The evaluation of corpus luteum blood flow using color-flow Doppler ultrasound for early pregnancy diagnosis in bovine embryo recipients.

The objective of this experiment was to evaluate corpus luteum blood flow (CLBF) as an early indicator of pregnancy status in bovine embryo recipients. Fifty crossbred beef cows were submitted to embryo transfer on Day 7 after estrus. On Days 7, 11, 13, 15, 17, 19, 21, 26, 33, and 40, a blood sample was taken, the CL examined using a color-flow Doppler ultrasound scanner, and video was recorded of each scanning session. Ultrasound data were grouped by the first day progesterone concentrations were <1 ng/mL (indicating early embryo loss, EEL) through Day 21 (EEL-17, n=3; EEL-19, n=9; EEL-21, n=3), absence of an embryo on Days 26, 33, or 40 (late embryo loss; LEL; n=12), or remained pregnant (P; n=23). The first decrease in CLBF of EEL-17, EEL-19, and EEL-21 cows compared to P cows occurred on Days 17, 19, and 21, respectively (P<0.05). There was no difference in CLBF between LEL and P cows on Days 17, 19, and 21. Six evaluators diagnosed pregnancy from randomized video clips on Days 17, 19, and 21. Evaluators made more (P<0.004) correct diagnoses on Day 19 than Day 17. Sensitivity (82.9+/-10.1%) was not affected by day. From Days 17 to 19, diagnostic specificity increased (P=0.046) from 43.2+/-3.0 to 54.3+/-3.0% but remained unchanged thereafter. Due to low specificity and sensitivity, evaluation of CLBF alone was insufficient for early pregnancy diagnosis.

Effect of a CIDR insert and flunixin meglumine, administered at the time of embryo transfer, on pregnancy rate and resynchronization of estrus in beef cattle.

The objectives of this study were to evaluate the effects of flunixin meglumine (FM), an inhibitor of PGF(2alpha) synthesis, and insertion of an intravaginal progesterone-releasing device (CIDR), on pregnancy rates in beef cattle embryo transfer (ET) recipients, and to examine the effect of a CIDR after embryo transfer on the synchrony of the return to estrus in non-pregnant recipients. Cows (n=622) and heifers (n=90) at three locations were assigned randomly to one of four groups in a 2x2 factorial arrangement of treatments with FM administration (500 mg i.m.) 2-12 min prior to ET, and insertion of a CIDR (1.38 g progesterone) immediately following ET as main effects. Fresh or frozen embryos (Stage=4 or 5; Grade=1 or 2) were transferred on Days 6-9 of the estrous cycle and CIDR devices were removed 13 days after ET. Recipients at Location 2 only were observed for signs of return to estrus. Recipients that returned to estrus at Location 2 were either bred by AI or received an embryo 7 days after estrus. Following the initial ET, there was an FMxlocation interaction on pregnancy rate (P<0.01; Location 1, 89% versus 57%; Location 2, 69% versus 64%; Location 3, 64% versus 67% for FM versus no FM, respectively). Pregnancy rates of embryo recipients were not affected by CIDR administration (P>0.05; 65% with CIDR, 70% without CIDR), however, the timing of the return to estrus was more synchronous (P<0.01) for recipients given a CIDR. Pregnancy rate of recipients bred following a return to estrus did not differ between cows receiving or not receiving a CIDR for resynchronization (P>0.13). Effects of FM on pregnancy rate were location dependent and CIDR insertion at ET improved synchrony of the return to estrus.

Cell interactions in initiation of mammary epithelial proliferation by oestradiol and progesterone in prepubertal heifers.

