From a strictly developmental standpoint, Lilja
(1983) put forth the concept that during the early
posthatch growth period, there is a hierarchy for available
nutrients that is divided among “supply” and “demand”
tissues. The “demand” tissues are largely users
of energy and protein (i.e. skeleton, muscle, adipose)
while the “supply” tissues would include the respiratory
and cardiovascular systems and the intestine.
Two excellent reviews on the biological relationship
between intestinal development and growth in altricial
versus precocial avian species (poultry) can be
found in Konarzewski et al. (1989, 1990). Immediately
posthatch, the proportional growth of the small intestine
is greater than that of BW and peaks within the
same approximate age range for both poults and chicks
(6 to 10 d; Katanbaf et al., 1988; Sklan, 2001).