Search

Melatonin has been documented to alleviate compromised pregnancies and enhance livestock performance traits. The objective of this study was to determine the effect of prenatal and postnatal melatonin supplementation on overall calf performance and dam milking traits in relation to calves, molecular factors involved in growth and metabolism of calves, along with testicular physiology and fertility traits in subsequent bulls. On days 190, 220 and 250 of gestation, dams (N = 60) were administered either two subdermal ear melatonin implants (preMEL) or no implants (preCON). After parturition, birth weights were recorded and calves were blocked based on prenatal treatment and sex. Calves received either melatonin implants (posMEL) or none (posCON) on days 0, 30, and 60 of age. On day 60 of lactation, a subset of dams (N = 32) were selected based on age, weight, and calf sex for milk collection and analysis. At weaning, (day 210 postnatally) calf weight, morphometric data, liver samples, and loin samples were collected. At 12 mo of age, bull (N = 30) scrotal circumference, scrotal temperature, and testicular artery measurements were recorded. Milk yield and fat percent from dams tended to decrease in the preMEL group (P < 0.07) compared with preCON group. Prenatal melatonin administration did not affect (P = 0.95) calf birth weight and similarly calf weaning weight was unaffected (P < 0.10) by prenatal or postnatal melatonin supplementation. Blood analysis demonstrated that plasma concentrations of melatonin were not different (P = 0.12) in dams; however, an increase (P < 0.001) in plasma concentrations of melatonin was observed in posMEL vs. posCON calves. A tendency (P < 0.10) for decreased MYF5 and MYOD1 expression in loin muscle was observed in the posMEL calves. Prenatal and postnatal melatonin administration did not affect subsequent bull scrotal measurements or testicular hemodynamics (P ≥ 0.14). Administering supplemental melatonin via implants during the prenatal and postnatal phase did not alter performance characteristics in offspring. In this study, dams were implanted in winter months, whereas calves were implanted in the spring months. Seasonal differences involving photoperiod and ambient temperature might have attributed to a lack of differences in melatonin levels during the prenatal phase. In the postnatal period, the level of developmental plasticity appears to be too low for melatonin properties to be effective.

A previous study reported that a 400-mg dose of medroxyprogesterone acetate (MPA) reduced male reindeer aggression and blocked development of secondary sexual characteristics but did not completely impair fertility. Here we have repeated that protocol in two separate trials. In 2017, tissues and blood samples, collected from MPA and control (CTL) reindeer bulls, euthanized at 30 and 60 d post-treatment were used to evaluate testes histology and morphometrics, cfos activity in the brain and androgen levels. While testes weight tended to decline from August to September in both groups, indices of spermatogenesis remained high. By September, indices of spermatogenesis were declining in both groups with sperm density lower (P = 0.05) in MPA compared to CTL bulls. Aug CTL bulls had the highest concentrations of androstenedione (A4) (P = 0.009) and testosterone (T) (P = 0.08), whereas these androgens were baseline in Aug MPA bulls. By September, A4 and T levels in CTL bulls declined to levels measured in MPA bulls. Cfos activity had a greater number (P = 0.02) of cfos positive neurons in the central amygdala in MPA compared to CTL bulls, suggesting a heightened fear response among the MPA bulls. In the second trial (2019), MPA-treated bulls, with (E, n = 4) and without (IE, n = 4) breeding experience, were blood sampled at key points from July through September when they were put in individual harems with estrous-synchronized cows. Concentrations of T were greatest (P 0.001) among E bulls prior to MPA treatment but 1 mo after treatment, both T and A4 were baseline in all eight reindeer. Semen collected by electroejaculation at 60 d post-MPA treatment revealed only minor differences in sperm abnormalities between E and IE bulls using both fresh and frozen/thawed semen. Only three bulls (2 E and 1 IE) sired offspring. Breeding success was not related to previous breeding experience, body weight, or bull age. The failure of some MPA bulls to breed appears to be a behavioral, not a physiological, limitation. Limited application of MPA is clearly a useful tool for managing rut-aggression in non-breeding reindeer. However, the possibility that semen could be collected from MPA-treated bulls using restraint and mild sedation rather than general anesthesia should be investigated. This could improve the quality of semen collection while enhancing the safety of both handlers and animals.A single 400 mg dose of MPA given to reindeer bulls just before the onset of rut eliminates aggressive behavior and suppresses androgen concentrations without dramatic differences in the gross or histological structure of the testes within the first 30 d of treatment. By 60 d post-treatment, there is evidence of smaller testes size and decreased sperm density in treated bulls. However, if given the opportunity, some treated bulls can still successfully breed. Breeding success in MPA bulls was not solely related to previous breeding experience, body weight, or bull age. Androgen concentrations and semen characteristics did not vary with previous breeding experience. Failure of some treated bulls to breed appears to be a behavioral limitation. Differences in brain activity between control and treated bulls were few except for increased cfos activity in the central amygdala of MPA bulls, potentially increasing the fear response in these reindeer.

