Evaluating Sustainable Dairy-Beef Production Systems

Beef production is currently under scrutiny because of its impact on the environment, use of limited land resources and use of human-edible food as a feed source for cattle. Nevertheless, beef-meat provides a high-quality source of protein and essential nutrients and makes a substantial contribution to the global economy. Approximately 63% of beef production in Ireland comes from the dairy herd. This thesis aimed to investigate the physical, economic, GHG, feed-food competition and land-use performance of alternative forage-based dairy-beef systems. The Grange Dairy Beef Systems Model (GDBSM) was substantially enhanced to include GHG, feed-food and land use performance assessment capabilities, and then used to analyze a number of research questions in four studies that form the main body of this thesis. Chapter 1 sets out the aims and objectives of the thesis, whilst Chapter 2 outlines current beef production systems along with the opportunities and challenges forage-based beef production systems currently face. Chapter 3 is a review of the literature on agricultural systems and mathematical modelling. Chapter 4 presents a study which investigated the biophysical, economic, GHG and feed-food competition performance of alternative dairy-beef steer systems. The results showed a wide range in farm net margins with systems finishing at pasture at the end of the second grazing season, at 20 months of age, being most profitable. These systems also had the lowest GHG emissions intensities. Steer systems finished at pasture during the third grazing season were the only net producers of human-edible protein, whilst all systems were net consumers of human-edible energy. Chapter 5 used experimental data to evaluate the variability of physical and economic performance, GHG emissions, feed-food competition and pastureland-use at differing stocking rates (SR). Results showed that across all treatments investigated, the low SR animals were heavier, with better carcass conformation and fat scores at slaughter. Increasing SR resulted in greater carcass output per hectare and subsequently high SR systems were, on average, 22% more profitable than those at the low SR. Heifer production systems had lower GHG emissions intensity, higher human edible protein and energy production but were less profitable than their steer counterparts due to their lower carcass weights but similar costs of production. Chapter 6 quantified and compared the national average (AVE) dairy-beef farms in Ireland with dairy-beef farms participating in farm improvement programs (IMP) and with research (RES) farms to compare key sustainability indicators. Results highlighted the substantially lower output values, on a per hectare basis, in the AVE and IMP farms compared to RES due to their lower stocking rates, increased age at slaughter and poorer slaughter performance: all of which had a negative impact on farm profitability. AVE and IMP had similar GHG emissions per kilogram of product produced: - which were higher than RES. Each of the three farm categories were net producers of human edible protein and net consumers of human edible energy. Chapter 7 examined a number of mitigation strategies based on management practices that can be implemented on dairy-beef production systems. Results showed that combining all mitigation strategies was found to be the most effective way of lowering the GHG emissions intensity of the modelled dairy-beef systems. Incorporating clover in grassland pastures was found to be the most profitable stand-alone mitigation strategy. Substituting feed by-products for barley in the concentrate ration converted all systems into net producers of human edible protein. This thesis demonstrates that there are inherent trade-offs between dairy-beef production systems and no one system optimised all metrics in terms of physical and economic performance, greenhouse gas emissions, feed-food competition and pasture land-use.