Is prolonged luteal phase a problem in lactating Holstein cows?

In this study, the main objective was to assess if long luteal phases could have causes other than pregnancy loss. We enrolled Holstein dairy cows ≥50 DIM from a commercial herd in Brazil from October 2016 to August 2017. All cows received an estradiol-based synchronization protocol, and, on the day of insemination (d 0), were randomly assigned either an AI or a placebo insemination (PBO) in a 3:1 ratio. An ultrasound was used to assess the presence of a corpus luteum (CL) on d 17, 24, and 31, which, combined to the information from patches for the detection of estrus, was used to determine the length of the luteal phase following AI or PBO. Pregnancy was assessed by ultrasound on d 31 and cows that were pregnant were excluded from the analyses. The length of the estrous cycles was categorized as short (<17 d), normal (17-23 d), long (24-30 d), and very long (≥31 d). We compared the proportion of cows in each category between the AI and PBO groups using a cumulative ordinal mixed model. We define prolonged luteal phase as estrous cycles ≥24 d and tested its association with potential risk factors (parity, season, DIM, uterine size and position score, milk production, BCS, and the presence of a CL at enrollment to the synchronization protocol) using mixed logistic regression models. Results are presented as odds ratio (OR) and 95% Bayesian credible intervals (BCI). Data from 876 inseminations (AI: n = 616, PBO: n = 260) was collected. Overall, 12% of estrous cycles were short, 31% were normal, 19% were long, and 38% were very long. There was no difference in the odds of being in longer estrous cycle categories for the AI compared with the PBO group (OR = 0.92; 95% BCI = 0.76-1.10). Season and presence of a CL at enrollment were associated with prolonged luteal phase. In the AI group, there was a possible effect of early pregnancy losses on the lifespan of the CL, but not the PBO group, which led us to conclude that long and very long estrous cycles were not all caused by the embryonic loss. In fact, the high prevalence of cows with an extended CL lifespan in the present study suggests this could be an under- or miss-reported characteristic of high-producing lactating Holstein cows. This finding may have important repercussions in the understanding of the CL function physiology of lactating Holstein cows.

Characterization of placentome vascular perfusion in relation to pregnancy associated glycoproteins throughout gestation in pregnant beef heifers.

During pregnancy, blood flow to the uterus changes to support fetal demand. Placentomes serve as vascular attachment sites on the placenta for exchange of gases, nutrients, and metabolic products. Non-invasive methods of ultrasonography and biomarkers have been described to assess placental health and fetal viability. Pregnancy associated glycoproteins (PAGs) are produced by the ruminant placenta and are detected in maternal circulation. In cattle, changes in circulating PAG concentrations are associated with embryonic and fetal outcomes. The objective of this study was to determine the association between placentome blood perfusion and circulating PAG concentrations as they relate to the health of the developing fetus. We hypothesized that placentome perfusion and PAG concentration will be positively correlated and associated with neonatal outcome. A prospective, observational study was designed using 26 pregnant, nulliparous, Angus heifers in which PAG concentration and placentome blood perfusion were assessed throughout gestation, with assessment of calving characteristics following parturition. Placentome blood perfusion was visualized at 30-day intervals via transrectal Doppler ultrasonography with power flow function. Ultrasound images were analyzed using ImageJ software to determine the percent area of perfusion and integrated pixel densities. Venous blood was collected and PAG concentrations were determined via serum PAG enzyme-linked immunoassay. Mean placentome blood perfusion increased as gestation advanced. PAG concentrations demonstrated the expected temporal trend, increasing with gestation length, and were positively linearly correlated with placentome perfusion (P < 0.0001). The relationship identified between circulating PAG concentration and placentome blood perfusion suggests the use of transrectal power flow Doppler ultrasonography as a noninvasive technique to determine placental blood flow morphometrics to assess conceptus wellbeing throughout pregnancy.

Characterizing pregnancy losses in Bos indicus beef females receiving a fixed-timed artificial insemination protocol.

