Journal Articles
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Item Greenhouse gas mitigation in pasture-based dairy production systems in New Zealand: A review of mitigation options and their interactions(Elsevier B.V., 2025-08) Kalehe Kankanamge E; Ramilan T; Tozer PR; de Klein C; Romera A; Pieralli SReducing greenhouse gas (GHG) emissions from dairy farming is crucial for mitigating climate change and enhancing the environmental credentials of New Zealand's dairy exports. This paper aims to explore potential GHG mitigation measures and their interactive effects when combined within New Zealand context, emphasising the practicality of these combinations, particularly focusing on recent studies of pasture-based dairy systems. The review assesses various mitigation options across animal, manure management, feed-based, soil-related, and system-related interventions and identifies immediately applicable mitigation options based on specific criteria. It also discusses the implementation costs, implications on emissions, and the combined effects of these options when applied as bundles in pasture-based systems using a combination matrix. It is indicated that mitigation options on New Zealand's dairy farms can yield diverse outcomes and costs based on farming characteristics. By analysing different combinations of short-listed, it was found that although most mitigation options are compatible, some may have a lower overall reduction potential because of interaction effects. Integrating lower N fertiliser use, low-emission feed, and reduced stocking rates with high-performing animals provides a practical approach for GHG reductions and potential cost savings. However, implementing compatible mitigation bundles requires better quantification of their interactions, economic viability, and compatibility with existing farming systems which need further research.Item A comparison of three nutritional models for estimating total metabolisable energy requirements for a ewe, beef breeding cow, lamb, and a calf/yearling in New Zealand's pasture-only system(Elsevier B V, 2025-09-01) Adjabui JA; Morel PHC; Morris ST; Kenyon PR; Tozer PRIn New Zealand (NZ), the metabolisable energy requirements (MER) of ruminants can be estimated using nutritional models from Nicol and Brookes (2017), CSIRO (2007), and NZ's Agricultural Inventory Model (AIM) of the Ministry for Primary Industries [MPI] (2022). The aim in this study was to calculate the total MER of a ewe, beef breeding cow, lamb, and a calf/yearling in a pasture-only system in NZ under the same assumptions to assess the extent and reasons for variations among the three commonly used nutritional models, and the implications for a given farm/s. The study utilised MER models from the three sources above using a factorial method. This method determines the MER for each physiological phase of an animal, to estimate total MER for each animal. The AIM (MPI 2022) model relative to Nicol and Brookes (2017), and CSIRO (2007) models respectively, estimated 13.4 % and 8.0 % higher MER for a ewe, 16.3 % and 16.6 % for a cow, 1.1 % and 2.0 % lower for a lamb, and 9.2 % and 9.2 % higher for a calf/yearling mainly due to a higher maintenance MER compared to the other models. This has implications for feed budgeting and stocking rates (SR) for a given farm, as the AIM (MPI 2022) model leads to a lower SR than the other two models for a given level of feed available. Energy balances and productivity could be negatively impacted if a model underestimates MER. This also yields different greenhouse gas (GHG) profiles, especially enteric methane, for a given farm and could potentially have financial consequences for farmers if an Emissions Trading Scheme was introduced. For consistency in ME estimates and GHG reporting, further research (feeding trials) is required to compare these model estimates to actual requirements of ruminants under NZ conditions. This could help identify the model that most accurately reflects MER for ruminants in the country.Item Are native shrubs a sustainable alternative to radiata pine on steep slopes? Insights using bioeconomic model for hill country farms in New Zealand(Taylor and Francis Group on behalf of the Royal Society of New Zealand, 2025-05-07) Wangui JC; Millner JP; Kenyon PR; Pain SJ; Tozer PRLimited data on native shrubs has hindered direct comparisons with pine radiata as afforestation options for steep slopes on New Zealand hill country sheep and beef farms. This study updated a native shrub sub-model (NSM) with new research data and developed a radiata pine sub-model (RPM) for integration into a bioeconomic model using STELLA Architect. The model assessed asynchronous afforestation of 10% of effective farm area with either