James P. Muir

Comparison of growth and performance in upland and lowland switchgrass types to water and nitrogen stress.

The objective of the study was to examine lowland (Alamo and Kanlow) and upland (Blackwell and Caddo) cultivars of switchgrass (Panicum virgatum L.) for differences in response to water deficit and nitrogen fertilizer. Cultivars were grown in pots with fritted clay at two water levels: well watered and deficit conditions (-0.1 and -1.0 MPa) and two nitrogen levels (10 and 100 kg ha(-1)). Nitrogen determined growth potential of the cultivars more than water availability. The lowland cultivars produced greater biomass yields than upland cultivars. However, upland cultivars showed a smaller response to drought stress. Under water stress conditions all cultivars exhibited a higher leaf percentage of total dry matter (DM), with the upland cultivars having the highest leaf percentage of total DM. Nitrogen proved to have more of an effect on single-leaf photosynthesis rates than water. Alamo demonstrated the greatest biomass production among all cultivars. The differences found between the two lowland cultivars suggest that Alamo would be better suited for forage and biomass production in central Texas, being a higher producer under drought and non-drought conditions than Kanlow as well as upland cultivars.

Molecular weight and protein-precipitating ability of condensed tannins from warm-season perennial legumes

The beneficial effects of forages containing condensed tannins (CTs) on ruminants are well documented, but the chemical features of CT that yield benefits have not been defined. Some evaluations of limited numbers of highly purified compounds have resulted in positive correlations between CT molecular weight (MW) and biological activity, while others have failed to show a correlation. The objectives of this study were to determine if MW of CT could predict biological activity relative to protein precipitability. MW of condensed tannin, protein-precipitable phenolics (PPP), and the amount of protein bound (PB) were determined for nine species of warm-season perennial legumes. There was no correlation between PPP or PB and MW (R2 0.11 and R2 0.02, respectively). However, CT concentration did correlate with PPP and PB (R2 0.81 and R2 0.69, respectively). It was concluded that CT MW does not explain the variation in protein precipitation by CT from the forage legumes surveyed.

Soils and forage quality as predictors of white-tailed deer Odocoileus virginianus morphometrics

Abstract Biologists tasked with managing cervids could benefit from models predicting physical characteristics. Differences in white-tailed deer Odocoileus virginianus morphometrics across soil resource areas in Mississippi, USA, provide opportunity to test the predictive capacity of soil chemical and forage quality variables. Using principal components analysis (PCA), we modeled variation in body mass and antler score of ≥ 1.5-year-old male deer against seven soil chemical variables and 12 forage quality variables to elucidate potential nutritional factors corresponding with physical variation among 21 deer populations. We developed separate sets of models at the levels of state and soil resource area (Delta, Thin Loess and Lower Coastal Plain) and compared statewide models with general linear models (GLM) that related deer morphometrics to nominal classification variables representing the three soil resource areas. PCA distinguished a gradient of increasing soil fertility and forage quality that explained 58% of body mass and 52% of antler score variation statewide. However, the GLM using soil resource area as the explanatory variable explained 78 and 61%, respectively, indicating that management models should use soil resource area to designate areas with broadly similar nutritional planes. Within soil resource areas, the region with the greatest soil fertility and forage quality (Delta) did not model successfully for either body mass or antler score. The Thin Loess was successfully modeled for antler score, but only the Lower Coastal Plain, which had the lowest level of soil and forage quality, was successfully modeled for both morphometric variables. The Delta may have represented an area with habitat quality sufficiently high to render small variations non-influential. In contrast, the generally poorer soil quality of Thin Loess and Lower Coastal Plain soils and forages may act as a limiting factor on physical expression, which allowed some response to relatively small fluctuations in range quality. The potential utility of soil and forage metrics within soil resource areas to estimate deer physical qualities appears to be primarily for fine-tuning estimates largely determined by factors such as density and land use.