This experiment evaluated pregnancy losses from day 30 of gestation to calving in Bos indicus females, and evaluated if serum haptoglobin concentrations during early gestation impacts subsequent pregnancy losses. A total of 4926 Nelore females were used, being 1802 nulliparous heifers inseminated as yearlings (precocious heifers), 1356 nulliparous heifers inseminated at 24 months of age (conventional heifers), 887 suckling primiparous cows, and 881 suckling multiparous cows. Cows were assigned to an ovulation synchronization + fixed-time artificial insemination (FTAI) protocol from day -11 to 0 of the experiment. Pregnancy status was verified using transrectal ultrasonography on days 30 and 60 after FTAI, via transrectal palpation on day 150 after FTAI, and according to calf birth. Blood samples were collected from all animals diagnosed pregnant on day 30 after FTAI, and analyzed for serum concentrations of haptoglobin and pregnancy associated glycoproteins (PAG). Pregnancy loss was greater (P < 0.01) from day 60-150 of gestation (10.2 %) compared with day 30-60 of gestation (6.0 %) and with day 150 of gestation to calving (7.4 %), and differed (P = 0.04) between these latter two periods. Pregnancy loss from day 30-60 of gestation did not differ (P = 0.26) among parities, whereas total pregnancy losses (day 30 to calving) were greater (P < 0.01) in precocious (28.4 %) and conventional (27.1 %) heifers compared with primiparous (16.4 %) and multiparous (13.0 %) cows. Serum PAG concentrations on day 30 after FTAI were less (P ≤ 0.03) in cows that lost the pregnancy (5.63 ng/mL) from day 30-60 of gestation, as well as those that lost the pregnancy from day 30 to calving (8.59 ng/mL) compared with cohorts that maintained the pregnancy (9.39 and 9.32 ng/mL, respectively). No differences in serum PAG concentrations on day 30 after FTAI were noted (P ≥ 0.23) according to pregnancy losses from day 60 to calving. Serum haptoglobin concentration on day 30 after FTAI also did not differ (P ≥ 0.48) between cows that maintained or lost the pregnancy. This experiment provides novel information about pregnancy losses after day 30 of gestation in B. indicus cattle, with most losses occurring as fetal mortality and not affected by systemic inflammation during early gestation. Pregnancy losses were nearly doubled in precocious and conventional heifers compared with parous cows, demonstrating the relevance of this reproductive failure to B. indicus replacement heifers.

Shifts in uterine bacterial communities associated with endogenous progesterone and 17ß-estradiol concentrations in beef cattle.

The relation between circulating concentrations of progesterone and 17ß-estradiol prior to insemination play a key role in optimizing fertility in cattle. This study aimed to determine the impact of endogenous progesterone (P4) and estradiol (E2) concentrations on uterine bacterial community abundance and diversity in beef cattle. Angus-influenced heifers were subjected to an industry standard estrous synchronization protocol. Uterine flushes were collected on d -2 (endogenous P4) and d 0 (endogenous E2) and used for targeting the V4 hypervariable region of 16S rRNA bacterial gene. Plasma was collected on d -2 and 0 for quantification of P4 and E2 concentrations by radioimmunoassay, respectively. Heifers were allotted to one of the following groups: High P4 + High E2 (H-H; n = 11), High P4 + Low E2 (H-L; n = 9), Low P4 + High E2 (L-H; n = 9), Low P4 + Low E2 (L-L; n = 11). Results indicated that Shannon's diversity index tended to be greater for H-L heifers compared to L-H heifers on d 0 (P = 0.10). For H-L heifers from d -2 to d 0, the relative abundance of Actinobacteria decreased and Tenericutes increased (P < 0.01). Within phylum Actinobacteria, the relative abundance of Corynebacterium decreased from d -2 to d 0 in treatment groups H-H, H-L, and L-L (P < 0.05); however, did not differ by d for L-H heifers. Within phylum Tenericutes, the relative abundance of Ureaplasma increased from d -2 to d 0 for H-L heifers (P = 0.01). Additionally for H-L heifers, the relative abundance of Bacteroidetes tended to increase from day -2 to on d 0 (P = 0.07). For H-L heifers, uterine pH increased from day -2 to d 0 (P = 0.05). These results suggest that differing endogenous concentrations of P4 and E2 may be associated with shifts in uterine microbiota and pH, and this could ultimately impact fertility outcomes in beef cattle.

