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One of the main determining factors of pregnancy per artificial insemination (P/AI) is an optimum concentration of progesterone (P4) in the early luteal phase. This study examined the effects of P4 supplementation on P/AI in lactating Holstein-Friesian cows. A total of 453 cows in 8 spring-calving herds were used in the study. Following AI, cows were randomly assigned to 1 of 2 treatment groups: (1) no subsequent treatment (control; n=221); (2) insertion of a Controlled Internal Drug Release device (CIDR) from day 4 to day 9 post-estrus (supplemented; n=232). Pregnancy per AI was determined by transrectal ultrasonography at day 30 following AI. Insertion of a CIDR increased concentrations of milk P4 in supplemented cows by 4.78ng/mL between day 4 and 4.5 in comparison with a 0.55ng/mL increase in control cows. Progesterone supplementation from day 4 to 9 after AI decreased P/AI by 12 percentage points (56 vs 44%). There was a positive linear and quadratic relationship between P/AI and milk concentration of P4 on day 4 post-estrus in control cows. An optimum concentration of 2.5ng/mL on day 4 was calculated from the logistic regression curve to achieve a probability of P/AI of 65%. When both treatments groups were included in the analysis, there was no association between P/AI and concentrations of P4 on day 4. The results of the study indicate that supplementation with P4 initiated in the early luteal phase had a negative effect on P/AI in dairy cows., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The aim of the present study was to investigate the effect of short-term progesterone (P4) supplementation during the early metoestrous period on circulating P4 concentrations and conceptus development in cattle. The oestrous cycles of cross-bred beef heifers were synchronised using a 7-day P4-releasing intravaginal device (PRID® Delta; 1.55 g P4) treatment with administration of a prostaglandin F(2α) analogue (Enzaprost; CEVA Sante Animale) the day before PRID® Delta removal. Only those heifers recorded in standing oestrus (Day 0) were used. In Experiment 1, heifers were randomly assigned to one of five groups: (1) control: no treatment; (2) placebo: insertion of a blank device (no P4) from Day 3 to Day 7; (3) insertion of a PRID® Delta from Day 3 to Day 7; (4) insertion of a PRID® Delta from Day 3 to Day 5; or (5) insertion of a PRID® Delta from Day 5 to Day 7. In vitro-produced blastocysts were transferred to each heifer in Groups 2-5 on Day 7 (n=10 blastocysts per heifer) and conceptuses were recovered when heifers were killed on Day 14. Based on the outcome of Experiment 1, in Experiment 2 heifers were artificially inseminated at oestrus and randomly assigned to one of three treatment groups: (1) placebo; (2) PRID from Day 3 to Day 5; or (3) PRID from Day 3 to Day 7. All heifers were killed on Day 16 and recovered conceptuses were incubated in synthetic oviducal fluid medium for 24 h; spent media and uterine flushes were analysed for interferon-τ (IFNT). In both experiments, daily blood samples were taken to determined serum P4 concentrations. Data were analysed using the PROC MIXED procedure of SAS (SAS Institute, Cary, NC, USA). Insertion of a PRID resulted in an increase (P<0.05) in serum P4 that declined following removal. In Experiment 1, P4 supplementation from Day 3 to Day 5 (17.0±1.4 mm) or Day 3 to Day 7 (11.3±2.3 mm) increased conceptus length compared with placebo (2.1±1.8 mm). Serum P4 was significantly lower from Day 9 to Day 14 (P<0.05) and the weight of the Day 14 corpus luteum (CL) was lower in the PRID Day 3-7 group than the placebo or control groups. In Experiment 2, supplementation from Day 3 to Day 5 (94.0±18.8 mm) or Day 3 to Day 7 (143.6±20.6 mm) increased conceptus length on Day 16 compared with placebo (50.3±17.4 mm). Serum P4 was significantly lower in the two supplemented groups following PRID removal compared with placebo (P<0.05) and was associated with a lower CL weight in the Day 3-7 group. Conceptus length was strongly correlated with the IFNT concentration in the uterine flush (r=0.58; P=0.011) and spent culture medium (r=0.68; P<0.002). The findings of the present study highlight the somewhat paradoxical effects of P4 supplementation when given in the early metoestrous period in terms of its positive effect on conceptus development and its potentially negative effects on CL lifespan.