The acute temporal effects of exogenous oestradiol (0.1 mg/kg per day), progesterone (0.25 mg/kg per day) or both together on the proliferative response of epithelial cells, fibroblasts, adipocytes and endothelial cells in the mammary tissue of prepubertal cross-bred heifers were determined. Mammary biopsies were taken immediately before, then 24, 48 and 96 h after the initiation of daily administration of hormones to three heifers per treatment group. Incorporation of [3H]thymidine into explants prepared from biopsies was evaluated after a 1-h incubation by measuring trichloroacetic acid (TCA)-insoluble radioactivity in explant homogenates as well as by quantitative histoautoradiography. Incorporation expressed as d.p.m./mg tissue or d.p.m./microgram DNA was increased (P < or = 0.05) approximately 11-fold by 96 h in oestradiol-treated heifers. Progesterone-treated animals were unresponsive and heifers treated with both hormones were intermediate in response compared with oestradiol-treated heifers. Autoradiographic data for ductal or terminal duct epithelial cells showed similar dramatic increases in labelling by 24 h with further increased (P < 0.01) labelling by 96 h (5.1% vs 0.1%) in heifers given oestradiol. As with incorporation, tissue from progesterone-treated heifers showed no time or treatment response compared with pretreatment biopsies and tissue from heifers given both showed intermediate responses, i.e. significantly increased labelling by 96 h compared with pretreatment (P < or = 0.05) but less labelling (P < 0.05) than oestradiol-treated heifers. A proliferative response of epithelial cells in oestradiol-treated heifers occurred prior to the response of fibroblasts adjacent to epithelial cells (< or = 50 microns).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of disclosure of traumatic events on illness behavior among psychiatric prison inmates.

To assess the health effects of writing about traumatic events in a clinical population, 98 psychiatric prison inmates were randomly assigned to 1 of 3 conditions in which they were asked to write about their deepest thoughts and feelings surrounding upsetting experiences (trauma writing condition), write about trivial topics (trivial writing control), or go about their daily routine without writing (no-writing control). Both writing groups wrote for 20 min per day for 3 consecutive days. Participants in the trauma condition reported experiencing more physical symptoms subsequent to the intervention relative to those in the other conditions. Despite this, controlling for prewriting infirmary visits, sex offenders in the trauma writing condition decreased their postwriting infirmary visits. These results are congruent with predictions based on stigmatization and inhibition.

Application of knowledge about corpus luteum function in control of estrus and ovulation in cattle.

Understanding corpus luteum (CL) function has led to development of methods of estrus synchronization in cattle that either extend the estrous cycle by administration of exogenous progestins or shorten the cycle by induction of luteolysis. Both methods have limitations, which have been reduced or overcome through sequential or combined treatment with progestin and luteolytic drugs. Future improvements in estrus synchronization methodology are most likely to come from achieving more synchrony between the development of a highly fertile ovulatory follicle and control of luteal function.

Isolation of a population of intact, highly-motile porcine spermatozoa using a discontinuous bovine serum albumin gradient.

This study was conducted to determine the efficacy of isolating intact, highly-motile porcine spermatozoa using a discontinuous bovine serum albumin (BSA) gradient. Either 0.25, 0.5, 1, 2.5 or 5x10(9) spermatozoa extended to 26 ml with Kiev extender were layered on a discontinuous BSA gradient (4% BSA over 10% BSA) contained within a 500-ml separatory funnel. After 1 h of sperm migration at 23 degrees C, four 30-ml aliquots designated Fractions 1, 2, 3, 4 and Fraction T were collected from the bottom of the funnel. Fraction 4 was the bottom fraction and Fraction T was the remnant of the applied sample. For all concentrations of applied spermatozoa, the percentage of progressively motile spermatozoa was greater in Fraction 4 than in Fractions T or 1 (P<0.05). Fraction 4 contained a greater (P<0.05) proportion of spermatozoa with normal apical ridge acrosomes than Fraction T. Regardless of the concentration of spermatozoa applied, Fraction 4 contained more than 90% of progressively motile spermatozoa and spermatozoa possessing normal apical ridge acrosomes. The percentage of applied cells recovered in Fraction 4 decreased as the concentration of spermatozoa applied to the gradient increased.

Reproductive responses of beef heifers after concurrent administration of vaccines, anthelmintic and progestogen.