Influence of body condition score and its change after parturition on pregnancy rates to fixed-timed artificial insemination in Bos indicus beef cows.

This experiment evaluated pregnancy rates to fixed-time artificial insemination (FTAI) in Bos indicus beef cows according to their body condition score (BCS) at calving and subsequent change until 30 days after FTAI. Non-pregnant, suckling Nelore cows (n = 593 primiparous, 461 secundiparous, and 893 multiparous) were evaluated for BCS at calving and FTAI, and at 30 days after FTAI when cow pregnancy status was verified. Cow BCS at calving was subtracted from BCS recorded at pregnancy diagnosis, and cows classified as those that lost BCS (L), maintained BCS (M), or gained BCS (G) during this period. Cows that calved with BCS ≥ 5.0 had greater (P < 0.01) BCS throughout the experiment, and greater (P < 0.01) pregnancy rates to FTAI compared with cows that calved with BCS < 5.0 (54.8 vs. 34.2%). Pregnancy rates to FTAI were greater (P < 0.01) for G and M cows compared with L cows (50.0%, 47.5%, and 36.0%, respectively), and similar (P = 0.46) between G and M cows. Moreover, pregnancy rates to FTAI in G cows that calved with BCS < 5.0 were less compared with L (tendency; P = 0.08) and M cows (P < 0.01) that calved with BCS ≥ 5.0 (42.2%, 48.3%, and 58.3%, respectively). In summary, pregnancy rates to FTAI were greater in B. indicus cows that calved with a BCS ≥ 5.0 regardless of parity and post-calving BCS change, and greater in M and G cows within those that calved with BCS < 5.0 or ≥ 5.0.

Evaluation of luteolysis, follicle size, and time to ovulation in Holstein heifers treated with two different analogs and doses of prostaglandin-F2α.

Objectives were to evaluate the effect of 2 analogs of PGF2α (cloprostenol vs. dinoprost) and 2 doses (1 injection vs. 2 injections) on luteolysis, follicle diameter, hormonal concentrations, and time to ovulation in dairy heifers. Holstein heifers were fitted with automated estrus detection devices and had their estrous cycle synchronized using PGF2α and an intravaginal insert containing progesterone. Heifers detected in estrus were blocked by weight and randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement: cloprostenol on d 7 after estrus (CLOx1; n = 45), cloprostenol on d 7 and 8 after estrus (CLOx2; n = 41), dinoprost on d 7 after estrus (DINx1; n = 43), or dinoprost on d 7 and 8 after estrus (DINx2; n = 44). Treatment with the first injection of PGF2α was defined as experiment d 0. Area and blood flow of corpus luteum (CL) and diameter of follicles >5 mm were recorded every 12 h from d 0 to estrus and every 6 h thereafter until ovulation. Blood was sampled every 6 h from d 0 until ovulation. Heifers treated with cloprostenol had shorter interval to luteolysis (± SEM; CLOx1 = 23.5 ± 2.2, CLOx2 = 22.9 ± 2.2, DINx1 = 32.6 ± 2.7, DINx2 = 26.4 ± 2.1 h); however, time to ovulation was not affected by treatment. A smaller proportion of heifers treated with a single injection of PGF2α underwent luteolysis compared with heifers treated with 2 injections (CLOx1 = 84.6 ± 6.2, CLOx2 = 100.0 ± 0.0, DINx1 = 59.7 ± 9.8, DINx2 = 96.3 ± 2.7%). Proportion of heifers that ovulated was smaller for DINx1 compared with other treatments (CLOx1 = 88.8 ± 5.1, CLOx2 = 100.0 ± 0.0, DINx1 = 55.2 ± 9.7, DINx2 = 94.4 ± 3.4%). Ovulatory follicle diameter was larger for DINx1 (18.2 ± 2.7 mm) compared with DINx2 (17.4 ± 2.7 mm), whereas dose did not affect the diameter of the ovulatory follicle in heifers treated with cloprostenol (CLOx1 = 17.6 ± 2.7 vs. CLOx2 = 17.8 ± 2.8 mm). Among heifers that underwent luteolysis, progesterone concentrations from 18 to 36 h after treatment were lesser in heifers treated with cloprostenol compared with those treated with dinoprost. Type of PGF2α did not affect progesterone concentrations past 36 h from treatment; however, heifers treated with 2 PGF2α injections had lesser progesterone concentrations and CL blood flow from 36 to 72 h after treatment compared with heifers that received a single PGF2α injection.

