The data are from Chatterjee and Hadi (2012) Regression Analysis by Example.

http://www1.aucegypt.edu/faculty/hadi/RABE5/Data5/P004.txt

Page 4, Table 1.1
Variable Defintion
Current: current month milk production in pounds
Previous: previous month milk production in pounds
Fat: percent of fat in milk
Protein: percent of protein in milk
Days: number of days since present lactation
Lactation: number of lactations
I79: indicator variable (0 if Days<= 79 and 1 if Days>79)