A study was conducted to determine whether concurrent administration of vaccines for reproductive diseases and an anthelmintic, given immediately prior to estrus synchronization with a progestogen, would affect subsequent estrous response and fertility in beef heifers. Two hundred ninety-five yearling crossbred beef heifers on 3 ranches in Oregon and Kansas were assigned to 1 of 2 treatments. Control heifers were vaccinated and dewormed 30 d prior to the anticipated breeding. Treated heifers received the same vaccination and deworming products 9 d prior to breeding. All heifers in both groups were treated with norgestomet (Syncro-Mate-B) for 9 d to synchronize estrus. The administered vaccine consisted of modified live virus for infectious bovine rhinotracheitis, parainfluenza and bovine viral diarrhea, with 5-way bacterin for leptospirosis and bacterin for vibriosis. Heifers were also administered ivermectin or fenbendazole for deworming. Heifers exhibiting synchronized estrus were artificially inseminated and subsequently exposed to fertile bulls. Pregnancy status was determined at a later date by palpation per rectum. Vaccination and deworming at the time of treatment with progestogen compared with immunizing and deworming 30 d prior to breeding did not impair the expression of behavioral estrus. The percentage of treated heifers conceiving to AI or natural service did not differ from that of the respective control heifers. These data suggest that vaccination, deworming and synchronization of estrus with norgestomet can be performed simultaneously without any detrimental effects upon occurrence of behavioral estrus or fertility.

Estrus synchronization and pregnancy rates in cyclic and noncyclic beef cows and heifers treated with syncro-mate B or Norgestomet and Alfaprostol.

Postpartum lactating cows (N=118) and virgin heifers (N=60) were treated with subcutaneous Norgestomet implants for nine days and received either an intramuscular injection (im) of 5 mg estradiol valerate and 3 mg Norgestomet at the time of implant insertion or an im injection of 5 mg Alfaprostol 24 hr before implant removal. Animals were artificially inseminated 12 hr after detection of estrus. Of the cows and heifers, 78% and 88%, respectively, were in estrus within five days after implant removal (P<0.09). There was no difference between treatments in the proportion of animals in estrus or in the timing of estrus (P<0.85). Estrus was detected in a greater (P<0.05) proportion of animals that were cyclic prior to treatment (88%) than among those that were anestrous prior to treatment (77%). Pregnancy rates after five days were similar between heifers that were cyclic (42%) or anestrous (47%) prior to treatment; however, the five-day pregnancy rate in cows that were anestrous prior to treatment was 38% lower than that in cows that were cyclic prior to treatment (17 vs 55%, P<0.01). Although the treatments synchronized or induced estrus in both cyclic and anestrous animals, marked variability in estrous response and fertility among previously cyclic or anestrous postpartum cows limited the effectiveness of the treatments.

Effects of varying the holding temperature and interval from collection to freezing on post-thaw development of bovine embryos in vitro.

The objective of this study was to evaluate the in vitro development of frozen-thawed bovine embryos held at room temperature or refrigerated for 2, 6 or 12 h prior to freezing. After recovery, embryos were randomly assigned to be placed in holding media for 2 h (n=131), 6 h (n=136) or 12h (n=133) prior to freezing. Approximately one-half of the embryos were refrigerated (5 degrees C; n=203) while the remaining half were held at room temperature (22 degrees C; n = 197) until freezing. Embryos were frozen in 10% ethylene glycol and stored in liquid nitrogen. After thawing, embryos were cultured for 72 h in Ham's F-10 media supplemented with 4% fetal bovine serum. Embryos were evaluated for quality and stage of development prior to freezing and after culture. At the end of culture, it was determined if each embryo had developed beyond the stage recorded prior to freezing and if the embryo had hatched from the zona pellucida. The percentage of embryos that developed during culture was greater (P < 0.001) for Grade 1 (81%) than for either Grade 2 (65%) or Grade 3 (48%) embryos. Likewise, a greater proportion (P < 0.001) of Grade 1 embryos developed to hatched blastocysts (60%) than either Grade 2 (40%) or Grade 3 (24%) embryos. The holding temperature from collection to freezing did not influence embryo development, regardless of the interval from embryo collection to freezing. The proportion of embryos that developed to expanded blastocysts and hatched was greater (P < 0.005) for embryos held 2 h prior to freezing (64%) than for embryos held for 12 h (33%). Hatching rate of embryos held 6 h prior to freezing (54%) tended (P < 0.08) to be lower than the hatching percentage for embryos held for 2 h. Thus, post-thaw embryonic development was impaired the longer embryos were held prior to freezing and temperature during the interval from collection to freezing did not affect post-thaw development.