Pregnancy maintenance following sequential induced prostaglandin pulses in beef cows.

The relationship between the maternal endocrine environment and late embryonic mortality (> 28 d of gestation) in cattle is poorly defined. A definitive rise and alterations in secretion patterns of prostaglandin F2α (PGF2α) concentration without luteal regression is a trademark of this period. The objective was to evaluate whether consecutively induced PGF2α pulses would alter steroid hormone production and luteal blood perfusion potentially influencing pregnancy success. Pregnant beef cows (n = 12) were selected to receive either an oxytocin injection (OT, n = 8) or saline injection (CON, n = 4) on d 30 and 31 of gestation to stimulate sequential prostaglandin releases 24 h apart. Blood samples were collected every 30 min for 1 h before and continuing for 4 h post oxytocin administration. Luteal blood perfusion was measured via Doppler ultrasound at the beginning and end of the OT challenge. Concentrations of prostaglandin F2α metabolite (PGFM) were quantified to show effectiveness of the treatment while concentrations of progesterone, estradiol and pregnancy-associated glycoproteins (PAG) were measured to examine the effect of PGF2α release. Control animals exhibited no changes in any quantified hormone and an expected numerical increase in circulating PAG concentrations. Peak concentrations of PGFM in OT cows were observed 2 h post OT administration and concentrations returned to basal levels by the end of the sampling period. Peak concentrations of PGFM were decreased on d 31 compared to d 30. Following OT administration, progesterone and estradiol concentrations did not change in response to PGF2α release but were decreased on d 31 compared to d 30. There were no changes in luteal blood perfusion in response to PGF release on d 30 or d 31. Repeated PGF2α release may alter steroid hormone production; however, it does not negatively affect pregnancy status during the transition between early and late embryonic development.

The effect of subclinical endometritis on reproductive performance in postpartum Bos indicus multiparous beef cows.

The objective was to investigate the prevalence of subclinical endometritis (SE) in postpartum Bos indicus multiparous beef cows using different polymorphonuclear cells (PMN) threshold ratios, and to evaluate the impacts of SE on their reproductive performance. A total of 689 postpartum Nellore cows (45.2 ± 7.8 days postpartum) were submitted to an estrus synchronization protocol + timed-artificial insemination (TAI). Endometrial cytology samples were collected by cytobrush before the beginning of the protocol. Cows were considered positive for SE if: (PMN) ≥ 3% (PMN3), PMN ≥ 5% (PMN5) and PMN ≥ 7% (PMN7). Pregnancy diagnosis was performed at 30 and 100 d after TAI. The prevalence of cows categorized as positive for SE increased (P < 0.05) as the threshold was lowered (PMN7 = 3.9%; PMN5 = 5.5%; PMN3 = 9.1%). Positive SE cows had similar (P > 0.41) BCS, days postpartum, and expression of estrus at TAI compared with negative SE cows. Positive SE cows had decreased (P = 0.04) pregnancy rates compared to negative SE cows in the PMN5 threshold (26.3 ± 8.7% vs 44.5 ± 4.1%); however, no difference (P > 0.45) was observed between positive and negative SE cows in the PMN3 and PMN7 thresholds. Embryonic mortality between days 30 and 100 was not affected by SE (P > 0.16). In conclusion, the prevalence of SE varies based on the PMN threshold used, whereas SE at the beginning of the TAI protocol decreased the pregnancy rates in postpartum Bos indicus beef cows when the PMN5 was used.

