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1 Department of Dairy Science, Louisiana State University Agricultural Center, Baton Rouge 70803
2 Department of Animal Sciences, University of Illinois, Urbana 61801
Corresponding author: H. G. Bateman, II; e-mail: hbateman{at}agcenter.lsu.edu.
A data set constructed from research trials published between 1979 and 1998 was used to derive equations to adjust published tabular values for the rumen-undegradable protein (RUP) content of feeds to better predict the passage of nonammonia nonmicrobial N (NANMN) to the small intestine of lactating dairy cows. Both linear and nonlinear forms of equations were considered for making adjustments. Iterative processes were used to estimate equation parameters. A logistic equation was developed and considered to be the most optimal for adjustment of published tabular RUP contents of feeds. The equation is a function of dietary dry matter intake (DMI) and includes terms for tabular RUP and nonprotein N contents of individual feeds. The equation has a standard error of prediction of 69.29 g of NANMN/ d per cow and a root mean square prediction error of 104.63 g of NANMN/d per cow. Independent evaluation of the equation indicated that the concept of variable RUP content for feeds based on DMI is correct. Further refinements may be needed as other data become available to quantify the effects of additional factors on the RUP value of feeds.
Key Words: protein degradability model dairy cow
Abbreviation key: MCPI = maintenance CP intake, MEI = maintenance energy intake, MPIAF = MCPI adjustment factor, MSPE = mean square prediction error, NANMN = nonammonia nonmicrobial N, RDTP = ruminally degradable true protein, RMSPE = root mean square prediction error, SEY = standard error of prediction
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