The effect of PGF-2 alpha on reproductive performance of naturally bred dairy cows with or without pyometra

Five hundred thirty-four naturally bred Holstein dairy cows from two Colorado dairies were examined $\text{per}$$\text{rectum}$ between 21 and 36 days after calving. Alternate cows in each herd received either 25 mg PGF-2 alpha or no treatment at the time of initial examination. No differences were found in days open or pregnancy rates between groups (P>0.25).Days open in 23 cows with pyometra were 98.7 ± 9.4, and 77.0 ± 2.2 in 493 herdmates without pyometra. The large inequalities in numbers precluded valid statistical comparisons between these groups. No overall difference (P>0.25) in reproductive performance was found in cows with pyometra treated at the initial examination compared to those not treated until two to four weeks after the initial examination. Contributing to the lack of significance were a number of cows with pyometra that had spontaneous cures before treatment was considered. Untreated cows that recovered spontaneously had better (P<0.05) reproductive performance than herdmates that required later treatments to initiate uterine evacuation. No overall advantage in reproductive performance was obtained by the routine treatment of postpartum dairy cows with PGF-2 alpha but treatment of cows with pyometra should not be delayed.     

Effect of Dermatophiluscongolensis infection on reproductive performance of dairy cattle

The effect of $\text{Dermatophilus}$$\text{congolensis}$ on reproductive performance and milk production of dairy cattle was investigated using a prospective cohort study design. The following results were obtained: the calving to conception interval was 122 vs 104 days (P<0.05) for cows with lesions (cases) and those without lesions (non-cases), respectively; the 180-day pregnancy rate was 70.3% vs 84.3% (P<0.02) for cases and non-cases, respectively; the interval to first service was 69 days for cases and 64 days for non-cases (P<0.05) and the interval from first to second service was 32.7 days for cases and 49.4 days (P<0.01) for non-cases. The prevalence of cows with lesions was 33% ($\text{66}\text{200}$). Lesions were most commonly found on the skin covering the coccygeal and sacral vertebrae and the gluteal muscles. White skin had a greater prevalence of lesions than did black skin (P<0.05).     

Effect of monensin and suckling on the GnRH induced luteinizing hormone surge and the effect of monensin on the postpartum interval in Brangus cows

Twenty-seven fall calving Brangus cows were randomly allotted to one of four treatment groups: nonsuckled monensin (NSM), suckled monensin (SM), nonsuckled control (NSC), and suckled control (SC). Cows were group fed 1.82 kg/hd/day concentrate and Coastal bermuda grass hay $\text{ad}$$\text{libitum}$. Monensin cows received 200 mg monensin/hd/day in the concentrate. At 0800 hr on day 21 postcalving, the calves were separated from the cows. Suckled monensin and SC cows were allowed to suckle their calves for 30 min at 6-hr intervals. Nonsuckled monensin and NSC cows were not suckled. Calves were given free access to the cows after 1400 hr on day 22 postpartum. At 0800 hr on day 22 postpartum, a blood sample was collected. A 100 μg GnRH challenge was administered IM at 0801 hr. Blood samples were collected at 15-min intervals for 6 hr postinjection. Changes in body weight and body condition from day 21 postpartum to the day of first estrus were not different (P>0.10) by dietary treatment. Monensin cows consumed 10.7% less hay than did the control cows. Serum luteinizing hormone (LH) following GnRH was greater (P<0.005) in suckled than nonsuckled cows. Control cows released more (P<0.005) LH in response to GnRH than did the monensin cows. The postpartum interval (to first estrus) for the monensin cows (92.4±14.7 days) was shorter (P<0.025) than the controls (138.5±9.5 days). A greater proportion (P<0.005) of the monensin cows (8 of 14) exhibited estrus by 90 days postpartum compared to the control cows (0 of 13). Monensin and suckling appear to exert independent and agonistic influences on pituitary function in the postpartum beef cow.     