Decisive points for pregnancy losses in beef cattle.

Beef cattle producers rely on each of their cows to produce a marketable calf each year to maintain a sustainable operation. Within the first month of gestation, pregnancy failures have been recorded to be upwards of 40-50%. From fertilisation to birth, there are numerous factors contributing to pregnancy failure. From the beginning of gestation oocyte competence is often a large factor impacting fertility as the dam contributes all mRNA for initial embryo development. Other factors contributing to early embryonic infertility include hormonal concentration and heat stress. After the embryo enters the uterus, it becomes critical for the uterus to be receptive to the developing conceptus. The embryo then begins to elongate and secrete interferon-tau to initiate maternal recognition of pregnancy; a requirement to establish and maintain bovine pregnancies. After a pregnancy completes these steps, placentation actively begins around day 22 of pregnancy and lasts until organogenesis. The fetal phase follows the embryonic phase where disease and/or toxins are often the cause of pregnancy failure at this period. However, fetal mortality has been reported to occur in less than 10% of pregnancies. Understanding of the many factors influencing infertility needs to be further investigated to increase pregnancy success in beef cattle.

Effects of body condition score at initiation of the breeding season on reproductive performance and overall productivity of Bos taurus and B. indicus beef cows.

This experiment was conducted to evaluate reproductive and productive responses of Bos indicus and B. taurus beef cows according to body condition score (BCS) at initiation of the annual breeding season. Non-pregnant, suckling multiparous cows were assigned to a fixed-time artificial insemination treatment regimen followed by natural service. Cows were classified as having a BCS < 5.0 (B. taurus, n = 158; B. indicus, n = 248) or BCS ≥ 5.0 (B. taurus, n = 173; B. indicus, n = 122). Calving rate was greater (P < 0.03) in cows with a BCS ≥ 5.0 (93.7 % and 85.1 % in B. taurus, 83.6 % and 73.3 % in B. indicus), which also calved earlier (P < 0.01) compared with cows with a BCS < 5.0. Cows with a BCS ≥ 5.0 weaned more (P ≤ 0.05) calves compared with those with a BCS < 5.0, which were older (P ≤ 0.04) and weighed more (P ≤ 0.09) at weaning (258 and 252 kg in B. taurus, 213 and 203 kg in B. indicus). Kilograms of calf weaned/cow in the breeding herd were greater (P ≤ 0.03) in cows with a BCS ≥ 5.0 compared with those with a BCS < 5.0 (221 and 200 kg in B. taurus, 159 and 129 d in B. indicus). Collectively, cows with a BCS ≥ 5.0 at initiation of the breeding season had greater reproductive and overall productivity during a cow-calf cycle, and these outcomes were observed in B. taurus and B. indicus cowherds.

Characterization of pregnancy-associated glycoproteins and progesterone as a predictor of twins and conceptus loss in high-risk-pregnancy Holstein cows.

