Exploiting multimedia in reproductive science education: research findings.

Education in reproductive science is operating from an outdated paradigm of teaching and learning. Traditionally, reproductive education follows the pattern where students read a textbook, listen to instructor presentations, re-read the textbook and class notes and then complete a test. This paradigm is inefficient, costly and has not incorporated the potential that technology can offer with respect to increases in student learning. Further, teachers of reproductive science (and all of science for that matter) have little training in the use of documented methods of instructional design and cognitive psychology. Thus, most of us have learned to teach by repeating the approaches our mentors used (both good and bad). The technology now exists to explain complex topics using multimedia presentations in which digital animation and three-dimensional anatomical reconstructions greatly reduce time required for delivery while at the same time improving student understanding. With funding from the Small Business Innovation Research program through the U.S. Department of Education, we have developed and tested a multimedia approach to teaching complex concepts in reproductive physiology. The results of five separate experiments involving 1058 university students and 122 patients in an OB/GYN clinic indicate that students and patients learned as much or more in less time when viewing the multimedia presentations when compared to traditional teaching methodologies.

Will there be another generation of reproductive scientists?

This paper outlines concerns pertaining to the future of professionals in the discipline of reproductive science. This discourse is based on the experiences, opinions and due considerations of the author. The major objective of this paper is to stimulate thinking, discussion and debate, as well as action aimed at correcting problems that may threaten the next generation of reproductive scientists. The most important points are that mentoring has been replaced with counting, and that academic positions with combined research and teaching components are less and less attractive due to the protracted PhD plus postdoctoral training periods, the extremely low funding rates for extramural grant proposals, and being rewarded on the basis of quantity rather than quality.

Emission pattern of high-energy pions: A new probe for the early phase of heavy-Ion collisions

The emission pattern of charged pions has been measured in Au+Au collisions at 1 GeV/nucleon incident energy. In peripheral collisions and at target rapidities, high-energy pions are emitted preferentially towards the target spectator matter. In contrast, low-energy pions are emitted predominantly in the opposite direction. The corresponding azimuthal anisotropy is explained by the interaction of pions with projectile and target spectator matter. This interaction with the spectator matter causes an effective shadowing which varies with time during the reaction. Our observations show that high-energy pions stem from the early stage of the collision whereas low-energy pions freeze out later.

Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy-Ion Collisions.

The production of pions and kaons has been measured in 197Au+197Au collisions at beam energies from 0.6 to 1.5A GeV with the kaon spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions, whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.

Angiotensin II as a semen extender component increases retention of spermatozoa within the uterus of the heifer.

The effects of angiotensin II (Ang II) as a semen extender were studied. In the first experiment, individual ejaculates from 10 bulls were split and extended in egg yolk citrate in the absence or presence of varying concentrations of Ang II (10[-5]-10[-10] M) to a final concentration of 35 x 10(6) sperm per mL. The percentage of intact acrosomes and percentage motility were determined in all treatments for all bulls at 0 h (immediately post thaw) and after incubation for 4 h at 37 degrees C. Extension of the semen with Ang II did not affect spermatozoal viability at either time studied. In the second experiment, mixed breed virgin heifers were induced into oestrus with intramuscular injections of prostaglandin F2alpha on Days 0 and 3. Animals that stood to be mounted were paired for bilateral intracornual insemination using a 0.5-mL French straw on each side approximately 8 h later. One of the paired heifers received semen containing Ang II (10[-5] M) while the other received control semen. A 1-mL aspirate of vaginal mucus was collected at hourly intervals for 8 h after insemination. Concentration of spermatozoa was determined by haemocytometry. There was a significant reduction in cumulative semen loss into the vagina of heifers inseminated with Ang II extended semen (14.4%) compared with heifers inseminated with control semen (19.7%). This suggests that Ang II, when added to extended semen, may reduce retrograde sperm loss following insemination without affecting sperm viability.

Relationships between days post partum, observed estrus and uterine microflora in commercial dairy cows.

This study was conducted to determine relationships between the uterine microflora and reproductive characteristics of dairy cows. Uterine lumina were swabbed during estrus immediately prior to artificial insemination (A I). Swabbings were cultured for bacteria and accessed for cytologic evidence of inflammation. The time of sampling averaged 104 d post partum. Bacteria in the uterus were cultured from 65% of the cows (n = 85). The number of cows with any given microbial genus ranged from 1 to 35 and the number of different genera per cow ranged from 0 to 8. There were on significant correlations between amount and type of uterine microflora, days post partum, numbers of observed estrus, conception rate and uterine inflammation. The number of observed estrus periods was not correlated with the presence of aerobic bacteria. No significant relationships were found between microbes and uterine inflammation or conception to the A.I. service at the time of sampling. A negative correlation between uterine inflammation and conception approached significance (r=-0.24, P > 0.10). Acquisition of uterine lumen samples by the technique utilized had no effect on conception to A I service.

