GxE across species, populations and environments.Significance StatementThe timing of plant seasonal development (phenology) has major impacts on fitness because of the negative consequences of plant-environment mismatches. Here we map the genetic basis of two phenological events, the start of above-ground growth and flowering, in two genetically and phenologically distinct populations of switchgrass. We do this at eight field locations spanning the latitudinal range of both populations. Our approach allows us to identify regions of the genome with effects that covary with weather-related environmental features at every location. For flowering, these features differed by population: the Midwest population had genetic effects that primarily covaried with cumulative growing degree days, a temperature-related measure, while the Gulf population had genetic effects that primarily covaried with photoperiod, a day-length-related measure.

Significance Understanding how individual genetic loci contribute to trait variation across geographic space is of fundamental importance for understanding evolutionary adaptations. Our study demonstrates that most loci underlying locally adaptive trait variation have beneficial effects in some geographic regions while conferring little or no detectable cost in other parts of the geographic range of switchgrass over two field seasons of study. Thus, loci that contribute to local adaptation vary in the degree to which they are costly in alternative environments but typically confer greater benefits than costs. Further, our study suggests that breeding locally adapted varieties of switchgrass will be a boon to the biofuel industry, as locally adaptive loci could be combined to increase local yields in switchgrass., Local adaptation is the process by which natural selection drives adaptive phenotypic divergence across environmental gradients. Theory suggests that local adaptation results from genetic trade-offs at individual genetic loci, where adaptation to one set of environmental conditions results in a cost to fitness in alternative environments. However, the degree to which there are costs associated with local adaptation is poorly understood because most of these experiments rely on two-site reciprocal transplant experiments. Here, we quantify the benefits and costs of locally adaptive loci across 17° of latitude in a four-grandparent outbred mapping population in outcrossing switchgrass (Panicum virgatum L.), an emerging biofuel crop and dominant tallgrass species. We conducted quantitative trait locus (QTL) mapping across 10 sites, ranging from Texas to South Dakota. This analysis revealed that beneficial biomass (fitness) QTL generally incur minimal costs when transplanted to other field sites distributed over a large climatic gradient over the 2 y of our study. Therefore, locally advantageous alleles could potentially be combined across multiple loci through breeding to create high-yielding regionally adapted cultivars.

Long-term climate change and periodic environmental extremes threaten food and fuel security1 and global crop productivity2–4. Although molecular and adaptive breeding strategies can buffer the effects of climatic stress and improve crop resilience5, these approaches require sufficient knowledge of the genes that underlie productivity and adaptation6—knowledge that has been limited to a small number of well-studied model systems. Here we present the assembly and annotation of the large and complex genome of the polyploid bioenergy crop switchgrass (Panicum virgatum). Analysis of biomass and survival among 732 resequenced genotypes, which were grown across 10 common gardens that span 1,800 km of latitude, jointly revealed extensive genomic evidence of climate adaptation. Climate–gene–biomass associations were abundant but varied considerably among deeply diverged gene pools. Furthermore, we found that gene flow accelerated climate adaptation during the postglacial colonization of northern habitats through introgression of alleles from a pre-adapted northern gene pool. The polyploid nature of switchgrass also enhanced adaptive potential through the fractionation of gene function, as there was an increased level of heritable genetic diversity on the nondominant subgenome. In addition to investigating patterns of climate adaptation, the genome resources and gene–trait associations developed here provide breeders with the necessary tools to increase switchgrass yield for the sustainable production of bioenergy., The genome of the biofuel crop switchgrass (Panicum virgatum) reveals climate–gene–biomass associations that underlie adaptation in nature and will facilitate improvements of the yield of this crop for bioenergy production.

In forage-animal nutrition modeling, diet energy is estimated mainly from the forage total digestible nutrients (TDN). As digestibility trials are expensive, TDN is usually estimated using summative equations. Early summative equations assumed a fixed coefficient to compute digestible fiber using the lignin-to-neutral detergent fiber (NDF) ratio. Subsequently, a structural coefficient (φ) was added to the summative equations to reflect an association between lignin and cell wall components. Additional modifications to the summative equations assumed a constant φ value, and they have been used as a standard method by many commercial laboratories and scientists. For feeds with nutritive values that do not change much over time, a constant φ value may suffice. However, for forages with nutritive values that keep changing during the grazing season owing to changes in weather and plant maturity, a constant φ value may add a systematic bias to prediction because it is associated with the variable lignin-to-NDF ratio. In this study, we developed a model to estimate φ as a function of the day of the year by using the daily TDN values of bermudagrass [Cynodon dactylon (L.) Pers.], a popular warm-season perennial grass in the southern United States. The variable φ model was evaluated by using it in the TDN equation and comparing the estimated values with the observed ones obtained from several locations. Values of the various measures of fit used—the Willmott index (WI), the modeling efficiency (ME), R2, root mean square error (RMSE), and percent error (PE)—showed that using the variable φ vis-à-vis the constant φ improved the TDN equation significantly. The WI, ME, R2, RMSE, and PE values of 0.94, 0.80, 0.80, 2.5, and 4.7, respectively, indicated that the TDN equation with the variable φ model was able to mimic the observed values of TDN satisfactorily. Unlike the constant φ, the variable φ predicted more closely the forage nutritive value throughout the grazing season. The variable φ model may be useful to forage-beef modeling in accurately reflecting the impacts of plant maturity and weather on daily forage nutritive value and animal performance.