Condensed Tannins' Effect on White-Tailed Deer Forage Digestibility in Mississippi

Abstract Condensed tannins (CT) can reduce digestibility of forages for white-tailed deer (Odocoileus virginianus), potentially confounding estimates of diet quality and nutritional carrying capacity. We collected 143 spring and 142 summer samples of 8 important deer forage species from 22 properties in Mississippi, USA, and tested for CT content using a modified butanol-HCl assay. Three species (partridge pea [Chamaecrista fasciculata], southern dewberry [Rubus trivialis], and roundleaf greenbrier [Smilax rotundifolia]) contained CT, ranging from 0.11% to 6.46% dry weight. Summer CT concentration was greater than in spring for 2 species. We ranked soil samples from least to most fertile using 8 chemical characteristics and found a positive correlation between fertility and CT concentration for 1 species and no correlation for 2 species. We tested effects of CT concentration on in vitro dry matter disappearance (IVDMD) and in vitro protein digestibility using samples of partridge pea and roundleaf greenbrier and rumen fluid from 3 free-ranging deer. Average IVDMD was reduced 1.9% for each 1% increase in CT concentration. In vitro protein digestibility was reduced 2.5% for each 1% increase in CT concentration. Assuming that our methods reflect the effects of CT on in vivo digestibility, maximum loss of available crude protein (CP) in our samples was 3.0 g/100 g dry-weight forage, and only 13 of the 112 CT-containing forage samples (12%) would have decreased available CP by >1 g/100 g dry-weight forage. Deer consuming equal portions of sampled forages would lose <1% of dietary CP to CT. Comparisons of foraging area quality using crude protein estimates should be unaffected by CT under reasonable restrictions of similar habitat types, soil fertility, and time. Given the ability of deer to forage selectively and the abundance of alternative forages in Mississippi, the potential for CT to substantially affect spring or summer diet quality of deer appears minimal.

Developing a conceptual model of possible benefits of condensed tannins for ruminant production.

Enteric methane (CH4) emissions from ruminants have compelled a wide range of research initiatives to identify environmental abatement opportunities. However, although such mitigations can theoretically be attained with feed additives and feeding strategies, the limited empirical evidence on plant extracts used as feed additives does not support extensive or long-term reductions. Nevertheless, their strategic use (i.e. alone or combined in a simultaneous or consecutive use) may provide not only acceptable CH4 abatement levels, but also relevant effects on animal physiology and productivity. Condensed tannins (CT) represent a range of polyphenolic compounds of flavan-3-ol units present in some forage species that can also be added to prepared diets. Methods to determine CT, or their conjugated metabolites, are not simple. Although there are limitations and uncertainties about the methods to be applied, CT are thought to reduce CH4 production (1) indirectly by binding to the dietary fibre and/or reducing the rumen digestion and digestibility of the fibre and (2) directly by inhibiting the growth of rumen methanogens. On the basis of their role in livestock nutrition, CT influence the digestion of protein in the rumen because of their affinity for proteins (e.g. oxidative coupling and H bonding at neutral pH) that causes the CT-protein complex to be insoluble in the rumen; and dissociate in the abomasum at pH 2.5 to 3.0 for proteolysis and absorption in the small intestine. CT may also reduce gastro-intestinal parasite burdens and improve reproductive performance, foetal development, immune system response, hormone serum concentrations, wool production and lactation. The objectives of this paper are to discuss some of the beneficial and detrimental effects of CT on ruminant production systems and to develop a conceptual model to illustrate these metabolic relationships in terms of systemic physiology using earlier investigations with the CT-containing legume Lotus corniculatus. Our conceptual model indicated four complex and long-lasting relationships (digestive, toxicological, physiological and morphological) that can alter the normal biology of the animal. These relationships are interdependent, integrative, and sometimes, complementary to each other. This conceptual model can be used to develop mechanistic models to improve the understanding of the interaction between CT and the ruminants as well as to guide research initiatives of the impact of polyphenol-rich foods on human health.

The future of warm-season, tropical and subtropical forage legumes in sustainable pastures and rangelands

Forage legumes have the potential to contribute substantially to warm-season, subtropical and tropical pastures and rangelands. Compared to grasses, they have advantages in accessing subsoil nutrients and moisture; legumes typically concentrate protein in forage, even in infertile soils, and they can also provide ruminants with plant proteins and soluble carbohydrates that increase digestibility of grasses when consumed in legume–grass mixtures. Yet their inclusion in warm-season, subtropical or tropical pasture seed mixes or rangeland rehabilitation is minimal considering the percentage of grasslands coverage in these regions. Why have past diligent attempts failed to develop the germplasm, agronomic techniques, dissemination and ultimate widespread acceptance by land managers in regions where these legumes are widely adapted? Successful forage legume reports indicate that farmers’ participation in technology development, persistence with minimal management, adequate seed supply following release of new varieties, meeting recognised needs, delivery of clear benefits and profits, and communication among researchers, extension and stakeholders are crucial. Current and future research and development programs based on limited past successes and widespread failures should enhance successful commercial use of warm-season, subtropical and tropical forage legumes.

