The aim was to assess the effect of progesterone before an Ovsynch-Controlled intravaginal drug releasing device (CIDR; 1.9 g P4) protocol on fertility in dairy cows with low body condition score (BCS; ≤ 2.75; scale 1–5). Lactating Holstein cows (n = 299) were assigned at the beginning of presynch to receive a 1.9 g CIDR on d −12 (Progesterone treatment, n = 148) or no treatment (Control, n = 151). On d −3, CIDR was removed and both treatments received 2 doses of 25 mg of PGF_2α (5 mL, i.m., Lutalyse) 12 h apart. At Day 0 (45 ± 3 DIM) all cows were enrolled in a synchronization protocol and treated with 10 µg of GnRH analog (2.5 mL, i.m., Receptal) and 1.9 g CIDR. On d 7, CIDR was removed and cows received 2 doses of 25 mg of PGF2α 12 h apart. Cows received a second dose of GnRH analog 56 h after first dose of PGF_2a and were TAI 16 h later (d 10). On d −12, parity, BCS, milk yield, DIM and stage of the estrous cycle were recorded. Ultrasonography of the ovaries was conducted on d −12 to determine the presence of a corpus luteum (CL). Pregnancy at AI (PAI) was diagnosed by ultrasonography at 32 d post AI. Logistic regression was used to evaluate the effect of treatment, parity, and presence of CL at d −12 and 2-way interactions on pregnancy. There was no difference (P = 0.18) in PAI between the progesterone treatment (33.1%) and control (30.5%). No interaction between treatment and parity was detected (P = 0.65). However, progesterone treatment before the CIDR-Ovsynch protocol increased (P = 0.04) PAI in cows without a CL on d −12 (32.2% vs. 18.7%) but not in cows with a CL (34.5% vs. 42.1%). Table 1 (Abstr. 327). Pregnant cows, adjusted odds ratio (AOR), and 95% CI for treatments adjusted by parity, CL at d −12 and interactions

Variable	Pregnancyper AI, % (no/no.)	AOR	95% CI	P-value
Treatment				0.18
Control	30.5 (46/151)	—	—
Progesterone	33.1 (49/148)	1.84	0.75–4.50
Parity				0.82
Primiparous	33.3 (41/123)	—	—
Multiparous	30.7 (54/176)	0.92	0.45–1.87
CL at d −12				0.75
No	26.1 (43/165)	—	—
Yes	38.8 (52/134)	1.12	0.55–2.28
CL at d −12 by treatment				0.04
No/Control	18.7 (14/75)	—	—
No/Progesterone	32.2 (29/90)	2.07	0.99–4.29
Yes/Control	42.1 (32/76)	3.16	1.51–6.62
Yes/Progesterone	34.5 (20/58)	2.29	1.03–5.07