Investigating the impact of early egg
production selection (the first 90 d of laying) on egg production features, cumulative selection response (CSR),
and the mRNA expression of gonadotropins (FSHb and
LHb), and their receptors (FSHR and LHR), in Japanese quails was the goal. The selection experiment
involved 1293 females in all, 257 from the base group
and 1036 from the 4 selected generations. Age and body
weight at sexual maturity (ASM, BWSM), weight of
the first egg (WFE), days to the first 10 eggs (DF10E),
egg mass for the first 10 eggs (EMF10E), egg weight
(EW), egg number at the first 90 d of laying (EN90D),
and egg mass at the first 90 d of laying (EM90D) were
all recorded. Most egg production traits had heritability
estimates that were low to moderate and ranged from
0.17 to 0.33., where the highest estimates were reported
for EN90D (0.33) and BWSM (0.32). With the exception of EN90D, low to moderate positive genetic
correlations were observed between ASM and other egg
production traits (0.17−0.44). The fourth generation
showed significantly (P < 0.05) lower ASM and DF10E
but higher BWSM, WFE, EN90D, EM10E, and EM90D
when compared with the base generation. CSR were
significant (P < 0.05) for ASM (6.67 d), BWSM (27.13
g), WFE (0.93 g), DF10E (1.25 d), EN90D (7.24 egg),
EM10E (10.57 g), and EM90D (140.0 g). FSHb, LHb,
FSHR, and LHR gene mRNA expression was considerably (P < 0.05) greater in the fourth generation compared to the base generation. In conclusion, selection
programs depending on the efficiency of egg production
(EN90D) could improve the genetic gain of egg production traits and upregulate the mRNA expression of
FSHb, LHb, FSHR, and LHR genes in selected quails
(fourth generation). These findings might help to
enhance breeding plans and create commercial lines of
high egg production Japanese quails.