there was no significant effect of cage type. However,
the number of cracked eggs significantly increased with
increasing days in lay (Table 1). Percentage cracked egg
was higher in the second half of the production cycle,
periods 6 to 10, than the first half of the production
cycle, periods 1 to 5. The percentage of soft-shelled
eggs was not affected by cage design. The influence of
the housing system on percentage of soft-shelled eggs
was only observed in periods 4 (CON = 0.10; ENR
= 0.02) and 9 (CON = 0.11; ENR = 0.22), in which
the number of soft-shelled eggs was higher and lower,
respectively, in conventional cages than in the enriched
cages. Consequently, these observed differences were
unable to elicit a cage × period interaction effect. As
with the percentage of cracked eggs, incidence of softshelled
eggs gradually increased with age (Table 1). The
overall percentage of dirty eggs, unlike the other egg
quality measurements, differed markedly between cage
designs (P < 0.0001; Table 2). The percentage of dirty
eggs in the conventional cages was consistently lower
throughout the laying cycle. There was a significant
(P < 0.0001) period effect for percentage of dirty eggs
(Table 1). Percentage of dirty eggs in enriched cages
remained relatively constant from period 1 to 2 but
increased steadily from period 3 to 10. A cage × period
interaction was brought about by the higher increase in
percentage of dirty eggs in period 3 and a more rapid
decline in period 6 in enriched cages.
At 37 and 61 wk, overall plumage condition was not
affected by cage type (Table 3). However, in the wing
region, feather score was higher in birds in conventional
cages than enriched cages. The mean score for each of
the other 5 individual body parts did not differ between
cages. The tail region consistently scored the lowest
(worst), wings, neck, and vent regions having intermediate
scores and the back and breast regions the highest
(best) score among all body regions (Table 3). Bone
mineral density of tibia and humerus of birds housed
in enriched cages was significantly higher (P < 0.05)
than birds in conventional cages (Table 4). A similar
but nonsignificant pattern was observed for bone mineral
content, ash weight, and percentage of calcium
and phosphorus of tibia and humerus. Mean values of
plasma corticosterone and antibody production (log2
antibody titer against NDV vaccine) before and after
vaccination for NDV (Table 5) and H/L ratio for laying
hens housed in conventional and enriched cages were
not affected by cage design (Table 6). Plasma corticosterone
level remained the same after NDV vaccination.
However, as expected, a significant increase in antibody
titer was observed in both housing systems postvaccination
(Table 5). Differential leukocyte counts were
similar in conventional and enriched cages except for
the number of lymphocytes, which was higher (P <
0.05) in conventional than in enriched cages (Table 6).