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Published online by Cambridge University Press: 20 November 2017
When the ratio between Metabolisable Protein (MP) and Metabolisable Energy (ME) is optimal for a given level of milk output (not constrained by genotype, management or other nutritional factors), further increases in milk output can be obtained by two strategies:
Strategy 1. Increased supply of ME and MP (maintaining optimal MP:ME), or
Strategy 2. Oversupply of MP (ie MP:ME > optimum)
Possible mechanisms underlying Strategy 2 include use of amino acids for gluconeogenesis or oxidation (Oldham, 1994), mobilisation of body energy reserves or, where forage is available ad libitum, increased forage intake (Newbold, 1994). For the purpose of this study, supply of MP above the theoretical optimum was assumed to increase milk protein yield only via the mechanism of increased forage intake.
The objective of this study was to evaluate the economic (cost of ration) and environmental (overall efficiency of N use) consequences of increasing milk yield by these two strategies.