Progesterone (P4) metabolism in dairy cattle can be manipulated by alterations in dry matter intake and diet composition. Our objectives were to determine the effects of grazing allowance and fat supplementation on P4 metabolism in lactating dairy cows. Forty mid- to late-lactation Holstein-Friesian dairy cows were used in a completely randomized block design, with a 2 × 2 factorial arrangement of treatments. Cows were assigned to receive 1 of 2 pasture allowances (ad libitum allowance [AL], 9.5 kg dry matter per day, or restricted allowance [R] 7 kg dry matter per day) and 1 of 2 fat supplementation treatments (750 g per day saturated fat [F] or no fat supplement [NF]). All cows received an additional 4 kg per day of concentrate. Grass dry matter intake (GDMI) was measured 5 wk after the initiation of dietary treatment. Cows were treated with prostaglandin F(2α) (PGF(2α)) to eliminate the endogenous source of P4, and two intravaginal progesterone-releasing devices (CIDR) were inserted into each cow for a period of 8 days. Regular blood samples were taken before and after the removal of the intravaginal progesterone-releasing devices, and analyzed for P4 concentrations. The half-life (t½) and metabolic clearance rate (MCR) of P4 was calculated for each cow. There was no effect of GDMI or fat supplementation on the t½ or MCR of P4. There was a tendency for an interaction between GDMI and fat supplementation on the t½ of P4; cows on the restricted-F diet tended to have a longer P4 t½ than cows on the ad libitum-F diet. It was concluded that greater alterations in GDMI than achieved in the current study are required to change P4 metabolism. A combination of fat supplementation and restricted feeding slows P4 clearance, which may have beneficial implications for fertility., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function, two different animal models were used. Experiment 1 compared Holstein-Friesian nonlactating heifers (n = 17) and lactating cows (n = 16) at three stages of preovulatory follicle development: 1) newly selected dominant follicle in the luteal phase (Selection), 2) follicular phase before the LH surge (Differentiation), and 3) preovulatory phase after the LH surge (Luteinization). Experiment 2 compared newly selected dominant follicles in the luteal phase in beef heifers fed a diet of 1.2 times maintenance (M, n = 8) or 0.4 M (n = 11). Lactating cows and 0.4 M beef heifers had higher concentrations of β-hydroxybutyrate, and lower concentrations of glucose, insulin, and IGF-I compared with dairy heifers and 1.2 M beef heifers, respectively. In lactating cows this altered metabolic environment was associated with reduced dominant follicle estradiol and progesterone synthesis during Differentiation and Luteinization, respectively, and in 0.4 M beef heifers with reduced dominant follicle estradiol synthesis. Using a combination of RNA sequencing, Ingenuity Pathway Analysis, and qRT-PCR validation, we identified several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, to be downregulated by the catabolic state. Based on this, we propose that the adverse metabolic environment caused by lactation or nutritional restriction decreases preovulatory follicle function mainly by affecting cholesterol transport into the mitochondria to initiate steroidogenesis.

Pregnancy per insemination is a major determinant of reproductive efficiency in cattle and is affected by concentrations of progesterone (P4) during early pregnancy. The relationship between pregnancy per artificial insemination (P/AI) and early luteal concentrations of P4, and repeatability of concentrations of P4 was examined on d 4, 5, 6, and 7 (day of standing estrus=d 0) in 118 Holstein Friesian heifers following 2 rounds of AI to 1 high-fertility sire. Repeatability estimates (R(e)) for P/AI were established following 4 rounds of AI. We found a linear and quadratic relationship between P/AI and concentrations of P4 on d 4 to 7 after estrus, as well as a linear and quadratic relationship between P/AI and the change in concentration of P4 from d 4 to 7 and from d 5 to 7. Optimum concentrations of P4 to maximize probability of P/AI were 2.5, 4.0, 5.0, 5.2, and 3.5 ng/mL for d 4, 5, 6, and 7, and the change from d 4 to 7, respectively. Repeatability of P/AI following 4 rounds of AI was low (R(e)=0.07). Repeatability estimates for concentrations of P4 from cycle to cycle indicated low repeatability between d 4 (R(e)=0.05) and 7 (R(e)=0.20). These data indicated the importance of P4 in the early luteal phase for pregnancy survival, but also demonstrated that high concentrations of P4 on these days have a deleterious effect on embryo viability. Early luteal (d 4 to 5) concentrations of P4 were a reasonable predictor of concentrations on d 7 and could be used as a diagnostic tool to identify animals at risk of subsequent embryo loss., (Copyright © 2012 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The postovulatory rise in circulating progesterone (P4) concentrations is associated with increased pregnancy success in beef and dairy cattle. Our study objective was to determine how elevated P4 alters endometrial gene expression to advance conceptus development. Synchronized heifers were inseminated (Day 0) and randomly assigned to pregnant high P4 or to pregnant normal P4. All high P4 groups received a P4-release intravaginal device on Day 3 after insemination that increased P4 concentrations up to Day 7 (P < 0.05). Tissue was collected on Day 5, 7, 13, or 16 of pregnancy, and endometrial gene expression was analyzed using the bovine Affymetrix (Santa Clara, CA) microarrays. Microarray analyses demonstrated that the largest number of P4-regulated genes coincided with the day when the P4 profiles were different for the longest period. Genes with the largest fold change increase (such as DGAT2 and MSTN [also known as GDF8]) were associated with triglyceride synthesis and glucose transport, which can be utilized as an energy source for the developing embryo. Temporal changes occurred at different stages of early pregnancy, with the greatest difference occurring between well-separated stages of conceptus development. Validation of a number of genes by quantitative real-time PCR indicated that P4 supplementation advances endometrial gene expression by altering the time (FABP, DGAT2, and MSTN) or duration (CRYGS) of expression pattern for genes that contribute to the composition of histotroph.