Elective termination of pregnancy in cattle by manual abortion

Abortion was induced in 91 cows and heifers by three manual methods applied $\text{per}$$\text{rectum}$. The three methods were: (1) rupture of the amnion and crushing of the fetus in cows pregnant 35 to 66 days, (2) decapitation of the fetus in cows 66 to 120 days into gestation, and (3) rupture of the amnion without crushing the fetus in cows pregnant less than 70 days. All the cows aborted between 10 and 54 days after treatment except three out of the 29 in the group in which the amnion was ruptured but the fetus not crushed. The mean interval (21.5 days) from treatment to abortion was shorter (P ～-.07) when fetal decapitation was done between 70 and 120 days of gestation compared to the interval (26.5 days) when the amnion was ruptured and the fetus crushed between 35 and 66 days of gestation. The average interval from treatment to estrus with amnion rupture was 38 days; with fetal decapitation it was 32 days (P>.10). After abortion, estrus occurred in an average of 15 days in the amnion rupture group and in 12 days in the fetal decapitation group (P>.10).     

Reproductive responses of beef heifers and cows to exogenous progesterone administered in silastic coils,oestradiol benzoate and pregnant mare serum gonadotropin

The aim of this study was to investigate a Progesterone Releasing Intravaginal Device, Oestradiol benzoate and PMSG combined treatment in 81 suckling charolais cows and 56 heifers of various breeds. The former were young primiparous cows aged 2 years and treated at a means of 43 days postpartum. Most of the heifers ($\text{44}\text{56}$) were not cycling and were believed to be prepuberal.In non-cycling females, the treatment induced ovulation in 98.5% of the cows and 78 to 100% of the heifers according to breed. In those females in which ovulation was induced, pregnancy rates determined by rectal palpation were 46.9% for the cows and 66.7% for the heifers. When taking into account all treated females including those with lost Progesterone Releasing Intravaginal Devices (5.8%) and those not ovulating, the pregnancy rates determined by rectal palpation 3 to 5 months after artificial insemination were 40.7% for the cows and 52% for the heifers.     

Effect of monensin on postpartum interval to first estrus and serum LH response to 0, 1, 2 or 4 mg estradiol-17β at 21 days postpartum

A 2×4 factorial design was used to evaluate the effects of monensin (0 vs 200 mg) and estradiol-17β (E2) dose (0, 1, 2 vs 4 mg) on postpartum interval (PPI) to first estrus and on serum LH release at 21 days postpartum. Forty-eight spring calving Brangus cows were randomly stratified by calving date and sex of calf into two feeding groups within 24 hr of calving. Each group received 2.7 kg/head/day of a milo:cottonseed meal (4:1) mixture containing either 0 or 200 mg monensin. Coastal bermuda grass hay and water were available $\text{ad}$$\text{libitum}$. During the period of E2 treatment and bi-hourly blood sampling, suckling was controlled at 6-hr intervals.Mean cow weight and body condition score within cell changed less than 23 kg and 0.5 points, respectively, from day 1 to day 21 postpartum and were unaffected by treatment (P>0.10). PPI was reduced (P<0.01) and proportion of cows exhibiting estrual behavior by 85 days postpartum was increased (P<0.05) by treatment with 200 mg monensin and unaffected by E2 dose. Monensin fed cows had a longer (P<0.05) interval to LH response (ILH) and to peak LH (ILHP) at the 4 mg E2 dose. Monensin had no effect (P>0.10) on LH variables at 0, 1 or 2 mg E2.     

Sulfation of gastrin in Zollinger-Ellison sera: evidence for association between sulfation and proteolytic processing

Sulfated gastrins were quantitated in sera from 15 patients with the Zollinger-Ellison syndrome (ZES) by specific radioimmunoassays. The total concentration of gastrin varied from 174 to 285000 pmol/1. Sulfated gastrins constituted $\text{44.8±5.5\%}$ (mean ± S.E.M.) of the gastrins in ZES sera compared with $\text{37.7±1.9\%}$ in sera from 100 control subjects ($\text{P>0.1}$). There was no correlation between gastrin concentration and sulfation ($\text{r=0.40}$). Gel and ion-exchange chromatography showed that up to 90% of the gastrins could be in the sulfated form. The highest degree of sulfation was found in sera where the small gastrin components dominated. Thus, the percentage of small gastrins (G-17 and G-14) correlated with the degree of sulfation ($\text{N = 15}$, $\text{r=0.75}$, $\text{P<0.01}$). We suggest therefore that proteolytic processing of the gastrin precursor and sulfation of tyrosyl are associated.     

