Grass-based finishing of early- and late-maturing breed bulls within suckler beef systems: Performance, profitability, greenhouse gas emissions and feed-food competition

Abstract

Demand for beef is increasing but concerns about the environmental impact of ruminant-protein production and food security are also increasing. Animal performance, profitability, greenhouse gas (GHG) emissions and feed-food competition within spring-calving suckler grass-based systems in which the males, progeny of either early- (EM) or late-maturing (LM) breed sires, were finished from pasture-alone or pasture-plus-concentrate supplementation, at 19.5 months-of-age, were evaluated. Sixty yearling bulls, previously offered grass silage ad libitum and supplementary concentrates during a first winter ‘store’ period, were assigned within breed type (EM or LM) to a pasture-finishing strategy of grass only (G-G) or grass + 3.2 kg dry matter of a barley-based concentrate daily (G-GC). Bulls rotationally grazed Lolium perenne-based swards over a 192 day grazing season. Concentrates were offered to G-GC treatments for the final 95 days following which all animals were slaughtered. The experimental data produced were used to populate a whole-farm systems economic and environmental model to determine beef output, profit, GHG emissions and feed-food competition of spring-calving suckler calf-to-beef systems. There were no finishing strategy × breed type interactions. Supplementation increased slaughter weight (+37 kg), carcass weight (+27 kg), carcass fat score (+1.1 units, 15-point scale), and resulted in more yellow subcutaneous fat. The LM bulls were heavier at slaughter (+65 kg), had a heavier carcass (+45 kg), greater kill-out proportion (+14 g/kg), a greater lean meat proportion in the carcass (+35 g/kg), superior carcass conformation score (+1.4 units, 15-point scale), lower carcass fat score (-1.2 units), and more yellow subcutaneous fat than EM bulls. Compared to G-GC suckler calf-to-beef systems, G-G systems had lower beef output, were less profitable, had higher GHG emission intensities (kg CO2 eq) per kg live- (10.2 v. 10.1), carcass- (18.6 v. 18.1) and meat- weight (26.1 v. 25.5), but superior human-edible protein (HEP) and energy efficiencies. The LM-sired systems were more profitable, had lower GHG emission intensities, and superior HEP and energy efficiency than EM systems. The HEP efficiency ratios exceeded 1.0 (i.e. were net producers of protein) for the G-G treatments and ranged from 0.9 to 1.0 for the G-GC treatments, when offered the ‘control’ barley-soyabean meal based concentrate: alternatively, using by-product concentrate feedstuffs increased the HEP ratios to 3.9 or greater. In conclusion, the existence of synergies and trade-offs between sustainability metrics makes the selection of a beef production system that optimises all performance metrics difficult.