Panicle traits exhibit quantitative variation controlled by genes, the environment, and their interaction. In switchgrass, a perennial biofuel crop, identification of quantitative trait loci (QTL) and QTL x E interactions controlling panicle architecture could aid breeding efforts and cultivar development by impacting seed productivity. In this study, we evaluate the genetic architecture of panicle traits including panicle length, primary branching number, and secondary branching number in an outcrossing switchgrass population grown across ten field sites in the central United States. We evaluated pleiotropic relationships between panicle traits and flowering time, tiller production and biomass. We also identified environmental factors correlated with QTL x E interactions and potential candidate genes underlying panicle trait QTL in switchgrass. Overall, our multi-environment mixed QTL model detected 18 QTL for panicle traits. Twelve of the QTL exhibited consistent effects (i.e., no QTL x E), and most (4 of 6) of the effects with QTL x E exhibited condition-specific effects. Many of the QTL x E effects were associated with yearly mean temperature and photoperiod. Panicle QTL co-localized with previously identified flowering time QTL and candidate genes associated with flowering, supporting a pleiotropic model of panicle development based on shared developmental genetics and responses to environmental signals.

Pathogens play an important role in the evolution of plant populations, but genetic mechanisms underlying disease resistance may differ greatly between geographic areas as well as over time. Local adaptation is thought to be an important step in plant evolution, and may be impacted by differential pathogen pressures in concert with abiotic factors. This study uses locally adapted ecotypes of the native perennial switchgrass (Panicum virgatum) to examine the temporal and spatial variation in the genetic architecture of resistance to fungal pathogens, namely switchgrass leaf rust (Puccinia novopanici). To identify loci underlying variation in pathogen resistance in switchgrass, we scored rust damage across an outcrossed mapping population at eight locations across the central United States from southern Texas to Michigan. We followed rust progression at these sites for three years and mapped quantitative trait loci (QTLs) using function-valued transformations of rust progression curves. Overall, we mapped 51 QTLs that varied in presence and strength over the three-year period. Two large-effect QTLs were consistently associated with variation in rust progression in multiple sites and years, and are therefore potentially the result of the same underlying resistance genes. Interestingly, these two large-effect QTLs were almost exclusively detected in northern sites. This pattern could be caused by geographic difference in genetic architecture. The distribution of rust strains or variation in climatic conditions across the field sites could result in genotype-by-environment interactions in efficacy of rust resistance loci. Beyond reducing rust damage by 34%, the beneficial alleles at the two loci also increased biomass by 44%, suggesting a direct benefit by pleiotropy or indirect benefit through genetic linkage. Our results suggest an important role for fungal pathogens in the local adaptation of switchgrass and illustrate an influential geographic component of the genetic architecture of plant disease resistance.

Cowpeas [Vigna unguiculate (L) Walp] as a summer cover crop have the potential to provide N to a cool‐season crop. The objectives of this study were to evaluate two cowpea cultivars grown as a cover crop to supply N for forage rye (Secale cereale L.) and to document cowpea N and C contributions to the soil. The 2‐yr study was conducted at the Texas A&M AgriLife Research Center at Overton on a Darco loamy fine sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudult) during 2014–2016. Treatments were arranged in a split‐plot design with four replicates with cover crop as the main plot and N rate as subplot. Cover crop treatments included ‘Combine’ (COM) and ‘Iron and Clay’ (IAC) cowpeas and summer fallow. In late summer, cowpeas were incorporated as green manure, and four rates of fertilizer N were applied to rye. Total 2‐yr cowpea biomass incorporated as green manure was similar at 4,596 kg ha−1 and 5,058 kg ha−1 for IAC and COM, respectively. Cowpea was not effective as a green manure crop at providing N for rye biomass. Total soil N showed no difference (P ≥ .34) between cowpea entries or N rate within a soil depth. Each N rate increased rye biomass (P

