Location: Forage and Range Research2012 Annual Report
1a. Objectives (from AD-416):
The objectives of this cooperative research project are: 1) Evaluate the relative livestock performance when grazing mixtures of pasture grasses and legumes; and 2) Evaluate the productivity of grass and legume mixtures; and 3) Breed pasture grasses and legumes with enhanced compatibility for use in grazing.
1b. Approach (from AD-416):
This research is an expansion and continuation of the research goals and objectives originally started under SCA #58-5428-4-373 entitled "Develop and evaluate plants for improved livestock performance." The new research will determine livestock performance and pasture productivity of grass-legume mixtures in comparison to commercially fertilized grass monocultures. Standard check cultivars and germplasm from ongoing ARS breeding programs will be established in large and small scale research plots. Large scale plots will be used to compare/determine animal performance, carrying capacity, and nutritional content of grass monocultures versus grass and legume mixtures. Results will be based upon livestock weight gain, forage dry matter production, and in-vitro forage quality analyses. Small plots, using multiple species of grasses and legumes in varying composition ratios, will be established to determine optimum grass-legume mixtures and plant densities that maximize pasture productivity in comparison to commercial fertilizer. Livestock grazing on these plots will ensure realistic pressures common to pastures. The role that endophyte infection of grasses has on grass-legume mixture compatibility may be evaluated. Livestock and plant data will be utilized in plant improvement programs to breed for improved compatibility among pasture grasses and legumes.
3. Progress Report:
During FY-2012: A two-yr grazing study was completed by evaluating the effects of finishing beef cattle grazed on tall fescue (TF) pastures without or with nitrogen (N) fertilization on growth performance, ruminal fermentation, and carcass characteristics. In response to N fertilization, overall average daily gain (ADG) was greater (P<0.05) and dry matter intake trended upward (P=0.07) in steers that grazed TF+NF pastures (P < 0.05). Regardless of N fertilization, ADG peaked between week four and eight (1.05 kg/d; P < 0.01), and then declined until week 16. Greater total volatile fatty acid (VFA) concentrations were detected in ruminal fluid of steers that grazed TF+NF (P < 0.01), but only a minor effect was shown on individual VFA (acetate, propionate, and butyrate) concentrations and acetate-to-propionate ratio. Back fat thickness, ribeye area, and intramuscular fat concentration did not differ between treatments. Overall results of this study indicate that N fertilization on TF affected ruminal fermentation which positively influenced growth performances, but did not affect carcass characteristics of grazing beef steers. In addition, readily fermentable carbohydrate supplementation is needed to improve utilization of increased dietary CP due to N fertilization and consequently enhance growth performances of grazing steers. A peer reviewed journal article on this study in the Professional Animal Scientist was accepted and is in press. An in vitro continuous culture study was conducted to investigate energy supplementation strategies on pasture forages to assess effects of energy supplementation [no concentrate, 30% ground corn, or 30% dried distilled grains with solubles (DDGS)] with four pasture forages [tall fescue (TF) without N fertilizer (TF-NF), TF with N fertilizer (TF+NF), TF-alfalfa mixture, and TF-birdsfoot trefoil mixture (TF+BFT)] on vitro ruminal fermentation and N utilization. The results indicated that supplementing pasture forages with corn or DDGS enhanced microbial assimilation of ammonia-N and shifted metabolic pathways of microbial fermentation and methane gas production. Supplementation of corn in the TF+BFT elicited a similar ammonia-N concentration compared when corn was supplemented in the TF+NF. Therefore, grass-legume mixtures would be a sustainable component in grass grazing systems to improve N utilization efficiency with appropriate energy supplementation. This study was recently published in the peer-reviewed journal, The Professional Animal Scientist. The small plots of binary mixtures of five grasses [orchardgrass (OG), tall fescue (TF), meadow brome (MB), timothy, and perennial ryegrass (PR)] and three legumes [alfalfa (AF), birdsfoot trefoil (BF), and cicer milkvetch (CM)] were established and data collection was initiated. Ratios in the mixtures included 0, 25, 50, and 75% legume composition. Tall fescue, OG, and MB grass-legume mixes averaged 6.0, 5.0, and 14.0% higher forage production than their respective grass monocultures. The highest seasonal forage production of TF combinations was 1.62 Mg/ha TF:AF (50:50), 1.63 Mg/ha TF:BF (75:25), and 1.64 Mg/ha TF:CM (75:25). Highest forage production of OG combinations was 1.10 Mg/ha OG:AF (50:50), 1.09 Mg/ha OG:BF (75:25), and 0.99 Mg/ha OG:CM (75:25). Highest seasonal forage production of MB combinations was 1.23 Mg/ha MB:AF (50:50), 1.25 Mg/ha MB:BF (75:25), and 1.11 Mg/ha MB:CM (75:25). These preliminary results suggest that grass-legume mixtures can be an effective strategy to improve pasture productivity. A Utah State University visiting scientist works to characterize orchardgrass germplasm for freezing tolerance and to characterize the relationship between high concentrations of water-soluble carbohydrates and resistance to abiotic stress such as freezing. Initial aspects of the research are now complete. Currently, work continues to refine growth chambers for use in the study and to propagate sufficient plant material for the freezing analyses. It is anticipated that the research will be completed this fall and the manuscripts submitted for publication in 2013.