Prostaglandin F(2alpha) and naloxone therapy in the anestrous postpartum beef cow.

Three experiments were conducted, using multiparous crossbred beef cows, to test the ability of exogenous prostaglandin F(2alpha) (PGF) and/or naloxone to reduce the duration of the postpartum interval to estrus and to improve subsequent reproductive performance. In each experiment, postpartum cows were assigned to treatments by calving date. In Experiment 1, cows (n=44) were assigned to 1 of 4 treatment groups: 1) control, 2) PGF on Day 25 post partum, 3) 400 mg naloxone (3 doses) at 12-h intervals on Day 30 post partum, and 4) PGF on Day 25 followed by 3 400-mg doses naloxone at 12-h intervals on Day 30 post partum. In Experiment 2, cows (n=126) were assigned either to 1) control or 2) PGF on Day 30 post partum In Experiment 3, cows (n=67) were again assigned to 1 of 4 treatments 1) control, 2) PGF on Day 30 post partum, 3) PGF on Day 40 post partum, and 4) PGF on Day 30 and 40 post partum. Serum progesterone was used to determine the postpartum interval to estrus in Experiments 1 and 3. In all 3 experiments, serum progesterone was used to determine the proportion of cows that had reestablished estrous cycles at the start of breeding. Pregnancy rate and calving interval were analyzed for all trials. Naloxone had no effect (P > 0.20) on any reproductive variable measured. The postpartum interval to estrus was similar (P > 0.30) for PGF-treated and control cows in Experiments 1 and 3. The proportion of cows cycling at the start of breeding and the calving interval were not affected (P > 0.20) by PGF treatment in any of the experiments. Only the administration of PGF on Day 40 post partum in Experiment 3 improved (P=0.04) the subsequent pregnancy rate. Analysis of data pooled across experiments showed that the pregnancy rate was higher (P=0.03) for cows treated with PGF than for control cows (91.4 and 72.9%, respectively). It was concluded that administration of PGF during the early postpartum period improves subsequent reproductive function in beef cows.

Evaluating recipient and embryo factors that affect pregnancy rates of embryo transfer in beef cattle.

The objectives of this experiment were to determine the effects of corpus luteum characteristics, progesterone concentration, donor-recipient synchrony, embryo quality, type, and developmental stage on pregnancy rates after embryo transfer. We synchronized 763 potential recipients for estrus using one of two synchronization protocols: two doses of PGF2alpha (25 mg i.m.) given 11 d apart (Location 1); and, a single norgestomet implant for 7 d with one dose of PGF2alpha (25 mg i.m.) 24 h before implant removal (Location 2). At embryo transfer, ovaries were examined by rectal palpation and ultrasonography. Of the 526 recipients presented for embryo transfer, 122 received a fresh embryo and 326 received a frozen embryo. Pregnancy rates were greater (P < 0.05) with fresh embryos (83%) than frozen-thawed embryos (69%). Pregnancy rates were not affected by embryo grade, embryo stage, donor-recipient synchrony, or the palpated integrity of the CL. Corpus luteum diameter and luteal tissue volume increased as days post-estrus for the recipients increased. However, pregnancy rates did not differ among recipients receiving embryos 6.5 to 8.5 days after estrus (P > 0.1). There was a significant, positive simple correlation between CL diameter or luteal tissue volume and plasma progesterone concentration (r = 0.15, P < 0.01 and r = 0.18, P < 0.01, respectively). There were no significant differences in mean CL diameter, luteal volume or plasma progesterone concentration among recipients that did or did not become pregnant after embryo transfer. We conclude that suitability of a potential embryo transfer recipient is determined by observed estrus and a palpable corpus luteum, regardless of size or quality.

Effects of once- versus twice-weekly transvaginal follicular aspiration on bovine oocyte recovery and embryo development.