Nutritional changes immediately after insemination cause increased embryonic mortality, but the mechanisms controlling this are not well known. Our objective was to evaluate the impact of nutritional change on estrus expression, steroid concentrations, peripheral and uterine luminal fluid metabolites, and embryo quality in beef heifers. Heifers (n = 139) were assigned to one of two pre-artificial insemination (AI) dietary treatments: LOW (≤ 90% NEm) or HIGH (≥ 139% NEm). Heifers were on treatment for 33-36 days before AI (d0) when half of the heifers in each treatment were randomly reassigned to generate four treatments; HIGH-HIGH, HIGH-LOW, LOW-HIGH, and LOW-LOW. Heifers remained on treatments until embryo collection (d 6-8). Negative energy balance was achieved among LOW heifers as demonstrated by body weight loss and increased NEFA concentrations (P 0.05). Pre-AI treatment influenced expression of estrus (P = 0.05; HIGH 80.4 ± 4.0% vs. LOW 69.4 ± 4.2%). Estradiol concentrations and interval to estrus were not affected by treatment (P 0.55); however, progesterone concentrations were reduced among LOW compared to HIGH (3.57 ± 0.27, 4.64 ± 0.26 ng/mL, respectively; P = 0.004), and heifers maintained on the HIGH pre-AI diet had consistently greater concentrations of progesterone from d 0 to d 8 (P = 0.014). Pre-AI treatment influenced embryo stage (P = 0.05; HIGH 3.61 ± 0.32 vs. LOW 2.72 ± 0.30). Post-AI treatment affected embryo grade (P = 0.02; HIGH 1.78 ± 0.23 vs. LOW 2.64 ± 0.27). In summary, pre-AI nutrient restriction caused decreased expression of estrus, reduced progesterone concentrations after AI, and negatively impacted embryo development, while post-AI restriction hindered embryo quality.

