|dc.description.abstract||Rising global population is driving the requirement for more sustainable food production. Although, pastoral milk production efficiency has improved to meet demand, the intensification of practices has simultaneously increased environmental footprint by increasing methane (CH₄) emissions and urinary nitrogen (UN) excretion. Therefore, design and evaluation of practical on farm mitigation methods are required. The objective of this thesis was to explore strategic feeding managements during early and late lactation, with the aim of reducing methanogenesis and UN excretion, while maintaining milk production.
For the purpose and objective of this work, the mechanistic and dynamic dairy cow model, MINDY (Gregorini et al., 2013, 2015, in press) was used.
The first modelling experiment evaluated the effect of altering herbage allowance (HA) on dry matter intake (DMI), milk solids (MS), UN, and CH₄ production. As expected, greater HA increased DMI and MS production at a diminishing rate. Increased HA heightened consumption of fermentable carbohydrates and N containing compounds, resulting in greater emissions of both CH₄ and UN. However, with increased HA the emission intensity (g kg MS⁻¹) and CH₄ yield (g CH₄ kgDM⁻¹) declined. The results from this experiment agree with other studies and was used as a basis to add additional strategic feeding management in the following experiments.
The second experiment examined altering the time of herbage allocation to reduce methanogenesis and UN excretion while maintaining MS production. The treatments were a factorial arrangement of HA (as the first experiment) and time of pasture allocation either after the morning (AM) or afternoon (PM) milking. The PM treatments on average had a greater DMI (1.9 and 1.7%) and MS yield (2.3 and 0.7%) as compared to AM, in EL and LL respectively. The PM treatments also produced 5.1 and 3.6% more CH4 and 4.7 and 7.8% less UN in EL and LL, respectively. Altering the time of HA is a simple and cost-effective management practice to reduce the environmental footprint of productive grazing dairy cows.
Finally, supplementation strategies were evaluated on top of experiment two’s treatments by the addition of either maize silage (MZ), maize grain (MG), or barley grain (BG) fed either prior to AM, PM, or each milking. When allocated BG, MZ, and MG in the PM rather than the AM cows respectively consumed 0.2, 8.9, and 1.2% more DM in EL and 4.0, 11.0, and 2.5% more DM in LL. Consequently, PM allocation of BG, MZ, and MG resulted in production of 0.2, 2.2, and 0.3 % more MS in EL, and 1.7, 3.6, and 1.0 % greater in LL. Similarly, the PM supplement allocation on average excreted less UN and emitted more CH₄. However, the weak positive relationship between CH₄ and UN indicates potential to simultaneously reduce their production by altering the time of herbage and supplement allocation.
Grazing and feeding management tools are inexpensive and easily integrated into practice yet aid in reaching both mitigation and production goals. Further empirical research is required to understand their usage under competitive grazing and use in conjunction with other mitigation techniques.||