Ultrasound-guided transvaginal follicular aspiration combined with in vitro maturation/in vitro fertilization (IVM/IVF) and culture was used to obtain bovine preimplantation stage embryos. Evaluated were the effects of aspiration frequency on oocyte recovery and embryo development following IVM/IVF. In Experiment 1, transvaginal follicular aspiration was performed once (n=5) or twice (n=5) weekly in multiparous Angus cows with the aid of a transvaginal sector transducer (5-MHz). In Experiment 2, aspiration was performed on Angus cows once weekly (n=6), twice weekly (n=4), or twice weekly after treatment with FSH (15 mg; n=4). Follicles (>2 mm) were punctured using a 55-cm needle (17g), and oocytes were aspirated through the needle and silastic tubing (2 m) by vacuum suction (75 mmHg). The oocytes were examined for morphology and were in vitro matured and fertilized. Following IVF, all ova were co-cultured in vitro for 7 d on Buffalo Rat liver cells. Oocyte recovery rates per aspïration session in Experiment 1 were not different between groups aspirated once or twice weekly (6.8+/-2.0 vs 6.3+/-1.1 oocytes/session; x+/-SEM) or in Experiment 2 between groups aspirated once, twice, or twice plus FSH treatment (7.7+/-1.8 vs 9.5+/-1.1 vs 6.2+/-1.1; P>0.10). In vitro development to the blastocyst stage was not different between the once, twice or twice-weekly aspiration plus FSH treatments or control oocytes obtained from cows at slaughter (23.1 vs 26.1 vs 18.0 vs 27.9%; P>0.10). Oocytes from the twice-weekly and twice-weekly plus FSH aspiration groups generated a higher percentage of Grade-1 quality embryos than the once-weekly group (P<0.05). In commercial bovine oocyte aspiration, more transferable embryos can be generated from twice-weekly aspirations than from once-weekly aspiration.

Reproductive performance of postpartum beef cows after short-term calf separation and dietary energy and protein supplementation.

Beef cows (n = 294) calving between November and April in six states were used to evaluate the effects of postpartum diet and calf separation on body weight, body condition score (BCS), reproductive performance, and weaning weight of calves. In each state, half of the 48 cows that calved during 60 d were group fed an additional 4.5 kg of a 20% crude protein supplement daily for 28 d starting an average of 30 d post partum (flush). Calves were separated from half of the flush and half of the nonflush cows for 48 h at 14 and 28 d after the beginning of flush. Progesterone was quantified in plasma samples obtained weekly during a 56-d breeding period to assess ovarian luteal activity. The breeding period started at the first calf separation. BCS ranged from 3.3 to 5.6 among states (on a scale of 1 to 9) at the start of the flush but was similar for treatments within a state. There was a state x flush (P < 0.008) effect on body weight at the end of the flush period. Weaning weights were influenced by state x separation x flush (P < 0.06) and were greatest for flush nonseparated calves in five of six states. There were state x flush (P < 0.08) and separation (P < 0.04) effects on ovarian luteal activity at the start of the breeding period. Flush and separation tended to increase ovarian luteal activity. During the breeding period, ovarian luteal activity was influenced only by state but there was a state x separation x flush effect (P < 0.001) on the number of weeks post partum to onset of ovarian luteal activity. Conception rate and days postpartum to conception were not influenced by either separation or flush but were affected by state (P < 0.001). These data indicate that flushing may increase weaning weights of calves and calf separation may hasten the onset of postpartum ovarian luteal activity, but conception rate and days postpartum to conception for cows in thin to moderate body condition were not influenced by the calf separation or flushing treatments.

Synchronization of estrus in postpartum beef cows with melengestrol acetate and prostaglandin F2 alpha.

At the beginning of the breeding season, most beef herds consist of a population of cyclic and anestrous postpartum cows. To be most effective and economical, an estrous synchronization method for postpartum beef cows must be capable of synchronizing estrus in cyclic cows and inducing estrus in anestrous cows. In the first of two experiments, the combination of melengestrol acetate (MGA) fed for 9 d and prostaglandin F2 alpha (PGF2 alpha) administered on the last day of MGA feeding synchronized estrus in cyclic cows (94%) and induced estrus in anestrous cows (66%) as effectively as combining PGF2 alpha with a progestin implant (97 and 75%, respectively). In the second experiment, MGA treatment was necessary for 7 d prior to administering PGF2 alpha to maximize the expression of estrus in cyclic and anestrous cows. In both experiments the proportion of cows exhibiting a synchronized estrus and the pregnancy rates tended to be higher for cows that were cyclic prior to treatment. However, the MGA-PGF2 alpha treatments consistently induced estrus in more than 50% of the anestrous cows and approximately one-third of the cows that were anestrous prior to treatment conceived during the synchronized breeding period. The MGA-PGF2 alpha treatment was 33 to 46% less expensive than a comparable estrous synchronization method that is approved by the U.S. Food and Drug Administration. If feeding MGA and administering PGF2 alpha is approved, it may be the treatment of choice for synchronizing estrus in cyclic cows and inducing estrus in anestrous cows when supplemental feeding is feasible.

