Endocrine alterations associated with extended time interval between estrus and ovulation in high-yield dairy cows

Short fertile half-lives of the male and female gametes in the female tract necessitate accurate timing of artificial insemination. We examined the possible association between extension of the estrus to ovulation (E-O) interval and alterations in concentrations of estradiol, progesterone, and the preovulatory LH surge before estrus and ovulation. High-yielding Holstein cows (n = 74 from a total of 106) were synchronized and were examined around the time of the subsequent estrus. They were observed continuously for estrual behavior. Blood samples were collected before and after estrus, and ultrasound checks for ovulation were made every 4 h. About three-quarters of the cows exhibited short (but normal) E-O intervals of 22 to 25 h (25%) or normal intervals of 25 to 30 h (47%); 17% of them displayed a long (but normal) E-O interval of 31 to 35 h, and about 10% exhibited a very long E-O interval of 35 to 50 h. Extended E-O interval comprised estrus-to-LH surge and LH surge-to-ovulation intervals that were both longer than normal. Pronounced changes in hormonal concentrations were noted before ovulation in the very long E-O interval group of cows: progesterone and estradiol concentrations were reduced, and the preovulatory LH peak surge was markedly less than in the other 3 groups. Postovulation progesterone concentrations during the midluteal phase were lesser in the very long and the long E-O interval groups compared with those in the short and normal interval groups. Season, parity, milk yield, and body condition did not affect the estrus to LH surge, LH surge to ovulation, and E-O intervals. The results indicate an association between preovulatory-reduced estradiol concentrations and a small preovulatory LH surge, on the one hand, and an extended E-O interval, on the other hand. Delayed ovulation could cause nonoptimal timing of AI, a less than normal preovulatory LH surge that may be associated with suboptimal maturation of the oocyte before ovulation, or reduced progesterone concentrations before and after ovulation. All may be factors associated with poor fertility in cows with a very long E-O interval.     

Use of estradiol cypionate as a substitute for GnRH in protocols for synchronizing ovulation in dairy cattle

Our purpose was to determine whether estradiol cypionate (ECP) could be substituted for the second GnRH injection of the standard Ovsynch protocol (injection of GnRH given 7 d before and 48 h after PGF(2alpha), with timed AI [TAI] 12 to 20 h after the second GnRH injection). Lactating dairy cows ranging from 61 to 82 d in milk at TAI were studied in 14 replicates. Main effects were hormone (ECP vs. GnRH) to induce ovulation and exposure to progesterone (P4) or not during the week preceding PGF(2alpha)-induced luteolysis. Four treatments were: 1) 100 microg of GnRH at 48 h after PGF(2alpha) (Ovsynch; n = 27); 2) same as Ovsynch, plus a P4-releasing intravaginal insert (CIDR) placed for 7 d beginning at the first GnRH injection (Ovsynch + CIDR, n = 20); 3) same as Ovsynch, but substituting 1 mg of ECP for GnRH, and injecting ECP at 24 h after PGF(2alpha) (Heatsynch; n = 33); or 4) Heatsynch + CIDR (n = 26). The largest follicle was identified by ultrasonography 24 h after PGF(2alpha) and was monitored every 6 h until ovulation. Incidence of estrus was less after GnRH (54%) than after ECP (87%), but more GnRH-treated cows had LH surges detected (95 vs. 65%) and ovulated (100 vs. 86%). Duration of LH surges, but not peak concentrations, was less after GnRH than after ECP (6.1 +/- 0.7 vs. 12.2 +/- 0.9 h). Pre-treatment with P4 reduced the incidence of LH surges but had no effects on incidence of estrus or ovulation. Intervals to the LH surge and ovulation were less after GnRH than after ECP, but intervals between onset of the LH surge and ovulation did not differ (26 +/- 2 vs. 30 +/- 3 h). We concluded that substituting ECP for GnRH resulted in more cows in estrus and slightly fewer ovulating.     

Short communication: Characterization of early postpartum estrous behavior and ovulation in lactating dairy cows using radiotelemetry

The objective of this study was to describe early postpartum estrous behavior and ovulation in lactating dairy cows using radiotelemetry. Cows (n=50) were continuously monitored for behavioral estrus with a radiotelemetric system, HeatWatch II (CowChips LLC, Manalapan, NJ), from d 14 to approximately d 49 postpartum. Blood collection for analysis of progesterone and ovarian ultrasonography were performed once weekly starting on d 14. First ovulation was associated with behavioral estrus in 5 cows and occurred at 28.2±10.8d (mean±SD; range 17 to 40d). The average duration of estrus was 6.0±4.9h (range 3 to 12.2h), and the mean number of standing events was 18.4±8.9 (range 4 to 26). Based on progesterone concentrations of ≥1ng/mL, estimated first postpartum ovulation occurred at 25.1±10.4d (range 10 to 49d) for 38 animals without evidence of behavioral estrus. The interval to estimated first ovulation without behavioral estrus was not different from the interval to first ovulation associated with behavioral estrus. Level of milk production and body condition score loss did not affect the interval to estimated first ovulation without estrus or first ovulation associated with estrus. Six animals did not show evidence of ovulation based on progesterone concentration, whereas 1 cow showed evidence of estrous behavior on the day before removal from the study. The majority of first postpartum ovulations (38/43; 88.4%) were not associated with behavioral estrus.     