The objective was to evaluate the impact of nutritional changes after artificial insemination (AI) on plasma metabolites, steroid hormones, and uterine histotroph. Beef heifers (n = 50) were randomly assigned to a post-AI dietary treatment (High=161.5% or Low=77.45% of maintenance energy) until uteri were flushed for embryo recovery (d14). Blood samples were collected on d -3, 0 (AI), 3, 6, 9, 12, and 14 for analysis of plasma non-esterified fatty acid (NEFA), total protein (protein), glucose, cholesterol, and progesterone concentrations. Uterine flushes (UF) were analyzed for concentrations of Mg, P, S, K, Ca, Cu, Zn, Se, Mn, Co, B, Cr, and Fe. Plasma NEFA, protein, glucose, cholesterol, and progesterone concentrations were analyzed as repeated measures in SAS (PROC MIXED). Mineral concentrations in UF were analyzed using the MIXED procedures in SAS. Diet influenced plasma NEFA concentrations, with Low heifers having elevated concentrations (P < 0.01); however, diet did not influence plasma protein, glucose, cholesterol, or progesterone concentrations (P > 0.10). Plasma NEFA, glucose, and progesterone concentrations changed over time (P < 0.05), but protein and cholesterol did not differ over time (P > 0.10). Diet by time interactions influenced plasma NEFA, protein, and cholesterol concentrations (P < 0.05), but glucose and progesterone concentrations were not different (P > 0.10). Presence of a recovered embryo by time interaction influenced plasma protein concentrations (P < 0.04), but NEFA, glucose, cholesterol, and progesterone concentrations were not affected by the interaction (P > 0.10). Embryo recovery and diet by embryo recovery by time did not impact plasma NEFA, protein, glucose, cholesterol and progesterone concentrations (P > 0.10). When an embryo was recovered, Mg (P = 0.02) and S (P = 0.02) were decreased in UF. Diet and diet by embryo recovery did not affect UF mineral concentrations (P>0.10). In conclusion, post-AI nutrition influenced plasma NEFA, protein, glucose, cholesterol, and progesterone concentrations. Additionally, uterine histotroph mineral concentrations were affected by presence of an embryo.

Preovulatory estradiol concentrations and expression of estrus have been associated with greater pregnancy rates in beef cattle following AI, thus an experiment was designed to determine if supplemental estradiol (E2) at GnRH-induced ovulation would improve pregnancy retention in postpartum beef cows after embryo transfer. Cows were synchronized with the 7-d CO-Synch + CIDR® protocol. On d0 (48h post-prostaglandin) cows were grouped by estrual status (Estrual; n=198, nonestrual; n=406). Nonestrual cows were administered GnRH and randomly assigned to either no treatment (Control; n=204) or administration of 0.1 mg (IM) estradiol 17-β (Estradiol; n=202). In a preliminary study, 0.1 mg (IM) estradiol 17-β increased plasma estradiol (17.11±3.4 pg/mL; P < 0.01) and remained elevated above baseline for approximately 8h compared to control (1.70±0.58 pg/mL). All cows received an in vivo produced embryo on d7. Embryos were matched by grade, stage, and flush across treatments. Pregnancy was classified on d30 by either plasma pregnancy-associated glycoproteins analysis (Year 1) or ultrasonography (Year 2). Plasma estradiol concentrations (d-2, d0h0, d0h2) were analyzed by PROC MIXED as repeated measures in SAS(9.4), while GLIMMIX procedures were used to analyze differences in pregnancy rates with treatment, group, year, and their interactions as fixed effects. There was a treatment by time interaction (P < 0.001) in E2 concentration. There was no difference in plasma E2 concentrations on d0h0 (P >0.30) between treatments. At d0h2, Estradiol cows (15.7±0.25 pg/mL) had greater plasma E2 compared to Estrual (4.0±0.13 pg/mL) or Control (3.4±0.25 pg/mL) cows (P < 0.001), and Estrual cows had greater plasma E2 than Control cows (P = 0.02). Control cows had decreased (26%) pregnancy rates compared to both Estradiol (37%; P = 0.03) and Estrual (40%; P = 0.01) cows. Pregnancy rates did not differ (P = 0.51) between the Estrual and Estradiol cows. In conclusion, elevated preovulatory concentrations of estradiol are critical for improved pregnancy retention following embryo transfer.

