Effect of copper, zinc, and manganese supplementation and source on reproduction, mineral status, and performance in grazing beef cattle over a two-year period.

Crossbred, multiparous beef cows (n = 178 in Year 1; n = 148 in Year 2) were used to evaluate the effects of Cu, Zn, and Mn supplementation and source on reproduction, mineral status, and performance in grazing cattle in eastern Colorado over a 2-yr period. Cows were stratified by expected calving date, age, BW, BCS, and liver mineral status and assigned to the following treatments: 1) control (no supplemental Cu, Zn, or Mn); 2) organic (ORG; 50% organic and 50% inorganic Cu, Zn, and Mn); and 3) inorganic (ING; 100% inorganic CuSO4, ZnSO4, and MnSO4). Free-choice mineral feeders were used to provide current NRC-recommended concentrations of Cu, Zn, and Mn from 82 d (Year 1) and 81 d (Year 2) before the average calving date of the herd through 110 d (Year 1) and 135 d (Year 2) after calving. At the end of Year 1, supplemented cows had greater liver Cu (P < 0.01), Zn (P < 0.05), and Mn (P < 0.01) concentrations compared with controls, whereas liver Cu concentration was greater (P < 0.01) in ORG vs. ING cows. At the end of Year 2, supplemented cows had greater (P < 0.01) liver Cu concentrations relative to controls, whereas control cows had greater (P < 0.02) liver Mn concentration than did supplemented cows. In Year 1, pregnancy rate to AI in control cows did not differ (P = 0.47) from supplemented cows, but there was a trend (P < 0.08) for pregnancy rate to be higher for ORG than ING cows. In Year 2, supplemented cows had a higher (P < 0.02) pregnancy rate to AI than controls. In both years, when cows were inseminated after an observed estrus, supplemented cows had a higher (P < 0.04) pregnancy rate than did controls. Also, for both years, overall 60-d pregnancy rate tended (P = 0.10) to be higher for supplemented cows than for controls. In Year 1, kilograms of calf weaned per cow exposed was greater (P < 0.02) in controls than in supplemented cows, and kilograms of calf weaned per cow exposed was greater (P < 0.01) in ING than ORG treatments. However, in Year 2, kilograms of calf weaned per cow exposed was greater (P < 0.02) in controls than in supplemented cows, and tended (P = 0.09) to be greater in ORG than ING treatments. Results indicate that supplementation and source of trace minerals affected mineral status and kilograms of calf weaned per cow exposed in grazing beef cows. Supplementation also improved pregnancy rate to AI compared with cows not supplemented with Cu, Zn, or Mn for more than 1 yr. Furthermore, mineral source may influence pregnancy rate to AI.

Fertilizing potential in vitro of semen from young beef bulls containing a high or low percentage of sperm with a proximal droplet.

Fertilizing potential of semen containing a high percentage of sperm with a proximal droplet was evaluated using IVF. Design criteria: (a) specified semen with >100 x 10(6) sperm/mL with >40% progressively motile spermatozoa, after collection via electro-stimulation; (b) designated a droplet group, bulls whose semen contained >30% spermatozoa with a proximal droplet and <25% with other morphological abnormalities, and a control group, with <25% abnormalities of any type; and (c) stipulated evaluations at 11 to 13 mo of age and again -4 wk later. At the initial evaluation, when a bull was assigned to the droplet group, the next bull meeting control criteria was designated his pair; 15 pairs in four herds were studied. Semen was extended in egg-yolk citrate, cooled to 5 degrees C over approximately 2.5 h, and held at 5 degrees C. After 20 to 44 h, spermatozoa were processed by swimup, incubated with heparin, and co-cultured with oocytes (35 to 56 oocytes/sample; 18 h). Ova were observed for cleavage approximately 42 h after co-culture, and further development was evaluated on day 8. At first evaluation, cleavage rates were 18 and 46% for droplet and control groups (P < 0.01); semen had 34 to 70% and 0 to 12% droplet spermatozoa. For 10 of 15 droplet bulls, <10% of ova were cleaved whereas cleavage rate was >15% for all control bulls. At second evaluation, only three droplet bulls still had >30% of spermatozoa with a proximal droplet. Cleavage rates increased accordingly; only four droplet bulls had <10% cleaved ova and 10 had >34% cleaved ova. Three control bulls had <10% cleaved ova and nine had > or = 34% cleaved ova. Considering all 60 ejaculates, correlation between percentage of spermatozoa with a proximal droplet and percentage of cleaved ova was -0.49 (P < 0.0 1). Correlations between percentages of motile or normal spermatozoa in field evaluations and outcome in IVF were 0.28 and 0.52. Laboratory evaluations of spermatozoa concomitant with preparation for IVF revealed that only incidence of proximal droplets appeared related to outcome in IVF. We concluded: (a) semen from most yearling beef bulls with a high incidence of proximal droplet spermatozoa had severely compromised IVF fertility; (b) as these bulls matured, the incidence of proximal droplets decreased, and IVF fertilizing potential increased; and (c) semen containing >30% spermatozoa with a proximal droplet is strong evidence that fertilizing potential of the bull will be low until the incidence decreases.

