The objective of this study was to compare effects of intramuscular and intrauterine injection of prostaglandin F₂α on estrous synchronization in Bali cattle and crossbreed-Ongole cattle.  A total of 80 Bali cows and 70 crossbreed-Ongole (PO) cows were used for the study. The average body weighs were 327±9.98 kg and 355±8.45 kg, and were aged between 4 - 8 years (parities 2 to 5) lactating for Bali and PO cattle, respectively.  The Bali cows and PO cows were divided into two the treatment groups and to each cow, two injections of PGF₂α, 14 days apart were administered.  Cows in groups 1 (Bali, n=40; PO, n=35) were injected witrh 25 mg Dinoprost^® (Glandins, Tad Pharmazeutisches werk Gmbh, West Germany) intramuscularly (i.m). Whereas, for the cows in groups 2 (Bali, n=40; PO, n=35), 5 mg dinoprost^® was injected into the intra uterine (i.u) using a modified AI gun. The percentage estrus first and second injection with i.m and i.u were no significant different (P>0.05) between Bali and PO cows. The percentage estrus response were significantly different (P<0.05) between first injection and second injection. The pregnancy rate after first injection with i.m and i.u were no significant different (P>0.05). Whereas, pregnancy rate after second injection with i.m and iu between Bali and PO cows were significant different (P<0.05). Thus, differences in breed and method of PGF­₂α administration were not significantly different (P>0.05). It was concluded that injection of PGF₂α via the i.u route resulted in similar estrus response and pregnancy rates compared with the i.m route of administration. Furthermore, the i.u application of the PGF₂α or its analogues may reduce the dose requirement of the drug.

Key words: Cows, Estrus Synchronization, Intramuscular, Intrauterine, Pregnancy rate, Prostaglandin F₂α