Reproductive studies of Brahman cattle I. Behavioral effect of various dose levels of Estradiol-17β upon ovariectomized Brahman,Brahman × Hereford and Hereford cows

Six ovariectomized mature cows each of Brahman (B), Brahman × Hereford (BH) or Hereford (H) breeding were injected intramuscularly with Estradiol-17β (E). Dose levels of 1, 2, 4 and 8 mg E were given in 2 ml corn oil. Cows were allowed a 2 week recovery period between treatments. After injection the cows were placed with 18 epididymectomized bulls and observed constantly for 36 hours. B failed to accept the bulls at any E dose level. Proportions of BH accepting the bull were $\text{2}\text{6}$, $\text{6}\text{6}$, $\text{6}\text{6}$ and $\text{6}\text{6}$ and proportions of H accepting the bull were $\text{5}\text{6}$, $\text{6}\text{6}$, $\text{5}\text{6}$ and $\text{6}\text{6}$ at 1, 2, 4 and 8 mg E, respectively. BH were less responsive at 1 mg E than H (P<.10) and B were less responsive at any level (P<.005). The number of stances increased significantly with dose level (P<.005) and a breed × dose level interaction (P<.10) was found. The duration of standing estrus behavior was longer in H cows at 1 and 2 mg E than in BH (P<.05) but was identical at 4 and 8 mg E. Duration of estrus was shorter in B except at the 2 mg dose level. Breed (P<.005) and breed × dose level interactions (P<.05) were found. Response time (injection of E to stance event) did not differ between dosages of E within breed groups. However, response time was significantly longer in B (19.3 hrs, P<.05) versus the response time of either H (10.1 hrs) or BH (12.8 hrs). If homosexual stance behavior is accepted as estrus, B were less responsive at 1, 2, 4 and 8 mg E than were BH or H (P<.10).     

Reproductive studies of Brahman cattle V. The effect of various dose levels of estradiol-17β upon serum luteinizing hormone in ovariectomized Brahman cows

Twelve mature chronically-ovariectomized Brahman cows were randomly assigned to receive three of six different dosages of estradiol-17_b (E2) at three different time periods such that at the termination of the trial six animals received each E2 dosage. The E2 was suspended in 0, 1, 2.5, 5, 10 and 20 milligrams. A two week period was maintained between injections. The cows were bled via coccygeal vessel puncture immediately before E2 injection, every 2 hr from 0 to 18 hr, every hr from 18 to 42 hr and every 2 hr from 42 to 48 hr postinjection. Blood was processed to yield serum and stored at ?20 Celsius. Serum luteinizing hormone (LH) was quantitated by validated radioimmunoassay. An LH surge was defined as a sustained elevation of LH at least two standard deviations above the level of LH prior to the rise and was observed in $\text{0}\text{6}$, $\text{3}\text{6}$, $\text{5}\text{6}$, $\text{5}\text{6}$, $\text{5}\text{6}$, and $\text{6}\text{6}$ cows administered 0, 1, 2.5, 5, 10, and 20 mg of E2, respectively. All animals injected with E2 responded with a significant initial decrease (independent of E2 dosage) in LH that persisted from 2 through 12 hr post E2 injection. No significant decrease in LH levels was recorded in animals injected with the corn oil vehicle. The time to the LH surge differed (P<.05) between 1 mg E2 (10 hr) vs 20 mg E2 (19.5 hr), 1 mg E2 vs 10 mg E2 (16.2 hr), and 2.5 mg E2 (12.4 hr) vs 20 mg estradiol-17_β. Luteinizing hormone concentrations at the onset of the surge did not differ (P>.10) between E2 dosages. The elapsed time from E2 injection to the peak LH value differed (P<.05) between 1 mg E2 (20.3 hr) vs 20 mg E2 (26.8 hr), and 2.5 mg E2 (21.2 hr) vs 20 mg estradiol-17_β. The peak LH value, the area under the LH curve and the duration of the LH surge did not differ (P>.10) with E2 dosage. The time to the end of the LH surge differed (P<.05) between 1 mg E2 (25.3 hr) vs 2.5 mg E2 (31.6 hr), 1 mg E2 vs 5 mg (34.4 hr), 1 mg E2 vs 10 mg E2 (34.8 hr), 1 mg E2 vs 20 mg E2 (37.3 hr), and 2.5 mg E2 vs 20 mg estradiol-17_β. Luteinizing hormone values at the termination of the surge did not differ (P>.10) between dosages nor did the LH values at the termination of the surge differ (P>.10) from LH concentrations observed at the onset of the LH surge.     

