Exogenous Dopamine Improves Reproductive Efficiency and Hatchability in Genetically Divergent Japanese Quail Lines

Dopamine is a neurotransmitter that plays an essential role in functions in birds and mammals such as motivation, mood, attention, memory, and movement coordination. This study aims to assess the impact of dopamine injection in two quail lines, namely brown and black Japanese quail breeds, on productive, sexual, and hatchability traits. Furthermore, the third generation was reared to receive dopamine treatment, administered intramuscularly into the breast muscle at a dose of 0.2 mL per bird to a final concentration of 20 µM. The treatments were applied as follows: group T1 was the control group, and group T2 was the dopamine injection group. A total of 24 birds were randomly allocated to the previously mentioned treatments, each consisting of three replicates, with four birds in every replicate at a sex ratio of (3 females: 1 male) for each genetic line. Accordingly, the findings revealed notable superiority (p ≤ 0.05) of dopamine injection over the control group in most sexual traits, including age at sexual maturity, which occurred earlier. It also improved fertility percentage and hatchability percentage and reduced embryonic mortality compared with the control group. It also produced the highest fertility rate in brown quail (100%) and the highest hatchability rate in black quail (97.04%). The results showed genetic differences between the lines, evidenced by higher egg production, better feed conversion, faster sexual maturity, and increased hatchability. We conclude that dopamine's positive effect comes from its role in inhibiting prolactin, reducing brooding, and supporting continuous production.