Effects of GnRH administered to cows at the onset of estrus on timing of ovulation,endocrine responses,and conception

Two experiments examined effects of GnRH administered within 3 h after onset of estrus (OE) on ovulation and conception in dairy cows. In experiment 1, 46 cows received either saline, 250 microg of GnRH, or 10 microg of the GnRH analogue, Buserelin. Cows were observed for estrus, blood samples were collected, and ovulations were monitored by ultrasound. In controls, 76% of cows had intervals from estrus to ovulation of < or = 30 h and 24% had intervals > 30 h. Treatment with either GnRH or GnRH analogue (data combined) increased magnitude of LH surges and decreased intervals from estrus to LH surge or to ovulation. Treated cows all ovulated < or = 30 h after OE. Among control cows, plasma estradiol concentrations before estrus correlated positively with amplitudes of LH surges. Higher plasma progesterone was observed in the subsequent estrous cycle in GnRH-treated cows compared to control cows with delayed ovulations. Experiment 2 included 152 primiparous and 211 multiparous cows in summer and winter. Injection of GnRH analogue at OE increased conception rates (CR) from 41.3 to 55.5% across seasons. In summer, GnRH treatment increased CR from 35.1 to 51.6%. Across seasons, GnRH increased CR from 36.0 to 61.5% in cows with lower body condition at insemination and GnRH increased CR (63.2 vs. 42.2%) in primiparous cows compared to controls. Use of GnRH eliminated differences in CR for cows inseminated early or late relative to OE and increased CR in cows having postpartum reproductive disorders. In conclusion, GnRH at onset of estrus increased LH surges, prevented delayed ovulation, and may increase subsequent progesterone concentrations. Treatments with GnRH increased conception in primiparous cows, during summer, and in cows with lower body condition.     

Induction of persistent ovarian follicular structures following administration of progesterone near the onset of estrus in dairy cattle

The objective of this study was to determine if progesterone administered near the onset of estrus in dairy cows would block the preovulatory surge of LH and result in subsequent persistence of ovarian follicular structures. Following synchronization of estrus with prostaglandin F2 alpha, 20 multiparous, non-lactating Holstein cows were randomly assigned into three groups: 1 ml ethanol administered i.m. at 12-h intervals for 24 h (n = 6; group 1); 1 mg progesterone administered i.m. at 12-h intervals for 24 h (n = 7; group 2); 2.5 mg progesterone administered i.v. at the onset of standing estrus (n = 7; group 3). Ovarian structures were palpated per rectum on the day of estrus and twice weekly for 14 d. Blood was collected every 2 h from onset of standing estrus for 30 h, and concentrations of LH and progesterone were determined. Numbers of cows diagnosed with persistent follicles 10 d after estrus were 1 of 6 (group 1), 2 of 7 (group 2), and 5 of 7 (group 3). The preovulatory surge of LH did not occur during the sampling period (30 h) for 1 of 6, 7 of 7 and 5 of 7 cows, for groups 1, 2, and 3, respectively, and mean serum concentrations of LH were higher in group 1 than in groups 2 and 3. Serum concentration of progesterone (ng/ml) was higher in group 1 (1.9 +/- .4) than in groups 2 (.9 +/- .4) and 3 (.9 +/- .4) 10 d following estrus. Blocking the preovulatory surge of LH with exogenous progesterone resulted in persistence of ovarian follicles.     