Uterine infections in the postpartum cow: I. Effect of dietary crude protein restriction

The relationship between adequate (0.96 kg per head daily) and deficient (0.32 kg per head daily) intake of crude protein between 150 days prepartum and 110 days postpartum and the incidence of postpartum infections in the bovine uterus was studied. The incidence of infection at 25 days postpartum was 52.2% and 48.1% (P > .10) for cows in the protein adequate and protein deficient groups, respectively. However, at 40 days postpartum, 21.7% of cows in the protein adequate group had infections $\text{vs}$ 51.9% (P < .05) of cows in the protein deficient group. In addition, the incidence of infection within the protein adequate group between sampling times was different (P < .10); whereas, the incidence within the protein deficient group between sampling times was not different (P > .10). Eighty-three bacterial isolates representing 27 species were recovered from the total of 100 samples. $\text{Corynebacterium}$$\text{pyogenes}$ and $\text{Fusobacterium}$$\text{necrophorum}$ were the most frequently isolated aerobe and anaerobe, respectively. Although there was no difference between diets (P > .10), these two organisms occurred most frequently in cows on the protein deficient diet and were associated with clinically severe uterine infections. These data suggest that the amount of crude protein in the diet affects both the incidence and duration of postpartum infections in the bovine uterus.     

Synchronized breeding in cattle using PGF2α and LHRH/FSHRH stimulatory analogs

Two studies were conducted to synchronize breeding in cattle using PGF₂α and LHRH/FSHRH analogs. In the first study, 60 mature lactating Angus cows were assigned at random to 4 treatment groups: saline and saline (SS); 30 mg PGF₂α tham salt + saline (PS); saline + 2 mg D-ala⁶-des-GlyNH₂¹⁰ LHRH/FSHRH ethylamide (D-ala⁶) (SA); 30 mg PGF₂α tham salt + 2 mg D-ala⁶ (PA). The first letter of the two-letter code for each group always indicates a dual injection at an 11-day interval. PGF₂α or saline was administered intramuscular (im) twice at an 11 day interval. D-ala⁶ or saline was administered 48 hr after PGF₂α treatment. In the SA group, the D-ala⁶ was administered at first signs of estrus, and cows were then artificially inseminated (AI) 24 hr later. All cows in the PS group were inseminated 72 hr after the second PGF₂α injection. In the SS group, cows were inseminated 24 hr after first signs of estrus. An additional 6 mature lactating Angus cows were added equally to the PS and PA groups to evaluate changes in serum LH. The percent calf crops was: SS = 40% (frsol|6/15); PS = 47% ($\text{7}\text{15}$); SA = 47% ($\text{7}\text{15}$); PA = 53% ($\text{8}\text{15}$). In the second study, 51 mature lactating Angus cows and 39 Holstein heifers were assigned at random to 3 treatment groups: saline + saline (SS); 33.4 mg PGF₂α tham salt + saline (PS); 33.4 mg PGF₂α tham salt + 1 mg D-leu⁶-des GlyNH₂¹⁰ LHRH/FSHRH ethylamide (D-leu⁶) (PL). PGF₂α tham salt or saline was administered im twice at an 11 day interval. D-leu⁶ or saline was administered 68 hr following the second PGF₂α treatment. Cows pretreated with PGF₂α were inseminated 80 hr after the second PGF₂α injection. In the SS group, cows were administered saline at the time of natural estrus and were artificially inseminated 12 hr later. Calving percent to the first AI was SS = 70% ($\text{21}\text{30}$); PS = 53% ($\text{16}\text{30}$) and PL = 40% ($\text{12}\text{30}$). An additional 10 mature lactating Angus cows were used to evaluate changes in serum LH. Five of the cows were assigned to the PS treatment and five to the PL treatment. Sequential blood samples were collected to monitor serum LH levels. Using the Chi-square test, there were no significant differences between calving percentages of the control and PGF₂α treated cows in either study. These results indicate that the PGF₂α treatments were successful in timed artificial insemination of cows without detection of estrus. The LHRH/FSHRH analogs did not improve the conception even though they appear to induce a pituitary release of LH simultaneously in all cows within 1 hr of treatment.     