Cool-season annual forages may supply seasonal forage for grazing and reduce needs for stored forages and concentrate supplements for beef cattle producers in the southeastern United States. Opportunity exists to use small grains that vary in their individual growth distribution to extend grazing during the fall–winter–early spring seasons. Small grains adapted to the region include cereal rye (Secale cereale L.), wheat (Triticum aestivum L.), oats (Avena sativa L.), and triticale (Triticosecale Wittm.). These species have a bimodal forage DM production trait during the autumn and early winter months and can be grown in monocultures or mixtures. Fall forage production potential of these species has been primarily dependent on planting method, seeding date, soil fertility or fertilization, and variety selection. Small grain varieties may also be grown in combination with annual ryegrass (Lolium multiflorum Lam.), clovers, or both to extend the seasons of grazing for fall or winter-calving cows or stockers. Annual ryegrass and legumes in the Southeast include cold-tolerant and rust-resistant diploid and tetraploid varieties of ryegrass, and adapted true clover (Trifolium sp.) varieties. Autumn-planted ryegrass or clovers including crimson (Trifolium incarnatum L.), arrowleaf (Trifolium vesiculosum Savi), ball (Trifolium nigrescens Viv.), and red clover (Trifolium pratense L.) provide minimal to nonexistent forage mass for grazing during the fall. Naturally reseeding ryegrass or clovers may provide earlier forage mass compared with small grains; however, DM is usually not adequate for stocking until late-January to mid-February, and it extends through May. Tetraploid varieties of ryegrass, when seeded into a prepared seedbed, can provide adequate forage mass for fall grazing similar to small grains. Earliness of forage mass for stocking among clovers ranges from crimson (earliest) to arrowleaf and ball (mid to late) to white and red (late to early summer). These cool-season forage systems provide suckling calf ADG that may approach or exceed 1.5 kg/d and stocker cattle ADG of more than 1 kg/d. Management strategies for sustainable cow-calf production include the strategic use of cool-season forages, assessment of fertilization demands and timing, and assessment of stocking rate to optimize forage utilization and desired animal performance.

Sustainability of cow-calf production in the United States has received increased attention during the past few years. The ever-increasing land values and ownership scenarios, redirected agricultural production objectives, and financial requirements for new ownership affects land use, livestock enterprises, and sustainability of the beef industry. Bermudagrass [ Cynodon dactylon (L.) Pers.] is the most sustainable and persistent warm-season perennial grass used for N-fertilized pastures in the southeastern United States. Management strategies that affect bermudagrass persistence and DM production goals include soil nutrient management, primarily N and K, and stocking rate, intensity, and duration. Overseeding bermudagrass with cool-season annual forages such as small grains, annual ryegrass ( Lolium multiflorum L.), or clovers ( Trifolium sp.) extends the active grazing period of pastures and provides the highest nutritive value of any forage class. Stocking strategies that incorporate the most adapted bermudagrass cultivars with soil type, soil nutrient availability, and use of cool-season annual forages provide the best options to achieve intensive forage utilization. Using stocking rates appropriate for forage utilization intensity objectives provides for enhanced gain per animal and gain per unit land area relationships. The economy of scale of operation, management objectives, and acceptable risk allow stakeholders to select their site-specific level of intensive cow-calf production. The most noteworthy aspects of bermudagrass pasture management have shown that the magnitude of forage mass can be immediately altered with implementation of levels of N fertilization and stocking rate to affect beef production per unit land area.

Growth of young cattle on forages and pastures has a major effect on the profitability of the stocker cattle industry. The objectives of this study were to estimate heritability of performance traits and additive genetic correlations of pairs of traits in Brahman and Brahman-influenced (0.25 or 0.5 Brahman) stocker cattle on rye (Secale cereale) + ryegrass (Lolium multiflorum) (RRG; n = 2,031) or bermudagrass [Cynodon dactylon (L.) Pers.] (BER; n = 1,322). Data from 1986 to 2014 at Overton, Texas, for BW, ADG, and BCS were analyzed for each stocking season. Main effects included stocking rate (3 levels), proportion of Brahman inheritance (3 levels on RRG: 0.25, 0.5, 1; 2 levels on BER: 0.25 and 1), supplementation status, and contemporary groups. Stockers receiving supplement were heavier (P

