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Effect of Initial Gn RH and Duration of Progesterone Insert Treatment on the Fertility of Lactating Dairy Cows
Author(s) -
Colazo MG,
Ambrose DJ
Publication year - 2015
Publication title -
reproduction in domestic animals
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.546
H-Index - 66
eISSN - 1439-0531
pISSN - 0936-6768
DOI - 10.1111/rda.12518
Subject(s) - ovulation , zoology , medicine , andrology , endocrinology , gynecology , biology , hormone
Contents The study compared response to prostaglandin F2 α ( PG ), synchrony of ovulation and pregnancy per AI (P/ AI ) in a 5‐ vs a 7‐day Ovsynch + PRID protocol and investigated whether the initial Gn RH affects P/ AI in lactating dairy cows. Two hundred and seventy‐six cows (500 inseminations) were assigned to one of four timed‐ AI ( TAI ) protocols: (i) PRID ‐7G; 100 μg Gn RH im, and a progesterone‐releasing intravaginal device ( PRID ) for 7 days. At PRID removal, PG (500 μg of cloprostenol) was given im. Cows received the second Gn RH treatment at 60 h after PRID removal and TAI 12 h later. (ii) PRID ‐5G; as PRID ‐7G except the duration of PRID , treatment was 5 days and PG was given twice (12 h apart). (iii) PRID ‐7NoG; as PRID ‐7G except the initial Gn RH , treatment was omitted. (iv) PRID ‐5NoG; as PRID ‐7NoG except the duration of PRID , treatment was 5 days. Response to treatments and pregnancy status at 32 and 60 days after TAI was determined by ultrasonography. The percentage of cows ovulating before TAI was greatest in PRID ‐7G (17.1%), and the percentage of cows that did not have luteal regression was greatest in PRID ‐5G (9.5%). The overall P/ AI at 32 and 60 days did not differ among TAI protocols. However, during resynchronization, cows subjected to the 5‐day protocols had greater (p < 0.05) P/ AI (45.3% vs 33.6%) than cows subjected to the 7‐day protocols. Pregnancy loss between 32 and 60 days tended (p = 0.10) to be greater in cows that did not receive initial Gn RH (14.8%) compared to those that received Gn RH (8.2%). In conclusion, the PRID ‐5G protocol resulted in fewer cows responding to PG , but P/ AI did not differ among TAI protocols. A 5‐day protocol resulted in more P/ AI in resynchronized cows, and cows that did not receive initial Gn RH tended to experience more pregnancy losses.