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The efficiency of conversion of metabolisable protein into milk true protein over a range of metabolisable protein intakes

Published online by Cambridge University Press:  01 August 2008

J. A. Metcalf ,
R. J. Mansbridge ,
J. S. Blake ,
J. D. Oldham  and
J. R. Newbold
J. A. Metcalf*
Affiliation:
ADAS Bridgets, Martyr Worthy, Winchester, Hampshire SO21 1AP, UK
R. J. Mansbridge
Affiliation:
ADAS Bridgets, Martyr Worthy, Winchester, Hampshire SO21 1AP, UK
J. S. Blake
Affiliation:
ADAS Bridgets, Martyr Worthy, Winchester, Hampshire SO21 1AP, UK
J. D. Oldham
Affiliation:
Scottish Agricultural Colleges, Bush Estates, Penicuik, Midlothian EH26 0QE, UK
J. R. Newbold
Affiliation:
BOCM PAULS, 47 Key Street, Ipswich, Suffolk IP4 1BX, UK
*
E-mail: john.metcalf@nutreco.ca
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Abstract

The aim of this work was to test the robustness of the 0.68 estimate of the efficiency of conversion of metabolisable protein into true milk protein (Agriculture and Food Research Council (AFRC), 1993) for protein-limiting diets and to determine whether a different value is appropriate for practical rationing. Seventy-two multiparous cows were blocked on the basis of milk energy output per unit of dry matter intake (DMI), and allocated at random to one of four treatments. Treatments supplied metabolisable energy (ME) at a fixed level to individuals within a block, but varied metabolisable protein (MP) supply from 25% below the estimated requirements, through −12.5% and +12.5% up to 25% above requirements for the average performance of animals within blocks at the start of the study. Cows were offered diets to meet their predicted ME requirements for each 3-week period with measurements performed in the last week of each period. Milk protein output was regressed against the estimated MP available for production for each cow and the efficiency of conversion of MP into milk true protein was calculated, assuming a maintenance requirement according to the MP system. The efficiency of conversion of MP into milk true protein decreased with the increasing supply of MP from 0.77 to 0.50. Using an iterative approach to determine the best fit of the data when supply matched requirement resulted in a range of efficiency values between 0.62 and 0.64 g of true milk protein per g of MP.

Keywords

dairy cowsmetabolisable proteinmetabolisable energynutrition

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Type
Full Paper
Information
animal , Volume 2 , Issue 8 , August 2008 , pp. 1193 - 1202
Copyright
Copyright © The Animal Consortium 2008

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