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
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Date
2025-09-01
Open Access Location
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Publisher
Elsevier B V
Rights
(c) 2025 The Author/s
CC BY 4.0
CC BY 4.0
Abstract
In 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.
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Keywords
Metabolisable energy requirements, Ruminant model comparison, Sheep, Beef cattle, Pasture-only system, New Zealand
Citation
Adjabui JA, Morel PHC, Morris ST, Kenyon PR, Tozer PR. (2025). 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. Livestock Science. 299.