Effect of interval from timed artificial insemination to initiation of resynchronization of ovulation on fertility of lactating dairy cows.
To compare 2 strategies for systematically resynchronizing ovulation, lactating Holstein cows (n = 763) at various days in milk and prior artificial insemination services were assigned randomly at timed AI (TAI) to receive the first GnRH injection of Ovsynch 26 (D26) or 33 (D33) d after TAI to resynchronize ovulation (Resynch) in cows failing to conceive. Cows in the D26 treatment received GnRH 26 d after TAI and continued Resynch only when diagnosed not pregnant by using ultrasonography 33 d after TAI, whereas D33 cows initiated Resynch only when diagnosed not pregnant 33 d after TAI. Cows were classified based on the presence or absence of a corpus luteum (CL) at the not-pregnant diagnosis, and cows without a CL received an intravaginal progesterone-releasing insert during Resynch. When analyzed as a systematic strategy, pregnancy rate per AI (PR/AI) was greater for cows assigned to the D33 than the D26 Resynch treatment (39.4 vs. 28.6%). A treatment x parity interaction was detected for PR/AI after Resynch for nonpregnant cows having a CL in which primiparous cows had a greater PR/AI than multiparous cows when Resynch was initiated 33 d after the initial TAI, and primiparous and multiparous cows when Resynch was initiated 26 d after the initial TAI. Pregnancy loss for Resynch was 6.4% between 33 and 40 d, and 2.6% between 40 and 61 d after Resynch TAI. We concluded that delaying initiation of Resynch until 33 d after TAI increased PR/AI for primiparous cows.
Sterry
R A
RA
Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
Welle
M L
ML
Fricke
P M
PM
D000034:Abortion, Veterinary / Q000453:epidemiology; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004973:Estrus Synchronization; D005260:Female; D005298:Fertility; D007315:Insemination, Artificial / Q000662:veterinary*; D007774:Lactation; D010062:Ovulation Induction; D011247:Pregnancy; D011256:Pregnancy Outcome; D013997:Time Factors