Anogenital distance is associated with postpartum estrous activity,intensity of estrous expression,ovulation, and progesterone concentrations in lactating Holstein cows

The objectives of this retrospective observational study were to determine the associations of anogenital distance (AGD) with (a) postpartum estrous activity, (b) diameter of the preovulatory follicle, (c) intensity of estrous expression, (d) postestrus ovulation, (e) corpus luteum (CL) size, and (f) concentrations of progesterone at estrus and on d 7 after estrus. Lactating Holstein cows (n = 178; 55 primiparous, 123 multiparous) were enrolled into the study during the first postpartum week. All cows were continuously monitored by a pedometer-based automated activity monitoring (AAM) system for estrus. Postpartum estrous activity was assessed using the AAM estrus alerts, in which cows with at least one true estrus alert (i.e., a relative increase in steps from each cow's baseline detected by the AAM and the presence of at least one follicle >15 mm, a CL <20 mm, or no CL detected by ultrasound) by the first 50 d in milk (DIM) were considered to have commenced estrous activity. At the estrus alert >60 DIM, ovulation was determined by ultrasound at 24 h, 48 h, and 7 d after estrus, and blood samples were collected at estrus alert and on d 7 after estrus for progesterone analysis. The AGD was measured from the center of the anus to the base of the clitoris and classified as either short- or long-AGD using 2 cut-points of 148 mm (predictive of the probability of pregnancy to first insemination; short-AGD, n = 115; long-AGD, n = 63) and 142 mm (the median AGD; short-AGD, n = 90; long-AGD, n = 88). Regardless of the cut-point used, early postpartum estrous activity by 50 DIM (67 vs. 54%), duration of estrus (11.6 vs. 9.7 h), and preovulatory follicle diameter (20 vs. 19 mm) were greater in short-AGD than in long-AGD cows. Increased peak of activity at estrus in short-AGD cows (354 vs. 258% mean relative increase) was affected by an interaction between AGD and parity in which multiparous long-AGD cows had lesser relative increase in activity than primiparous cows (217 vs. 386%, respectively). Mean progesterone concentration at estrus was lesser in short-AGD (0.47 vs. 0.61 ng/mL) than in long-AGD cows. The ovulatory response at 24 h did not differ, but at 48 h (91 vs. 78%) and on d 7 after estrus (97 vs. 84%) it was greater in short-AGD cows. Although CL diameter on d 7 after estrus did not differ, short-AGD cows had greater progesterone concentration 7 d after estrus than long-AGD cows (4.1 vs. 3.2 ng/mL, respectively). In conclusion, greater proportions of short-AGD cows commenced estrous activity by 50 DIM, had larger preovulatory follicles, exhibited greater duration of estrus, had reduced progesterone concentration at estrus, had greater ovulation rates and progesterone concentration 7 d after estrus compared with long-AGD cows, with no difference in CL size between AGD groups. Because all the differences in physiological characteristics of short-AGD cows reported herein favor improved reproductive outcomes, we infer that these are factors contributing to improved fertility reported in short-AGD cows compared with long-AGD cows.     

Assessing ovulation detection performance in commercial dairy herds using progesterone concentrations from limited numbers of strategically collected milk samples

It is important to assess ovulation detection performance in commercial dairy herds both to investigate low reproductive performance and to enable herd managers to monitor the effectiveness of their system for detecting ovulations. A method was developed to assess ovulation detection performance that uses limited numbers of strategically collected milk samples, assesses performance over the period when herd managers are making maximal effort to detect ovulations, and when assessing proportions of ovulations detected, accounts for false positive diagnoses of estrus and for cows that have not recommenced postpartum ovulatory cycles. Milk was sampled from cows not diagnosed in estrus early in the breeding program (about d 26 in year-round calving herds and d 22 in seasonal calving herds); milk samples were also collected from cows on the day of insemination. Cows with high milk progesterone concentrations were assumed to have had undetected ovulations and false positive diagnoses of estrus, respectively. The method was successfully implemented in 161 of 167 commercial dairy herds. Positive predictive values (PPV; the proportions of ovulation diagnoses where ovulation was, in fact, imminent) were generally high in both year-round and seasonal calving herds (median values were 0.96 and 0.97, respectively), but 25% of herds had PPV <0.95. Ovulation detection sensitivities (ODS) were low in most year-round calving herds, but many seasonal calving herds had high ODS values; median ODS were 0.73 and 0.94, respectively. However, in 25% of seasonal calving herds, ODS was <0.91. These findings indicate that this method for assessing ovulation detection performance can be successfully implemented in commercial dairy herds with appropriate professional support. The wide range of ODS and the absence of correlation between ODS and PPV suggest that it is possible for managers of many commercial herds in Australia to achieve increased reproductive efficiency through increases in ODS and PPV.     

