180 Effects of Forage Mixtures on Rumen Fermentation Parameters as Assessed by Continuous Culture

The impact of using diverse forage mixtures on rumen performance is poorly characterized. The objective of this study was to evaluate the impact of feeding diverse pastures on rumen performance using in vitro continuous culture fermenters. Treatments were assessed using a 4 x 4 Latin square design. Each 10-d period included 7-d of adaption followed by 3-d of sample collection. Dietary treatments (DM basis) included 1) 50% orchardgrass + 50% alfalfa (OG-ALF); 2) 50% OG-ALF + 50% red clover (RC); 3) 50% OG-ALF + 50% pearl millet (MIL); and 4) 50% OG-ALF + 50% sorghum x sudangrass (SUD). Forage diets (131 g DM/ fermenter/ d) were divided into 4 portions/d (33%, 0600 h; 17%, 0720 h; 33%,1800 h; 17%, 1920 h). Fermenter pH measurements were collected every min for the entire experiment. Methane concentrations were measured using a gas probe and recorded twice daily (0530 h,1730 h) in triplicate on d 7, 8, 9, and 10. Daily total effluent samples were collected on d 8, 9, and 10 for VFA analysis. Results were analyzed using PROC MIXED of SAS. There were no differences in total VFA concentrations (P = 0.08), molar proportions (P = 0.22), or individual VFA ratios (P > 0.05) as a result of treatment. Fermenter pH did not differ between fermenters as a result of treatment (P > 0.05). Fermenters receiving OG-ALF had the greatest methane concentration (50.8 mg/dL), which was higher (P < 0.05) than methane concentrations in fermenters receiving MIL (6.2 mg/dL), SUD (6.9 mg/dL), or RC (21.2 mg/dL). Methane concentrations from the MIL, SUD and RC treatments did not differ (P > 0.05). This indicates that binary forage mixtures may have lower nutritional value compared with diverse mixtures, and this diversification could provide nutritional benefits.

175 Effect of age at calving on greenhouse gas emissions from simulated beef farms grazing four stockpiled forage species in late fall/early winter

The impact of age at first calving (2 versus 3 yrs) and type of forage species grazed in late fall/early winter on lifetime greenhouse gas (GHG) emissions from a cow-calf herd over an 8 or 9 yr period was examined. Farm simulations, based in Manitoba, Canada, were assessed using the Holos model to determine whole-farm GHG emissions for each scenario. The baseline herd consisted of 170 cows, 6 bulls, and their progeny which were sold at weaning, apart from herd replacements. Each simulation began with 207 newborn, female calves, with GHG emissions measured annually. From October to December, 1 of 4 stockpiled forages/forage mixtures were grazed: i) standing corn (COR), ii) tall fescue/meadow bromegrass (TFM), iii) orchardgrass/alfalfa (OGA), and iv) tall fescue/alfalfa/cicer milkvetch (TAC). All other feeding phase diets did not differ across all scenarios. Herd GHG emissions (Mg CO2e) were lower with heifers calving at 2 yrs (3,938 ± 71 Mg CO2e) versus 3 yrs (4,634 ± 72 Mg CO2e). Enteric methane (CH4) was the largest source of GHG emissions accounting for 66% of the total in both the 2- and 3-yr scenarios. Average enteric CH4 values were 3,820±61, 4,251 ± 68, 4,887±79, and 4,220 ± 68 Mg CO2e for simulations grazing COR, TFM, OGA, and TAC, respectively and were inversely related to total digestible nutrient (TDN) content of the forage mixtures with 72, 54, 45 and 55% TDN. Emissions were highest from OGA, the lowest quality forage, in both calving scenarios. Nitrous oxide emissions from livestock manure were the second highest contributing source, representing 15% of total emissions. Reducing age at first calving (2 versus 3 yrs) and providing higher energy forage in late fall/early winter reduced cow-calf GHG emissions. The adoption of management strategies such as reducing age at first calving and improving forage quality for extended grazing may reduce emissions from the cow-calf sector.