Embryonic loss from 30 to 60 days post breeding and the effect of palpation per rectum on pregnancy.

This study was conducted over a 12-mo period to determine the rate of bovine embryo death between 30 and 60 d of gestation. In addition, palpation per rectum as a means of pregnancy detection was evaluated as a possible cause of embryo death. Estrus was synchronized in Holstein heifers (n = 1358), weighing > or = 385 kg, with a single intramuscular injection of 25 mg prostaglandin F(2alpha). Estrus was primarily detected by the absence of paint marks on the tailhead. The heifers were artificially inseminated with semen from 5 Holstein sires. Blood was collected between 30 and 45 d after breeding, and sera were evaluated for the presence of bovine pregnancy-specific protein B (bPSPB) by RIA to determine pregnancy. Palpation for fetal membrane slip was conducted by an experienced technician in approximately one-half of the inseminated heifers. To determine embryonic survival, a second blood sample was collected at approximately 60 d from 862 heifers that were determined to be pregnant at the first blood sampling. Embryonic loss averaged 5.3% during the interval between the initial detection of pregnancy at 30 to 45 d and the subsequent detection of pregnancy at 60 d of gestation. Embryo loss in heifers that were palpated was 6.5% compared with that of 4.3% in the control heifers (X(2): P = 0.145). These findings establish that there was substantial loss of embryos between 30 and 60 d post breeding but that embryo loss was not affected by palpation per rectum.

Effect of phenylephrine, ergonovine, oxytocin and norepinephrine as an extender ingredient on viability of bovine spermatozoa.

We evaluated effects of three concentrations of phenylephrine, ergonovine, oxytocin and norepinephrine (myometrial stimulants) on viability of spermatozoa when they were included in a seminal extender. Using a split ejaculate technique, ejaculates from each of 10 bulls were extended in egg-yolk citrate to a final concentration of 35 x 10(6) sperm/ml, including 20 mg/ml, 2 mg/ml and .2 mg/ml, of phenylephrine or ergonovine, 20 IU/ml, 2 IU/ml and .2 IU/ml oxytocin or 200 micrograms/ml, 20 micrograms/ml and 2 micrograms/ml norepinephrine prior to freezing. Extended semen without a myometrial stimulant served as the control. Percentage of intact acrosomes was determined prior to freezing for all treatments. Motility and percentage of intact acrosomes were determined immediately after thawing (0 h) and again after 4 h incubation at 37 degrees C. Percentage of intact acrosomes was reduced (P less than .05) prior to freezing by phenylephrine (20 mg/ml) and ergonovine (20 mg/ml) (phenylephrine = 56%; ergonovine = 63%; control = 74%). The same doses of phenylephrine and ergonovine reduced (P less than .05) post-thaw motility and percentage of intact acrosomes at both 0 and 4 h compared with controls. Sperm exposed even to the intermediate concentration (2 mg/ml) of ergonovine had lower (P less than .05) motility 4 h post-thaw. No other compound or concentration of compound or concentration of compound affected percentage of intact acrosome or motility. There were no two or three-way bull x compound and concentration interactions (P greater than .2).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of group thawing on post-thaw viability of bovine spermatozoa packaged in .5-milliliter French straws.

The objective of this study was to determine the effects of thawing groups of 2, 5, 10, 15, or 20 .5-ml French straws on post-thaw spermatozoal viability. Thermostatically controlled and nonthermostatically controlled thawing baths were compared. Using a split-plot design, semen from 10 bulls was extended in egg yolk citrate, frozen, and then thawed (in the respective groups) at 36 degrees C in two types of thawing baths. Motility and percentage of intact acrosomes were determined immediately after thawing (0 h) and again after 4 h of incubation at the respective temperature of each thawing bath. Neither percentage of intact acrosomes nor motility was influenced by the number of straws thawed at 0 h (P greater than .05). Thawing bath had no effect (P greater than .05) on motility or percentage of intact acrosomes at 0 h. Bull variation was significant in both the 0- and 4-h evaluations. After 4 h of incubation, there was a significant (P less than .05) straw number x thawing bath interaction. When 15 or 20 straws were thawed in the thermostatically controlled bath there was a reduction (P less than .05) in motility and percentage of intact acrosomes. However, in the nonthermostatically controlled bath there was no reduction in motility and percentage of intact acrosomes as the size of straw group increased. Our results indicate that, when using a nonthermostatically controlled thawing bath, semen packaged in .5-ml straws can be thawed in groups of 20 without an effect on post-thaw sperm viability.