Effects of diagnostic low-volume uterine lavage shortly before first service on reproductive performance, culling and milk production

The objective was to evaluate if uterine sampling by low-volume uterine lavage, done shortly before the end of the voluntary waiting period, affected reproductive performance, milk production, or culling. Approximately 20 cows (40 and 60 d postpartum) were sampled in each of 38 herds (total, 752 cows), whereas all remaining cows concurrently between 40 and 60 d were a non-sampled reference cohort (n = 2,252 cows). There was an interaction between parity and sampling for first-service conception, calving to conception interval, and milk production. When stratified by parity, there was a tendency for impaired reproductive performance in sampled primiparous cows compared with non-sampled primiparous cows (Odds Ratio for pregnancy to first-service = 0.78 (95% C.I. 0.58-1.04). The Hazard Ratio for pregnancy in sampled primiparous cows was 0.89 (95% C.I. 0.77-1.04) compared to non-sampled primiparous cows. Sampling did not affect first-service conception rate (Odds Ratio for pregnancy Odds ratio (OR) for pregnancy = 1.03; 95% C.I. 0.80-1.33) or calving-to conception interval in multiparous cows (Hazard Ratio = 1.04; 95% C.I. 0.91-1.18). Sampling did not affect culling risk (Hazard Ratio HR = 0.92; 95% C.I. 0.77-1.11) after accounting for covariates. After stratification by parity, milk production was not affected by sampling except in fourth- and fifth-parity cows where sampled cows produced more milk than non-sampled cows after controlling for first test-day milk production and days-postpartum at first test-day. In conclusion, sampling by low-volume uterine lavage did not have significant detrimental effects on reproduction, culling, or milk production. However, there was a tendency for lower first-service conception in sampled primiparous cows, but the procedure appeared to be benign in multiparous cows.     

Supplementing previously treated anestrous dairy cows with progesterone does not increase first-service conception rate

The objective of this study was to investigate the effect of supplementing previously treated anovulatory anestrous (AA) dairy cows with progesterone delivered intra-vaginally for 7 days, commencing 4 or 5 days after insemination, on first-service conception rate. A clinical trial, involving 990 AA dairy cows in 14 dairy herds, was conducted during the 2002/2003 breeding season. On Day -8, all cows were treated with a progesterone-containing intravaginal device (Cue-Mate). The devices were removed on Day -2; on Day -1, all cows were given 1mg of estradiol benzoate im. Cows in the control group (n = 499) received no further treatments. Cows in the treatment group (n = 491) that had been inseminated on Day 0 or 1 had a new device inserted (on Day 4 or 5), with removal of the device after 7 days. First-service conception rates for the control and treatment groups were not different (35.0% versus 36.7% respectively; P = 0.41). Furthermore, there was no difference in conception rates between cows that had devices inserted on Day 4 or 5 (31.3% versus 37.2% respectively; P = 0.45). In conclusion, supplementation of previously treated AA dairy cows with an intravaginal progesterone-releasing device for 7 days (commencing 4 or 5 days after insemination) did not significantly improve first-service conception rate.     

Improvement of first-service pregnancy rate in cows with gonadotropin-releasing hormone analog

The effect of an intramuscular injection of a new analog of gonadotropin-releasing hormone (GnRH), fertirelin, on the first-service pregnancy rate in cows was investigated by a double blind experiment. A total of 1,194 cows was injected intramuscularly either with 100 mug of GnRH or placebo (physiological saline solution) at the time of first insemination postpartum. Pregnancy rate (number of cows calved/ number of cows serviced) was 57.2 % in 605 cows treated with GnRH, while the performance was 49.7 % in 589 cows of the placebo group. The difference of pregnancy rates in both groups was significant (P<0.05). GnRH injected at insemination was effective, especially in cows at the first and third lactations, cows at 101 days postpartum or later, cows with daily milk yield of 26-30 kg, and also in cows from the area where a regional average fertility was relatively low.     