Local changes in blood flow within the preovulatory follicle wall and early corpus luteum in cows

Haemodynamic changes are involved in the cyclic remodelling of ovarian tissue that occurs during final follicular growth, ovulation and new corpus luteum development. The aim of this study was to characterize the real-time changes in the blood flow within the follicle wall associated with the LH surge, ovulation and corpus luteum development in cows. Normally cyclic cows with a spontaneous ovulation (n = 5) or a GnRH-induced ovulation (n = 5) were examined by transrectal colour and pulsed Doppler ultrasonography to determine the area and the time-averaged maximum velocity (TAMXV) of the blood flow within the preovulatory follicle wall and the early corpus luteum. Ultrasonographic examinations began 48 h after a luteolytic injection of PGF(2alpha) analogue was given at the mid-luteal phase of the oestrous cycle. Cows with spontaneous ovulation were scanned at 6 h intervals until ovulation occurred. Cows with GnRH-induced ovulation were scanned just before GnRH injection (0 h), thereafter at 0.5, 1, 2, 6, 12, 24 h and at 24 h intervals up to day 5. Blood samples were collected at the same time points for oestradiol, LH and progesterone determinations. Cows with both spontaneous and GnRH-induced ovulation showed a clear increase in the plasma concentration of LH (LH surge) followed by ovulation 26-34 h later. In the colour Doppler image of the preovulatory follicle, the blood flow before the LH surge was detectable only in a small area in the base of the follicle. An acute increase in the blood flow velocity (TAMXV) was detected at 0.5 h after GnRH injection, synchronously with the initiation of the LH surge. At 12 h after the LH surge, the plasma concentrations of oestradiol decreased to basal concentrations. The TAMXV remained unchanged after the initial increase until ovulation, but decreased on day 2 (12-24 h after ovulation). In the early corpus luteum, the blood flow (area and TAMXV) gradually increased in parallel with the increase in corpus luteum volume and plasma progesterone concentration from day 2 to day 5, indicating active angiogenesis and normal luteal development. Collectively, the complex structural, secretory and functional changes that take place in the ovary before ovulation are closely associated with a local increase in the blood flow within the preovulatory follicle wall. The result of the present study provides the first visual information on vascular and blood flow changes associated with ovulation and early corpus luteum development in cows. This information may be essential for future studies involving pharmacological control of blood flow and alteration of ovarian function.     

Naturally occurring mastitis effects on timing of ovulation, steroid and gonadotrophic hormone concentrations, and follicular and luteal growth in cows

The effects of naturally occurring subclinical chronic or clinical short-term mastitis on time of ovulation, plasma steroid and gonadotropin concentrations, and follicular and luteal dynamics were examined in 73 lactating Holstein cows. Cows were sorted by milk somatic cell count and bacteriological examination into an uninfected group (n = 22), a clinical mastitis group (n = 9; events occurring 20 ± 7 d before the study), and a subclinical chronic mastitis group (n = 42). In addition, uninfected and mastitic cows were further sorted by their estrus to ovulation (E-O) interval. About 30% of mastitic cows (mainly subclinical) manifested an extended E-O interval of 56 ± 9.2 h compared with 28 ± 0.8 h in uninfected cows and 29 ± 0.5 h in the other 70% of mastitic cows. In mastitic cows with extended E-O interval, the concentration of plasma estradiol at onset of estrus was lower than that of uninfected cows or mastitic cows that exhibited normal E-O intervals (3.1 ± 0.4, 5.8 ± 0.5, and 5.5 ± 0.5 pg/mL, respectively). The disruptive effect of mastitis on follicular estradiol probably does not involve alterations in gonadotropin secretion because any depressive effects of mastitis on pulsatile LH concentrations were not detected. Cortisol concentrations did not differ among groups. The preovulatory LH surge in mastitic cows with delayed ovulation varied among individuals, being lower, delayed, or with no surge noted compared with the normal LH surge exhibited by uninfected cows or mastitic cows with normal E-O interval (6.8 ± 0.7 ng/mL). The diameter of the second-wave dominant follicle was larger and the number of medium follicles was smaller in uninfected and subclinical cows with normal intervals compared with subclinical cows with extended intervals (13.4 ± 0.5 vs. 10.9 ± 0.9 mm, and 3.8 ± 0.2 vs. 6.7 ± 0.14 follicles, respectively). Mid-luteal progesterone concentrations were similar in uninfected and mastitic cows. These results indicate for the first time that around 30% of cows with subclinical chronic mastitis exhibit delayed ovulation that is associated with low plasma concentrations of estradiol and a low or delayed preovulatory LH surge.     

