Regimens of progesterone supplementation for lactating dairy cows according to the presence of corpora lutea (CL) at the initiation of the timed AI program

Abstract Text: Objectives were to evaluate the effects of supplemental progesterone on fertility of dairy cows according to the presence of CL at the initiation of the Ovsynch-56 program (d-10 GnRH, d-3 PGF_2α, h-16 GnRH, d0 AI). Cows had their ovaries evaluated by ultrasonography (d-10) and those without CL were assigned randomly to receive 0 (NoCL; n=558) or 2 intravaginal inserts containing progesterone (CIDR) from d-10 to d-3 (2CIDR; n=544). Cows with CL on d-10 were matched by pen and used as positive controls (Diestrus; n=543). The remaining cows bearing CL were assigned randomly to receive 0 (Control; n=388) or 1 CIDR inserts (1CIDR; n=393). Ovaries were scanned on d-3 for assessment of ovulation after the first GnRH and the presence of a newly formed CL. A subgroup of cows (n=365) had their ovaries scanned on d-1 and d1 for measurement of the ovulatory follicle and evaluation of the response to the second GnRH. Estrus was detected based on removal of tail chalk beginning on d-10. Pregnancy was evaluated 32 and 60 d after AI. Data were analyzed using the GLIMMIX procedure of SAS. A greater (P<0.01) proportion of NoCL and 2CIDR cows had a new CL on d-3 compared with Diestrus (71.6, 68.7, 43.2%), whereas no difference was observed between Control and 1CIDR (51.2, 56.6%). Fewer (P<0.01) NoCL and 2CIDR cows had CL on d-3 compared with Diestrus (71.6, 68.7, 88.0%) and no difference was observed between Control and 1CIDR (86.4, 87.6%). Progesterone supplementation reduced (P=0.05) the proportion of cows without CL inseminated before timed AI for first postpartum AI (2CIDR=10.9, NoCL=17.7%), but not for subsequent AI (2CIDR=19.0, NoCL=17.5%) or cows with CL (1CIDR=7.8, Control=9.1%). Ovulation to the second GnRH was not affected by treatment and averaged 86.5%. The diameter of the ovulatory follicle tended to be reduced (P=0.07) by progesterone supplementation in cows lacking CL (2CIDR=17.0±0.4, NoCL=18.1±0.4 mm), but not in those with CL (1CIDR=17.5±0.4, Control=17.8±0.4 mm). Pregnancy per AI was greater (P≤0.08) for 2CIDR compared with NoCL and intermediate for Diestrus on d 32 (38.4, 32.7, 35.9%) and 60 (33.3, 28.3, 31.4%). This benefit was observed exclusively in cows not detected in estrus at AI. Progesterone supplementation reduced (P=0.05) P/AI in 1CIDR compared to Control on d 32 (38.3, 45.7%) but not on d 60 after AI (33.4, 37.4%), which was associated with smaller (P=0.04) pregnancy loss in the 1 CIDR group (4.0, 12.6%).

Keywords: Anovulation, dairy cow, progesterone