Two studies were conducted to evaluate the effects of trace mineral supplementation on traditional and novel measures of bull fertility. In Experiment 1, 37 mature bulls received one of three dietary supplements daily for 71 d: 1) Supplement without Cu, Zn, and Mn (CON); 2) Supplement with Cu, Zn, and Mn sulfate (SULF); and 3) Supplement with basic Cu chloride, and Zn and Mn hydroxychloride (CHLR). In Experiment 2, 128 Angus or Angus-Hereford bull calves were maintained on a growing diet for 75 d (year 1) or 119 d (year 2) in Calan gate equipped pens without mineral supplementation. Bulls (n = 32 head/treatment) received one of four trace mineral supplements daily for 84 d: 1) Zn with no Cu (ZN), 2) Cu with no Zn (CU), 3) Cu and Zn (ZNCU), or 4) no Cu or Zn (CON). Bull fertility measures included a breeding soundness evaluation (BSE) and novel fertility measures conducted using flow cytometry. In mature bulls, final liver Zn concentration was positively correlated (P = 0.02) with sperm concentration (r = 0.31) and tended (P = 0.06) to be negatively correlated with acrosome damage (r = -0.39). Peripubertal bulls receiving ZNCU had greater ADG than bulls in the CU group (P = 0.05). Each BSE and novel fertility component improved from Day 0-84 in peripubertal bulls and were not affected (P 0.10) by mineral supplementation. Bulls that received no supplement (CON) had greater (P 0.01) percentage of sperm with distal midpiece reflex (6.9 vs 4.0% for CON and TM supplement, respectively) and Dag or Dag-like defect (2.6 vs 1.4% for CON and TM supplement, respectively) in their ejaculates. Sperm viability after 30 min of incubation were not affected by trace mineral supplementation, but after 3 h incubation, sperm viability tended to differ (P = 0.06) between treatments and tended to be less for CON bulls (48.5%) compared to ZNCU bulls (55.1%). Among contrast comparisons, trace mineral supplemented bulls had greater (P 0.05) percentage of viable sperm at 3 h post collection and reactive oxygen resistant sperm than CON bulls. Addition of Zn to trace mineral containing Cu (ZNCU) improved (P 0.05) percentage of sperm in the ejaculate with high mitochondrial energy potential and viable sperm with intact acrosome membrane. In summary, it appears the homeostasis mechanisms for bull trace mineral maintenance are extremely efficient and mineral supplementation of mature and peripubertal bulls did not have major improvements in any laboratory or chute-side measures of bull fertility, however bulls exposed to breeding or in environments with diet antagonists might respond differently.

The objective of this study was to determine factors impacting abundance of pregnancy-associated glycoproteins (PAGs) after embryo transfer. Cows were synchronized using the 7-d CO-Synch+CIDR® protocol and grouped by estrus expression 48h after prostaglandin (d0) [Estrual (PC): n = 198; Non-estrual: n = 406]. Non-estrual cows were administered GnRH and randomly assigned to Estradiol treatment (E2: n=202; 0.1mg estradiol 17-β) or no treatment (NC: n = 204). In vivo produced embryos were transferred on d7, with grade, stage, and flush balanced across treatments. Circulating concentrations of estradiol and progesterone were determined on d0 and d7, respectively. Abundance of PAGs was determined on d24 and d26. Cows that were pregnant on d30 were grouped by age (H: 2, C: >2 years) and subjected to analysis. Correlations were analyzed using PROC CORR in SAS, while PAGs were analyzed using PROC GLIMMIX with treatment, age, year, sire, and embryo grade and stage as fixed effects. Abundance of PAGs on d24 was influenced by treatment (P = 0.01; PC=0.75±0.09, E2=0.59±0.09, NC=0.56±0.08), age (P < 0.01; H=0.75±0.09, C=0.52±0.08), year (P < 0.0001; 2019=0.42±0.08, 2020=0.84±0.09), and sire (P = 0.02; A=0.49±0.12, B=0.62±0.09, C=0.47±0.11, D=0.77±0.08, E=0.83±0.21), but not embryo grade (P = 0.89) or stage (P = 0.40). There was a negative correlation between d0 estradiol and d24 PAGs (P < 0.0001, r=-0.34), and a positive correlation between d7 progesterone and d24 PAGs (P < 0.0001, r=0.36). On d26, PAGs tended to differ by treatment (P = 0.09; PC=2.43±0.20, E2=2.33±0.21, NC=2.03±0.20). Age (P = 0.02; H=2.48±0.22, C=2.05±0.16), and sire (P = 0.0007; B=2.01±0.20, D=2.52±0.17) influenced PAGs, but embryo grade (P = 0.33) and stage (P = 0.32) did not on d26. Sire was associated with PAGs, and presumably embryo attachment, but not pregnancy rate. Increased progesterone concentrations on d7 were correlated with earlier attachment as measured by PAGs. Estrus expression prior to d0 may enhance earlier attachment of the fetal/maternal interface, and supplemental estradiol on d0 may improve attachment by d26 when ovulation is induced. Funded by NIFA 2019-67015-29411.