Low progesterone concentrations and diminished ovarian reserves (total number of healthy oocytes) during reproductive cycles are linked to infertility in single-ovulating species like cattle. However, the extent and mechanisms whereby the inherently high variation in ovarian reserves may negatively affect progesterone production are unknown. Cattle were chosen to address these questions because the size of their ovarian reserves can be predicted based on an antral follicle count (AFC) during follicular waves. The present study determined if progesterone concentrations, differentiation and function of the corpus luteum (CL), and endometrial thickness differed during reproductive cycles of age-matched healthy young adult cattle with low versus high AFC during follicular waves. The results showed that, despite enhanced LH secretion, progesterone concentrations were lower during estrous cycles for animals with low versus high AFC. Animals with low versus high AFC also had a decreased basal, LH-, and 25-hydroxycholesterol-induced capacity of luteal and granulosal cells to produce progesterone, reduced amounts of STAR and mRNAs for STAR and LH receptor in the CL, and no change in endometrial thickness during estrous cycles. Taken together, these results 1) supported the conclusion that high variation in ovarian reserves of young adults is associated with alterations in differentiation and function of the CL and 2) provided insight into the potential factors that may cause suboptimal luteal function (e.g., heightened LH secretion and desensitization of the LH receptor, diminished LH responsiveness, diminished STAR, inherent deficiency in capacity of granulosal cells to undergo luteinization) and infertility (e.g., low progesterone, poor endometrial growth) in individuals with diminished ovarian reserves.

When managed under grass-based systems of production, the New Zealand (NZ) strain of Holstein-Friesian cow has superior reproductive performance compared to the North American (NA) strain despite having similar solids-corrected milk (SCM) yields. This study compared the ontogeny of early pregnancy events in NZ and NA cows. Ten NZ and 10 NA cows were submitted to a superovulation protocol on three occasions. Blood samples were collected daily from every cow from days -3 to +7 relative to a synchronized oestrus during each superovulation protocol. Pre-ovulatory oestradiol concentrations, follicle diameter, post-ovulatory progesterone concentrations, corpus luteum (CL) diameter, and circulating insulin-like growth factor-I concentrations did not differ between the two strains. Uteri were non-surgically flushed 7 days post-AI, embryos were isolated and graded. The proportion of transferable embryos recovered was higher (P<0.01) in the NZ cows compared with the NA cows. A greater (P=0.01) proportion of the recovered structures were at the blastocyst stage in the NZ cows. Peak SCM yield and body condition score (BCS) at the time of peak SCM yield were not different between strains. However, during the experimental period the NA cows maintained significantly higher daily SCM yields, whereas the NZ cows replenished significantly greater levels of BCS. The results indicate that differences in periovulatory steroid concentrations and size of ovarian structures do not explain the differences in embryo quality between the two strains. However, strain differences in nutrient partitioning from the time of peak SCM yield through late lactation may provide the key signals responsible for superior embryo quality in NZ cows.