Evaluation and characterization of estrus alerts and behavioral parameters generated by an ear-attached accelerometer-based system for automated detection of estrus

Our objectives were to evaluate the performance of an ear-attached automated estrus detection (AED) system (Smartbow; Zoetis) that monitored physical activity and rumination time, and to characterize AED system estrus alert features (i.e., timing and duration). Lactating Holstein cows (n = 216) commenced a protocol for the synchronization of estrus at 50 ± 3 DIM or 18 ± 3 d after artificial insemination. For 7 d after induction of luteolysis with PGF_2α (d 0), we used visual observation of estrous behavior (30 min, 2 times per day) and data from an automated mounting behavior monitoring system based on a pressure-activated tail-head sensor (HeatWatch; Cowchips LLC) as a reference test (RTE) to detect behavioral estrus. Concomitantly, estrus alerts and their features were collected from the AED system. Progesterone levels confirmed luteal regression, and transrectal ultrasonography confirmed the occurrence and timing of ovulation. Performance metrics for the AED system were estimated with PROC FREQ in SAS, using the RTE or ovulation only as a reference. Performance was also estimated after the removal of cows with a discrepancy between the RTE and ovulation. Continuous outcomes with or without repeated measurements were evaluated by ANOVA using PROC MIXED in SAS. Based on the RTE, 86.6% (n = 187) of the cows presented estrus and ovulated; 1.4% (n = 3) presented estrus and did not ovulate; 6.4% (n = 14) did not present estrus but ovulated; and 5.6% (n = 12) did not present estrus or ovulation. We found no difference in the proportion of cows detected in estrus and with ovulation for the AED system (83.4%) and the RTE (86.6%). Compared with estrus events as detected by the RTE, sensitivity for the AED was 91.6% (95% CI: 87.6–95.5) and specificity was 69.2% (95% CI: 51.5–87.0). Using ovulation as reference, sensitivity was 89.6% (95% CI: 85.3–93.8) and specificity was 86.7% (95% CI 69.5–100). For all cows with agreement between the RTE and ovulation, sensitivity was 92.5% (95% CI: 88.7–96.3) and specificity was 91.7% (95% CI: 76.0–100). The mean (±SD) interval from induction of luteolysis to estrus alerts, estrus alert duration, and the onset of estrus alerts to ovulation interval were 72.2 ± 18.1, 13.5 ± 3.8, and 23.8 ± 7.1 h, respectively. We concluded that an ear-attached AED system that monitored physical activity and rumination time was effective at detecting cows in estrus and generated few false positive alerts when accounting for ovulation, cow physiological limitations, and the limitations of the RTE.     

Effect of adrenocorticotropin and cortisol on luteinizing hormone surge and estrous behavior of cows

In six cows, twice daily administration of 100 IU corticotropin for 3.5 days during the follicular phase delayed the preovulatory luteinizing hormone surge and onset of behavioral estrus. Corticotropin increased progesterone and decreased estradiol and basal luteinizing hormone concentrations of blood. Following corticotropin withdrawal, a shortened period of behavioral estrus (50% of control) was accompanied by an apparent luteinizing hormone surge and ovulation. To ascertain if these effects were caused by the elevated corticosteroid concentrations induced by corticotropin, we infused intravenously four heifers with cortisol sodium succinate. During this infusion, luteinizing hormone surge and estrous behavior were inhibited; however, estradiol and basal luteinizing hormone concentrations were not affected. Furthermore, there was no luteinizing hormone surge, ovulation, or behavioral estrus after cessation of cortisol treatment. These results are consistent with a role for corticosteroids in mediating inhibitory effects on reproduction produced by corticotropin administration.     

Synchronization of estrus in dairy cows with prostaglandin F2 alpha and estradiol benzoate

A field study using 322 lactating dairy cows in seven commercial and two university herds was conducted to determine if treatment with estradiol benzoate 40 to 48 h after treatment with prostaglandin F2 alpha would enhance synchronization of estrus. Estrogen treatment tended to increase the proportion of cows in estrus within 5 d (synchronized) after prostaglandin treatment (66.9% versus 58.9%). Of synchronized cows, a greater proportion treated with estrogen (66.9%) were in estrus on d 3 than those not receiving estrogen (48.2%). First service conception rate (31.9%) and interval to second service (35.6 d) were not affected by treatment with estrogen. Milk progesterone was measured in university herds. More cows with milk progesterone concentrations greater than or equal to 8 ng/ml were synchronized (75.4%) than those with less than 8 ng/ml (63.3%). Treatment with estrogen increased synchrony of cows with high progesterone (90.3%) more than prostaglandin alone (60.0%). Based on progesterone concentrations at breeding and 22 to 24 d later, estimated conception rate was 58.7%, and net conception rate based on palpation was 41.3%. Tighter synchrony of estrus can be achieved by using estradiol benzoate 40 to 48 h after prostaglandin. Concentrations of milk progesterone might predict success of treatment.     