Soil organic carbon pools under switchgrass grown as a bioenergy crop compared to other conventional crops.

Abstract Switchgrass ( Panicum virgatum L.) has been proposed as a sustainable bioenergy crop because of its high yield potential, adaptation to marginal sites, and tolerance to water and nutrient limitations. A better understanding of the potential effects of biomass energy crop production practices on soil biological properties and organic matter dynamics is critical to its production. Our objective was to evaluate changes in C pools under a warm-season perennial switchgrass in different soils compared to typically-grown crops collected at College Station, Dallas, and Stephenville, TX in February 2001. Sampling depths were 0–5, 5–15, and 15–30 cm. Switchgrass increased soil organic C (SOC), soil microbial biomass C (SMBC), mineralizable C, and particulate organic matter C (POM-C) compared to conventional cropping systems. Soil C concentrations were in the order: long-term coastal bermudagrass [ Cynodon dactylon (L.) Pers.] Panicum coloratum L.) planted in 1992 > switchgrass 1997 > conventional cropping systems. Soil C concentrations tended to increase with increasing clay content. Greater microbial biomass C followed the order of Dallas > College Station > Stephenville, and ranged from approximately 180 mg C kg −1 soil at Stephenville to 1900 mg C kg −1 soil at Dallas. Particulate organic C was more sensitive than other fractions to management, increasing as much as 6-fold under long-term coastal bermudagrass compared to conventional cropping systems. Our study indicated that conversion of conventional cropping systems into switchgrass production can sequestrate more SOC and improve soil biological properties in the southern USA.

Effects of using ground redberry juniper and dried distillers grains with solubles in lamb feedlot diets: Growth, blood serum, fecal, and wool characteristics

Effects of using ground redberry juniper and dried distillers grains with solubles (DDGS) in Rambouillet lamb (n = 45) feedlot diets on growth, blood serum, fecal, and wool characteristics were evaluated. In a randomized design study with 2 feeding periods (Period 1 = 64% concentrate diet, 35 d; Period 2 = 85% concentrate diet, 56 d), lambs were individually fed 5 isonitrogenous diets: a control diet (CNTL) that contained oat hay but not DDGS or juniper or DDGS-based diets in which 0 (0JUN), 33 (33JUN), 66 (66JUN), or 100% (100JUN) of the oat hay was replaced by juniper. During Period 1, lambs fed CNTL had greater (P < 0.05) DMI and ADG and tended to have greater (P < 0.10) G:F than lambs fed 0JUN or lambs fed DDGS-based diets. Lamb DMI, ADG, and G:F quadratically increased (P < 0.008) as juniper increased in the DDGS-based diets. During Period 2, lambs fed CNTL had greater (P < 0.05) DMI than lambs fed 0JUN or lambs fed DDGS-based diets, but ADG was similar (P > 0.41). Compared to 0JUN, lambs fed CNTL had similar (P = 0.12) G:F and tended to have less G:F (P = 0.07) than lambs fed DDGS-based diets. Among lambs fed DDGS-based diets, DMI was similar (P > 0.19), ADG increased linearly (P = 0.03), and G:F tended to decrease quadratically (P = 0.06) as juniper increased in the diet. Serum IGF-1, serum urea N (SUN), and fecal N were greater (P < 0.05) and serum Ca and P and fecal P were similar (P > 0.13) for lambs fed CNTL vs. lambs fed DDGS-based diets (CNTL). Within lambs fed DDGS-based diets, SUN increased quadratically (P = 0.01) and fecal N increased linearly (P = 0.004), which can partially be attributed to increased dietary urea and condensed tannin intake. Most wool characteristics were not affected, but wool growth per kilogram of BW decreased quadratically (P = 0.04) as percentage of juniper increased in the DDGS-based diets. When evaluating the entire 91-d feeding trial, results indicated that replacing all of the ground oat hay with ground juniper leaves and stems in lamb growing and finishing diets is not detrimental to animal performance and that DDGS-based diets can reduce total feedlot costs, as compared to sorghum grain and cottonseed meal-based diets. However, compared to using juniper or oat hay as the sole roughage source, using both during the growing period (Period 1) enhanced growth performance and further reduced total feedlot costs.

