Higher energy concentration traits in perennial ryegrass (Lolium perenne L.) may increase profitability and improve energy conversion on dairy farms

Abstract

The effect of improving energy concentration of pasture dry matter (DM) in perennial ryegrass (Lolium perenne L.) on two dairy farms in temperate regions (south west Victoria and Tasmania) of Australia was modeled in this study. A deterministic, dynamic model of a pasture based dairy system was used to assess how annual farm operating profit (OP), and energy conversion efficiency (as greenhouse gas emissions per unit of product) may be affected by an increase in metabolizable energy (ME) concentration of pasture compared to a ‘Base Scenario’ (with no changes in ME). Changes in OP were calculated over 20 1-year periods using three methods of utilizing additional ME from perennial ryegrass. These included the effect of an arbitrary 1 MJ/kg of dry matter (kg DM) increase in ME concentration of pasture on, milk production per cow with no change in the number of cows (‘Base1M Scenario’), no change in milk production per cow but an increase in stocking rate (‘Base1 + SR Scenario’), or a proportionate reduction in purchased concentrates (‘Base1-Conc Scenario’). The mean increase in OP relative to the Base Scenario was AUD482/ha.year for Terang and AUD783/ha.year for Elliott in the Base1M Scenario. This assumed additional ME in pasture was converted into greater milk production per cow using factors of 5.19 MJ/L milk for Terang and 5.23 MJ/L milk for Elliott. Changes in OP for the two other scenarios (Base1 + SR Scenario and Base-Conc Scenario) still provided between 40% and 54% increases in OP compared to the respective Base1M Scenarios. If the energy requirements of additional milk production was increased by 3 MJ/L milk, the OP in the Base1M Scenarios for Terang and Elliott were still 24% and 27% greater than the respective Base Scenarios. In terms of energy conversion, reductions of 10–13% of greenhouse gas emissions per unit of energy corrected milk were estimated for a 1 MJ/kg DM increase in pasture ME in the Base1M Scenarios compared to the respective Base Scenarios. The magnitude of changes in OP using alternative methods of calculation supports the hypothesis that increasing ME concentration of pasture could provide benefit to grazing-based dairy farms, regardless of how a farmer utilizes the additional ME. This study provides a valuable method to aid investment decisions about the value of the ME concentration trait and where best to allocate resources towards achieving these traits in perennial ryegrass.