Impacts of administering prostaglandin F2α analogue 24 h prior to progesterone insert removal on expression of estrus in beef females
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© 2019 Two experiments investigated the effects of administering prostaglandin (PG) F2α analogue 24 h prior to controlled internal drug release (CIDR) device removal in beef females assigned to GnRH-based synchronization protocols. In Exp. 1, 305 nulliparous heifers received 100 µg of GnRH and a CIDR containing 1.38 g of progesterone (P4) on day 0. Heifers were randomly assigned to receive 500-µg of cloprostenol on day 6 (PG6, n = 155) or day 7 (PG7, n = 150). The CIDR was removed on day 7, and heifers were monitored for estrus activity for 84 h after CIDR removal using detection patches. Heifers were artificially inseminated (AI) 12 h after being detected in estrus. Heifers that were not in estrus by 84 h after CIDR removal received GnRH (100 µg) and were inseminated 12 h later. Estrus expression was greater in PG6 vs. PG7 heifers at 48 h, but greater in PG7 vs. PG6 heifers at 60 h (P = 0.09) and 72 h (P < 0.01) after CIDR removal (treatment × time; P < 0.01). Cumulative estrus incidence was greater (P < 0.01) in PG6 vs. PG7 heifers by 60 h after CIDR removal (treatment × time; P < 0.01). No differences in pregnancy rates were observed (P = 0.43). In Exp. 2, 365 suckled multiparous cows received 100 µg of GnRH and a CIDR on day 0, and were assigned to treatments as in Exp. 1 (25 mg of dinoprost tromethamine; PG6, n = 147; PG7, n = 162). The CIDR was removed on day 7, and cows received 100 µg of GnRH and fixed-time AI on day 10. An estrus detection patch was applied to each cow on day 7, and estrus expression assessed at AI. Blood samples were collected on day 0 to determine the presence of a corpus luteum via plasma P4 (CL, P4 ≥ 1.0 ng/mL; NOCL, P4 < 1.0 ng/mL). Estrus expression was greater (P < 0.01) in PG6 vs. PG7 cows classified as CL, but similar (P = 0.96) within NOCL (treatment × CL status; P = 0.05). Pregnancy rates did not differ between treatments (P = 0.53), despite a 20% increase (P = 0.15) in PG6 vs. PG7 cows classified as CL. Therefore, PG6 increased the proportion of beef females that expressed estrus by 60 h after CIDR removal within a GnRH-based synchronization protocol, without substantially improving pregnancy rates to AI.
author list (cited authors)
Fontes, P., Cooke, R. F., Oosthuizen, N., Timlin, C. L., Dias, N. W., Currin, J. F., ... Mercadante, V.