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1. T193 INSERTION OF USED CIDRS ON DAY 3 TO 5 POST-INSEMINATION IN HEIFERS TO IMPROVE PREGNANCY RATEC.E. Ferguson1, B. Pousson, H. Nordberg, J. Veillon, W. Storer, D.J. Kesler Department of Agricultural Sciences, McNeese State University, Lake Charles, LA Department of Animal Sciences, University of Illinois, Champaign-Urbana, IL RESULTS Table 3. Plasma P4 concentrations for control pregnant and open heifers for Spring 2011 breeding season (heifers with no blood sample > 1ng/ml were removed) OBJECTIVES MATERIALS & METHODS DISCUSSION MATERIALS & METHODS REFERENCE The objectives of this experiment were to determine if previously used CIDRs, reinserted on day 3 and removed on day 5 post-breeding, would increase pregnancy rates, and to determine any differences in plasma P4 concentrations between pregnant and open heifers. Previously used CIDRs were selected because a cost-effectiveness method of increasing P4 concentrations from day 3 to 5, was desired. On day 3 post-GnRH, in replicate 2, all heifers had blood samples collected via jugular venapuncture and the treatment group (n = 30) received a previously used CIDR. Blood collections were continued daily for the next two days and all blood samples were collected in sodium heparinized tubes, stored on ice until centrifugation. On day 5, post-GnRH, the used CIDR was removed. Plasma P4 concentrations were determined via radioimmunoassay at an independent laboratory (Louisiana State University) using a commercially available RIA kit (Diagnostic Systems Laboratory, Webster, TX) with a sensitivity of 0.1 ng/mL, an intra-assay and inter-assay coefficient of 7.3% and 9.3%, respectively. Statistical difference between the proportion of heifers becoming pregnant were determined using proc glimmix for binomially distributed data with LSmeansin SAS (SAS Institute, Inc., Gary, NC). Independent variables included in this model were, replicate, treatment, P4 concentration per day and change in P4 concentration and were removed in a stepwise fashion if they have no effect (P>0.05). Change in P4 was calculated by subtracting the concentration from day 4 from day 5 and so forth, and total change was calculated from subtracting the concentration from day 5 from day 3. A total of 92 heifers were used in two replicates (replicate 1, n = 32; replicate 2, n = 60) of this experiment. All heifers were randomly allocated to either the control group (no CIDR) or treatment group (used CIDR) following ovulation synchronization using the CO-Synch + CIDR protocol with timed artificially inseminated (TAI) 56 hours following CIDR removal (Figure 1). All heifers were TAI with fertile semen from proven bulls. On day 3 post-GnRH, in replicate 1, control heifers (n = 16) were passed through a hydraulic chute and restrained, and treatment heifers (n = 16) received a used CIDR (Figure 2). It is unknown at this time why pregnancy rates were different between replicate 1 and 2. This could have been an effect of more bosindicusinfluenced heifers in replicate 1 compared with replicate 2. Also, it could be the result of more heifers cycling in replicate 1 compare with replicate 2 or differences in P4remaining in a used CIDR. The P4 data is in agreement with previous research (Ferguson et al., 2012) where fertile cows with a greater increase in P4 were more likely to become pregnant. This indicates the timing of P4 supplementation may be effective, the dosage or length of supplementation may not be optimal. Ferguson CE, Kesler, DJ, Godke, RA. 2012. Low doses of progesterone on days 3 to 5 post-breeding in repeat-breeder cattle increases 30 day pregnancy rates. Journal of Applied Animal Research (DOI:10.1080/09712119.2011.645038) INTRODUCTION Progesterone (P4), a steroid produced by the corpus luteum on the ovary of the cow, functions to maintain pregnancy by stimulating nutrient release within the uterus which enables the embryo to grow and develop. Previous research has reported that elevated P4 concentrations from day 3 to 5 increased pregnancy rate in repeat-breeder cattle. Today, there are multiple methods of P4 administration; the most commonly used method is via a controlled drug releasing device (CIDR). Figure 2. Plasma P4 concentrations from day 3 to day 5 in control pregnant and open heifers (heifers with no blood sample > 1ng/ml were removed). RESULTS Table 1. Pregnancy rate for cross-bred heifers for the Spring 2010 breeding season that were treated with a used CIDR day 3 to 5 post-ovulation or served as controls Figure 1. The CO-Synch + CIDR ovulation synchronization protocol used for artificial insemination and experimental treatment regimes. Table 2. Pregnancy rate for cross-bred heifers for the Spring 2011 breeding season that were treated with a used CIDR day 3 to 5 post-ovulation or served as controls (a) (b)