Different protocols using PGF2α as ovulation inducer in Nelore cows subjected to estradiol-progesterone timed AI based protocols

Optimisation of Early Pregnancy Diagnosis and Resynchronisation in Beef Cows

The objectives of this study were (1) to investigate the effects of the preovulatory follicle (POF) size on the accuracy of Doppler-based early pregnancy detection, and (2) to determine whether the removal of PGF2α (PGF) treatment during the resynchronisation protocol would affect fertility in beef cows. In Experiment 1, Nelore suckling cows (n = 224) were enrolled in an estradiol-progesterone-based timed artificial insemination (TAI) protocol. At TAI, cows were separated based on the range of POF diameters, as follows: ≤11.0 mm (n = 50), 11.1-12.9 mm (n = 64), 13.0-14.4 mm (n = 62) and ≥14.5 mm (n = 48). On day 22 after TAI, the corpus luteum (CL) blood flow (CLBF) of all cows was examined by colour Doppler ultrasonography to diagnose nonpregnant cows. The cows with the largest POF had the greatest positive predictive value (88.6%; 31 of 35) and diagnostic accuracy (91.7%; 44 of 48). In Experiment 2, Nelore cows (n = 233) were subjected to the same TAI protocol. Fourteen days after TAI, all cows were started on a resynchronisation protocol. Cows diagnosed as nonpregnant based on CLBF, on day 22, received 0.5 mg estradiol cypionate intramuscular (im) and were assigned to receive either 150 μg of PGF (PGF; n = 50) or 2 mL of saline (control; n = 47). Cows treated with PGF had a P/AI of 30.0% compared with a 48.9% P/AI in controls (p = 0.06). Our findings demonstrate that the POF size affects the accuracy of a CLBF-based early pregnancy diagnosis and that the removal of PGF treatment from the resynchronisation protocol tended to increase P/AI of the second TAI.

Effects of estradiol cypionate dosage and body condition on reproductive performance of Nellore cattle synchronized for timed-artificial insemination

This experiment was designed to evaluate the effects of increasing doses of estradiol cypionate (ECP) and different body condition score (BCS) on reproductive performance of Bos indicus beef females assigned to a timed-artificial insemination (TAI) management. In this experiment, 1683 Bos indicus Nellore cows were blocked by parity and assigned to receive 1) an intravaginal P4 device (1.9 g of P4) and 2.0 mg of estradiol benzoate on day -11, 12.5 mg (i.m.) of dinoprost tromethamine, 300 IU (i.m.) of equine chorionic gonadotrophin, 0.6 mg (i.m.) of estradiol cypionate and CIDR withdrawal on day -2, followed by TAI on day 0 (n = 849; 0.6ECP) or 2) the same synchronization protocol with 1.0 mg of ECP on day -2 (n = 834; 1.0ECP). In both treatments, estrus expression was measured between days -2 and 0. Body condition score (BCS) was evaluated on days -11, 31, and 71 of the experiment and the BCS variation (Δ) was also determined between these timepoints. Transrectal ultrasonography was performed on days 31, 71, and 111 for pregnancy rate determination. All binary data were analyzed using cow as the experimental unit with GLIMMIX, whereas continuous variables were analyzed with the MIXED procedure of SAS. No treatment effects were observed on estrus expression rate. Treatment × BCS interactions were observed for pregnancy rates in all time points (days 31, 71, and 111), as 1.0ECP cows with a LOW BCS also had a greater P/AI than cows assigned to 0.6ECP. In summary, increasing the dose of ECP benefited the reproductive performance of Nellore beef cows with a reduced BCS (≤2.75), whereas no benefits were seen when the BCS was considered adequate (>2.75).

Seasonal expressions of COX-1, COX-2, and EP4 in the scent glands of muskrats (Ondatra zibethicus)

Prostaglandins (PGs) serve as signaling molecules that regulate various physiological processes, including inflammation, immune response, blood clotting, and reproduction. The aim of this study was to investigate the immunolocalizations and expression patterns of prostaglandin-E2 (PGE2), cyclooxygenase (COX)-1, and COX-2, as well as its receptor subtypes 4 (EP4) in the scent glands of muskrats (Ondatra zibethicus) during the breeding and nonbreeding periods. There were significant seasonal differences in the scent glandular mass, with higher values in the breeding season and relatively low in the nonbreeding season. PGE2, EP4, COX-1, and COX-2 have been immunolocalized in the scent glandular and epithelial cells in both breeding and nonbreeding seasons, whereas no immunostaining was observed in the interstitial cells. The protein and mRNA expression levels of EP4, COX-1, and COX-2 were higher in the scent glands of the breeding season than those of the nonbreeding season. The mean mRNA levels of EP4, COX-1, and COX-2 were positively correlated with the scent glandular weights. The circulating follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), and PGE2, as well as scent glandular PGE2 and dihydrotestosterone (DHT) concentrations, were also significantly higher in the breeding season. In addition, the transcriptomic study in the scent glands identified that differentially expressed genes might be related to fatty carboxylic monocarboxylic acid, steroidogenic-related pathways, and prostanoid metabolic processes. These findings suggested that prostaglandin-E2 might play an essential autocrine or paracrine role in regulating seasonal changes in the scent glandular functions of the muskrats.

