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Evaluation of Progesterone Supplementation in a Prostaglandin F₂-Based Presynchronization Protocol Before Timed Insemination

Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853-6401

¹ Corresponding author: rcb28{at}cornell.edu

The objective of the study was to determine the effects of treatment with a controlled internal drug-release (CIDR) insert containing progesterone in a PGF₂-based presynchronization protocol on pregnancy rates at first service in lactating Holstein cows. A total of 1,318 (656 treatment and 662 control) cows from 5 farms were used in the analysis. Cows received a CIDR insert as part of the presynchronization protocol of 2 PGF₂ injections given 14 d apart. The CIDR insert was applied during 7 d before the second PGF₂ injection, whereas control cows received no CIDR insert. Serum progesterone concentrations were measured in samples collected at 37 ± 3 d in milk (DIM; 7 d after the first PGF₂ injection) and at 58 ± 3 DIM, just before initiation of the Ovsynch protocol. According to serum concentrations of progesterone, cows were classified as having either high (1 ng/mL) or low (<1 ng/mL) progesterone. The proportion of cows with low progesterone at 37 ± 3 DIM was similar for cows treated later with the CIDR insert (60.7%; n = 654) and for control cows (59.2%; n = 657). In contrast, use of the CIDR insert resulted in fewer low-progesterone cows (17.4%; n = 402) compared with control cows (30.6%; n = 399) at 58 ± 3 DIM. No significant effect of the CIDR insert was detected on overall pregnancy rates. Pregnancy rates, as measured by the percentage of cows pregnant at 37 ± 3 d post timed artificial insemination, for control cows having high or low progesterone at 58 ± 3 DIM were 46.6 and 22.1%, respectively. For the CIDR group, pregnancy rates were 40.4 and 11.4%, respectively, for high- and low-progesterone cows at 58 ± 3 DIM. Overall pregnancy rates were 36.4 and 34.5% for control cows and cows receiving the CIDR insert, respectively. A significant decreasing trend was observed in the proportion of cows having low progesterone as the body condition score increased, at 37 ± 3 and 58 ± 3 DIM. A significant increasing trend in the pregnancy rate was observed as body condition score increased. In conclusion, incorporation of CIDR inserts into a presynchronization protocol reduced the proportion of cows having low progesterone; however, the pregnancy rate did not differ between control cows and those receiving the CIDR insert. Earlier expression of estrus after the second PGF₂ injection, and consequently improper timing of initiation of the Ovsynch protocol, could have negatively affected fertility in the CIDR-treated cows.

Key Words: controlled internal drug-release insert • presynchronization • dairy cow