Melatonin has been documented to alleviate compromised pregnancies and enhance livestock performance traits. The objective of this study was to determine the effect of melatonin supplementation on milking traits in beef cattle dams and subsequent influence on calf performance. Cows (n = 60) were blocked based on embryo transfer donor and sire, potential calf breed and embryo grade. At d190, 220 and 250 of gestation, dams were administered either 2 subdermal ear melatonin implants (preMEL) or no implants (preCON). After parturition, birth weights were recorded and calves randomly received either melatonin implants (posMEL) or none (posCON) on approximately d 0, 30, and 60. At approximately d 60 of lactation, a subset of dams (n = 32) were selected based on age, weight and calf sex for milk collection and analysis. At weaning, calf weight and morphometric data were collected and adjusted according to weaning age. Prenatal melatonin administration did not change calf birth weight (P = 0.956). Milk yield tended to decrease in the preMEL group (P = 0.054) at 2.368 kg ± 0.11 compared to preCON at 2.054 kg ± 0.11. Milk fat percent tended to decrease (P = 0.07) in preMEL at 3.25 ± 0.19 versus preCON at 3.92 ± 0.19. There were no differences in prenatal treatment in respect to milk protein, lactose, solid non-fats, somatic cell count, and urea nitrogen (P > 0.16). At weaning, calf head circumference decreased (P < 0.031) in the preMEL group at 77.92cm ± 0.42 versus preCON at 79.31cm ± 0.45. Otherwise, there were no prenatal or postnatal treatment differences in respect to weaning weight, crown-rump length, hip height and head length (P > 0.12). Previous studies show crown-to-rump length and ponderal index differences. Our lack of differences might be attributed to geographical locations that impact day length or endogenous melatonin status.

The objective of this study was to evaluate nutrition before and after artificial insemination (AI) on follicular dynamics, expression of estrus, and steroidogenesis. Seventy-nine beef heifers were randomly assigned to one of two dietary treatments (High;155% and Low;86% of maintenance energy) 30d prior to AI. Estrus was synchronized (PG 6-d CIDR protocol) and heifers received AI (d0) 8 to 12h following onset of estrus. On d0, heifers were randomly reassigned diets generating four Pre-x-Post-AI nutritional treatments; High-High (HH, n = 20), High-Low (HL, n = 20), Low-High (LH, n = 19), and Low-Low (LL, n = 20). Heifers remained on new diet treatments until embryo collection (flush; d7-8). Blood samples were collected daily from d-3 to d0, and on d1, 3, 5, 7 and 8 for plasma concentrations of estradiol (E2) and progesterone (P4). Dominant follicle diameter was evaluated on d-3 and d0, and CL diameter was recorded at flush. Statistical analyses were completed in SAS using the MIXED (body weight, E2, P4), GLIMMIX (expression of estrus), and GLM (ovarian parameters, interval to estrus) procedures. There were Pre-AI (P < 0.0001) and Post-AI by time (P < 0.0001) interactions on body weight; heifers in high and low treatments gained and lost weight, respectively, during both periods. Estradiol concentrations increased (P < 0.0001) from d-3 (2.18±0.15pg/mL) to d0 (6.05±0.04pg/mL). Pre-AI diet increased the proportion of heifers in estrus (80±6.3% vs. 59±7.9%; P = 0.05), and dominant follicle size (11.7±1.42mm vs. 10.68±1.33mm; P = 0.0016) in High vs. Low, respectively. Additionally, High Pre-AI heifers had greater P4 after AI compared to Low Pre-AI heifers (4.85±0.37ng/mL vs. 3.53±0.38ng/mL; P = 0.015). Post-AI treatment did not influence concentrations of P4 (P = 0.88). There was no effect of Pre, Post or Pre-x-Post-AI treatment on initial follicle size, follicle growth rate, E2 concentrations, interval to estrus, or CL size at flush (P > 0.10). In conclusion, nutrient restriction before AI negatively impacted ovarian function, steroidogenesis, and expression of estru.