Application of PGF2α at the moment of fixed-time artificial insemination in crossbred beef cows

Although studies have shown positive effects of gonadotropin releasing hormone (GnRH) or prostaglandin F_2α (PGF_2α) at the moment of fixed-time artificial insemination (FTAI) in the conception rate (CR) of cattle, its effects on treatments based on progesterone (P4) and estradiol benzoate (EB) is still not conclusive. The objective of this study was (1) to evaluate the effect of a PGF_2α analogue at FTAI in the CR of crossbred beef cows submitted to a 11d FTAI protocol based on P4 and EB; and (2) to describe the CR between PGF_2α-treated and control cows in different body condition scores (BCS) and parity categories. Crossbred (½ Nellore and ½ Angus) beef cows were submitted to a synchronization protocol and randomly assigned into 2 groups: Control (n = 163), at FTAI cows received 2 mL of saline solution as a placebo, and PGF_2α (n = 163), at FTAI cows were treated with PGF_2α analogue (10 mg of dinoprost tromethamine). Pregnancy diagnosis was performed 33d post-FTAI. Binary logistic regression model was used to analyze the effect of PGF_2α treatment on CR. There was no difference in CR between PGF_2α and control groups (P > 0.05; odds ratio (OR) = 0.92; confidence interval (CI) = 0.59-1.4). A greater CR was found in heifers (P = 0.0006, OR = 2.65, CI = 1.61 - 4.38) and multiparous (P = 0.0006, OR = 2.12, CI = 1.04 - 4.3) when compared to primiparous cows. Cows with low BCS (4; 9-point scale) showed lower CR when compared with moderate BCS (5-6; 9-point scale) (P < 0.05; OR = 0.10; CI = 0.06 - 0.18). There was no numerical difference on CR between PGF_2α-treated and control cows in different BCS and parity categories. The results suggested that the CR in this study was not influenced by 10 mg PGF_2α analogue at FTAI.

GnRH34: An alternative for increasing pregnancy in timed AI beef cows

Two experiments evaluated the effects of gonadotropin releasing hormone (GnRH) treatment on fertility of suckled Nelore beef cows treated with an estradiol/progesterone (P4)-based protocol for timed artificial insemination (TAI). Experiment 1 was designed to determine the effect of GnRH administered 34 h after P4 insert removal (GnRH34) on time of ovulation. Suckled cows (n = 34) were treated with 2 mg estradiol benzoate (EB) and an intravaginal insert containing 1.9 g of P4. Eight days later, P4 inserts were removed, and all cows received 150 μg of d-cloprostenol (prostaglandin F2 alpha analogue), 300 IU of eCG, and 1 mg of estradiol cypionate (ECP). On Day 9 (05:00 p.m.), cows were randomly distributed, according to the diameter of the pre-ovulatory follicle, in two treatments: 1) GnRH (n = 17) cows that received 10.5 μg of buserelin acetate, or 2) no further treatment (control, n = 17). Cows treated with GnRH 34 h after P4 insert removal ovulated earlier (P = 0.02) than control cows (66 ± 0.0 and 77.2 ± 4.3 h). Experiment 2 was designed to determine the effect of GnRH34 on the fertility of suckled beef cows. Nelore cows (n = 506) were treated as Experiment 1. On Day 8, cows were painted in the sacrocaudal region to identify cows that displayed estrus. On Day 9 (05:00 p.m.), cows were randomized to receive same treatment as Experiment 1, control (n = 252), or GnRH (n = 254). All cows were TAI 48 h after P4 insert removal. At TAI, estrus was evaluated, and deemed to have occurred in cows without a tail-head chalk mark (>75% paint loss). Cows treated with GnRH 34 h after P4 insert removal had greater (P = 0.01) pregnancy per AI (P/AI) than cows that only received ECP (63.0% and 50.4%). No difference (P = 0.5) was observed in the proportion of cows that displayed estrus between treatments. Furthermore, cows that displayed estrus had greater (P < 0.01) P/AI than cows that did not. Treatment with GnRH, given at 34 h after P4 insert removal, increased (P < 0.05) P/AI in cows that did not show estrus at TAI. In summary, treatment with GnRH 34 h after P4 insert removal was associated with earlier ovulation and resulted in greater P/AI in suckled Nelore cows treated with an estradiol/P4-based protocol for TAI.