Effects of induced clinical mastitis during preovulation on endocrine and follicular function

The objective of the study was to determine if experimentally induced clinical mastitis before ovulation resulted in alterations of endocrine function, follicular growth, or ovulation. On d 8 (estrus = d 0), cows were challenged (TRT; n = 19) with Streptococcus uberis or were not challenged (control; n = 14). Forty-eight hours after induction of luteal regression on d 12, blood samples were collected to determine estradiol-17β, LH pulse frequency, and occurrence of the LH surge. Ovaries were scanned to monitor follicular growth and ovulation. Cows with clinical mastitis (n = 12) had elevated rectal temperatures, somatic cell counts, and mammary scores. Estrus and ovulation occurred in 4 of 12 clinically infected cows and in all control cows. Cows that were challenged but did not develop clinical mastitis (n = 5) displayed estrus and ovulated. Due to differences in expression of estrus, cows were further subdivided for analyses into 4 groups: control, TRT-EST (infected cows that displayed estrus; n = 4), TRT-NOEST (infected cows that did not display estrus; n = 8), and NOMAS (cows that were inoculated but did not develop mastitis; n = 4). Ovulation rate was 100% for CON, NOMAS, and TRT-EST compared with 0% for TRT-NOEST cows. Size of the ovulatory follicle (“presumed” ovulatory follicle in TRT-NOEST cows) was similar for all groups. Frequency of LH pulses was decreased in TRT-NOEST compared with CON, TRT-EST, and NO-MAS. Estradiol-17β increased over time in CON, NO-MAS, and TRT-EST cows, but did not increase in TRT-NOEST cows. Cows with clinical mastitis may exhibit estrus and ovulate normally or have disruptions in normal physiology including decreased LH pulsatility, absence of an LH surge and estrous behavior, suppressed estradiol-17β, and failure to ovulate.     

Testosterone antagonist (flutamide) blocks ovulation and preovulatory surges of progesterone, luteinizing hormone and oestradiol in laying hens

The preovulatory release of luteinizing hormone (LH) in the domestic hen occurs after the initiation of a preovulatory surge of testosterone. The objective of this study was to determine whether this testosterone surge has functional significance in the endocrine control of ovulation. Groups of laying hens (n = 10-22) were treated with the androgen receptor antagonist, flutamide, at 8 h intervals for 24 h at doses of 0, 31.25, 62.5, 125 and 250 mg. All doses reduced egg laying (P < 0.001), with the highest dose being the most effective. In a second study, laying hens (n = 9) were treated with 250 mg flutamide at 8 h intervals for 24 h with a control group being given placebo (n = 10). Blood samples were taken for hormone measurements at 2 h intervals for 18 h starting 4 h before the onset of darkness. The percentage of hens laying per day did not differ between groups before treatment (control, 88% vs flutamide, 86%). Ovulation was blocked in all hens treated with flutamide within 2 days while the control hens continued to lay at the pretreatment rate (80%). Preovulatory surges of plasma testosterone, progesterone, oestradiol and LH were observed in control hens but with the exception of testosterone, flutamide treatment blocked the progesterone, oestradiol and LH surges. LH concentrations declined progressively with time in the flutamide-treated hens. It is concluded that inhibition of testosterone action blocks egg laying and the preovulatory surges of progesterone, luteinizing hormone and oestradiol demonstrating a key role for the preovulatory release of testosterone in the endocrine control of ovulation in the domestic hen.     

Infrared thermography and behavioral biometrics associated with estrus indicators and ovulation in estrus-synchronized dairy cows housed in tiestalls

Most Canadian dairy herds operate in tiestall housing (61%), where average estrus detection rates may be lower than 54%. The objective of this study was to evaluate infrared thermography and behavioral biometrics as indicators of estrus in dairy cows. Eighteen cyclic multiparous cows (Synch) were subjected to an estrus synchronization protocol, and 18 pregnant cows (control) received a sham protocol on the same schedule and frequency as the cyclic cow treatment. A decline in plasma concentrations of progesterone and the appearance of a dominant follicle using transrectal ultrasonography were used as indirect indicators of estrus, and the disappearance of a dominant follicle was used to confirm ovulation. All cows were monitored via visual cameras to determine the frequency of treading, drinking, neighbor interaction, tail movement, lying, and shifting behaviors. Infrared thermograms were recorded at the eye, muzzle, cheek, neck, front right foot, front left foot, rump, flank, vulva area, tail head, and withers. To evaluate the accuracy of behavioral and thermal parameters, a predefined minimum acceptable value (i.e., threshold) for estrus alerts (>0.30 Youden J index and >0.60 area under the curve) was used. Ovulation was confirmed in 14 (77.7%) out of 18 Synch cows. Eye, cheek, neck, rump, flank, vulva area, and wither thermograms exhibited higher temperatures at 48 h [cycle threshold (Δt) = +0.30 to 1.20°C] and 24 h before ovulation compared with 4 d prior to ovulation (Δt = 0.06 to 0.11°C) and during ovulation day (Δt = 0.03 to 0.32°C) in the Synch group. In addition, control cows exhibited greater treading activity per day compared with Synch cows (20.84 ± 0.39 vs. 16.35 events/5 min ± 0.34), and tail movement frequency was greater in Synch cows compared with control cows (14.84 ± 2.7 vs. 10.11 ± 4.7 events/5 min). However, within Synch cows, tail movement was the only behavior that significantly increased in frequency 2 d before ovulation (11.81 ± 1.71 events/5 min) followed by a decrease in frequency 1 d before ovulation (4.67 ± 1.05 events/5 min) compared with ovulation day (0 d; 6.10 ± 1.25 events/5 min) and during luteolysis (3 d before ovulation; 6.01 ± 1.25 events/5 min). Upon evaluation of all variables (thermograms and behavior frequencies) as estrus indicators at 48 and 24 h before ovulation, treading and tail movements before milking and 9 thermal locations satisfied the predefined minimum acceptable value for estrus alerts. This study demonstrates that fluctuations in radiated temperature measured at specific anatomical locations and the frequency of tail movements and treading behaviors can be used as a noninvasive estrus alerts in multiparous cows housed in a tiestall system.     