Approximately 44% of the beef cow herd in the United States resides in the 13 southeastern states. The objectives of our study were to identify and quantify the issues that affect research and extension educational programs concerned primarily with cow-calf production and secondarily with stocker cattle. A 29-question survey was sent to research and extension faculty associated with pasture-based beef production programs with land-grant universities in Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Virginia. Our objectives were to access information about faculty appointments, location of facilities, objectives and area of programs, resources allocated to programs, funding availability, and sources of funding. The majority of research scientists that responded were located off campus, which was also the primary location of pastures, beef infrastructure, and research facilities. Cow-calf and pasture projects were the predominant (60 to 80%) beef cattle programs for all scientists. Primary objectives of cow-calf or stocker calf research and extension scientists’ programs pertained to forage evaluation and grazing management, and nutrition. Reproduction in cow-calf and animal health in stocker programs ranked third in importance of scientists’ programs. Internal and extramural funding sources and availability were the primary constraints for development of research and extension programs in cow-calf production. Research and extension programs identified as needed for stakeholders included components of forage management and nutrition. Faculty indicated that the most likely, fundable programs should include environment, ecosystem services, greenhouse gas emissions, carbon sequestration, and molecular genetics for research, and economics and reproduction for extension scientists. A balance between the needs of the stakeholder and the perceptive needs by funding agency programs will be required to maintain the plant–animal discipline in the southeastern United States.

Poor stand establishment, failure to recover after grazing, and premature plant death have reduced the utilization of arrowleaf clover (Trifolium vesiculosum Savi) as a forage crop in the southeastern United States in recent years. Clover plants collected from poor stands in east Texas pastures during the 1995 to 1996 and 1996 to 1997 seasons first exhibited root disease symptoms as young seedlings in the fall. Symptoms consisted of one or more of the following: tan discoloration of lateral roots and taproot; root pruning; and small, tan, sunken lesions on the taproot and crown. Many Rhizobium nodules were brown and dead. Toward spring, symptoms increased in severity. Root lesions became larger and darker, and internal crown discoloration was observed. Disease incidence reached 100% in both growing seasons. Premature death of plants also was observed, especially in pastures where plants had been grazed. Most of the fungi isolated from diseased roots were Pythium, multi- and binucleate Rhizoctonia, and Fusarium spp. Many plants were infected with two or three pathogens simultaneously. Two Rhizoctonia isolates (AR96-17 and -26) were identified as R. solani anastomosis group 4 (AG4; D. R. Sumner, University of Georgia). AR96-8 was identified as Fusarium proliferatum (T. Matsushima) Nirenberg (Fusarium Research Center, Penn State University; deposited as isolate M-8382). Three Pythium isolates (AR96-7, -11 and -39) were identified as P. irregulare Buisman, based on oogonial and sporangial characteristics. Eight other Pythium isolates were not identified. Pythium isolate AR97-1, found in 1997, was identified as P. ultimum Trow. Greenhouse studies to confirm pathogenicity of these isolates were conducted by sowing cv. Yuchi arrowleaf clover seed into artificially infested soilless medium. In pathogenicity tests for P. ultimum, seedling emergence for controls was 69% after 8 days, but no seedlings emerged from P. ultimum-infested media. Several seeds showed imbibition and emerging radicles but were symptomatic. The pathogen was reisolated from necrotic radicles. After 19 weeks, survival and root disease symptoms were recorded for plants infected by the other isolates. Pathogens were reisolated from diseased plants. Disease symptoms were similar to those observed on plants collected in the field, and differed among pathogens. The Pythium isolates and P. irregulare caused tan discoloration and pruning of the entire root system, sometimes leaving only stubs along the taproot. Survival of clover plants infected by Pythium spp. and P. irregulare isolates averaged 79 and 83%, respectively. R. solani AG4 isolates caused internal crown discoloration, root lesions, and severe root rot, and plant survival was only 31%. F. proliferatum caused hyperelongation of the hypocotyl and stem, mild chlorosis, tan discoloration of roots, and 94% plant survival. Survival was 86% for control plants. P. ultimum, P. irregulare, R. solani AG4, and F. proliferatum are part of a larger disease complex occurring on arrowleaf clover in east Texas that also includes bean yellow mosaic virus (1) and possibly other root and crown rot diseases. This report is the first to identify some of the components of this disease complex impacting arrowleaf clover in Texas, and to demonstrate pathogenicity of each fungal pathogen individually. There are no arrowleaf clover cultivars currently known to have resistance to any of these pathogens. Reference: (1) I. J. Pemberton et al. Phytopathology 81:1001, 1991.