Control of estrus and ovulation in dairy cows

The efficiency of a synthetic prostaglandin analog (ICI 80996) for the control of the estrus cycle in dairy cows has been tested with and without simultaneous use of progestagen implants (SC 21009, Searle). Synchronization of estrus is closer after combined progestagen-prostaglandin treatments than after prostaglandins alone (78.7 % in estrus in 48h vs 60.2 % ; P<0.001).The percentage of cows not observed in estrus during the first 96h after the end of treatment was also lower after combined treatments (20.7 % vs 31.8 % ; P<0.05). The best estrus synchronization was obtained by injecting prostaglandin analog two days before implant removal (86 % in estrus in 48h and 14.0 % not observed in estrus within 96h).Fertility was studied in a field trial after one or two inseminations at a predetermined time for each treatment. A higher pregnancy rate was obtained with two inseminations after combined progestagen-prostaglandin treatment (49.1 %). This pregnancy rate differed significantly (P<0.05) from those obtained with one A.I. after the same treatment or two A.I. after the prostaglandin treatment but did not differ from the pregnancy rate obtained with one A.I. 80h after the second prostaglandin injection. The most important problem in dairy cows is the fall in pregnancy rate between 21 days and 6 months (19.7 to 35.1 % depending on treatment ; P<0.05).     

Induced parturition in dairy cattle: A comparison of a corticoid (flumethasone) and a prostaglandin (PGF2α) in different age groups

Parturitions were induced in 66 dairy cows and heifers of the German Black Pied breed, 11 to 13 days before term, using either a highly potent corticosteroid (flumethasone: 2 × 5 mg, 10 to 14 hr apart), or prostaglandin F_2α (20 mg i.v.) and initiating treatments either in the morning (A.M.) or late afternoon (P.M.). At those dose levels parturition was induced in $\text{50}\text{50}$ animals treated with flumethasone, and in $\text{9}\text{9}$ heifers, but only in $\text{5}\text{7}$ cows treated with PGF_2α; placentas were retained in all cases in which parturition was induced. Intervals between initiation of treatments and parturition were shorter in flumethasone-treated animals (flumethasone: 42.5 hr; PGF_2α 57.2 hr); with both drugs, they were approximately 10 to 15 hr shorter in younger animals. The first flumethasone treatment at P.M. prolonged the intervals to parturition in cows (first treatment A.M.: 37.8 hr; P.M.: 52.9 hr), but not in normal age heifers (A.M.: 27.6 hr; P.M.: 25.9 hr); in early bred heifers, this trend was reversed (A.M. 41.6 hr; P.M.: 31.8 hr). No circadian differences in response to PGF were noted. Mean intervals to postpartum conceptions were 93 and 94 days for PGF_2α-treated cows and heifers, and 123.5 and 125 days for flumethasone-treated cows and heifers, respectively.     

The effect of calf removal on estrous response and pregnancy rate of beef cows after SYNCRO-MATE-B treatment

The effect of calf removal on estrous response and pregnancy rate of cows given SYNCRO-MATE-B (SMB) was determined. Two hundred forty three lactating beef cows treated with SMB were allotted to three treatments: treatment 1, no calf removal; treatment 2, 24 hr calf removal and treatment 3, 48 hr calf removal. Calf removal time began with removal of the SMB implant. All cows were artificially inseminated 48 to 54 hr after implant removal. Body condition of cows in each heard was visually appraised as adequate or marginal. At each location, technicians and sires were stratified across all treatments.Estrous response of cows (n=143) was different (P<.01) between treatments which averaged 23, 40 and 77 percent for treatments 1, 2 and 3, respectively. Pregnancy rates of cows (n=243) after the first artificial insemination (AI) were 32, 28 and 46 percent for treatments 1, 2 and 3, respectively. The pregnancy rate was greater (P<.05) for treatment 3 than other treatments. After 25 days of breeding, the pregnancy rates were 59, 58 and 72 percent, respectively, for the three treatments. There was a linear relationship between days postpartum at the time of treatment and estrous response (P<.01) and first service pregnancy rate (P<.05). The partial regression coefficients for estrous response and first service pregnancy rate were 1.2 and .6 percent, respectively.In summary, estrous response and pregnancy rate of lactating beef cows treated with SMB were increased by 48 hr calf removal, compared to no calf removal or 24 hr calf removal, when calf removal time began with removal of the SMB implant.     