A GnRH/LH surge without subsequent progesterone exposure can induce development of follicular cysts

Our hypothesis was that follicular cysts would develop if cows experienced an estradiol-induced GnRH LH surge in the absence of an ovulatory follicle. Further, we hypothesized that estradiol would fail to induce a subsequent GnRH/LH surge in these cows until they were treated with progesterone. In experiment 1, seven cows were synchronized with a controlled internal drug releasing device (CIDR) for 9 d and each received 500 microg of cloprostenol on d 7. All follicles (> or = 5 mm in diameter) were aspirated at the time of CIDR removal using transvaginal follicular aspiration. Two days after aspiration, cows were treated with 5 mg of estradiol benzoate (EB) to induce a GnRH/LH surge in the absence of an ovulatory-sized follicle. All cows had an LH surge following the estradiol treatment and three of seven developed an anovulatory condition that resembled follicular cysts. The four cows that did not develop follicular cysts luteinized remaining cells from one aspirated follicle each. Thus, all cows with a progesterone elevation after the estradiol/GnRH/LH surge had subsequent ovulatory cycles, whereas the absence of progesterone was followed by follicular cysts. After 49 d, the anovulatory cows were induced back to normal cyclicity by insertion of a CIDR for 7 d. In two subsequent experiments, nine of 26 cows were induced to have follicular cysts by follicular aspiration followed by 5 mg of EB. After 26 d of observation, all cystic cows received a second treatment with 5 mg of EB and none of the cows showed an LH surge or ovulation. Cystic cows were untreated (n = 4 controls) or treated for 7 d with a CIDR (n = 5). All cystic cows were subsequently treated for a third time with 5 mg of EB. All CIDR-treated cows had an LH surge and ovulated, whereas none of the control cows had an LH surge or ovulation after the estradiol treatment. Thus, a large follicle anovulatory condition, similar to follicular cysts, can be induced by estradiol induction of a GnRH/LH surge in the absence of subsequent luteinization, and this condition prevents a GnRH/LH surge in response to high doses of estradiol. Progesterone eliminates this condition by reinitiation of GnRH/LH surges in response to estradiol.     

Short communication: Simultaneous measurements of estrus behavior and plasma concentrations of estradiol during estrus in lactating and nonlactating dairy cows

Estrus is an important behavior that can potentially be subjected to genomic selection. Circulating estradiol concentrations at estrus may be a useful phenotype if the absolute concentrations of estradiol are associated with overt phenotypes for estrus (activity, rump touches, or both; e.g., mounts, chinrests) that can be easily observed. The objective was to measure plasma estradiol concentrations at estrus and associate these measurements with the increase in activity (steps per hour) and rump touches received at estrus. We also tested the effect of lactation on the estrus traits that we measured. Cows (n = 11 lactating and n = 9 nonlactating) were treated with PGF_2α to synchronize estrus. A jugular vein was cannulated to collect blood every 2 h for plasma estradiol measurement. Plasma LH was measured during the periestrual period to determine the time of the LH surge. Cows were fitted with an accelerometer to measure activity (steps per hour) and a capacitive touch sensing device to measure the number of rump touches and total touch time. Plasma estradiol concentrations were poorly correlated with overt signs of estrus during the period leading up to maximum estrus activity. After peak estrus activity (when cows were going out of estrus and plasma estradiol concentrations were decreasing), a stronger correlation was detected between overt signs of estrus and plasma estradiol concentrations. Effective selection for improved estrus expression based on plasma estradiol concentrations will depend on whether the cow is coming into or going out of estrus at the time of blood sampling. An association existed between lactation and fewer number of hours in estrus when estrus was defined by an increase in activity (steps per hour). Lactating cows had a shorter interval from the onset of estrus to the LH surge, and the shorter interval to the LH surge may have reduced the period of elevated estradiol during estrus in the lactating cows. Understanding mechanisms that control the sensitivity of the cow to estradiol and making appropriate selection decisions based on these mechanisms will likely increase overt signs of estrus in dairy cows.     