Scaling of relative velocity between vehicles.

Data are presented on the ability of drivers to perceive and scale the relative velocity between their own and a lead vehicle. Experiments were carried out on four groups of subjects using Ekman's ratio-rating method. Only when the subtended angular velocity of the lead vehicle exceeded about 0.003 rad/s were the subjects able to scale the relative velocity. The threshold subtended angular velocity obtained in the experiments was very much affected by the ability of subjects to use the concept of a ratio-engineering students found this a simpler task than did subjects from the general population. The result of this was that the values used by engineering students were closer to the real values. The relative velocity was perceived non-linearly, with a Stevens' power law exponent of about 0.8. It was found that linear models gave as good a fit to the data. The implications of the results of the experiments are (i) traffic flow models that include human visual characteristics must consider the "dead zones" in response produced by thresholds of subtended angle change subtended angular velocity; (ii) it may be necessary to consider the non-linear relationship between perceived relative velocity and actual relative velocity; (iii) in overtaking, the driver will not be able to scale the speed of the oncoming vehicle as the subtended angular velocity will be below the threshold value at the time of making the decision to overtake.

In vitro penetration into bovine oocytes and zona-free hamster oocytes by bull spermatozoa treated with liposomes.

The objectives of this study were 1) to determine whether in vitro penetration of bovine and zona-free hamster oocytes, using spermatozoa treated with the lipid dilauroylphosphatidylcholine, was correlated with the fertility of bulls and 2) to determine whether utilizing results from several laboratory assays could effectively evaluate fertility. Cryopreserved semen was used from 12 bulls having lifetime nonreturn rates ranging from 66 to 81%. The lipid concentration that maximized penetration of hamster oocytes was determined as well as the number of spermatozoa entering all hamster oocytes, number of spermatozoa in each penetrated hamster oocyte, fertilization of bovine oocytes, blastocyst development of bovine oocytes, and the percentage of motile spermatozoa of each sample. Correlations were low between the lipid concentration that maximized each individual parameter and nonreturn rate (r < or = 0.34). The six-parameter regression equation accounted for 71% of the variation in bull fertility, and a four-parameter equation accounted for 61% of the variation in fertility. Pooling data for pairs of bulls into six fertility groups to increase information per data point still resulted in poor predictions of fertility for individual parameters. However, a four-variable model, including the penetration rates for hamster and bovine oocytes, the number of spermatozoa that penetrated hamster oocytes, and the percentage of motile spermatozoa, accounted for 98% of the variability in bull fertility.

Effects of a dexamethasone implant on deposition of intramuscular fat in genetically identical cattle.

Administration of exogenous glucocorticoids has been shown to enhance deposition of intramuscular fat in cattle. In this study, six pairs of genetically identical (cloned) steers were used to determine the effects of an implant containing 100 mg of dexamethasone on intramuscular fat deposition and on other carcass and meat quality traits. One steer in each pair served as a negative control (CON), whereas the other steer received a dexamethasone implant 30 to 60 d from slaughter (DEX). Treatment with dexamethasone did not (P > .05) enhance intramuscular fat deposition. However, DEX steers had greater (.33 cm; P < .05) thickness of external fat, larger (5.94 cm2; P < .05) longissimus muscle areas, and higher (1.9 percentage points; P < .05) dressing percentages than did CON steers. In addition, treatment with dexamethasone increased (P < .01) serum insulin concentrations. Dexamethasone had no effect (P > .05) on cooked beef palatability traits or on 24-h calpastatin activity. Although the DEX implant tested in this study was not effective for improving carcass quality grade, use of the implant increased external fat thickness and was effective for increasing carcass muscularity and dressing percentage.

Vesicular adenitis syndrome in beef bulls.

Vesicular adenitis syndrome was diagnosed in 69.3% (52/75) of a group of yearling bulls on breeding soundness examination. Association of Haemophilus somnus infection with vesicular adenitis syndrome was confirmed in these bulls by microbial culture of vesicular gland fluid or semen samples and serologic testing.

Drivers' estimates of time to collision.