The objective of this study was to characterize plasma concentrations of pregnancy-associated glycoprotein (PAG) and progesterone (P4) as predictors of twins and pregnancy loss in Holstein cows with high-risk pregnancies. High-risk pregnancy was characterized using transrectal ultrasonography 37 d after artificial insemination (AI) based on the following criteria: small embryo size <15 mm, n = 10), slow heartbeat (<60 beats per minute, n = 11), and extra-amniotic membrane (additional amniotic membrane, n = 3). A cohort of twins (n = 41) diagnosed at d 37 post-AI was also enrolled. Each high-risk and twin pregnancy cow was paired with a cow of the same parity carrying a normal singleton at d 37 post-AI (control, n = 65). Blood samples were collected to measure PAG and P4 at d 37, 44, and 51 post-AI. Statistical analysis was performed using ANOVA, logistic regression, and receiver operator characteristic (ROC) curve with JMP software (SAS Institute Inc., Cary, NC). Pregnancy loss at d 51 post-AI was greater in high-risk pregnancies than in controls and twins (control = 1.5%; high-risk = 87.5%; twins = 12.2%). Concentration of PAG at d 37 post-AI did not differ among groups (control = 5.3 ± 0.7; high-risk = 4.8 ± 1.2; twins = 4.0 ± 0.9 ng/mL). Concentration of P4 at d 37 post-AI was greater in twins than in high-risk pregnancies and control, and lesser in high-risk pregnancies than in controls (control = 7.0 ± 0.3; high-risk = 5.9 ± 0.4; twins = 8.4 ± 0.3 ng/mL). Regression and ROC analysis for PAG at d 37 post-AI did not find a threshold to predict pregnancy loss or twins. Regression and ROC analysis for P4 at d 37 post-AI found that a threshold of 6.5 ng/mL predicted pregnancy loss with an area under the curve (AUC) of 0.64, and a threshold of 7.2 ng/mL predicted twins with AUC of 0.71. In summary, pregnancy loss and twins were predicted with only moderate accuracy by P4 concentration at d 37 post-AI, and the variability in PAG concentrations at d 37 post-AI was not sufficient to generate a threshold to predict pregnancy loss and twins in Holstein lactating cows.

Pre-synchronization of ovulation timing and delayed fixed-time artificial insemination increases pregnancy rates when sex-sorted semen is used for insemination of heifers.

This study was conducted to determine effects of pre-synchronization of ovulation timing among heifers and delayed fixed-time artificial insemination (TAI) with sex-sorted semen on proportion of heifers pregnant after TAI (PR/AI). Heifers were assigned to one of eight treatments: 1 and 2), 7-d CO-Synch + CIDR treatment regimen with administration of gonadotropin-releasing hormone and a CIDR insert on Day 0, prostaglandin F2α (PGF) at CIDR removal on Day 7, and TAI occurring 54 h later with conventionally processed (CTRL54-CNV) or sex-sorted semen (CTRL54-SEX); 3 and 4), same as CTRL54 but TAI delayed to 72 h with conventionally processed (CTRL72-CNV) or sex-sorted semen (CTRL72-SEX); 5 and 6), same as CTRL54 but additional administration of PGF on Day -7 and TAI with conventionally processed (PRE54-CNV) or sex-sorted semen (PRE54-SEX); 7 and 8), same as PRE54 treatments but TAI delayed to 72 h with conventionally processed (PRE72-CNV) or sex-sorted semen (PRE72-SEX). Proportion of heifers pregnant after TAI was greater (P ≤  0.02) with conventionally processed semen compared with sex-sorted semen, yet PR/AI did not differ (P =  0.14) between heifers in PRE72-CNV and PRE72-SEX groups. There were greater PR/AI in the PRE72-SEX (P =  0.03) than CTRL54-SEX group (46.1 % and 36.9 %) and there was no difference (P =  0.31) in PR/AI between CTRL54-CNV and PRE72-SEX groups (50.4 % and 46.1 %). In conclusion, pre-synchronization of ovulation timing among heifers combined with delayed TAI resulted in increased PR/AI with sex-sorted semen compared with the 7-d CO-Synch+CIDR treatment regimen.

Effects of nutrient restriction on the metabolic profile of Bos indicus-influenced and B. taurus suckled beef cows.