Coastal Bermudagrass (Cynodon dactylon) Yield Response to Various Herbicides

Several new herbicides have been registered for pasture weed control, but their effect on ‘Coastal’ bermudagrass dry matter (DM) yield has not been documented. The objective of this study was to determine the effect of clopyralid, fluroxypyr, imazapic, picloram, picloram + fluroxypyr, picloram + 2,4-D amine, triasulfuron + dicamba, triclopyr amine + clopyralid, triclopyr ester, triclopyr ester + fluroxypyr, trifloxysulfuron, 2,4-D amine + dicamba, and 2,4-D ester on Coastal bermudagrass yield. Total DM yields of Coastal bermudagrass were not reduced by 0.84 kg/ha clopyralid, 0.031 kg ai/ha triasulfuron + 0.44 kg ai/ha dicamba, 1.205 kg ai/kg 2,4-D amine + 0.42 kg/ha dicamba, and 2.31 kg/ha 2,4-D ester. Although 0.227 kg ai/ha picloram + 0.84 kg/ha 2,4-D amine, 0.945 kg ai/ha triclopyr amine + 0.315 kg ai/ha clopyralid, and 1.68 kg ai/ha triclopyr ester reduced Coastal bermudagrass DM yields in harvest 1, there was no cumulative loss in total production in either 2001 or 2002 with these herbicides compared with that of the nontreated control. Coastal bermudagrass total DM yields were reduced by 52% with 0.158 kg ai/ha imazapic when applied to dormant bermudagrass in 2001, and by 26% with 0.021 kg ai/ha trifloxysulfuron when applied to actively growing bermudagrass in 2001; however, neither herbicide reduced total cumulative yield in 2002. In 2001 and 2002, total DM yield was reduced by an average of 25% with 0.42 kg/ha fluroxypyr, by 45% with 0.105 kg/ha imazapic, by 57% with 0.158 kg/ha imazapic, by 65% with 0.21 kg/ha imazapic, by 25% with 0.56 kg/ha picloram, by 20% with 0.188 kg/ha picloram + 0.188 kg/ha fluroxypyr, and by 18% with 0.63 kg/ha triclopyr ester + 0.21 kg/ha fluroxypyr, when applied to actively growing Coastal bermudagrass. Nomenclature: Clopyralid; dicamba; fluroxypyr; imazapic; picloram; triasulfuron; triclopyr amine; triclopyr ester; trifloxysulfuron; 2,4-D amine; 2,4-D ester; bermudagrass, Cynodon dactylon (L) Pers. ‘Coastal’ #3 CYNDA. Additional index words: Bermudagrass tolerance, injury, yield.

The role of ruminant animals in sustainable livestock intensification programs

Food supply has improved considerably since the eighteenth century industrial revolution, but inadequate attention has been given to protecting the environment in the process. Feeding a growing world population while reducing the impact on the environment requires immediate and effective solutions. Sustainability is difficult to define because it embodies multifaceted concepts and the combination of variables that make a production system sustainable can be unique to each production situation. Sustainability represents the state of a complex system that is always evolving. It is an intrinsic characteristic of the system that needs to be shaped and managed. A sustainable system has the ability to coexist with other systems at a different output level after a period of perturbation. Resilience is the ability of a system to recover and reestablish a dynamic equilibrium after it has been perturbed. Sustainable intensification (SI) produces more output(s) through the more efficient use of resources while reducing negative impact on the environment; it provides opportunities for increasing animal and crop production per area while employing sustainable production alternatives that fully consider the three pillars of sustainability (planet, people, and profit). Identifying the most efficient animals and feeding systems is the prerequisite to successful applications of sustainable livestock intensification programs. Animal scientists must develop strategies that forecast the rate and magnitude of global changes as well as their possible influences on the food production chain. System modeling is a powerful tool because it accounts for many variables and their interactions involved in identifying sustainable systems in each situation.