Influence of cornual insemination on endometrial damage and microbial flora in the bovine uterus.

The objectives were to determine effects of cornual insemination on endometrial characteristics and uterine bacterial flora. Forty cows were assigned randomly (10/group) to each of the following treatments: 1) control--no uterine manipulation; 2) uterine body insemination--deposition of the inseminate at the internal cervical os; 3) cornual insemination--one-half of inseminate deposited into each uterine horn anterior to the internal bifurcation and 4) cornual insemination plus endometrial biopsy--insemination into each uterine horn and trauma induced by endometrial biopsy. Animals were slaughtered and reproductive tracts were removed 5 d after treatment. Bacterial populations of the uterine lumen were evaluated by both flushings and swabbings of each horn. Treatment did not influence the presence of luminal bacteria as determined by flushing or swab samples. Gross endometrial characteristics were quantitated in all tracts. Characteristics considered were total endometrial surface area, discolored regions that appeared to be distinctly darker than the remaining portion of the endometrium and obvious surface damage. Discolored regions were evaluated as both total areas and percentage of endometrium. Treatment did not influence total or percent discolored areas. Microscopic evaluation of these tissues revealed increased edema when compared with nondiscolored regions but no disruption of the luminal epithelium was found. Surface damage was found only in the biopsied treatment group. Observation of the endometrium revealed that extensive regeneration occurred by 5 d after treatment. The data suggest that cornual insemination does not result in uterine trauma or bacterial presence 5 d after breeding, and the endometrium is capable of regeneration after trauma during estrus.

Influence of cooling rates and extenders upon post-thaw viability of bovine spermatozoa packaged in .25- and .5-ml French straws.

Post-thaw survival of bovine spermatozoa was compared for semen packaged in either .25- or .5-ml French straws and frozen at three different cooling rates in moving N2 vapor. Using a split ejaculate technique, nine ejaculates were extended in heated skim milk, egg yolk-citrate and egg yolk-Tris and packaged in .25- and .5-ml French straws. Semen packaged in the .25- and .5-ml straws was frozen simultaneously at initial N2 vapor temperatures of -140, -110 or -80 C. Semen was thawed in a water bath at 35 C for 1 min. Recovery of spermatozoa was evaluated immediately post-thaw (0 h) and again after 3 h of incubation at 37 C. Motility estimates and motility counts were made using phase contrast microscopy; percentage of spermatozoa possessing intact acrosomes was quantitated using differential interference contrast microscopy. There was a packaging unit X cooling rate interaction (P less than .05) for all three viability measures. However, there was no consistent trend with regard to cooling rate or packaging unit among the three extenders examined. Post-thaw viability for each characteristic varied (P less than .01) among extenders, but not for cooling rate or packaging unit (P greater than .05). Spermatozoa extended and frozen in egg yolk-Tris had greater (P less than .05) post-thaw viability than those extended in skim milk or egg yolk-citrate regardless of cooling rate or volume of the seminal package.

Influence of thawing time and post-thaw temperature on acrosomal maintenance and motility of bovine spermatozoa frozen in .5-ml French straws.

The objective was to determine the relationship between thawing time and post-thaw temperature when the final temperature of the semen was brought to 40 C. One ejaculate from each of 12 dairy bulls was packaged in .5-ml French straws. Semen in five straws from each ejaculate was thawed in a 35 c water bath for 12 s or 1 min. The straws were then immediately placed in water baths at 0, 10 or 20 C for 1 min and then transferred to a water bath at 40 C for 1 min. Control treatments were thawed at (1) 35 C for 1 min, plunged into a 35 C water bath for 1 min and transferred to a final water bath at 40 C for 1 min, and (2) thawed at 40 C for 1 min, plunged into 40 C water bath for 1 min and transferred to a final water bath at 40 C for 1 min. Semen was incubated at 40 C and evaluated at 0, 4 and 8 h of incubation for percentage of motile spermatozoa (%MOT) and percentage of spermatozoa with intact acrosomes (PIA). Semen thawed at 35 C for 12 s and held at 0 C before being warmed to 40 C sustained immediate acrosomal damage (P less than .05) due to a delay in complete thawing of the semen. Semen thawed at 35 C for 1 min, held at 0 C and then warmed to 40 C also sustained immediate acrosomal damage which was due to cold shock. Cold shock damage was greater than damage due to a delay in complete thawing, therefore, precautions should be taken to prevent post-thawing cold shock. The 10 C post-thaw treatment resulted in spermatozoal damage with both thawing times, however, the effects were latent since damage was not observed until the 4- and 8-h evaluations. The 20 C post-thaw treatment did not decrease (P greater than .05) % MOT or PIA with either thawing time.

