DLZ presents data on 79 Australian cows which were fed one of three
different diets for up to 19 weeks. There were 25 cows on a barley
diet, 27 cows on a barley and lupins diet, and 27 cows on a lupins
diet. Milk was collected weekly and analyzed for its protein
content. Scientific interest lies in learning if the different diets
are associated with different protein levels.

The data are in the order cows on barley followed by cows on barley and
lupins followed by cows on lupins. The trend over time is non-linear.

NOTE: the publicly available data set (with 19+27+27=73 observations)
does NOT contain all the original observations (with 25+27+27=79 
observations) used in the analyses in Diggle, Heagerty, Liang, and 
Zeger (Oxford University Press, 2002), so results cannot be exactly duplicated.