Abstract
Thirty six (mongrels) dogs was ranged from (2 – 5) years were used to investigate the effect of. L-carnitine, L-tyrosin and GnRH on improving fertility of male dogs (Libido and semen quality).Serum and semen samples were collected for three weeks (twice per week) before treatment to serve as control and for 9 weeks after treatment, the animals were grouped into 2 groups. The first group( low libido) : consisted of 3 subgroups as followings the first subgroup consisted of 5 dogs that were received the same basal diet and supplemented with 2 g per head of L-carnitine (Kariniking 50 %) for 14 days., the second subgroup that were fed on the same basal diet supplemented with single oral dose of L-tyrosine (1 gm/10 Kg body weight) and the third subgroup consisted of 5 dogs that fed on the same basal diet and injected with GnRH (Receptal). 2.5 ml priming dose 1 ml once per week for 2 weeks.
The second group (low semen quality): consisted of 3 subgroups each group consist of 7 dogs and received treatment as the first group.On semen collection site, libido index was measured and the collected semen samples were evaluated for ejaculate volume, pH, individual sperm motility, percentage of live sperm, sperm cell concentration (millions/ml) and sperm abnormalities (primary and secondary). Testosterone concentration was assessed in serum samples using RIA technique. Results revealed that, The fertility of male dogs which represented in reproductive characters improved after treatment than before through, improving the testosterone hormone, semen volume, pH and conception rate in GnRH followed by L-carnitine treated group and both of them improve the efficiency than the L-tyrosine, the GnRH followed by L-tyrosine gave a higher libido appearance than L-carnitine treated group. The semen quality in the second group.
The results cleared that, the higher sperm concentration and lower sperm defects (using a quantitative ultrastructural analysis) observed in the group treated with GnRH, followed by L-carnitine treated groups, and all of them higher than that of L-tyrosine treated group.

Key words: GnRH stimulant, C R, L-carnitine, male dogs, libido, semen, fertility.