Journal Articles
Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915
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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 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 Simulating Beef Cattle Herd Productivity with Varying Cow Liveweight and Fixed Feed Supply(MDPI (Basel, Switzerland), 2021-01-06) Farrell LJ; Morris ST; Kenyon PR; Tozer PRThe liveweight of New Zealand beef cows has increased in recent decades due to selection for higher growth rates. Published data suggest that the efficiency of beef cow production decreases with increasing cow liveweight. Changes in beef herd size, feed demand, production, and cash operating surplus (COS) were simulated with average mature cow liveweight varied to 450, 500, 550, and 600 kg. With total annual beef feed demand fixed at the same level, in all scenarios cow numbers and numbers of weaned calves decreased with increasing cow liveweight. When the model was run with consistent efficiency of calf production across the mature cow liveweights (scenario A), heavier cows were more profitable. However, using published efficiency data (scenarios B and C), herds of heavier cows were less profitable. The likely most realistic scenario for New Zealand hill country farms (scenario B) had COS decrease from New Zealand Dollars (NZD) 456/ha with a herd of 450 kg cows to NZD 424/ ha with 600 kg cows. Reductions in COS were relatively small, which may not deter farmers from breeding heavier cows for higher calf growth rates. However, the results of this analysis combined with indirect potential economic impacts suggest that the heaviest cows may not be optimal for New Zealand hill country conditions.Item Modelling a Transition from Purebred Romney to Fully Shedding Wiltshire-Romney Crossbred(MDPI (Basel, Switzerland), 7/11/2020) Farrell LJ; Morris ST; Kenyon PR; Tozer PRConsidering the current low prices for coarse wool (fibre diameter > 30 µm), a grading up transition to a shedding flock may eliminate wool harvesting costs and increase sheep farm profit. This transition could be achieved by breeding non-shedding ewes with Wiltshire rams. A bio-economic system-dynamics model of a pastoral sheep farming enterprise was used to simulate this grading up transition from 2580 Romney ewes to a similarly-sized flock of fully shedding third or fourth cross Wiltshire-Romney ewes. The total annual sheep feed demand was constrained within a ±5% range to minimise disruption to the on-farm beef cattle enterprise. Wool harvesting expenses were eliminated after seven years of transition, and with reduced feed demand for wool growth, the post-transition shedding flocks had more ewes producing more lambs and achieving greater annual profit compared with the base Romney flock. The net present values of transition were 7% higher than the maintenance of the base Romney flock with a farmgate wool price of $2.15/kg. Results suggest that coarse wool-producing farmers should consider a grading up transition to a shedding flock, and the collection of data on the production of Wiltshire-Romney sheep in New Zealand would improve the accuracy of model predictions.