Higher systemic progesterone in the immediate post-conception period is associated with an increase in embryonic growth rate, interferon-tau production and pregnancy rate in cattle. The objective of this study was to examine the effect of increasing progesterone concentration on Day 3 on subsequent embryo survival and development. Oestrus (Day 0) was synchronised in beef-cross heifers (n=210) and approximately two-thirds of the heifers were inseminated with semen from a proven sire, while the remainder were not inseminated. In order to produce animals with divergent progesterone concentrations, half of the animals received a progesterone-releasing intravaginal device (PRID) on Day 3 of the oestrous cycle, which was left in situ until slaughter. The four treatment groups were: (i) pregnant, high progesterone; (ii) pregnant, normal progesterone; (iii) non-pregnant, high progesterone; and (iv) non-pregnant, normal progesterone. Animals were blood-sampled twice daily from Days 0 to 8 and once daily thereafter until slaughter on Days 5, 7, 13 or 16, corresponding to the 16-cell stage, the blastocyst stage, the beginning of elongation and the day of maternal recognition of pregnancy, respectively. Embryos were recovered by flushing the tract with phosphate-buffered saline and characterised by stage of development and, in the case of Days 13 and 16, measured. Data were analysed by mixed models ANOVA, Chi-square analysis and Student's t-test where appropriate. Insertion of a PRID on Day 3 increased (P<0.05) progesterone concentrations from Day 3.5 onwards. There was no difference between treatments in the proportion of embryos at the expected stage of development on Days 5 or 7 (P>0.05). While not significantly different, the proportion of viable embryos recovered was numerically greater in the high progesterone group on both Day 13 (58 v. 43%) and Day 16 (90 v. 50%). Elevation of progesterone significantly increased embryonic length on Day 13 (2.24+/-0.51 mm v. 1.15+/-0.16 mm, P=0.034) and Day 16 (14.06+/-1.18 cm v. 5.97+/-1.18 cm, P=0.012). In conclusion, insertion of a PRID on Day 3 of the oestrous cycle increased serum progesterone concentrations on subsequent days, which, while having no phenotypic effect on embryonic development on Days 5 or 7, was associated with an increase in embryonic size on Days 13 and 16.

Our previous work indicates that ewe breed differences in fertility following cervical AI with frozen-thawed semen are due to failure of normal sperm transport and/or early embryo development. Here we examined differences in hormone concentrations about the time of ovulation among more (Finnish Landrace and Belclare) and less (Suffolk and Texel) fertile ewes after AI with frozen thawed semen. In Experiment 1, oestradiol concentrations were measured in samples collected frequently from 12h before to 18h after the LH surge and progesterone was measured in samples collected from 9 to 27h after the LH surge in Suffolk (n=24), Texel (n=20) and Finnish Landrace (n=27) ewes. In Experiment 2, oestradiol concentrations were measured in samples collected frequently from 24h before to 6h after the LH surge and progesterone was measured in samples collected from 6h to 6 days after the LH surge in Suffolk (n=35) and Belclare (n=30) ewes. In Experiment 1, there was an effect of breed, time and their interaction (P<0.001) on oestradiol concentrations between -12 and +6h but only breed differences at +12 and +18h (P<0.01). Progesterone concentrations increased over time (P<0.001) and the rate of increase was significantly greater in Finnish Landrace than in the other two breeds. In Experiment 2, oestradiol concentrations were unaffected by breed. There was an interaction between breed and time with the rate of increase of progesterone being greater in Belclare than Suffolk ewes (P<0.001). In conclusion, differences in hormone concentrations in the periovulatory period are not consistent with ewe breed differences in fertility; however, we have showed that progesterone concentrations rise earlier in the more prolific breeds and suggest that this may explain reported ewe breed differences in embryo development.

Twin bearing mature ewes (n=40) were treated with exogenous progesterone (100mg daily in oil) or vehicle (oil control) from Day 143 of gestation until lambing to investigate the effects on gestation length, foetal survival and colostrum yield and composition. Compared to control ewes, progesterone treated ewes had increased (P<0.05) serum progesterone concentrations (by 4.3 ng/ml) before lambing and in the first day post-partum (by 10 ng/ml). Progesterone treatment increased gestation length (150.4+/-0.6 days versus 147.8+/-0.6 days, P<0.05) and colostrum yield at 1h after lambing (P<0.05) but the colostrum had a lower concentration of IgG (P=0.02). In the first 24h after lambing, total colostrum and IgG yields were not different between groups. Four (20%) of the progesterone treated ewes produced either one or two dead lambs, while one ewe died on day 155 without initiating the birth process. We conclude that the daily administration of 100mg progesterone resulted in extended gestation length and reduced lamb survival but did not lower colostrum yield.

