Abstract
Reproductive performance of two types of timed artificial insemination (TAI) protocols with or without intravaginal progesterone insert (CIDR) was investigated in a commercial herd of Holstein heifers. A total of seventy-four heifers with 14.4 months of age were allocated to two groups; Ovsynch (n=44) and estradiol benzoate (EB) used Heatsynch (EB-Heatsynch, n=30), and each group was additionally divided into two subgroups with CIDR insertion from day 0 to 7 (n=36) and without CIDR group (n=38). Blood was collected for progesterone (P4) analysis and ovarian finding was monitored with ultrasonography. Heifers in CIDR-treated group resulted in higher pregnancy rate as compared to No-CIDR-treated group (63.9% vs 21.1%, P<0.01). Heifers with functional corpus luteum (CL) on day 0 resulted in significantly higher pregnancy rate in CIDR-treated group than No-CIDR-treated group (day 0: 67.9% vs 13.0%, P<0.01). CIDR insertion suppressed the intermediate ovulation during the first 7 days and the period from the second GnRH or EB administration to TAI as compared to No-CIDR-treated group (first 7 days: 33.3% vs. 52.6%; P<0.05, before TAI: 11.1% vs. 37.0%; P<0.05). In conclusion, the selected TAI protocols with CIDR provided acceptable pregnancy rate and contributed to the economical improvement by shortening the average age of first calving approximately for 2.5 months as compared to the previous management without TAI protocols.