Efficiency of animal production is an important component of the beef industry. The research objectives of this 2-yr study were to (1) estimate residual feed intake (RFI) of yearling Brahman (Bos indicus) bulls grazing Coastal bermudagrass [Cynodon dactylon (L.) Pers.] using DMI measured with n-alkanes; (2) compare RFI under grazing (RFIg) with RFI determined in confinement under restricted feed intake at 2.8% of BW (RRFIc); and (3) assess the relationships of carcass traits and gastrointestinal tract anatomy to RFIg. Bulls RRFIc-phenotyped as efficient (n-RFI) and inefficient (p-RFI) in both 2009 and 2010 were assigned to 2 replicate pastures at either low or high stocking intensity (STK) for 60 d. In 2009 there was no difference (P > 0.3) between n-RRFIc and p-RRFIc for initial or final BW, ADG, DMI, or feed-to-gain ratio. There was an interaction of RFIg × STK (P = 0.043) for ADG in which p-RFIg bulls on low STK had the greatest gain. The p-RFIg bulls had the greatest DMI regardless of STK (P

Forage-management principles have been structured from small-plot experimentation targeted at evaluating defoliation regimens, fertilization, and other factors on growth and persistence of forage varieties or germplasm. Seasonal and total forage-mass attributes have been the primary benchmark for sustainable grass pastures. Forage mass affects level of grazing intensity and stocking rates to maximize gain per unit land area. Forage nutritive value sets the upper limits on gain per animal. Both forage mass and nutritive value are uniquely linked to animal performance; however, the priority role is different for C3 versus C4 forages because of the substantial differences in percentage of protein and digestible DM. The value of grazing-intensity and stocking-rate experimentation includes identifying ADG × gain per hectare relationships, and the mathematical expressions of other factors including forage allowance. The calculated forage allowance (forage DM:animal BW) has moved past the original point-in-time reference to be more inclusive of the average forage allowance for an entire season. Forage-allowance databases provide management decisions for stocking strategies to affect forage-animal pasture systems. Forage allowance of a pasture may provide management decisions for setting initial grazing intensities, or these calculated values may provide stocking strategy choices to optimize ADG or gain per hectare. The role of forage management is a dynamic, evolving, data-driven process with the inclusion of heuristic approaches to serve as correction factors to optimize forage utilization. Grazing research provides grazing-experiment databases to direct and redirect the role of forage-management decisions to enhance biological-economic efficiencies and sustainable pastures.

Telomeres are comprised of G-rich nucleotide sequences (5’-TTAGGG-3’) at the chromosome termini that are responsible for protecting chromosomes; however, attrition of these sequences has been observed in conditions of physiological and psychological stress. The purpose of this study was to compare telomere length (TL) in 4-yr-old Brahman cows grouped by first parity (n = 8) and second parity (n = 11). Cows were bled by jugular venipuncture, weighed, and had BCS recorded d+28 prior to calving and d-7 and d-28 post calving. Cows were observed for duration of labor (Tlabor) and calving ease (CE) at the time of parturition. Calf birth weight (CBW) and gender (CG) were recorded. Peripheral leukocytes were isolated, complete blood counts (CBC) were recorded, and genomic DNA was extracted utilizing silicone membrane spin column kits. The relative quantity of telomere products, which is proportional to the average TL, was determined by multiplex quantitative PCR analysis using the ratio of bovine telomere and β-globulin DNA. An absolute standard of bovine telomere (1012–107 dilution series) and β-globulin (109-104 dilution series) genes was utilized to produce relative copy number. All samples were run in triplicate and samples were included if triplicate Cq difference was less than 0.25 cycles. Parity was the fixed effect of interest and random effects included sire and day repeated with cow as the subject. No differences in CBC were seen. Tlabor, CE, CG, and CBW did not impact TL (P > 0.1). A trend was observed for day-parity interaction (P = 0.0918). TL between parity differed most on d-28 (P = 0.1046; parity one 127292 ± 6483; parity two 111045 ± 5376). The stress of parturition and raising the first calf of a cow’s life may be responsible for slight attenuation in TL.

Natural, organic, and grass-fed beef provides alternative products for consumers. During 2 consecutive yr, Bonsmara steers (n = 130) grazed winter pasture at 2 environments [semiarid, Uvalde (UVL), and humid, Overton (OVT)] and received pasture only (PAS) or pasture plus 0.8% BW/steer per day corn (SUPL) to quantify growth and carcass traits. Each year, 8 steers each from UVL and OVT were slaughtered off pasture and after a 90-d feedlot (FED) period. From initiation to termination (mid-May) of stocking on Maton rye (Secale cereale L.) plus TAM-90 annual ryegrass (Lolium multiflorum Lam.) at OVT and irrigated TAM-90 at UVL, ADG was greater (P 0.05) FED ADG. Growth in BW was linear (P 0.05) by SUPL. Tenderness was enhanced (P

