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1 Department of Animal and Veterinary Science and
2 Statistical Programs, College of Agricultural and Life Sciences, University of Idaho, Moscow 83844
Corresponding author: A. N. Hristov; e-mail: ahristov{at}uidaho.edu.
This meta-analysis was undertaken to determine the impact of dietary components on dry matter intake (DMI), milk yield (MY), and milk protein yield (MPY) in Holstein dairy cows. Diets (n = 846) from 256 feeding trials published in Volumes 73 through 83 of the Journal of Dairy Science were evaluated for nutrient composition using 2 diet evaluation models: CPM Dairy (a computer program based on the principles of the Cornell Net Carbohydrate and Protein System) and NRC (2001). Data were analyzed with and without the effect of stage of lactation as a dummy variable (<100 d in milk or 
100 d in milk). A mixed model regression analysis was used to completely investigate the potential relationships among composition variables and DMI, MY, and MPY. Protein and carbohydrate fractions were the main components within the DMI models, and DMI played a dominant role in estimating MY and MPY. Inclusion of stage of lactation substantially improved the MY models but did not affect model fits or residual structure for DMI and MPY.
Key Words: diet composition • dry matter intake • milk yield
Abbreviation key: AC = all cows, BIC = Bayesian Information Criterion, CHO = carbohydrate, DIM 1 = early lactation cows, DIM 2 = mid and late lactation cows, MY = milk yield, MPY = milk protein yield, PE = milk protein N efficiency
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