option, comparing impacts on feed supply, sheep dynamics, and farm economics. NSM was updated with growth curve, foliage biomass, and carbon stock data from two New Zealand sites. RPM used literature for growth curve, carbon, and log production data. Simulations included a pasture-only (base) and afforestation with either species at 10% and 20% planting rates. Native shrubs reduced feed supply by 2.5% and 4.0%, while radiata pine reduced it by 7.0% and 7.4% at 10% and 20% planting rates. Reduced feed led to smaller flocks and lower cash flow. Radiata pine generated surplus through carbon and log income, offsetting reduced sheep flock cash flow, while native shrubs did not. Carbon prices of 64.2 and137.4 NZD/NZU would be needed for viability in the best- and worst-case scenarios. Native shrubs are potential land use option on steep slopes but require policy intervention to lower establishment costs and carbon prices.Item Nutritional composition of New Zealand native shrubs edible portions with fodder potential for ruminants(Taylor and Francis Group, 2024-11-13) Wangui JC; Pain SJ; Kenyon PR; Tozer PR; Simmonds G; Millner JPIn New Zealand, willow and poplar are used on hill farms for erosion control and to supplement pasture during low pasture periods. Some native shrubs are browsed by wild herbivores but remain unexplored for farmed ruminants. We evaluated the seasonal nutritional composition of five native New Zealand shrubs (Karamū, Pāpāuma, Karo, Whauwhaupaku, and Houhere) and compared them with willow (Kinuyanagi). Leaf and edible stem were analysed for nutritional composition and in vitro digestibility following AOAC procedures. Results showed that except Houhere, all other native shrubs leaves had lower crude protein (CP) (11 MJ/ kg DM) than Kinuyanagi. Kinuyanagi leaves were comparable to Houhere in ME and CP in spring but had lower CP in summer. Stem nutritional composition was similar across all shrubs. Acid and neutral detergent fibres in edible portions were comparable to those in common pastures, fodder crops, and forages in New Zealand. The findings suggest native shrubs could supplement low ME in summer pastures or winter herbage scarcity, but further research is needed on animal preference and intake.Item Enhancing climate resilience in northern Ghana: A stochastic dominance analysis of risk-efficient climate-smart technologies for smallholder farmers(Elsevier B.V., 2024-07-17) Ahiamadia D; Ramilan T; Tozer PRNorthern Ghana is a semi-arid region characterised by a unimodal rainfall pattern, and hot and dry weather conditions. Heavy reliance on rain-fed agriculture and the lack of resources for irrigation, makes smallholder farmers in the region increasingly vulnerable to climate-related crop failures. In recent years, climate-smart technologies (CSTs) such as changing planting dates (PD), compartmental bunding (CB), mulching (M), and transplanting (TP) have been recommended to minimise yield losses. However, there is limited information on the most risk-efficient CSTs for crops cultivated in the region. This study used a stochastic dominance approach to identify the most risk-efficient CSTs for maize, rice, and sorghum. The stochastic modelling process employed the Aqua-crop model to simulate climate-related yield variability using Ghana climate data, and gross margin variability with crop budgets from literature sources. From the study's findings, changing planting date from April to May was the most risk-efficient choice for maize and sorghum under farmers' and recommended practices. In contrast, transplanting was the most risk-efficient technology for rice farming in the study area. The study also highlights the importance of considering the risk-averse nature of smallholder farmers when selecting CSTs. By identifying the most risk-efficient CSTs, the study can help improve the resilience of smallholder farmers. These findings have important implications for the development and adoption of CSTs in northern Ghana.Item A bio-economic modelling comparison of a Friesian Bull-Beef system and a New Generation Beef system with Friesian bulls slaughtered at 10–14 months old(Taylor and Francis Group on behalf of the Royal Society of New Zealand, 2024-02-05) Farrell LJ; Morris ST; Kenyon PR; Tozer PRFinishing of dairy-origin calves in an accelerated ‘New generation beef’ (NGB) beef finishing system for slaughter up to 14 months of age has potential co-sector benefits. These include production efficiencies and a reduced number of dairy calves slaughtered at a very young age. In the present study, a NGB system and an 18-month Bull-Beef system were first modelled separately, both purchasing three-month-old Friesian bull calves. Then Mixed systems with varying proportions of both NGB and