Contents lists available at ScienceDirect Research in Veterinary Science journal homepage: www.elsevier.com/locate/rvsc Use of prostaglandin F2α as ovulatory stimulus for synchronizing dairy cattle N.A. Castro a , P.M.A. Neves b , J.P. Cestaro b , V.T.O. Melo b , A. Schneider a , L.F.M. Pfeifer c, ⁎ a Federal University of Pelotas, Pelotas, Brazil b Faculdades Integradas Aparício Carvalho, Porto Velho, Brazil c Brazilian Agricultural Research Corporation, Porto Velho, Brazil ARTICLE INFO Keywords: Cattle Estradiol cypionate Prostaglandin Ovulation inductor ABSTRACT The aim of this study was to evaluate if prostaglandin F2α (PGF) can be used to induce ovulation in a GnRH- progesterone based protocol. In Experiment 1 crossbred dairy cows (n = 32) were synchronized with a pro- gesterone-GnRH based protocol for seven days, where the luteolytic dose of 150 μg PGF was given 24 h prior progesterone device removal (CIDR). On Day 8 cows were separated into two groups to receive: 1) 2 mL of Saline (Control Group, n = 15) or 2) 150 μg of PGF (PGF Group, n = 17). Ovulation rate was higher in the PGF than Control group (100% vs 53.3%, P = 0.001, Odds ratio = 30.88). The percentage of cows that ovulated syn- chronously tended to be higher in the PGF than Control group (P = 0.1, Odds ratio = 9.6). Experiment 2 was performed in a cross-over (3 × 3) design. Crossbred dairy cows (n = 25) received a CIDR for seven days and GnRH on Day 0. Seven days later 150 μg of PGF was given and the progesterone device was removed, and 24 h later cows were distributed into three groups to receive: 1) 2 mL of Saline (Control Group, n = 25), 2) 150 μg of PGF (PGF Group, n = 25) or 3) 1 mg of ECP (ECP Group, n = 23). Diameter of ovulatory follicle was larger in the PGF and Control than ECP Group (P = 0.002, Effect size > 4.0). Synchronized ovulation rate (between 72 and 96 h after CIDR removal) tended to be higher in PGF group in Control group (P = 0.1, Odds ratio = 0.35). Results suggest that PGF is equally efficient to ECP to induce synchronized ovulation in dairy cows subjected to progesterone-GnRH based protocols. Estrous cycle synchronization protocols have been widely used in cattle since they allow the widespread use of fixed time artificial in- semination (FTAI). Over the last few decades several protocols have been developed (Yilmazbas-Mecitoglu et al., 2014). The substitution of GnRH for estradiol cypionate (ECP) to induce ovulation was an im- portant modification for reducing the costs of the Ovsynch protocol (Stevenson et al., 2004). However, the use of estradiol esters has been restricted in several countries. Therefore, the development of efficient alternative low-cost ovulation inducers is needed, and represents a current challenge. Prostaglandin F2α (PGF) has been shown to induce ovulation by a mechanism independent of luteolysis (Leonardi et al., 2012). Although this mechanism is not yet fully understood, it was suggested that PGF increases the ability of the pituitary to respond to GnRH in postpartum cows (Randel et al., 1996). Additionally, there is an increase in the expression of PGF and PGE2 receptors in theca and granulosa cells of preovulatory follicles, suggesting a local effect can also take place (Bridges and Fortune, 2007). Furthermore, PGF has a similar effect to ECP and estradiol benzoate (EB) for inducing ovulation in cows subjected to estradiol-progesterone based FTAI protocols in beef (Pfeifer et al., 2014) and dairy cows (Pfeifer et al., 2016). However, the effect of PGF on estradiol-free protocols is not yet well defined. Therefore, the aims of this study were to: 1) evaluate whether a PGF analogue is able to induce ovulation in a synchronized manner; and 2) to compare a PGF analogue with ECP as ovulation inducer in GnRH- progesterone based TAI protocols. The Committee for Ethics in Animal Experimentation from the Brazilian Agricultural Research Corporation (Embrapa – Rondônia) approved all procedures performed in this experiment (Number F.02/ 2014). In the Experiment 1, 32 crossbred dairy cows (Gyr × Holstein) were used. On Day 0, all females were given 100 μg of lecirelin (GnRH- analogue, Gestran plus®, Tecnopec, São Paulo, Brazil) i.m., plus an in- travaginal progesterone-releasing device (CIDR®, 1.9 g progesterone, Pfizer Animal Health, São Paulo, Brazil). On Day 6, 150 μg of D- Cloprostenol (PGF-analogue, Croniben®, Biogénesis-Bagó, Curitiba, Brazil) i.m. was given and 24 h later the CIDRs were removed. On Day 8, cows were randomly assigned into one of the two treatments: 1) 2 mL https://doi.org/10.1016/j.rvsc.2018.01.010 Received 29 May 2017; Received in revised form 22 December 2017; Accepted 14 January 2018 ⁎ Corresponding author. E-mail addresses: nataliavetufpel@gmail.com (N.A. Castro), luiz.pfeifer@embrapa.br (L.F.M. Pfeifer). Research in Veterinary Science 118 (2018) 151–154 0034-5288/ © 2018 Elsevier Ltd. All rights reserved. T