Variation is normally seen in milk butterfat tests. This variation is seen between morning and night milkings for the same day and between different days. An example of the normal variation in milk production and milkfat test for two first-calf heifers (6-10 weeks into lactation) over a 6-day period is shown in the table below. Each heifer was fed the same amount of feed each day in two equal feedings. Cows were milked in a stanchion barn with a milk bucket at 6:30AM and 5:00PM. Although these data are from a small number of cows, they do show the normal variation seen in milk production and butterfat test.

DayMilk Production (lbs)Fat %
Cow # 8907
Monday693.76
Tuesday673.24
Wednesday673.46
Thursday683.02
Friday663.31
Saturday723.21
Cow #8907
Monday59No samples
Tuesday614.08
Wednesay613.49
Thursday604.05
Friday613.62
Saturday644.48
Fat % listed is a weighted average of AM and PM milkings which were collected separately.

Author: Donna Amaral-Phillips

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