Effect of expression of estrus and treatment with GnRH on pregnancies per AI in beef cattle synchronized with an estradiol/progesterone-based protocol

Three experiments evaluated the effects of expression of estrus and gonadotropin releasing hormone (GnRH) treatment on pregnancies per AI (P/AI) in beef cattle that were treated with an estradiol/progesterone (P4)-based protocol for fixed-time artificial insemination (FTAI). In Experiment 1, 20 non-lactating beef cows were treated with 2 mg estradiol benzoate (EB) and an intravaginal device containing 0.5 g of P4. Seven days later, P4 devices were removed and all cows received prostaglandin F2 alpha (PGF_2α) and 0.5 mg estradiol cypionate (ECP). Estrus was detected using tail paint and cows that did not show estrus by 48 h after P4 device removal were randomized to receive GnRH or no treatment. Ovulation, as determined by ultrasonography, occurred earlier in cows that showed estrus (68.0 ± 2.5 h) than in cows that did not (82.0 ± 2.1 h, P < 0.05). Furthermore, cows that received GnRH ovulated earlier (78.0 ± 2.6 h) than those that did not (86.0 ± 2.0, P < 0.05). Experiment 2 determined whether expression of estrus and the administration of GnRH to animals that did not show estrus increased P/AI. Non-lactating beef cows and heifers (n = 1356) were treated as in Experiment 1 (P4 device removal, PGF2α and ECP administration on Day 7) or extended until Day 8. All animals in estrus by 48 h after P4 device removal were inseminated and those not showing estrus received GnRH or no treatment and were FTAI 8 h later (i.e., at 56 h). P/AI were greater (P < 0.01) in animals that were observed in estrus by 48 h (56.4%) than in those that did not show estrus (46.5%). Likewise, animals that did not show estrus but were treated with GnRH had greater P/AI (53.8%, P < 0.04) than those that did not receive GnRH (37.9%). Experiment 3 was designed to determine the effect of delaying GnRH treatment to the time of FTAI (at 56 h) in cows not showing estrus by 48 h after P4 device removal. Suckled beef cows (n = 969) were treated as in Experiment 1, except that all cows also received 400 IU of eCG at the time of P4 device removal on Day 7. Cows that showed estrus by 48 h or 56 h had greater P/AI (62.3%, P < 0.05) than those did not show estrus (51.5%). Furthermore, when cows that did not show estrus by 48 h were analyzed separately, P/AI were greater (P < 0.05) in those that received GnRH at 48 h and were FTAI by 56 h (64.9%) than in those that received GnRH concurrent with FTAI by 56 h after device removal (54.6%). In summary, expression of estrus was associated with earlier ovulations and resulted in greater P/AI in cows and heifers treated with an estradiol/P4-based protocol for FTAI. Furthermore, GnRH treatment in animals that did not show estrus hastened the time of ovulation and increased P/AI.

Seasonal expressions of COX-1, COX-2 and EP4 in the uteri of the wild Daurian ground squirrels (Spermophilus dauricus)

Prostaglandins (PGs) play a pivotal role in uterine reproductive process including maternal recognition of pregnancy, cell proliferation, and myometrium contractions in mammals. In this study, we investigated the immunolocalizations and expression levels of Prostaglandin E2 synthases cyclo-oxygenase (COX)-1 and COX-2, as well as one of PGE2 receptor subtypes 4 (EP4) in the uteri of the wild Daurian ground squirrels (Spermophilus dauricus) during the breeding and non-breeding seasons. Histologically, the thickness of endometrium: myometrium ratio in the uteri of the breeding season was higher than that of the non-breeding season. The immunostainings of COX-1, COX-2 and EP4 were observed in stromal cells, glandular cells and myometrium cells in the breeding and non-breeding seasons. The protein and mRNA expression levels of COX-1, COX-2 and EP4 were higher in the uteri of the breeding season than those of in the non-breeding season. The mean mRNA levels of COX-1, COX-2 and EP4 were positively correlated with uterine weights. In addition, the PGE2 concentration of uterine tissues as well as plasma PGE2, 17β-estradiol, progesterone, LH and FSH levels were also significantly higher in the breeding season compared to those of the non-breeding season. These results suggested that PGE2 might play an important autocrine or paracrine role in the regulation of seasonal changes in the uterine functions of the wild Daurian ground squirrels during the breeding and non-breeding seasons.