The objective of this study was to evaluate estrus synchronization and pregnancy rate of Friesian lactating cows during postpartum period in melengesterol acetate (MGA) based protocols for estrus synchronization. The total 30 dairy cows were used in this study, average age between 25–68 months and weighting 440 – 620 kg and 1-5 parities was used in this study. At the beginning of the experimental period, the experimental cows were divided }}}into three similar groups, 10 in each. Cows in the 1^st treatment were fed on 0.5 g MGA/cow/day for 14 days. In the 2^nd treatment, cows were fed on 0.5 g MGA/cow/day for 14 days followed 33 days later by injection with 3 ml PGF₂α. In the 3^rd treatment, cows were fed 0.5 g MGA/cow/day for to 14 days followed 26 intramuscularly injected with the 1^st dose of 5 ml GnRH, followed 33 days injected with 3 ml PGF_2α followed 36 days injected with the 2^nd dose GnRH and fixed-time insemination. Results revealed that estrus response after the end of hormonal protocols were statistically (P<0.05) significantly higher in MGA and MGA+PGF_2α protocols (90%) than the MGA select protocol (70%). Pregnancy rates assessed in all cows after AI tended to be higher (90%) for the MGA+PGF_2α protocol and moderate in MGA select protocol (80%) than in the MGA protocol being for lower (70%). Progesterone concentration (P4) was above 1 ng/ml in all treated animals pre-treatment ranging 2.308 - 3.073 ng/ml. After the oral feeding MGA 0.5 g/cow/day, P4 concentration at days of 7 and 14 was increased in all animals of different protocols than in all animals in pre-treatments. On day 24 post-service, concentration of P4 was higher in responded animals, indicating incidence of pregnancy which were conceived after the PGF₂α injection in MGA+PGF_2α protocol and GnRH injection of MGA select protocol. The economic evaluation indicated that MGA protocol had the cheapest cost (L.E 4.9/cow), followed by MGA+PGF_2α protocol (L.E 16.9/cow). While, MGA select protocol showed the highest cost (L.E 56.9/cow).
Inconclusionscows treated by MGA+PGF_2α protocol at insemination based on heat incidence to improve their reproductive performance. From the economic point of view, MGA+PGF_2α protocol showed the best results (conception rate and costs) compared to the other protocols.