Recent research from our group demonstrated that Bos indicus-influenced suckled beef cows had greater resilience to withstand nutrient restriction and establish pregnancy compared with B. taurus cows exposed to the same conditions. To further understand these findings, differences in metabolic profile between these same B. indicus-influenced and B. taurus females were explored. Suckled beef cows (n = 134) were enrolled in a completely randomized design with a 2 × 2 factorial arrangement of treatments. On day -21, Angus (AN; Bos taurus) and Brangus (BN; B. indicus-influenced) cows were randomly assigned to 1) a diet that met daily energy maintenance requirements (MAINT), or 2) a diet that restricted intake to 70% of the daily energy maintenance requirements (RESTR). Cows were exposed to an estrus synchronization protocol and received an embryo 7 d after ovulation was pharmacologically induced on day 0. Blood samples were collected on days -21 and 19 to determine circulating concentrations of non-esterified fatty acids (NEFA), ß-hydroxybutyrate (BHB), insulin, glucose, and IGF-1. Pregnancy status after embryo transfer was determined on day 28. As a consequence of the proposed diets, cows in the RESTR diet had less body condition score (BCS) on day 19 (P = 0.008) across breed types. Moreover, BCS change from day -21 to 19 was included as independent covariate into subsequent analyses, allowing for the comparison of breed types under an equivalent level of body reserve mobilization. A breed × diet interaction was observed for plasma insulin (P = 0.03) and IGF-1 (P = 0.04) on day 19, where AN-RESTR cows had less plasma concentrations on day 19 compared with AN-MAINT cows. Diets did not impact (P > 0.10) plasma insulin and IGF-1 concentrations in BN cows. No diet or breed effects were observed in circulating concentrations of NEFA, BHB, and glucose (P > 0.10). Across breed types and nutritional treatment, there was positive linear effect (P ≤ 0.04) of plasma concentrations of insulin and IGF-1 on the probability of pregnancy to fixed-time embryo transfer. In summary, the negative impacts of nutrient restriction on the somatotropic axis, independently of body tissue mobilization, were heightened in Bos taurus females compared with B. indicus-influenced cohorts, which corroborate with the differences observed in fertility between these subspecies.

Progesterone dose during synchronization treatment alters luteinizing hormone receptor and steroidogenic enzyme mRNA abundances in granulosa cells of Nellore heifers.

The objective was to investigate effects of progesterone (P4) dose on abundance of luteinizing hormone receptor (LHCGR), aromatase (CYP19A1), 3ß-hydroxysteroid dehydrogenase (HSD3B1), and other steroidogenic mRNA transcripts in granulosa cells from dominant follicles. Nellore heifers were assigned to one of six groups: new, first-use controlled internal drug release device (CIDR1) inserted for 5 days (Large-P4-dose-D5; n = 7) or 6 days (Large-P4-dose-D6; n = 8), prostaglandin (PG)F2α administered on D0 and 1 previously-used CIDR (CIDR3) inserted for 5 days (Small- P4-dose-D5; n = 8) or 6 days (Small-P4-dose-D6; n = 8), CIDR1 inserted on D0 and removed plus PGF2α on D5 (Large-P4-dose-proestrus (PE); n = 7), and CIDR3 and PGF2α on D0 and 1, CIDR3 removed plus PGF2α on D5 (Small-P4-dose-PE; n = 7). Duration of P4 treatment (D5 compared to D6) affected abundances of CYP19A1 mRNA transcripts, with there being greater abundances on D6 than D5 (P ≤ 0.05). Heifers treated with the large dose of P4 had a smaller dominant follicle, less serum and intra-follicular estradiol (E2) concentrations (P ≤ 0.05) and lesser LHCGR, CYP19A1, and HSD3B1 transcript abundances (P ≤ 0.05). Heifers treated to induce PE had a larger follicle diameter (P = 0.09), greater intra-follicular E2 concentrations and larger abundances of CYP19A1 mRNA transcript (P ≤ 0.05) than heifers of the D6 group. Overall, treatment with larger doses of P4 resulted in lesser abundances of LHCGR, HSD3B1, and CYP19A1 mRNA transcripts; thus, potentially leading to development of smaller dominant follicles and lesser E2 concentrations.

Induced prostaglandin release alters steroid concentrations but not pregnancy survival in cows.