Bull-Beef animals were modelled. Production, feed balance and profitability were compared, using cash operating surplus (COS) as a profit indicator. In the NGB scenario, double the number of animals were finished compared with the Bull-Beef scenario; however, monthly feed demand was less synchronous with predicted pasture supply, requiring more feed transfer via pasture baleage. The COS for the NGB system was $−571/ha, with less income and greater costs than the Bull-Beef system (COS = $2026/ha). Break-even prices for NGB animals were up to 74% above current prices, but break-even prices were less in Mixed systems with a greater proportion of Bull-Beef animals. Without high price premiums, challenges remain for the NGB systems appeal to beef finishers due to their low slaughter weights and sale prices.Item Bioeconomic Modelling to Assess the Impacts of Using Native Shrubs on the Marginal Portions of the Sheep and Beef Hill Country Farms in New Zealand (article)(MDPI (Basel, Switzerland), 2021-10-18) Wangui JC; Kenyon PR; Tozer PR; Millner JP; Pain SJNew Zealand hill country sheep and beef farms contain land of various slope classes. The steepest slopes have the lowest pasture productivity and livestock carrying capacity and are the most vulnerable to soil mass movements. A potential management option for these areas of a farm is the planting of native shrubs which are browsable and provide erosion control, biodiversity, and a source of carbon credits. A bioeconomic whole farm model was developed by adding a native shrub sub-model to an existing hill country sheep and beef enterprise model to assess the impacts on feed supply, flock dynamics, and farm economics of converting 10% (56.4 hectares) of the entire farm, focusing on the steep slope areas, to native shrubs over a 50-year period. Two native shrub planting rates of 10% and 20% per year of the allocated area were compared to the status quo of no (0%) native shrub plantings. Mean annual feed supply dropped by 6.6% and 7.1% causing a reduction in flock size by 10.9% and 11.6% for the 10% and 20% planting rates, respectively, relative to 0% native shrub over the 50 years. Native shrub expenses exceeded carbon income for both planting rates and, together with reduced income from sheep flock, resulted in lower mean annual discounted total sheep enterprise cash operating surplus for the 10% (New Zealand Dollar (NZD) 20,522) and 20% (NZD 19,532) planting scenarios compared to 0% native shrubs (NZD 22,270). All planting scenarios had positive Net Present Value (NPV) and was highest for the 0% native shrubs compared to planting rates. Break-even carbon price was higher than the modelled carbon price (NZD 32/ New Zealand Emission Unit (NZU)) for both planting rates. Combined, this data indicates planting native shrubs on 10% of the farm at the modelled planting rates and carbon price would result in a reduction in farm sheep enterprise income. It can be concluded from the study that a higher carbon price above the break-even can make native shrubs attractive in the farming system.Item In Vitro Fermentation of Browsable Native Shrubs in New Zealand(MDPI (Basel, Switzerland), 2022-08-10) Wangui JC; Millner JP; Kenyon PR; Tozer PR; Morel PCH; Pain SJInformation on the nutritive value and in vitro fermentation characteristics of native shrubs in New Zealand is scant. This is despite their potential as alternatives to exotic trees and shrubs for supplementary fodder, and their mitigation of greenhouse gases and soil erosion on hill-country sheep and beef farms. The objectives of this study were to measure the in vitro fermentation gas production, predict the parameters of the in vitro fermentation kinetics and estimate the in vitro fermentation of volatile fatty acids (VFA), microbial biomass (MBM), and greenhouse gases of four native shrubs ( Coprosma robusta, Griselinia littoralis, Hoheria populnea, and Pittosporum crassifolium) and an exotic fodder tree species, Salix schwerinii. The total in vitro gas production was higher (p < 0.05) for the natives than for the S. schwerinii. A prediction using the single-pool model resulted in biologically incorrect negative in vitro total gas production from the immediately soluble fraction of the native shrubs. However, the dual pool model better predicted the in vitro total gas production and was in alignment with the measured in vitro fermentation end products. The in vitro VFA and greenhouse gas production from the fermentation of leaf and stem material was higher (p < 0.05), and the MBM lower (p < 0.05), for the native shrubs compared to the S. schwerinii. The lower in vitro total gas production, VFA, and greenhouse gases production and higher MBM of the S. schwerinii may be explained by the presence