Effects of different doses of estradiol cypionate in E2/P4 based protocols at TAI and FTET in lactating cows

This study aimed to evaluate the use of different dosages of estradiol cypionate (ECP) to synchronize ovulation in dairy cows subjected to a TAI and FTET protocols. In Exp.1 (FTAI), 643 Holstein cows received the following protocol: d0- 2mg of estradiol benzoate im (2.0mL Estrogin®, Farmavet, SP, Brazil ) + CIDR (1.9g of P4, Zoetis Animal Health, SP, Brazil ) + GnRH im (2.0mL Cystorelin®, Merial Animal Health, SP, Brazil); d7- PGF im (5.0mL Lutalyse®, Zoetis Animal Health, SP, Brazil); d9- CIDR withdrawal + PGF; d11- FTAI. Animals were randomly assigned to receive at d9 0.5mL (1.0mg) or 1.0mL (2.0mg) im ECP (Zoetis Animal Health, SP, Brazil). In Exp.2 (FTET), 593 lactating Girolando cows received the following protocol: d0- im 2mg of EB+CIDR; d7-im PGF; d9- withdrawal of CIDR; d18- GnRH im + FTET. Animals were randomly assigned to receive on d9 0.5mL (1.0mg) or 1.0mL (2.0mg) im ECP (Zoetis Animal Health, SP, Brazil). Binomial distributed variables were analyzed with PROC GLIMMIX. In Exp.1 ovulation rate was similar (P=0.59) between treatments. The treatment with 1.0mL of ECP showed higher (P 3.5) animals showed greater P/AI in the 1mL treatment, compared to the 0.5mL treatment [thin= 0.5mL-15.4%(n=12/104) vs 1.0mL-22.0%(n=21/107); fat= 0.5 mL-26% (n=4/18) vs 1.0mL-38.6% (n=10/28)] in animals with good BCS (BCS≥2.75≤3.25), 0.5mL treatment showed higher P/AI at 60d compared to 1.0mL treatment [0.5mL-26.2%(n=51/204) vs 1.0mL-18.1%(n=30/182)]. In Exp.2 ovulation rate was similar (P=0.23) between treatments, an increased expression of estrus rate was observed in the 1mL treatment [0.5mL- 68.5%(n=148/216) vs 1.0mL-81.8%(n=184/225); P<0.01]. There was no effect of treatment on rate of P/ET at 30d [0.5mL-51.6%(n=147/285) vs 1.0mL-46.8%(n=144/308); P=0.24] and 60d [0.5mL-40.4%(n=115/285) vs 1.0mL- 35.1%(n=108/308); P=0.18] and pregnancy loss [0.5mL-21.8%(n=32/147) vs 1.0mL-25%(n=36/144); P=0.52]. In the cows without CL at d0 there was a tendency (P=0.06) in the 1.0 mL treatment to reduce the P/ET at 60d [0.5mL- 40.3%(n=50/124) vs 1.0mL-29.3%(n=39/133)]. In thin and fat cows there was no effect (thin P=0.97; fat P=0.94) between treatments in P/ET at 60d, in animals with good BCS, the 1.0mL reduced the P/TE at 60d [0.5mL- 40.3%(n=60/149) vs 1.0mL-29%(45/155); P=0.04]. In conclusion, increasing dosage of estradiol cypionate increased the percentage of animals with expression of estrus, did not affect ovulation rate and affected the P/AI or P/ET at 60 d by BCS.