191 Yield and nutritive quality of summer annual forage mixtures

Summer annual forage mixtures are both high yielding and contain a high nutritive quality. They provide a summer forage option for maintaining stockers, forage-finished beef, and replacement heifers on with little to no external inputs needed. Recently, sugarcane aphid infestations have limited production of sorghum × sudangrass (Sorghum bicolor var. bicolor*bicolor var. sudanese; S). This study investigated mono-, bi-, and tri- cultures of S, cowpea (Vigna unguiculata; C), and crabgrass (Digitaria ciliaris; R). Forage yield, CP, NDF, ADF, ADL, and sugarcane aphid counts were determined for each treatment. Sugarcane aphid counts were conducted on a weekly basis during the study and forage samples were harvested twice during each season. A forage subsample was taken for determination of CP, NDF, ADF, and ADL using wet chemistry. Data were analyzed using Proc Glimmix of SAS 9.4 (SAS inst., Cary, NC). During Year 1, the only difference in yield among treatments was observed in R, which was lower than other plots (949 and 1,259 kg/ha, respectively; P < 0.05). Neutral detergent fiber was greatest (P < 0.0001) in treatments containing S, whereas C and C+R had the least NDF (64.6%, 55.1%, and 56.6%, respectively; P < 0.02). Sugarcane aphids were greater (P < 0.0001) in S+C compared to S+R and SI on July 12 (33.5, 21.1, and 22.4 aphid days/ two leaf sample, respectively). During Year 2, there were no differences in yield among plots (996 kg/ ha, P > 0.9); NDF was greatest in S and lowest in plots containing C and C+R (63%, 46%, and 45.6%, P < 0.0001). While there appeared to be no reduction in sugarcane aphid pressure in the mono- and mixed- cultures of S, C+R showed promise as a summer annual mixture with similar yield and higher quality to that of S and S mixtures.

91 Growth performance of landrace hair sheep lambs under different forage environments

Lambs for the project were produced under semi-continuous lambing using accelerated mating in a dual flock system of landrace hair sheep (Barbados Blackbelly and St. Croix). Lamb cohorts were born every 4 mo. At 4 mo of age, lambs were rotationally stocked on pastures consisting of either tall fescue, summer and winter annual forage mixtures, or were provided bermudagrass hay in sacrifice pastures. Lambs were rotated based on forage availability, and forage was sampled for nutrient analysis at each rotation. Soyhull pellets were provided at 1–3% BW. Lambs were removed as they reached 36 kg. Weights were recorded (n = 1945) from 7 cohorts between December 2017 and September 2019 as lambs moved between forage environments (6 to 40 d). The grazing lamb flock was made up of two cohorts (initial size: 25–53 lambs) at any given time. The effect of breed, sex, cohort class (4–7 mo, and 8–11 mo), and forage environment (classified as cool and warm season annual, perennial pasture, and hay) on ADG was determined. Mean ADG was higher in St. Croix than Barbados Blackbelly (105 vs. 93 g/d; P< 0.05), and ram than ewe lambs (115 vs. 84 g/d; P < 0.001). Older cohorts in each grazing period had higher ADG than younger cohorts (105 vs. 94 g/d; P < 0.05). There was a wide range in ADG for individual weigh periods (16 to 310 g/d), but warm and cool season annuals and hay feeding forage environments produced similar ADG (110–117 g/d); while summer perennial forage grazing was lower (56 g/d; P < 0.001). Supplementing forage with soyhull may have masked differences in lamb growth between forage environments despite higher crude protein and TDN in the annual forages (11 to 20%; and 55 to 85%) than in hay and perennial summer grazing (8 to 10%; and 50 to 55%).

Benefits of mixed grass–legume pastures and pasture rejuvenation using bloat-free legumes in western Canada: a review

Forage mixtures containing legume out-yield monocultures, fix atmospheric nitrogen, and have lower carbon footprints. However, evidence-based information on creating forage mixtures by direct seeding legumes into existing pastures is limited, and information on bloat-free legumes is nonexistent. Traditionally, pastures requiring improvement in western Canada were fully replaced by breaking up the old stand and reseeding. With new and improved forage cultivars, better seeding equipment, and increased knowledge about pasture management, there is a growing interest among producers in rejuvenating pastures instead of replacing them. Pasture rejuvenation refers to the improvement in biomass productivity and (or) nutritional quality of existing pasture without removing the existing vegetation. This can be done through fertilizer application, which is generally expensive and causes negative environmental impacts. Amelioration of compacted pastureland via mechanical aeration is short-lived and can lead to weed problems. As an alternative, direct seeding of productive, nutritive and bloat-free legume species into existing pasture is an attractive option for pasture rejuvenation. For high performance grazing systems, identification of suitable bloat-free legumes and methods for direct seeding into old grass and legume stands will be essential strategies. This review includes information on the benefits of mixed pastures and seeks possible methods of introducing bloat-free forage legumes into existing pastures in western Canada for rapid improvement in productivity and quality while positively influencing animal, soil, and environmental health.