Pasture fertilization plays a vital role in the biological and economic successes of forage-based livestock systems. Sustainability of productive, warm-season perennial forage systems depends, to a major extent, on management–utilization strategies and pasture fertilization. As soil nutrient reserves are exhausted, forage production and nutritive value are reduced proportionally. Despite the vast scientific literature suggesting that warm-season forage crops can respond favorably to high levels of N fertilization, the increasing costs of commercial fertilizers and environmental concerns have prompted the need to reexamine optimumefficient fertilizer levels, sources, and methods of application that can sustain economic pasture production. Because the fate of fertilizers applied to grassland systems is extremely complex and is affected by several factors, including application rate and timing, fertilizer source, and soil and environmental characteristics, it is critical to implement management strategies for soil fertility that integrate all the factors that affect fertilizer efficiency, sustainable forage production, and protection of natural resources. The primary objective of this review paper is to present some of the basic principles of soil-fertility management for warm-season perennial forages and fertilization strategies for sustainable

Field observations revealed greater retention of green leaf area and growth of ‘Tifton 85’ compared to common and ‘Coastal’ bermudagrass [ Cynodon dactylon (L.) Pers.] under water stress. Our objective was to compare phenotypic and physiological responses to increased water stress between Tifton 85 and Coastal and between Tifton 85 and ‘Tifway’ bermudagrass under greenhouse conditions. Bermudagrass green leaf area, shoot and root dry weights, leaf CO 2 exchange rate (CER), H 2 O exchange rate (WER), and conductance were measured under well-watered and reduced watering in two experiments. Tifton 85 retained greater green leaf area than Tifway under water stress in Exp. 1. The CER, WER, and conductance were less for Tifton 85 than Tifway, but water stress over 8 d reduced each variable for Tifway only. In Exp. 2, soil water content and green leaf area declined more for Tifton 85 than for Coastal bermudagrass over 14 d after watering ended. Greater root dry weight below the 13-cm depth indicated Tifton 85 depleted water content of the fi nite pot volumes more rapidly than Coastal under reduced watering. After 14 d without watering during Exp. 2, mean CER of green leaves was less than well-watered pots for Tifton 85 but not for Coastal bermudagrass. Similar to phenotypic traits, leaf CER, WER, and conductance responses of Tifton 85 differed between experiments. These greenhouse experiments documented variation of responses to reduced soil water supply among bermudagrass and revealed the need to evaluate traits affecting water access and use for Tifton 85 and other bermudagrass under fi eld conditions.D. Husmoen, 103 Whispering Pines, Norton, KS 67654; D.M. Vietor, 176 Seeley Street, Apt 4B, Brooklyn, NY 11218; F.M. Rouquette, Jr., Texas AgriLife Research, Overton, TX 75684; J.T. Cothren, Soil and Crop Sciences Department, Texas A&M University, College Station, TX 77843-2474. Received 11 Jan. 2012.

SUMMARYThe objectives of the current study were to determine the variation structure within a day and across days when determining dry matter intake (DMI) of Coastal bermudagrass (Cynodon dactylon (L.) Pers.) pasture using dotriacontane (C32) as an external marker, to determine the optimal times for faecal collection for forage DMI estimation and to compare C31 and C33 as internal markers in estimating forage DMI in Brahman bulls. Sixteen Brahman bulls were allocated by weight to four pastures, and stocked at a moderate to low grazing pressure for 63 days from late June to the end of August. Three intake measurement periods (P1, P2, P3) were used; each period consisting of 10 days of twice daily C32 (400 mg/day) administration. Faecal collections were taken during the last 5 days (07.00, 11.00, 15.00 and 19.00 h). The C32 was individually hand fed using Calan gates, with maize gluten as a carrier for the alkane. Gas chromatography was used to determine n-alkanes in the forage and faecal samples. The concentration of C31 was less than C33 in the bermudagrass for all periods (P 31 and C33 in faeces was not significantly different (P > 0·05). The average concentration of C32 in the forage was 5·1, 7·6 and 9·6 mg/kg dry matter (DM), for P1, P2 and P3, respectively, with an average of 7·5 mg/kg DM for all periods. During P1 and P2, the estimation of forage DMI using C33 had a better fit (smaller –2 × log and Akaike's information criterion (AIC)) than using C31 either with or without adjustments for C32. The variation in estimated forage DMI decreased when forage C32 was not included. The variances of forage DMI were similar using C31 across days, but the Pearson correlations between days were low, which suggested that several days of collection were needed to estimate forage DMI accurately. Correlations between collection times within days were medium to high for all periods and varied from 0·65 to 0.97 for C31 and from 0·26 to 0·96 for C33. When all periods were analysed together, estimates of forage DMI either using C31 or C33 had low correlations between days of collection. Adjustment for C32 did not improve the variance and (co)variance matrix. In summary, C33/C32 had the lowest variation in estimating forage DMI, and at least 5 days of faecal collection were needed to decrease the variability of estimating forage DMI. The optimum times for faecal collection were 07.00 and 19.00 h, and it was important to adjust for C32 alkane concentration in estimating forage DMI in Brahman bulls grazing Coastal bermudagrass.

