Pregnancy rates in lactating dairy cattle following supplementation of progesterone after artificial insemination

Poor conception rates in highly productive lactating cattle is especially prevalent in large, intensively-managed commercial herds. One of the causative factors is sub-optimal pre-implantation embryonic development which appears to result from inadequate circulating concentrations of progesterone. In the present study, the efficacy of very modest progesterone supplementation, between Days 3.5 and 10 post-AI, on pregnancy rates was determined in a commercial herd where bovine somatotropin (bST) was used as a management tool. All lactating cattle that were deemed to be in estrus and inseminated over a 4-week period were randomly assigned to either a control group (no treatment) or CIDR-1.9 g (previously used for estrous synchronization) treatment from Day 3.5 to Day 10 post-AI. Milk samples were collected four times: on the day of AI, at Day 2 or 3, at Day 4 and at Day 22 post-AI and were analyzed for progesterone, content, Data from a total of 130 breedings wore used in the final analysis, The CIDR treatment increased circulating concentrations of progesterone in treated animals over those of control animals on Day 4 by 0.7 ng/ml (P < 0.05) and increased pregnancy rate from 35% (22/63) to 48% (32/67) (P = 0.068). The effect of treatment was greater in first and second lactation cows, where pregnancy rates were 33% (18/55) in controls and 51% (31/61) in treated animals (P = 0.03). The results of this study indicate that the timing of onset of the progesterone influence is important for successful pregnancy outcome, particularly in first and second lactation cows. (c) 2007 Elsevier B.V. All rights reserved.