Embryonic mortality (EM) is a major factor limiting reproductive efficiency in cattle, and despite negative connotations related to reproductive performance, prostaglandin F2α (PGF2α) is capable of being released by the uterus by Day 30 of gestation. Therefore, the objective was to evaluate differences in PGF2α release after an oxytocin challenge between cows with high circulating concentrations of pregnancy-associated glycoproteins (PAGs) vs low PAG because of the association of increased PAG concentrations with pregnancy success. At Day 30 of gestation, pregnant cows were divided into oxytocin treatment (OT; n = 13) and control (CON; n = 12) groups. Treatment cows were further subdivided by circulating PAG concentration (high PAG, n = 7; and low PAG, n = 6). Blood samples were collected every 30 min beginning 1 h before oxytocin administration and continuing for 4 h. Prostaglandin F2α metabolite (PGFM), progesterone, estradiol-17ß (E2), and PAG concentrations were quantified. The peak concentration of PGFM occurred 2 h after oxytocin injection in treatment animals and returned to baseline levels by 4 h. No correlations were observed between PAG and PGFM, progesterone, or E2 concentrations (P > 0.05). There was no difference in initial or final PGFM concentrations between groups (P > 0.05). Progesterone and E2 concentrations decreased in cows after treatment of oxytocin (P < 0.05); however, only progesterone returned to basal concentrations by the end of the sampling period. In summary, cows with high vs low PAG concentrations at Day 30 of gestation have a similar PGFM response to oxytocin challenge.

Increasing the length of an estradiol with progesterone timed artificial insemination protocol with 2 controlled internal drug release devices improves pregnancy per artificial insemination in lactating dairy cows.

The objective of this study was to compare the effects of different lengths of ovulation synchronization protocols using 2 controlled internal drug release (CIDR) devices on ovarian dynamics and pregnancy outcomes in lactating dairy cows. Lactating Holstein cows (n = 1,979) were randomly assigned to receive timed artificial insemination (TAI; d 0) following 1 of 2 treatments: (1) 9-d protocol (n = 988; 9D) with 2 intravaginal devices containing 1.9 g of progesterone (CIDR) and 2.0 mg of estradiol benzoate on day -11; 25 mg (i.m.) of dinoprost tromethamine (PG) and withdrawal of 1 CIDR on d -4; 1.0 mg (i.m.) of estradiol cypionate, second CIDR withdrawal, and PG on d -2; and TAI on d 0 and (2) 10-d protocol (n = 991; 10D) with 2 CIDR and 2.0 mg of estradiol benzoate on d -12; 25 mg of PG and withdrawal of 1 CIDR on d -4; 1.0 mg of estradiol, second CIDR withdrawal, and PG on d -2; and TAI on d 0. There was no effect of protocol on estrus detection, whereas a greater percentage of cows from 10D had ovulated close to TAI [no corpus luteum (CL) at AI and a CL at d 7] versus cows assigned to 9D protocol. A protocol × heat stress (average cow temperature ≥39.1°C on day of AI and d 7) interaction was observed in a manner that pregnancy per AI (P/AI) was greater in non-heat-stressed 10D versus 9D cows, whereas P/AI did not differ when cows were under heat stress. Furthermore, 10D protocol did not increase P/AI when all cows that received AI were included in the analysis or in cows that ovulated near TAI. However, animals assigned to 9D without any event of heat stress had a reduced P/AI when compared with cows assigned to 10D without heat stress. A protocol × CL presence at the beginning of the protocol interaction was observed and cows with a CL at the beginning of the protocol had a greater P/AI in 10D versus 9D; meanwhile, in cows without a CL, no differences on P/AI were observed. The protocol × CL presence at the beginning of the protocol interaction on P/AI was also observed for cows that ovulated near TAI. A greater percentage of cows assigned to 9D had follicles of medium size (13-15.9 mm), and greater percentage of cows assigned to 10D had larger follicles (>16 mm). Increasing the length of an estradiol with progesterone-based ovulation synchronization protocol (10D vs. 9D) increased the proportion of cows with larger follicles (>16 mm) and increased P/AI in cows without heat stress and in cows with a CL at beginning of the protocol. Moreover, the 10D protocol increased the proportion of cows with ovulation near TAI, demonstrating the effectiveness of this protocol in improving the reproductive performance of lactating Holstein cows.