Drivers' estimates of time to collision were determined in a laboratory simulation using film segments made from a following vehicle approaching a lead vehicle, which was also in motion. Headway, approach speed, and viewing time were varied to make a total of 48 conditions. It was found that, provided the angular velocity subtended by the lead vehicle was above a threshold value of about .003 radians/sec, the driver was able to give reasonable estimates of time to collision. The standard deviation of the estimates varied linearly with the time to collision. Although drivers underestimated the time to collision when it was small, the large standard deviation shows the possibility of rear-end collisions due to poor estimation of time to collision, especially when the times for control action and vehicle deceleration are considered.

Causes and costs of calf mortality in Colorado beef herds participating in the National Animal Health Monitoring System.

Seventy-three Colorado cow/calf operations were monitored for calf mortality from birth to weaning as part of their participation in the National Animal Health Monitoring System. Producer-observed causes of calf mortality, and the costs associated with these deaths were obtained. The overall calf mortality during the study was 4.5%, with a total associated cost of $237,478. The mean cost per calf death was $216, of which $208 was attributed to the potential value of the calf and an additional $8 was for veterinary, drug, producer's labor, and carcass disposal expenses. The most commonly reported causes of calf mortality were dystocia (17.5%), stillbirth (12.4%), hypothermia (12.2%), diarrhea (11.5%), and respiratory infections (7.6%). These 5 disease conditions accounted for > 60% of all calf deaths. A cause was not determined for 19.7% of the calf deaths. Beef producers and veterinarians have the potential to decrease calf mortality and increase profits in cow/calf operations by implementing management strategies and herd health programs designed to decrease the number of calf deaths caused by these disease conditions.

Abnormal bovine parturition. Obstetrics and fetotomy.

The veterinarian is in a unique position to assist and improve the profitability of producers by educating clients on proper intervention and delivery techniques. This paper describes some procedures for intervention, evaluation, and management of dystocia by mutation, forced extraction, and fetotomy. In addition, a brief summary of the factors influencing dystocia is presented. When these techniques are used properly, losses due to dystocia are minimized.

Development and testing of a bovine trichomoniasis vaccine.

Eighteen culled dairy cows were randomly allocated into 1 of 5 treatment groups. Six cows were vaccinated twice (2V), 21 days apart, 3 with whole cell (2WC) and 3 with fragmented cell membrane (2FC) containing 1 x 10(9)Trichomonas fetus organisms or protein equivalent in a commercial mineral oil adjuvant vaccine. Six more cows were vaccinated once (1V), 3 with whole cell (1WC) and 3 with fragmented cell vaccine (1FC), using the same vaccine, while 6 cows were used as the unvaccinated controls. All cows were challenged with 1 x 10(5) organisms 4 weeks after the second or the only vaccination. After challenge, cervico-vaginal mucus (CVM) samples were cultured for T . fetus weekly for 9 weeks. Whole cell vaccines were superior to fragmented cell vaccines, and both performed better than no vaccination for apparent elimination of trichomonad infections in dairy cows. In addition, 2V was superior to 1V, which, in turn, was superior to no vaccination. Furthermore, clearance time was reduced most by 2V and whole cell vaccination compared with 1V and fragmented cell vaccination. Clearance time was decreased significantly in all vaccinated cows compared with that in unvaccinated cows.

Testing of trichomoniasis vaccine in heifers mated to infected bulls.

This study was conducted to evaluate the effectiveness of a Trichomonas fetus vaccine to protect heifers from infection when bred to infected bulls. The vaccine consisted of a whole cell vaccine of T. fetus organisms stabilized in formaldehyde and adjuvanted in a mineral oil base. In the trial, fewer vaccinated heifers became infected than unvaccinated controls (69.4 vs 93.0%, respectively; P<0.08). The vaccinated heifers tended to clear the infections sooner than the controls (48.9 vs 68.5 days, respectively; P<0.10). The average number of days open was shorter in the vaccinated heifers than in the controls (33.2 vs 56.9 days, respectively; P<0.07). The first service conception rate was higher in the vaccinated heifers than in the controls (66.7 vs 33.3%, respectively; P<0.05). The number of services per conception in conceiving heifers was lower in vaccinated than in control heifers (1.44 vs 1.73, respectively; P<0.16). Cervicovaginal mucus (CVM) samples were collected every 14 days following first challenge (first service). On average, more CVM samples were positive for T. fetus for a longer period of time in the control than in the vaccinated heifers (3.9 vs 1.85 sampling periods, respectively; P<0.08). We concluded that, under the conditions of this trial, some protection to T. fetus was afforded by double vaccination with a whole cell vaccine. However, vaccination does not completely prevent heifers from developing infection.