Evaluation of American Wagyu sires for scrotal circumference by age and body weight.

Thirty-six percent of American Wagyu bulls do not meet the current minimum standards set by the Society of Theriogenology for the breeding soundness exam. In contrast, only 15% of bulls of domestic breeds do not meet the minimum standards. Scrotal circumference measurements of Wagyu are smaller than those of other breeds. The objective of this research was to describe scrotal circumference of Wagyu bulls as it relates to age and BW. The data set consisted of 190 Wagyu bulls housed at two locations. One hundred forty-one bulls constituted the first set of data (location 1); scrotal circumference was measured one to six times per bull aged between 13 and 70 mo. Ninety-four of the bulls underwent semen evaluation for motility and morphology. Forty-nine bulls constituted the data set for which scrotal circumference and BW was measured one to nine times per bull between 5 and 21 mo of age (location 2). Mean scrotal circumference of bulls within each age group was as follows: 12 to 14 mo, 29.8 0.2 cm (mean +/- SE); 15 to 17 mo, 31.8 +/- 0.2 cm; 18 to 20 mo, 32.9 +/- 0.3 cm; 21 to 24 mo, 31.8 +/- 0.5 cm; and > 24 mo, 35.5 +/- 0.2 cm. Both age and BW were highly correlated to scrotal circumference (r = 0.81 and 0.82, respectively). Within each age group, there were a percentage of bulls that did not meet the minimum standard for scrotal circumference set by the Society of Theriogenology. The percentages were as follows: 12 to 14 mo, 46%; 15 to 17 mo, 25%; 18 to 20 mo, 33%; 21 to 24 mo, 42%; and > 24 mo, 32%. Morphology and motility were > 50% each in 91% of the bulls between ages 12 and 20 mo at location 1. Based on these data, it is recommended that Wagyu bulls be evaluated with the breed-specific minimum standards for scrotal circumference of 26 cm from 12 to 14 mo, 29 cm from 15 to 17 mo, and 30 cm from 18 to 20 mo of age.

Distribution and retention of spermatozoa with acrosomal and nuclear abnormalities in the cow genital tract.

Two experiments were conducted to evaluate the fate of sperm following uterine insemination. In Exp. I, five pairs of Holstein cows were inseminated with egg yolk-Tris extended semen (approximately 1.0 X 10(9) sperm; .5 ml) from five ejaculates from a single bull that had high levels (approximately 70%) of morphologically abnormal sperm. Cows were slaughtered 12 h after insemination. The genital tracts were removed and promptly clamped into defined regions. Sperm were recovered by flushing with 2.9% sodium citrate buffer. Proportions of abnormal sperm in the various regions were compared with those in the inseminate. Sperm numbers were also determined from each region. Regions of the tract varied in number of sperm (P less than .001), proportions of knobbed acrosomes (P less than .001), tapered heads (P less than .001), protoplasmic droplets (P less than .001), tail abnormalities (P less than .029) and total abnormalities (P less than .002). A total of 63.5 +/- 6.4 X 10(6) sperm was recovered. These sperm were distributed throughout the tract as follows: vagina, 91.8%; cervix, 5.4%; uterine horns, 2.7%, and uterotubal junctions-isthmi, .04%. No sperm were recovered from ampullae. Because retrograde movement of sperm from the uterus occurred in Exp. I, we conducted Exp. II to determine the extent of sperm loss from the genital tract following insemination. Three pairs of Holstein cows were inseminated with .42 X 10(9) sperm (.5 ml; egg yolk-Tris extender) from the same bull used in Exp. I (three ejaculates). All discharged mucus and urine was collected for 12 h after insemination for recovery of sperm. Aspirates (approximately 1 ml) of mucus from the vagina were evaluated during the 12-h post-insemination period for numbers of sperm and leucocytes. Sperm were also recovered from the tract following slaughter (approximately 12 h) to determine retention. Overall, 73 +/- 3.7% of inseminated sperm were recovered. Components were: inseminate lost from the genital tract in discharged mucus, 60 +/- 4.6%; lost in urine, .06 +/- .02%; aspirated from the vagina, 4.4 +/- 1%; adhered to equipment, 1.3 +/- .3%, and retained in the genital tract, 6.5 +/- 1.6%. Predicted numbers of sperm contained in discharged mucus 2 h post-insemination were greater (P less than .009) than at subsequent hours.(ABSTRACT TRUNCATED AT 400 WORDS)

