Lactation Curves

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Abstract
Factors for adjusting beginning of lactation were developed for milk, fat, and protein yield. Records used were test day observations from New York and New Jersey [USA] from July 1982 through November 1983. Lactation curves were developed using a model that included fixed effects due to season by days in milk, days carried calf, age, and herd; random effects in the model included cow included cow and error terms. A log transformation was performed on the data to account for a variance mean relationship for test day data. Analysis for the three yield traits was conducted for the three lactation groups within five production groups. Lactation curves were estimated for six seasons of freshening by five production groups for the lactation groups for three yield traits, forming a total of 270 curves (90 for each trait). Lactation curves differed for three yield traits by production and season of freshening. Estimates of age and days carried calf, day of peak yield, and persistency estimates are presented for three yield traits stratified by herd production and lactation group. Plots of first lactation curves are presented for milk, fat, and protein for six seasons of freshening for lowest and highest production groups. An example of factors for different production groups and season of freshening are presented. Factors were too irregular to fit a regression equation. Factors developed were greater in magnitude than those currently used.