7.3 An experimentwas performed to determine the effect of the enzyme lactase (which hydrolyses the sugar lactose) on the composition of the milk in a sheep’s udder. In each side of the udder in each of eight lactating sheep, the levels of fat and of lactose in the milk (%)

were measured during a pre-experimental period. Thiswas followed by a treatment period, at the beginning of which lactase was injected into one side of the udder, chosen at random.

It was assumed that this injection did not affect the composition of the milk in the other side, which therefore served as a control. A day later, the levels of fat and lactose were measured again. This was followed a week later by a second treatment period, at the beginning of which lactase was injected into the other side of the udder. Again, a day later the fat and lactose levels were measured. The results are presented in Table 7.10 (Data reproduced by kind permission of Roberta Bencini, Faculty of Natural and Agricultural Sciences, The University of Western Australia).

The final levels of fat and lactose are the response variables in this experiment.