Field evaluation of 2 collar-mounted activity meters for detecting cows in estrus on a large pasture-grazed dairy farm

This study tested the hypothesis that a commercially available system for detecting estrus based on cow activity would perform similarly to that of typical, visual assessment of mounting indicators placed on the tail head of the cow. The hypothesis was applied to a large, pasture-grazed, seasonal-calving dairy herd, and the technology was tested as a stand-alone system. One of 2 types of commercially available collar-mounted activity meters was fitted to 635 cows, and the activity data collected during the 37-d artificial breeding period were analyzed. The first collar-mounted activity meter monitored activity only (AO collars), whereas the second meter measured activity and rumination characteristics (AR collars). Only activity data were used in the current study. Activity-based estrus alerts were initially identified using the default activity threshold value recommended by the manufacturer, but a range of activity threshold values was then analyzed to determine their effect on estrus detection performance. Milk progesterone data and insemination records were used to identify gold standard positive (n = 835) and negative (n = 22,660) estrus dates, to which activity alerts were compared. Visual assessment of mounting indicators resulted in a manual detection performance of 91.3% sensitivity (SN), 99.8% specificity (SP), and 94.5% positive predictive value (PPV). The AR collars achieved 76.9, 99.4, and 82.4% for SN, SP, and PPV, whereas the AO collars achieved 62.4, 99.3, and 76.6% for SN, SP, and PPV, respectively. The observed performance of the activity systems may be underestimated due to test design and applied assumptions, including determining the date of estrus. Lowering the activity threshold from the default value improved sensitivity but the number of false positive alerts was considered to become unmanageable from a practical perspective as sensitivity reached peak values. Time window analysis, receiver operating characteristic curves, and curves of SN and PPV were found to be useful in the analysis and interpretation of results. They generate relevant performance data that allow for meaningful comparisons between similar studies. Although the 2 activity systems tested did not perform to the high level of manual estrus detection found in this study, the potential exists for these systems to be a valuable tool on farms with lower estrus detection performance or for farmers managing larger herds.     

Validation of a novel milk progesterone-based tool to monitor luteolysis in dairy cows: Timing of the alerts and robustness against missing values

Automated monitoring of fertility in dairy cows using milk progesterone is based on the accurate and timely identification of luteolysis. In this way, well-adapted insemination advice can be provided to the farmer to further optimize fertility management. To properly evaluate and compare the performance of new and existing data-processing algorithms, a test data set of progesterone time-series that fully covers the desired variability in progesterone profiles is needed. Further, the data should be measured with a high frequency to allow rapid onset events, such as luteolysis, to be precisely determined. Collecting this type of data would require a lot of time, effort, and budget. In the absence of such data, an alternative was developed using simulated progesterone profiles for multiple cows and lactations, in which the different fertility statuses were represented. To these, relevant variability in terms of cycle characteristics and measurement error was added, resulting in a large cost-efficient data set of well-controlled but highly variable and farm-representative profiles. Besides the progesterone profiles, information on (the timing of) luteolysis was extracted from the modeling approach and used as a reference for the evaluation and comparison of the algorithms. In this study, 2 progesterone monitoring tools were compared: a multiprocess Kalman filter combined with a fixed threshold on the smoothed progesterone values to detect luteolysis, and a progesterone monitoring algorithm using synergistic control, PMASC, which uses a mathematical model based on the luteal dynamics and a statistical control chart to detect luteolysis. The timing of the alerts and the robustness against missing values of both algorithms were investigated using 2 different sampling schemes: one sample per cow every 8 h versus 1 sample per day. The alerts for luteolysis of the PMASC algorithm were on average 20 h earlier compared with the ones of the multiprocess Kalman filter, and their timing was less sensitive to missing values. This was shown by the fact that, when 1 sample per day was used, the Kalman filter gave its alerts on average 24 h later, and the variability in timing of the alerts compared with simulated luteolysis increased with 22%. Accordingly, we postulate that implementation of the PMASC system could improve the consistency of luteolysis detection on farm and lower the analysis costs compared with the current state of the art.