Abstract #446

# 446
Effect of decreasing the duration of a PRID-synch protocol and addition of a second prostaglandin F treatment on fertility after resynchronization of ovulation in lactating Holstein cows.
V. G. Santos*1,2, P. D. Carvalho1, C. Maia3, B. C. Carneiro3, A. Valenza4, E. M. Bettencourt2, P. M. Fricke1, 1Department of Dairy Science, University of Wisconsin-Madison, Madison, WI, 2Departamento de Medicina Veterinária, Escola de Ciências e Tecnologia, Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Instituto de Investigação e Formação Avançada, Universidade de Évora, Núcleo da Mitra, Évora, Portugal, 3Diessen Servicos Veterinarios Lda, Évora, Portugal, 4CEVA Sante Animale, Libourne, France.

Our objective was to evaluate the effects of (1) decreasing the interval between the first GnRH treatment (G1) and the PGF (PGF) treatment and (2) a second PGF treatment 24 h after the first during hormonal protocols for resynchronization of ovulation and timed artificial insemination (TAI). Lactating Holstein cows (n = 249) from 3 commercial dairy farms were randomly assigned at a nonpregnancy diagnosis to 1 of 3 hormonal protocols for resynchronization of ovulation: (1) a 7-d PRID-synch protocol with 1 PGF injection (7D1P: d 0; GnRH +PRID; d 7, PGF -PRID; 56 h, GnRH; 16 h, TAI); (2) a 7-d PRID-synch protocol with 2 PGF injections (7D2P: d 0, GnRH +PRID; d 7, PGF -PRID; 24 h, PGF; 32 h, GnRH; 16 h TAI); and (3) a 5-d PRID-synch protocol with 2 PGF injections (5D2P: d 0, GnRH +PRID; d 5, PGF -PRID; 24 h, PGF; 32 h, GnRH; 16 h, TAI). Ovaries of all cows were examined at G1 using transrectal ultrasonography, and cows were classified as either having or lacking a CL. Data were analyzed by logistic regression using PROC GLIMMIX of SAS. Pregnancy diagnosis was conducted 32 d after TAI using transrectal ultrasonography. Overall, P/AI 32 d after TAI did not differ (P = 0.83) between primiparous and multiparous cows [47% (35/75) vs. 44% (77/174), respectively]. At 32 d after TAI, P/AI tended to differ (P = 0.09) among treatments and was least for 7D1P cows, intermediate for 5D2P cows, and greatest for 7D2P cows [39% (35/89) vs. 44% (34/77) vs. 52% (43/83), respectively]. Furthermore, P/AI did not differ (P = 0.20) between cows classified as having or lacking a CL at G1 of the resynchronization protocols [48% (83/174) vs. 39% (22/56), respectively]. Based on these preliminary data, addition of a second PGF injection to a 7-d PRID-synch protocol increased (P = 0.03) P/AI 32 d after TAI by 13 percentage points (7D2P vs. 7D1P cows), whereas decreasing the interval between G1 and the PGF injection (5D2P vs. 7D2P cows) did not increase (P = 0.62) P/AI 32 d after TAI in resynchronized Holstein cows. Supported by CEVA Sante Animale.

Key Words: timed AI, dairy cow, resynchronization