Commercial splitting of bovine embryos

Independent studies were undertaken at Alberta Livestock Transplants (ALT) and at Select Embryos, Inc. (SEI) to develop procedures for splitting bovine embryos. At both locations embryos were recovered seven days after the onset of estrus and superovulation. Initially, survival after splitting was evaluated by culture $\text{in}$$\text{vitro}$ for 18 to 24 hours. Culturing half or demi-embryos without a zona pellucida at ALT resulted in 15% survival compared to 35% survival when both halves were in separate zonae. Culturing demi-embryos on a monolayer of luteal cells at SEI did not improve survival $\text{in}$$\text{vitro}$. In fertility trials, best results were obtained at ALT when both demi-embryos within separate zonae were nonsurgically transferred into separate uterine horns of the same recipient (55% pregnancy rate) and at SEI when one demi-embryo was surgically transferred into the uterine horn ipsilateral to the corpus luteum (65% pregnancy rate). Culturing demi-embryos more than 4 hours reduced fertility at both locations. Splitting embryos was a worthwhile addition to the commercial ET programs and further trials are in progress to improve survival $\text{in}$$\text{vitro}$ and pregnancy rates.     

Attenuation of noradrenergic neurotransmission by the thromboxane synthetase inhibitor,UK 38,485

The purpose of this study was to determine the effects of chronic administration of the thromboxane synthetase inhibitor, UK 38,485, on noradrenergic neurotransmission. Male Sprague Dawley rats (n=14) were treated once daily with either UK 38,485 (100 mg/kg; n=7) or the vehicle of UK 38,485 (olive oil; n=7) by gavage. The dose of UK 38,485 chosen was sufficient to inhibit $\text{ex vivo}$ platelet TXB₂ production by >90% for 24 hours. One week into the treatment animals were prepared for $\text{in situ}$ perfusion of their mesenteric vascular beds. Vasoconstrictor responses to both exogenous norepinephrine and periarterial nerve stimulation were determined both before and during an infusion of angiotensin II (9ng/min) into the superior mesenteric artery. UK 38,485 significantly (P<0.02) attenuated the vascular response to periarterial nerve stimulation without altering the vascular response to either norepinephrine or angiotensin II. UK 38,485 did not influence the baseline perfusion pressure, the mean arterial blood pressure or the potentiation of neurotransmission by angiotensin II. These data indicate that in the $\text{in situ}$ rat mesentery UK 38,485 attenuates the release of neurotransmitter from sympathetic nerve terminals.     

The effect of exogenous progesterone on plasma LH and milk progesterone concentrations in multiple-suckling post-partum cows

Fourteen Friesian cows each suckling four calves were treated for a 7-day period (a) between days 20–40 post partum with progesterone-releasing intravaginal devices (PRID) containing 2% progesterone (Group 1; n = 5), (b) between days 51–264 post partum with PRIDS containing 2% progesterone (Group 2; n = 6) and (c) between days 29–214 days post partum with PRIDS containing 0% progesterone (Group 3; n = 3). Mean plasma LH concentrations decreased during PRID treatment in Group 2 cows only and pre-ovulatory LH surges were observed in $\text{5}\text{6}$ of these cows between 38 and 84 h after coil removal. All Group 2 cows underwent at least one ovarian cycle following PRID removal. No pre-ovulatory LH surges were observed in either Group 1 or Group 3 cows and only one cow (Group 3) underwent an ovarian cycle after treatment. It is suggested that there is an increase in pituitary responsiveness to the feedback effects of progesterone during the post-partum period.