of condensed tannins (CT), although this was not measured and requires further study. In conclusion, the results from this study suggest that when consumed by ruminant livestock, browsable native shrubs can provide adequate energy and microbial protein, and that greenhouse-gas production from these species is within the ranges reported for typical New Zealand pastures.Item Producing Higher Value Wool through a Transition from Romney to Merino Crossbred: Constraining Sheep Feed Demand(MDPI (Basel, Switzerland), 2021-10-01) Farrell LJ; Tozer PR; Kenyon PR; Cranston LM; Ramilan TA strategy to increase wool income for coarse wool (fibre diameter > 30 µm ) producers through a transition to higher value medium wool ( fibre diameter between 25 and 29 µm) was identified, with previous analyses allowing sheep feed demand increases to impractical levels during the transition period. This study modelled a whole flock transition from Romney breed to a 3/4Merino1/4Romney flock through crossbreeding with Merino sires, with sheep feed demand constrained between 55% and 65% of total grown feed. Transition was complete after 12 years, and the final 3/4M1/4R flock had higher COS (cash operating surplus; NZD 516/ha) than the base Romney flock (NZD 390/ha). Net present value analyses showed the transition always had an economic benefit (up to 13% higher) over the Romney flock. In a sensitivity analysis with sheep and wool sale prices changed by ±10%, higher sheep sale prices reduced the economic benefit of the transition (NPV up to 11% higher) over the Romney flock, as sheep sales comprised a higher proportion of income for the Romney flock, and higher wool sale prices increased the benefit (NPV up to 15% higher) of the transition to 3/4M1/4R over the Romney flock. This study demonstrated a whole flock transition from Romney to 3/4M1/4R breed was profitable and achievable without large variation in sheep feed demand, although the scale of benefit compared to maintaining a Romney flock was determined by changes in sheep and wool sale prices.Item Determining the Impact of Hogget Breeding Performance on Profitability under a Fixed Feed Supply Scenario in New Zealand(MDPI (Basel, Switzerland), 2021-05-01) Farrell LJ; Kenyon PR; Tozer PR; Morris STHoggets (ewe lambs aged 4 to 16 months) can be bred from approximately 8 months of age for potentially increased flock production and profit, however most New Zealand hoggets are not presented for breeding and their reproductive success is highly variable. Bio-economic modelling was used to analyse flock productivity and profit in four sets of scenarios for ewe flocks with varying mature ewe (FWR) and hogget (HWR) weaning rate combinations. Firstly, hogget breeding was identified to become profitable when break-even HWRs of 26% and 28% were achieved for flocks with FWRs of 135% and 150%, respectively. Secondly, relatively smaller improvements in FWR were identified to increase profit to the same level as larger improvements in HWR. Thirdly, a high performing flock with FWR and HWR both ≥ the 90th percentile currently achieved commercially, was the most profitable flock modelled. Fourthly, a FWR was identified with which a farmer not wishing to breed hoggets could have the same profit as a farmer with a flock achieving current industry average FWR and HWR. Overall, the relative profit levels achieved by the modelled flocks suggest that more farmers should consider breeding their hoggets, though improvements in FWRs should be prioritised.Hoggets (ewe lambs aged 4 to 16 months) can be bred from approximately 8 months of age for potentially increased flock production and profit, however most New Zealand hoggets are not presented for breeding and their reproductive success is highly variable. Bio-economic modelling was used to analyse flock productivity and profit in four sets of scenarios for ewe flocks with varying mature ewe (FWR) and hogget (HWR) weaning rate combinations. Firstly, hogget breeding was identified to become profitable when break-even HWRs of 26% and 28% were achieved for flocks with FWRs of 135% and 150%, respectively. Secondly, relatively smaller improvements in FWR were identified to increase profit to the same level as larger improvements in HWR. Thirdly, a high performing flock with FWR and HWR both ≥ the 90th percentile currently achieved commercially, was the most profitable flock modelled. Fourthly, a FWR was identified with which a farmer not wishing to breed hoggets could have the same profit as a farmer with a flock achieving current industry average FWR and HWR. Overall, the relative profit levels achieved by the modelled flocks suggest that more farmers should consider breeding their hoggets, though improvements in FWRs should be prioritised.