The greatest effects of nutrition on bull fertility occur by providing a relatively high plane of nutrition during calfhood when the seminiferous epithelium of the testes is developing. A high plane of nutrition from 5 to 25 weeks of age results in greater circulating gonadotropin concentrations, greater testicular volume, and greater sperm production at maturity. At this age, diet can be manipulated by creep feeding bull calves with both protein and energy supplements which could accelerate puberty and increase sperm production. Increased rate of gain in bull calves post-weaning can accelerate puberty a few weeks, but excess post-weaning gain and fat buildup in the neck of the scrotum can have detrimental effects on fertility. Considerable emphasis has been placed on specific micronutrient (especially minerals) effects on peripubertal bull fertility. Trace mineral supplementation is believed to be critical for optimal fertility and both copper (Cu) and zinc (Zn) supplementation have influenced male fertility in other species. However, there are no guidelines for recommended levels of these minerals to ensure fertility. Providing organic or complexed compared to inorganic mineral to peripubertal bulls have increased liver concentrations of mineral and in some cases, have accelerated puberty, but enhanced fertility-associated measures have not been realized. Because both Cu and Zn are present in the ejaculate, mineral needs during the breeding season may differ from the off-season. During the breeding season, bulls can lose 10 to 20% of their weight and need to re-gain this weight before the next breeding season. Divergent planes of nutrition provided to mature bulls during the off-season revealed enhanced sperm energy and stress-fighting potential with decreasing plane of nutrition. Specific mineral supplementation during the off-season in mature bulls provides no beneficial effect on fertility-associated measures. In summary, significant effects of nutrition post-weaning on bull fertility-associated measures have not been realized.

The effects of medroxyprogesterone acetate (MPA) on velvet antler cleaning, hypophagia, aggressive behavior and fertility were evaluated in farmed reindeer bulls during a 2-year study. Eight reindeer bulls aged 1–4 years were divided into 2 groups balanced for age. During each year, one group (MPA, n = 4) was treated with MPA 2 wk prior to the expected onset of rut while the other group (CTL, n = 4) served as untreated controls. Feed consumption, behavior and antler cleaning were recorded daily or 3 x weekly for 3 mo. Each year a dominant CTL and MPA bull were put into separate harems of estrous synchronized females for 1 wk in mid-September. Following harem breakup, semen was collected from all bulls via electroejaculation and evaluated. In Year 2 the bulls were switched such that year 1 MPA bulls received the CTL treatment and year 1 CTL bulls received MPA treatment. In Year 2 all eight bulls received MPA treatment/booster following semen collection. In both years, MPA treatment reduced rut associated body weight loss (p ≤ 0.05), rut associated hypophagia (p ≤ 0.001), interfered with velvet antler cleaning, and abolished aggressive rut related behavior. All of these changes suggest suppression of testosterone mediated effects. Alternatively, semen parameters differed little between treatment groups with the exception of reduced sperm concentration and total sperm production in MPA bulls (p ≤ 0.05). All CTL bulls in Year 2 exhibited full rut behavior with the dominant bull successfully breeding 100% of females available for breeding, suggesting no carryover effect of MPA treatment from the previous year. The MPA bull successfully bred 4 of 6 females (Year 1) but the MPA bull in Year 2 failed to sire any offspring. A single 400 mg treatment of MPA just prior to rut was sufficient to suppress rut associated aggression and hypophagia on a short-term (3 mo) basis. It did not however, completely suppress fertility.