The objectives of this study were to use the in vitro gas production (IVGP) technique to evaluate the pattern and parameters of anaerobic fermentation of forages from south Texas pastures throughout the year to (i) obtain empirical relationships between the IVGP technique fermentation parameters and chemical composition of the forages and (ii) develop equations to compute total digestible nutrients (TDN). During four consecutive years (2006–2009), forage samples were collected monthly (n = 39) at the King Ranch, TX, and chemical analyses and IVGP were obtained. For 2006, 2007, 2008 and 2009, the average lag times, h, were 6·47 ± 0·54, 7·75 ± 0·65, 7·49 ± 2·01 and 5·44 ± 1·46, and the average ratio of millilitre of gas per milligram of dry matter was 0·41 ± 0·11, 0·34 ± 0·09, 0·34 ± 0·07 and 0·26 ± 0·10 respectively. There was a moderate negative correlation (r = −0·53) between lignin and neutral detergent fibre (NDF) and a moderate positive correlation (r = 0·58) between crude protein and NDF digestibility. The predicted fractional passage rate (kp) by the large ruminant nutrition system model using the level 2 solution was on average 0·0366 h−1. The average computed TDN assuming a kp of 0·04 h−1 was 55·9%. We concluded the IVGP technique may be used to predict TDN values of warm-season forages.

By using the temperament selection criterion of exit velocity (EV), cattle typically exhibiting hypercortisolism and a blunted response to exogenous corticotrophin-releasing hormone (CRH) can be identified via individual behavioral responses to handling. To further characterize hypothalamic–pituitary–adrenal (HPA) axis dysfunction associated with bovine temperament, the present study compared pituitary and adrenal activity, following stimulation with exogenous vasopressin (VP), in steers with an excitable or calm temperament. Serial blood samples were collected via indwelling jugular cannula for 6 h preceding and 6 h following administration of a VP bolus. Plasma concentrations of adrenocorticotropic hormone (ACTH) and cortisol were quantified by RIA to determine pituitary and adrenal responsiveness within temperament groups. Cortisol concentrations in excitable steers during the pre-challenge period revealed an increased initial adrenal reactivity to interactions with humans. Subsequent acclimation to the experimental surroundings yielded greater baseline cortisol concentrations in the cattle with an excitable temperament. Pituitary stimulation with VP resulted in a greater ACTH output from the excitable compared to the calm animals. The data presented herein provide additional evidence that HPA axis function in cattle of an excitable temperament may be akin to a state of chronic stress. The bovine temperament model may be of further use to both decipher mechanisms associated with HPA dysfunction and to elucidate physiological phenotypes or pathologies that have parallels in other species.

Stocking strategies for cow-calf and stocker programs will require different management decisions in response to increasing input costs. With yearlong ownership of cows, costs of fertilization for DM production of pastures and storage of forages are the primary obstacles for positive economic returns. The implementation of legumes into both cool-season and warm-season perennial grass pastures for biological N fixation is intensified by management seeking to reduce input costs. Biological N fixation by the symbiotic forage legume-Rhizobium relationship is dependent on environmental factors as well as the specificity between legume species and Rhizobium strain. The quantity of atmospheric N fixed through forage legume biological N fixation can range as high as 200 kg/ha per year. The seasonality attributes of stocker cattle ownership allow for stocking strategies that may actually intensify short-term fertilizer inputs but use the strategic impact of nutrient cycling to enhance or sustain the perennial grass-based pasture systems. The transfer of N fixed by legumes to companion or follow-up grasses is much less than that of N fixation and is primarily dependent on animal excreta and legume plant decomposition. Stocking rate becomes the primary management strategy of concern that strives to match forage DM production with animal performance expectations and sustainable pastures for economic ventures.