Relationship between milk expected progeny differences of polled Hereford sires and actual milk production of their crossbred daughters.

One hundred sixteen spring-calving Polled Hereford x Angus cows were milked using milking machines after receiving 20 IU of oxytocin. Sires of the cows had been divergently selected on yearling weight (YW) and total maternal (MAT) EPD to form four groups: high YW, high MAT EPD; high YW, low MAT EPD; low YW, high MAT EPD; and low YW, low MAT EPD. Average milk production after 12-h calf separation was 3.7 +/- 1.3 kg. Actual milk production of cows was regressed on their sires' milk EPD, where the milk EPD estimates the additive maternal genetic contribution of a sire to the weaning weight of his daughters' calves. The regression of actual 12-h milk production on sire milk EPD was .038 +/- .014 kg/kg, and the correlation was .26 (P less than .006), close to its expected value, based on the accuracy of the prediction, heritability of the trait, and the relationship between sire and daughter. Extension of results of a single milking to an entire lactation is difficult, but over the range of sire milk EPD sampled (-10 to 16 kg), the range in daughters' milk production predicted from the regression analysis was 27% of the mean actual milk production, corresponding to an increase of about 1% more milk per kilogram of milk EPD.

Luteotropic effects of bovine blastocysts.

A series of experiments was conducted to determine whether 18-day bovine blastocysts could stimulate synthesis of progesterone by dispersed bovine luteal cells in vitro. Both blastocyst homogenates and extracts of blastocyst homogenates were luteotropic. The luteotropic activity of the blastocysts appeared to be due to one or more heat-labile substances with a molecular weight of less than 12,000 daltons.

Effects of ewe breed and ram exposure on estrous behavior in May and June.

Two groups of purebred ewes (A and B), each consisting of 25 Dorsets and 25 Hampshires, were used to study effects of ewe breed and ram exposure on ovulation and estrus in May and June. Ewes lambed in January and February and were isolated from mature rams for at least 5 mo. From May 8 to June 11 (Period 1), Group A ewes were penned with vasectomized rams fitted with marking harnesses and Group B ewes were isolated from rams. From June 11 to July 13 (Period 2), rams were placed with Group B ewes and Group A ewes were isolated from rams. Ovulation was monitored by biweekly serum progesterone assays and crayon marks were used to detect estrus. For Group A ewes in Period 1, more Dorsets ovulated (96%) than did Hampshires (72%), and of ewes that ovulated, more Dorsets mated (83 vs 28%). Fifty-five percent of Dorsets, but only 20% of Hampshires, appeared to have been spontaneously cycling at the start of the experiment. Of ewes mated in Period 1, more Dorsets than Hampshires continued to cycle during Period 2 (65 vs 0%). For Group B ewes in Period 1, 44% of Dorsets, but only 8% of Hampshires, ovulated in the absence of rams. In Period 2, 92% of Dorsets and 84% of Hampshires ovulated. Of ewes that ovulated, more Dorset ewes mated (78 vs 52%). Of ewes that mated, more Dorsets appeared to be cycling spontaneously at ram introduction (39 vs 0%). Throughout the study, 24% of Dorsets, but no Hampshires, cycled continuously.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex ratio after insemination of bovine spermatozoa isolated using a bovine serum albumin gradient.

