Seed contamination of sheep by barley grass (Hordeum spp.) in southern Australia: livestock production and economic interactions

Context Barley grass (Hordeum spp. L.) is a pervasive annual grass weed of southern Australian crops and pastures, producing seeds that contaminate sheep carcasses and, causing weight loss and discounts at processing of affected meat and wool. Previous modelling of barley grass control highlighted effective control strategies for reducing seed banks in lucerne over 10 years. However, the impacts of weed management strategies on the productivity of lamb enterprises grazing pastures of varying infestation levels currently remain unknown. Aims This study assessed the capacity of a ex ante bioeconomic modelling approach to simulate the impacts of variable barley grass seed contamination and weed control strategies on the profitability and productivity of weaned lambs grazing a barley grass-infested lucerne pasture in southern Australia. Methods A bioeconomic model was developed by incorporating a barley grass population model, a livestock growth model (incorporating impacts of seed contamination) within an economic framework to simulate impacts of weed control strategies applied to the barley grass population. Control strategies were activated in the model at various weed densities to investigate differences in lamb production and were simulated over a 10-year period to identify optimal weed control strategies. Key results Simulating the absence of barley grass control demonstrated incursion of large losses (A$793/ha) to the lamb production system over 10 years. Economic returns tended to remain highest under integrated management scenarios at lower weed densities (≤50 seedlings/m2). Maximum profitability could be attained through strategies targeting weed fecundity, particularly at the lowest weed density (5 seedlings/m2). Conclusions Integrated management of barley grass produced the greatest economic benefit at low weed densities when control targeted seed production. The simulation of repeated mowing constrained the barley grass infestation and showed promise as a non-chemical practice for reducing seed contamination in sheep. Further field studies and development of associated model relationships will facilitate further substantiation of model outputs. Implications Results highlighted the potential for combined model frameworks to determine economic consequences of weed management in livestock grazing systems and to identify optimal strategies that maximise livestock health, welfare and production.