A total of 2,520 male Cobb 500 broilers that had
been sexed by wings and vaccinated against fowl pox
and Marek’s disease at the hatchery were used in the
experiments. During both experiments, the birds were
housed in a 3-m-high masonry broiler house with an
asbestos monitor roof, concrete floor, 0.40-m-high wire
mesh side walls, and plastic curtains to control the
house temperature and prevent drafts. The house was
divided into 1.0 × 2.0-m pens that were provided with
wood-shaving litter, nipple drinkers, and tube feeders.
The drinkers, feeders, curtains, and birds were managed
according to the recommendations of the manual
for this genetic strain (Cobb-Vantress, 2003). Water
and feed (mash) were supplied ad libitum during both
experiments. Before the beginning of each experimental
period, the birds were fed commercial feed. A 24-h
light (natural + artificial) regimen was used during the
entire experimental period. The chicks were brooded
using infrared lamps, and the height was adjusted for
bird comfort.