Water is a particularly diffi cult nutrient to study. Defi ciency symptoms
are not easily determined unless water insuffi ciency is extreme, and response criteria that work effectively in studies of other nutrients tend to
be unsatisfactory, or at least incomplete, in the case of water. The pig, like
other species, is well equipped with homeostatic mechanisms to conserve
water when intake falls below a certain level; the production of hypertonic
urine is but one example of adaptive mechanisms that are well advanced
in all mammalian species (Koeppen and Stanton, 2001).