Journal of Dairy Science, Vol 78, Issue 2 457-465, Copyright ©
1995 by American Dairy Science Association
Production evaluation techniques based on lactation curves
C. P. Van Tassell, L. R. Jones and S. W. Eicker
Cornell University, Ithaca, NY 14853, USA.
Test day data on milk yield for individual cows were generated using
Monte Carlo simulation consisting of 1000 herds. Each herd contained
30 second lactation cows for each of 2 yr. Three scenarios were
simulated with increasing effects of test day and seasonality. For
each test day, several statistics were calculated for each cow: test
day data on yield deviated from expectations, deviated test day data
on yield transformed to account for correlation of consecutive test
day data on yields, 305-d mature equivalent estimates, and changes in
these values from the previous test day. A probability value for each
herd was calculated for test of month of lactation effects using
ANOVA models with and without cows in the model. No month of
lactation effects were simulated. The distribution of generated
probability values were tested for uniformity using a chi-square test.
The distribution of probability values associated with the change in
test day deviations were most nearly uniform, and results for these
variables were similar when the cow effect was removed from the
analysis model. The transformed variables also provided a fairly
uniform set of probability values, although interpretation of these
statistical tests was more difficult. Tests based on mature
equivalent, 305-d records were oversensitive.
