Retention of a functional corpus luteum and peripheral concentrations of 13,14-dihydro-15-keto-prostaglandin F-2 alpha following metestrus administration of Syncro-Mate-B

This study was conducted to examine the effects of metestrus administration of Syncro-Mate-B (SMB) on PGF(2 alpha) secretion and corpus luteum (CL) de velopment. In a study replicated over 2 yr, cows were observed for spontane ous estrus in yr 1, and cows received an injection of 25 mg of PGF(2 alpha) and were observed for subsequent estrus in yr 2. At standing estrus (estru s = d 1), cows were randomly allotted to receive either the standard SMB re gimen (n = 40) on d 3 of the estrous cycle or no treatment (n = 8). Fifty p ercent (n = 20) of SMB-treated cows were administered PGF(2 alpha) on d 10 of the estrous cycle 48 h prior to implant removal. Twice-daily blood sampl es were collected in the morning (ARI) and evening (PM) from d 2 AM through d 14 AM: of the treated estrous cycle and subsequently analyzed for proges terone (P-4) and PGF(2 alpha) metabolite (PCFM). Prior to statistical analy sis, SMB- and SMB/PGF(2 alpha)-treated cows were sorted according to Pq con centration, at d 10 of the treated estrous cycle to either a CL functional group (P-4 greater than or equal to 1 ng/mL; n = 20) or a CL nonfunctional group (P-4 < 1 ng/mL; n = 17). Following d 10 AM administration of PGF(2 al pha), functional and nonfunctional groups were further subdivided based on treatment. The groups were as follows: untreated control cows (n = 8); SMB- treated cows retaining a functional CL (SMB-F; n = 8); SMB-treated cows wit h a nonfunctional CL(-SMB-N; n = 11); SMB/PGF(2 alpha)-treated cows retaini ng a functional CL (SMB/PG-F; n = 12); and SNIB/PGF(2 alpha)-treated cows w ith a nonfunctional CL (SMB/PG-N; n = 6). Of all SMB-treated cows, 54% reta ined a functional CL through d 10 AM of the treated estrous cycle. Mean ser um P-4 concentrations increased for cows in all groups until d 7, after whi ch P-4 concentrations increased for cows in SMB/PG-F, SMB-F, and control gr oups and decreased for cows in SNIB/PG-N and SMB-N groups. Following PGF(2 alpha) administration on d 10, mean serum P-4 concentrations remained < 1 n g/mL for cows in SMB/PG-N and SMB-N groups, decreased to < 1 ng/mL for cows in the SMB/ PG-F group, and remained > 1 ng/ml for cows in SMB-F and contr ol groups. Mean serum PGFM concentrations tended (P = .06) to increase in c ows with nonfunctional CL compared with control cows on d 8 ANI and were gr eater (P < .05) in cows with functional CL on d 8 PM through d 9 PM. These results indicate that retention of a functional rather than a nonfunctional CL following metestrus adminis- tration of SMB is dependent on a premature release of uterine PGF(2 alpha).