Bulls show no preference for a heifer in estrus in preference tests.

The objective of this experiment was to determine whether sexually experienced bulls would demonstrate a preference (using primarily olfaction) between a heifer in estrus and a heifer in diestrus (luteal phase) when physical contact was denied. In Exp. 1, a heifer in estrus and a heifer in diestrus (n = 18 pairs) were individually enclosed in opposite ends of a pen. During each period (n = 18), three bulls were individually introduced into the pen and allowed 5 min to demonstrate preference between the heifer in estrus and the heifer in diestrus. The total time that a bull spent within 2.5 m of either heifer was used to evaluate his preference. The total time that bulls spent adjacent to the heifer in estrus was not greater (P greater than .05) than the total time that bulls spent adjacent to the heifer in diestrus. In Exp. 2, five bulls were used and were evaluated using the same method as in Exp. 1. In addition, the number of flehmen reactions were recorded for each bull. Six heifers were ovariectomized and each heifer was induced into estrus with one of three doses of estradiol 17 beta (5, 10, and 20 mg) over the 5-wk treatment period. Estradiol 17 beta-treated heifers were always paired with a non-estradiol-treated (control) heifer. The goal of Exp. 2 was to determine whether heifers treated with pharmacological doses of estradiol 17 beta would be preferentially selected from non-estradiol-treated (control) heifers by bulls.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of cornual insemination on conception in dairy cattle.

The objective of this study was to compare conception to artificial insemination (AI) services in dairy cattle when semen was deposited into the uterine body or into both uterine horns (cornual insemination). Nine herdsman inseminators (HI) in four commercial dairy herds in Washington constituted the experimental units. Herds ranged in size from 393 cows to 964 cows. The duration of the experiment was 12 mo in three herds and 18 mo in the fourth herd. At the beginning of the experiment all inseminators were trained to deposit semen in the body of the uterus. Inseminators were instructed to use this method for 6 mo. Following employment of body deposition, the same inseminators were retrained to deposit one-half of the semen into the right uterine horn and one-half into the left uterine horn. Cornual inseminations were performed for 6 mo. A total of 4,178 services constituted the data set. Milk samples were collected from cows on the day of insemination and later were assayed for progesterone (P4). There was variation (P less than .01) in conception associated with month of insemination and insemination method (P less than .001). The monthly variation was not associated with season of the year. Least squares means for conception when semen was deposited in the uterine body was 44.7%, compared with 64.6% when cornual insemination was employed. The insemination treatment X inseminator interaction was not significant. Results suggest that cornual insemination provides an alternative to deposition of semen in the uterine body.

Influence of varying levels of blood progesterone upon estrous behavior in cattle.

The effect of four levels of progesterone on the occurrence and intensity of estrous behavior was determined in ovariectomized cows. Twelve Holsteins were bilaterally ovariectomized at least 2 mo before treatment. Progesterone (P4) was administered im two times/day for 5 d followed 72 h later with 2 mg estradiol (E2) im to induce estrous behavior. Treatments were control = oil, 100 mg P4/d, 300 mg P4/d and 500 mg P4/d. Each animal received all P4 treatments in a 4 X 4 Latin-square design. From d 2 through 6, with d 1 being the first day of P4 treatment, serum P4 concentrations averaged .3, 2.5, 6.1 and 12.3 ng/ml in treatments I to IV, respectively. Progesterone levels at the time of peak E2 (d9) were less than 1 ng/ml for treatments I, II and III and 1.8 ng/ml for treatment IV. Peak E2 levels for all groups averaged 23.9 pg/ml (12 h after E2 injection). Cows were observed continuously for 48 h after E2 injection to quantitate estrous behavior. Behavioral traits measured were: mounts initiated, mounts received, standing when mounted, chin rests initiated and chin rests received. Progesterone treatment caused a decrease in frequency of all five traits measured. As P4 levels increased, there was a linear (P less than .01) decrease in frequency of a behavioral trait. The percentage of the cows that showed each behavioral trait and mean time to first occurrence of each trait were not different after progesterone treatment, with the exception of standing behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiographic evaluation of bovine artificial inseminating technique among professional and herdsman-inseminators using .5- and .25-ml French straws.