Antral follicle development in cattle is initially FSH dependent and then LH dependent. The aim of the present study was to determine the effects of oestradiol- and progesterone-induced suppression of FSH and LH on growth and differentiation of first wave follicles. Cyclic heifers (n = 45, n = 6-10 per group) received the following i.m. injections or treatments beginning 30 h after oestrus: (i) saline (controls); (ii) 0.75 mg oestradiol benzoate (ODB); (iii) insertion of a progesterone-releasing intravaginal device (PRID) for 42 h (progesterone); (iv) 0.75 mg oestradiol benzoate plus PRID (ODB plus progesterone); (v) 0.75 mg ODB plus injection of 1 mg Ovagen(TM) at 33, 39 and 45 h after onset of oestrus (ODB plus FSH). In Expt 1, follicle development was monitored by ovarian ultrasonography once a day. In Expt 2, heifers were ovariectomized. Emergence of the first follicle wave and dominant follicle selection were delayed in ODB plus progesterone-treated heifers compared with controls. Interval to nadir FSH concentration was shorter in ODB-, progesterone- and ODB plus progesterone-treated heifers compared with controls. Frequency of LH pulses was unaffected in ODB- or ODB plus FSH-treated heifers, decreased in progesterone-treated heifers and further decreased in ODB plus progesterone-treated heifers. Intrafollicular oestradiol concentrations were lower in the largest follicle from ODB plus progesterone-treated heifers compared with control (66 h) heifers, but follicle diameter and concentrations of insulin-like growth factor binding proteins (IGFBPs) and inhibin forms were unaffected. Treatment with ODB decreased follicular oestradiol concentration in smaller follicles in the cohort. It is concluded that growing cohort follicles are uniformly responsive to increased FSH concentration but differentially responsive to suppressed FSH and LH release, which is consistent with an LH-mediated survival advantage of the largest follicle in the cohort before cessation of the growth of remaining follicles in the cohort occurs.

The uterine histotroph provides essential nutrition to the developing conceptus during the preimplantation period of pregnancy. The objective of the present study was to examine the effects of cycle stage and progesterone (P4) concentrations in the blood on the recoverable quantities of amino acids and glucose in the histotroph during the preimplantaion period of conceptus development. Following oestrus, dairy heifers were assigned to low, control or high P4 groups (n = 6 heifers per treatment and time point). The uterine horn ipsilateral to the corpus luteum was flushed on either Day 7 or Day 13. The present study quantified 24 amino acids and glucose in the uterine flushings using HPLC and fluorometry, respectively. Heifers in the low P4 group had lower plasma concentrations of P4 throughout the cycle, whereas heifers in the high group had higher plasma concentrations of P4 between Days 3 and 7 compared with the control group (P < 0.05). Total recoverable neutral (Ser, Gln, Gly, Thr, Cit, β-Ala, Tau, Ala, Tyr, Trp, Met, Val, Phe, Ile, Leu, Pro and Cys), acidic (Glu) and basic (His, Arg, Orn and Lys) amino acids were greater (P < 0.05) on Day 13 than on Day 7. There was no significant difference in the amount of Asp or Asn between Day 7 and Day 13. The amount of amino acids recovered on Day 7 was similar across treatment groups. On Day 13, the amount of Asn, His and Thr was lower (P < 0.05) in the low P4 heifers compared with the controls and/or high P4 heifers. Quantities of glucose were not altered by cycle stage or P4 treatment. In conclusion, the stage of oestrous cycle and P4 play important roles in modulating amino acids in the histotroph, a potentially critical factor for early embryonic and/or conceptus survival. [ABSTRACT FROM AUTHOR]

