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

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 (<0.15 ng/mL) on d after CIDR removal, were considered in the final analyses (n =30). CIDR-E had lower circulating concentrations of P4 during the treatment period compared to CIDR-N and CIDR-W in cycling heifers and non-lactating cows and a significant interaction of treatment x d from CIDR insertion was observed. CIDR-W had lower P4 compared to CIDR-N in heifers, but not in cows. With the three treatments combined, non-lactating cows had lower circulating concentrations of P4 than heifers. The 1st wave dominant follicle became atretic followed by a new wave of follicles in 4 of 5 non-lactating cows and heifers treated with CIDR-N compared to 1 of 12 in the CIDR-E and 3 of 13 in CIDR-W treatments during the 7 d treatment period. In summary, reduced steady state serum concentrations of progesterone from a CIDR device resulted in continued growth of persistent follicles in cows and heifers compared to a non-manipulated CIDR device.