Using radiography, inseminating syringe tip location and inseminate distribution in excised bovine reproductive tracts were described for 20 professional and 20 herdsman-inseminators using .5- and .25-ml French straws. Inseminations (20 by each participant) were performed in tracts placed on a device that stimulated the anatomical position of the reproductive organs in vivo. A computer-coupled graphics information digitizer was used to quantitate the precise location of the syringe tip and to estimate the distribution of radiopaque inseminate within the tract from each pair of radiographs. Neither category of inseminator (professional or herdsman) nor volume of inseminate (.5 vs .25 ml) influenced (P greater than .05) syringe tip placement or subsequent distribution of the radiopaque inseminate within the tract. The proportion of syringe tip placements in various anatomical locations (586 attempts) were: uterine body, 39%; cervix, 25%; left uterine lumen, 13% and right uterine lumen, 23%. The variability among inseminators was high, with the ability to position the syringe tip in the uterine body ranging from 0 to 85% of the 20 attempts. Among all inseminators, 82% were unable to place the syringe in the uterine body greater than 60% of the time. When averaged across all inseminations (n = 666), 40% of the inseminate was located in the uterine body and(or) equally distributed in the uterine lumina. The remainder of the inseminate was located in the cervix (17%) or disproportionately in one uterine lumen (43%). Syringe tip placement in the uterine body was correlated (r = .73; P less than .05) with the proportion of inseminate located in the uterine body and(or) equally distributed to the lumen of both uterine horns. Measurements of various anatomical components of the reproductive tract were made from the first radiograph. The means were: cervical diameter, 5.9 cm; length from internal cervical os to external uterine bifurcation, 16.4 cm; uterine body length, 1.7 cm and uterine body surface area, 3.6 cm2. There was no relationship between the palpable anatomical components and uterine body size.

The influence of the stage of the estrous cycle and novel cows upon mounting activity of dairy cattle.

The objectives of this study were to determine directly if mounting activity in dairy cattle varied as a function of stage of the estrous cycle and to determine if mounting by cows could be stimulated when novel estrous cows were introduced. Detector cows were normally cycling. Estrous cows were ovariectomized and injected with estradiol cyprionate and progesterone to induce standing estrous behavior. Familiar estrous cows (prior exposure to detector cows) and novel estrous cows (no prior exposure to detector cows) encountered each detector cow (n = 19) in a one-on-one manner for a 10-min period. Mounting activity by detector cows was determined by observation on d 5, 10, 15, day of estrus and d 5 of the subsequent cycle (52). The first d 5 was considered an acclimation day and was deleted from the data because all estrous cows (n = 4) used were novel. These novel estrous cows then became familiar estrous cows on the subsequent days (10, 15, estrus, 52). On these days, familiar (n = 4) and novel (n = 2) estrous cows encountered individually each detector cow in a prearranged sequence. Stage of the estrous cycle influenced (P less than .001) the frequency of mounting by detector cows. Mounting activity of detector cows was inversely related (r = -.64, P less than .001) to concentrations of plasma progesterone. The introduction of novel estrous cows tended to stimulate (P = .07) mounting when all days were considered. In addition, the introduction of novel estrous cows stimulated (P less than .001) mounting on d 15 and 52. A second experiment was conducted to determine if the introduction of novel estrous cows stimulated mounting in the detector cows on the day of estrus if a longer encounter time (30 min) was used. A total of eight detector cows and eight estrous cows (four familiar and four novel) were used. When the detector cow was in standing estrus, she encountered one-on-one each of two familiar estrous cows and each of two novel estrous cows in a prearranged sequence for 30-min. The introduction of novel estrous cows stimulated (P = .001) mounting by the detector cows on the day of estrus (6.50 +/- .48 vs. 4.37 +/- .48 mounts for N and F cows, respectively). We conclude that mounting activity is reduced during midcycle and that the introduction of novel cows stimulated mounting activity on d 15, day of estrus and on d 5 of the estrous cycle.