Systemic progesterone affects the timing and duration of uterine endometrial gene and protein expression and has significant effects on conceptus development. The objective of the present study was to examine how changes in progesterone concentrations during the early luteal phase affect retinol-binding protein (RBP4) mRNA and protein concentrations in the uterus. Endometrial tissue and uterine flushings were recovered on Days 7 and 13 of the oestrous cycle in heifers with high, normal and low progesterone concentrations. RBP4 mRNA and protein concentrations were higher (P < 0.05) on Day 13 compared with Day 7 in heifers with high and control progesterone concentrations. However, there was no difference in RBP4 protein concentrations between Days 7 and 13 in heifers with low progesterone (P > 0.05). On Day 7, although heifers with low progesterone had lower RBP4 mRNA expression compared with controls (P < 0.05) there was no difference in protein concentrations between treatment groups. On Day 13, RBP4 mRNA was 2-fold higher (P < 0.001) in heifers with high and control progesterone compared with their low-progesterone counterparts and RBP4 protein concentrations were over 2-fold higher (P < 0.001) in heifers with high compared to low progesterone. In conclusion, progesterone modulates uterine RBP4 mRNA and protein abundance in a time- and concentration-dependent manner. Embryo survival is a major factor affecting reproductive success with both systemic progesterone and retinol demonstrating significant effects on embryo development. Our aim was to determine the effects of systemic progesterone on the uterine expression of retinol's transportation protein, RBP4, in cyclic dairy cattle. RBP4 expression in the bovine uterus was altered by progesterone in a time- and concentration-dependant manner and therefore may play a role in regulating embryo development in cattle. [ABSTRACT FROM AUTHOR]

The failure of cows to successfully establish pregnancy after insemination is an important limiting factor for the efficiency of dairy production systems. The physiological reasons for this are many and pertain to the post partum and early pregnancy periods. Cows that suffer severe negative energy balance after parturition are prone to diseases (including uterine infection) that are, in part, explained by reduced function of the immune system, having negative consequences for subsequent fertility. In high-producing dairy cows, the duration and intensity of oestrus is low as a consequence of low circulating oestradiol concentrations, and after insemination, high embryo mortality is the single biggest factor reducing calving rates. Embryo mortality occurs as consequences of poor oocyte quality (probably caused by the adverse metabolic environment) and by poor maternal uterine environment (probably caused by carry-over effects of uterine infection and low circulating progesterone concentrations). Immediate improvements in the fertility of lactating cows on many farms can be achieved by applying existing knowledge, but longer-term sustained improvement will require additional knowledge in many areas including the physiology of the tissues that contribute to reproduction. [ABSTRACT FROM AUTHOR]

An abstract of the study "Effect of Short Term Progesterone Supplementation on Circulating Progesterone Concentration, Corpus Luteum Size, and Early Embryo Development in Cattle," by L. O'Hara and colleagues is presented.

The objective of this study was to characterize the estrous cycle of cows with similar proportions of Holstein genetics, similar genetic merit for milk production traits, but with good (Fert+) or poor (Fert-) genetic merit for fertility traits. In total, 37 lactating cows were enrolled on a protocol to synchronize estrus. Nineteen Fert+ and 12 Fert- cows that successfully ovulated a dominant follicle and established a corpus luteum underwent daily transrectal ultrasonography. Blood sampling was carried out at 8-h intervals from d 0 to 6 and from d 15 to ovulation, and once daily from d 7 to 15. Blood samples were analyzed for progesterone, estradiol, follicle stimulating hormone, and luteinizing hormone. Estrus behavior was recorded using neck activity collars and mounting pads. The Fert+ cows tended to have fewer follicular waves (2.2 vs. 2.7) and had a shorter estrous cycle (21.0 vs. 25.1 d) than Fert- cows. We observed no effect of genotype on day of first-wave emergence or day of first-wave dominant follicle peak diameter, but the peak diameter of the first-wave dominant follicle tended to be larger in Fert- cows. During the first 13 d of the cycle, Fert+ cows developed a corpus luteum that was 16% larger than that in Fert- cows. Circulating progesterone concentrations were 34% greater in Fert+ than in Fert- cows (5.15 vs. 3.84 ng/mL, respectively) from d 5 to 13. During the final follicular wave, the interval from preovulatory follicle emergence to ovulation and the interval from preovulatory follicle dominance to ovulation were similar in both genotypes. Maximum preovulatory follicle diameter was larger in Fert+ than Fert- cows (17.9 vs. 16.8 mm, respectively); however, circulating concentrations of estradiol were not different between genotypes. A greater proportion of Fert- cows ovulated to a silent heat than Fert+ cows (22 vs. 2%, respectively). Of cows that showed behavioral estrus, Fert+ cows had 41% greater mean activity count; however, no difference was seen in mounting behavior between genotypes. These results demonstrate, for the first time, that genetic merit for fertility has pronounced effects on corpus luteum development, progesterone concentration, pre-ovulatory follicle diameter, and behavioral estrus. [ABSTRACT FROM AUTHOR]