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The incidence of different types of luteal activity postpartum and their effect on reproductive performance were studied in 21 postpartum dairy cows. Progesterone concentrations in defatted milk collected 3 times a week were determined by EIA. Reproductive tract examination was undertaken every other week postpartum. Body weight and body condition score (BCS) were measured before and after calving and the average 100-day milk yield was calculated. Nine (42.9%) cows had normal ovarian activity (first luteal activity &lt; or = 50 days postpartum followed by regular cycles), 5 (23.8%) had prolonged luteal phase (PLP; ovarian cycle with luteal activity &gt; or = 20 days pre-service) and in 7 (33.3%) cows the first luteal activity was shown later than 50 days postpartum (DOV). When compared with normal cows, both PLP and DOV had longer interval to first insemination (63.1 +/- 22.0 days versus 77.6 +/- 21.6 and 93.0 +/- 22.3 days, P&lt;0.05 and P&lt;0.01, respectively), lower first insemination conception rate (88.9% versus 0.0% and 57.1%, P&lt;0.01 and P&lt;0.05, respectively) and greater BCS loss (0.81 +/- 0.2 versus 1.05 +/- 0.21 and 1.04 +/- 0.10, respectively, P&lt;0.01). Cows with PLP showed longer interval to uterine involution than normal and DOV groups (54.0 +/- 8.3 days versus 42.4 +/- 5.5 and 43.3 +/- 8.3 days, respectively, P&lt;0.01) and higher 100-day milk yield (38.8 +/- 2.7 kg versus 33.6 +/- 4.7 and 29.9 +/- 6.1 kg, respectively, P&lt;0.01). In conclusion, more than half of the cows had abnormal luteal activity postpartum, which adversely affected reproductive performance.

Onset and Duration of Luteal Activity Postpartum and Their Effect on First Insemination Conception Rate in Lactating Dairy Cows