The objective was to evaluate the impact of nutritional changes prior to and after artificial insemination (AI) on uterine environment and plasma cholesterol concentrations. Beef heifers (n = 79) were randomly assigned to two dietary treatment groups (High=155% or Low=86% of maintenance energy) for 30 d prior to AI (pre-AI). At AI, heifers were randomly assigned new treatment groups (post-AI) which created four pre- x post-AI diet treatments (High-High, High-Low, Low-High, and Low-Low). Post-AI dietary treatments continued until uteri were flushed for embryo recovery (d 7 or 8 post-AI). Blood samples were collected on d -3,-2,-1, 0 (AI day), 1,3,5,7, and 8 for analysis of plasma cholesterol concentrations using a colorimetric assay. Uterine flushes were analyzed for concentrations of Mg, Al, P, S, K, Ca, Cu, Zn, Se, and Fe by ICPMS. Plasma cholesterol (repeated measures) and uterine mineral concentrations were analyzed using the MIXED procedures in SAS. Plasma cholesterol concentrations changed over time (P < 0.0001); however, there were no differences between treatments (P > 0.10). There was an effect of embryo presence on uterine flush mineral concentrations for Mg (P < 0.04), Al (P < 0.01), S (P < 0.01), K (P < 0.01), and Ca (P < 0.01), with decreased concentrations when uterine flushes contained an embryo. There was no effect of pre-AI diet on mineral concentrations; however, there was an effect of post-AI diet on S (P < 0.02) and Ca (P = 0.03). High diet heifers had increased S and Ca concentrations compared to low diet heifers. Sulfur concentration was affected by a pre-AI diet by embryo interaction (P < 0.03). There was a post-AI by embryo interaction on P (P < 0.03), Zn (P = 0.02), and Se (P = 0.02). Also, there was a pre-AI by post-AI by embryo interaction on Mg (P < 0.05). In conclusion, changing plane of nutrition pre- and post-AI had no effect on plasma cholesterol concentrations; however, presence of an embryo affected uterine mineral concentrations.

Two experiments were conducted to examine the effect of plasma concentrations of 17β-estradiol (E2) preceding and progesterone (P4) subsequent to ovulation on proportions of beef cows pregnant following embryo transfer. Timing of ovulation (d 0) among postpartum cows was synchronized and cows that expressed estrus were removed from each study. In Experiment 1, plasma E2 concentration on d 0 was used to classify cows (n = 353) into Low, Medium, and High E2 groups. Pregnancy rate for cows with Low, Medium, or High E2 concentrations were different (P < 0.05). In Experiment 2, there were multiple administrations of PGF2α to evaluate the independent effects of Low or High E2 before ovulation and Low or Normal (no treatment) P4 after ovulation on proportions of cows pregnant. Treatment groups in Experiment 2, therefore, were: Low E2-Low P4 (LL; n = 71), Low E2-Normal P4 (LN; n = 69), High E2-Low P4 (HL; n = 74), and High E2-Normal P4 (HN; n = 73). Concentrations of P4 on d 7 subsequent to ovulation were less (P < 0.05) in cows of the HL compared to HN, and in LL compared to LN groups. Concentrations of E2 on d -2, 0, and change in E2 (d -2 to d 0) had a positive effect (P < 0.008) on pregnancy rates. In summary, relatively greater E2 concentrations preceding ovulation; and relatively greater P4 concentrations subsequent to ovulation combined with lesser E2 concentrations preceding ovulation had a positive effect on proportions of postpartum cows pregnant.