Bioeconomic and sustainability performance of dairy-beef steer and heifer production systems differing in stocking rate

There is little published research on dairy-beef heifer systems or comparisons of heifer and steer dairy-beef production. Furthermore, given its impact on the productivity and economics of dairy-beef systems, any comparison of gender must also consider potential interactions with stocking rate (SR). The objective of this study was to evaluate the variability of physical and economic performance, greenhouse gas emissions, feed-food competition and pasture land-use of dairy-beef production steer and heifer systems at differing stocking rates. Performance data from a two (gender: Steers and Heifers) x two (SR: Low and High) x two (breed-types: Early-maturing (EM) and Late-maturing (LM) factorial experiment was used to parameterize a bio-economic farm systems model. Low SR animals were heavier, had higher fat scores and better conformed at slaughter. High stocking rate resulted in greater carcass output per hectare and subsequently were, on average, 22 % more profitable than their Low SR counterparts. Late-maturing animals were found to be more profitable than early-maturing, and steers were more profitable than heifers. GHG emissions of the eight treatments investigated ranged from 10.7 to 17.7 kgs of carbon dioxide equivalents (kg CO₂eq) per kilogram of carcass weight produced, with both High SR and heifer systems having lower GHG emissions per kg of product than their Low SR and steer counterparts. Human edible protein efficiency was only favorable for the steer systems. High SR systems had, on average, lower land use per kg of product than their Low SR counterparts. Results from this study indicate that no single treatment was optimal across the range of performance metrics considered.