Inducing sub-luteal circulating concentrations of progesterone and persistent follicles in Holstein heifers and non-lactating cows using a modified CIDR device

Abstract Reducing progesterone from Controlled Internal Drug Release (CIDR) devices may allow for the comparison of contrasting steady state concentrations of progesterone (P4) in non-lactating dairy cows and heifers. This technical study was designed to determine if circulating P4 concentrations from the CIDR device could be reduced in cattle via ethanol extraction, and if reduced steady state concentrations of P4 would increase the percent of cows and heifers that developed a persistent follicle. Holstein heifers and non-lactating cows were treated with Ovsynch (100 μg GnRH, 7 d later, 25 mg dinoprost tromethamine, 2 d later, 100 μg GnRH) to initiate a new cycle. Only heifers and cows that synchronized were included in this study. On d 7 of the newly induced estrous cycle, animals were assigned to three treatments all treated with new CIDRs as follows: CIDR-N, CIDR that was not manipulated; CIDR-W, CIDR immersed in water, or CIDR-E, CIDR immersed in a mixture of equal parts water/ethanol. All heifers and cows received 25 mg dinoprost tromethamine at time of treatment to ensure regression of the d 7 corpora lutea (CL). Only data from heifers and cows having morphological CL regression observed with ultrasonography on d 1 and 2 following treatment, and with basal P4 concentrations (