The objective of this study was to characterize residual feed intake (RFI) and to estimate phenotypic and genetic correlations with performance and ultrasound carcass traits in growing heifers. Four postweaning feed efficiency trials were conducted using 468 Brangus heifers. The complete Brangus pedigree file from Camp Cooley Ranch (Franklin, TX), which included 31,215 animals, was used to generate genetic parameter estimates. The heifer progeny from 223 dams were sired by 36 bulls, whereas the complete pedigree file contained 1,710 sires and 8,191 dams. Heifers were individually fed a roughage-based diet (ME = 1.98 Mcal/kg of DM) using Calan gate feeders for 70 d. Heifer BW was recorded weekly and ultrasound measures of 12th- to 13th-rib fat thickness (BF) and LM area (LMA) obtained at d 0 and 70. Residual feed intake (RFIp) was computed as actual minus predicted DMI, with predicted DMI determined by linear regression of DMI on mid-test BW(0.75) (MBW) and ADG with trial, trial x MBW, and trial x ADG as random effects. Overall means for ADG, DMI, and RFI were 1.01 (SD = 0.15), 9.51 (SD = 1.02), and 0.00 (SD = 0.71) kg/d, respectively. Stepwise regression analysis revealed that inclusion of gain in BF and final LMA into the base model increased the R(2) (0.578 vs. 0.534) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted RFI (RFIc) were strongly correlated phenotypically and genetically with DMI and FCR, but not with ADG or MBW. Gain in BF was phenotypically correlated (P < 0.05) with RFIp (0.22), but not with FCR or RFIc; however, final BF was genetically correlated (P < 0.05) with RFIp (0.36) and RFIc (0.39). Gain in LMA was weakly phenotypically correlated with FCR, but not with RFIp or RFIc; however, gain in LMA was strongly genetically correlated with RFIp (0.55) and RFIc (0.77). The Spearman rank correlation between RFIp and RFIc was high (0.96). These results suggest that adjusting RFI for ultrasound carcass composition traits will facilitate selection phenotypically independent of growth, body size, and carcass composition; however, genetic relationships may still exist between RFI and carcass composition.

Cancer of the eye in cattle with white faces occurs less frequently in cattle with pigmented eyelids. Corneoscleral pigmentation is related to eyelid pigmentation and occurrence of lesions that may precede cancer. Objectives of this study were to assess 1) variation in the proportion of eyelid and corneoscleral pigmentation in Hereford, Bos taurus, and Bos indicus crossbreds and 2) the occurrence of lesions with the presence of pigmentation in those areas. Hereford and Bos indicus crosses (Brahman or Nellore with Angus and Hereford and straightbred Brafords) and Bos taurus crosses (Angus-Hereford) were included in the study (n = 1,083). Eyelid pigmentation proportions were estimated by pixel quantification and were evaluated as total proportions and for upper and lower eyelids distinctly for each eye. Fixed effects included breed type, age categories, and sex of the animal. Lesion presence (1) or absence (0) was obtained by visual appraisal of image and was assumed to be binomially distributed. Eyelid pigmentation proportions (overall, upper, and lower eyelids) for Hereford ranged from 0.65 ± 0.03 to 0.68 ± 0.03 and were significantly lower than Bos indicus (range from 0.93 ± 0.02 to 0.95 ± 0.02) or Bos taurus (ranged from 0.88 ± 0.02 to 0.92 ± 0.02) crosses. Corneoscleral pigmentation in Hereford cows (0.17 ± 0.06) did not differ (P = 0.91) from Hereford calves and yearlings (0.16 ± 0.07). Bos indicus and Bos taurus crossbred cows had larger corneoscleral pigmentation (0.38 ± 0.05 and 0.48 ± 0.04 for left eyes and 0.37 ± 0.05 and 0.53 ± 0.04 for right eyes, respectively) than all calves (P < 0.001), and their corneoscleral pigmentations were greater than that of Hereford cows (P < 0.003). Bos indicus and Bos taurus cows had greater proportions of left eye corneoscleral pigmentation (0.38 ± 0.05 and 0.48 ± 0.04, respectively) than Hereford cows (0.17 ± 0.06) and all young animal breed types (P < 0.05). Right eye proportions differed for all cow groups (P < 0.05; 0.53 ± 0.04, 0.37 ± 0.05, and 0.17 ± 0.06). Among calves and yearlings, Hereford had a lower right eye corneoscleral pigmentation proportion (0.16 ± 0.07) than Bos taurus (P = 0.02). The lesion proportion for Hereford (0.08 ± 0.03) was significantly greater than that of either Bos indicus (0.01 ± 0.005) or Bos taurus (0.01 ± 0.003). Crossbreeding with Bos taurus or Bos indicus animals appears to increase eye pigmentation, which may help reduce the occurrence of cancer in eyes of cattle with white faces.