This experiment was undertaken to determine if a method reported to successfully enrich the proportion of Y-chromosome-bearing spermatozoa in human semen could be adapted for separation of bovine spermatozoa. Semen was collected from four Angus bulls and aliquots were either separated on discontinuous gradients of bovine serum albumin (BSA) or untreated before processing for cryopreservation. Two hundred seventy-one cows or heifers were assigned randomly to be artificially inseminated (20 X 10(6) sperm/insemination) with separated or unseparated spermatozoa. The proportions of male offspring were 45 and 54% after inseminations with separated or unseparated spermatozoa, respectively. In a second phase of the experiment, pooled semen from three Holstein bulls was either extended and frozen without separation or frozen after separation using the discontinuous BSA gradient. Separated and unseparated spermatozoa were analyzed by flow cytometry to determine the ratio of X- and Y-chromosome-bearing spermatozoa based on differences in DNA content. The ratios of X- and Y-bearing spermatozoa in separated or unseparated samples were indistinguishable. We concluded that the separation method did not enrich the proportion of Y-bearing bovine spermatozoa.

The use of ultrasound in monitoring reproductive physiology of beef cattle.

Real-time, B-mode ultrasonography provides the opportunity to improve the methods of evaluation of ovarian function and diagnoses of pregnancy in beef cattle. Determination of the sex of a fetus early in pregnancy (d 55 to 85) and verification of embryo viability by monitoring fetal heartbeat are unique methods involving ultrasound scanning. These techniques and a method for evaluating the technique of artificial insemination can be used to improve reproductive management of cattle. The way in which ultrasound technology may have its greatest impact is as a tool for improving on the method of palpation per rectum for monitoring ovarian function and pregnancy in beef cows and heifers. Determination of fetal sex and monitoring embryo mortality are less likely to be applied regularly in herd management, but these procedures will be valuable in conducting research in reproductive physiology of beef cattle.

The effects of varying the interval from follicular wave emergence to progestin withdrawal on follicular dynamics and the synchrony of estrus in beef cattle.

The objective of this experiment was to examine the effects of varying the interval from follicular wave emergence to progestin (controlled internal drug-releasing insert, CIDR) withdrawal on follicular dynamics and the synchrony of estrus. A secondary objective was to assess the effects of causing the dominant follicle (DF) to develop in the presence or absence of a corpus luteum (CL) on follicular dynamics and the synchrony of estrus and ovulation. The experiment was designed as a 2 x 2 x 2 factorial arrangement of treatments with injection of GnRH or estradiol-17 beta and progesterone (E2 + P4) at treatment initiation, duration of CIDR treatment, and injection of PG (prostaglandin F2 alpha) or saline at the time of CIDR insertion as main effects. Estrous cycles (n = 49) in Angus cows were synchronized, and treatments commenced on d 6 to 8 of the estrous cycle. Cows were randomly assigned to receive a CIDR containing 1.9 g of P4 for 7 or 9 d. Approximately half the cows from each CIDR group received either GnRH (100 micrograms) or E2 + P4 (1 mg of E2 + 100 mg of P4) at CIDR insertion. Cows in GnRH or E2 + P4 groups were divided into those that received PG (37.5 mg) or saline at CIDR insertion. All cows received PG (25 mg) 1 d before CIDR removal. Daily ovarian events were monitored via ultrasound. The intervals from GnRH or E2 + P4 treatment to follicular wave emergence were 1.4 and 3.3 d, respectively (P < 0.05). The interval from follicular wave emergence to CIDR removal was longer (P < 0.05) for cows treated with GnRH (6.6 d) than those treated with E2 + P4 (4.7 d) and longer (P < 0.05) for those fitted with a CIDR for 9 d (6.5 d) than those with a CIDR in place for 7 d (4.8 d). Cows treated with PG or GnRH at CIDR insertion had a larger (P < 0.05) DF at CIDR removal than those treated with saline or E2 + P4. Treatment with a CIDR for 9 d also resulted in a larger (P < 0.07) DF at CIDR removal compared with cows fitted with a CIDR for 7 d. The interval from CIDR removal to estrus was shorter (P < 0.05) in cows treated with PG than those treated with saline. The synchrony of estrus and ovulation was not affected by any of the treatments (P > 0.05). Altering the interval from follicular wave emergence to progestin removal or creating different luteal environments in which the DF developed caused differences in the size of the DF at CIDR removal and the timing of the onset of estrus, but it did not affect the synchrony of estrus or ovulation.