Investigating optimal bull:heifer ratios required for estrus-synchronized heifers.

The objectives of this study were to determine 1) the effect of bull:heifer ratio on reproductive performance and associated costs and return on heifers in synchronized estrus and 2) the effect of estrus synchronization on reproductive performance and economic variables, in a multiple-sire, pasture breeding situation. Eight hundred yearling beef heifers and 28 mature, sexually experienced beef bulls were allotted to four treatments (two replicates per treatment) at bull:heifer ratios of 2 per 100 (1:50; Treatment 1), 2 per 100 (1:50; Treatment 2), 4 per 100 (1:25; Treatment 3), and 6 per 100 (1:16; Treatment 4). Treatment 1 (control) used nonsynchronized heifers, whereas heifers in Treatments 2, 3, and 4 were synchronized using the 33-d melengestrol acetate (MGA)-prostaglandin F2 alpha (PGF2 alpha) program. Pregnancy results after a 28-d breeding season indicate that there may be a limit to how many estrus-synchronized heifers bulls can impregnate. Treatment 2 showed a 6% decrease (P < .10) in pregnancy rate (77%) compared with Treatment 3 (83%), indicating that the bulls probably were not able to service all the synchronized heifers. Treatments 3 and 4 had similar pregnancy rates (83 and 84%, respectively). Treatment 4 had a 3-d advantage (P < .01) over Treatment 3 in average day of conception. However, based on economic analysis, Treatment 3 exhibited greater returns. Estrus synchronization failed to provide any advantage in pregnancy rate or day of conception. For unknown reasons, the control, nonsynchronized heifers cycled and conceived as if they were synchronized.(ABSTRACT TRUNCATED AT 250 WORDS)

Extra enforcement and the use of seat belts by drivers in Illinois.

The use of seat belts by drivers was measured in three target and three control cities in Illinois before, during, and after the application of heightened police enforcement of the seat belt law in the target cities. The extra enforcement produced increases in the use of seat belts by drivers during the four months of the heightened enforcement. Observations of seat belt use continued for four months after the end of the enforcement, and a substantial residual effect remained in two of the three target cities. In one target city the use of seat belts had dropped close to the level at the start of the project by the end of the second month after the end of enforcement. Taking account of the percentage of drivers who became aware of the increased enforcement suggested that a sustained program of enforcement may result in 60%-70% of drivers using seat belts.

Costs of veterinary services and vaccines/drugs used for prevention and treatment of diseases in 86 Colorado cow-calf operations participating in the National Animal Health Monitoring System (1986-1988).

Eighty-six cow-calf operations involved in the Colorado National Animal Health Monitoring System were monitored for a 12-month period, and data were collected on the incidence, prevention, and costs of disease. The costs of veterinary services and vaccines/drugs used in the treatment and prevention of disease conditions in these beef herds were determined and expressed on a per cow basis. Beef producers in this study spent an average of $2.04 ($0 to $29.88) per cow annually on veterinary services for treatment of disease conditions. The cost of veterinary services was a relatively small percentage (5.4%) of the total mean cost of disease incidence. The reproductive tract disease class was the most costly class in terms of veterinary services for disease treatment ($0.99/cow). Dystocia was the disease condition with the largest veterinary treatment cost. The total mean annual cost of drugs used in the treatment of disease conditions was $1.22/cow. The enteric, miscellaneous, and respiratory tract disease classes had similar mean drug costs for disease treatment and ranged from $0.31 to $0.39/cow. The total mean annual cost of veterinary services for administration of preventive measures in these herds was $1.85/cow ($0 to $12.03). Pregnancy examination, breeding soundness examination in bulls, brucellosis vaccination, pulmonary arterial pressure test, and campylobacteriosis vaccination accounted for over 90% of the money spent for preventive veterinary services. Approximately 60% of the total mean annual disease prevention cost was attributed to the purchase of vaccines/drugs ($6.59/cow).(ABSTRACT TRUNCATED AT 250 WORDS)

Annual costs associated with disease incidence and prevention in Colorado cow-calf herds participating in rounds 2 and 3 of the National Animal Health Monitoring System from 1986 to 1988.

Thirty-nine and 47 randomly selected Colorado cow-calf operations were monitored for health events and their associated costs during rounds 2 and 3, respectively, of the National Animal Health Monitoring System (NAHMS). Data were collected from each operation for a one-year period by NAHMS veterinarians through monthly interviews, and the costs associated with the incidence and prevention of disease conditions were determined and expressed on a per cow basis. The beef producers involved in this study spent an average of $32.75 per cow in round 2 and $40.97 per cow in round 3 on an annual basis for the treatment of disease conditions. These costs were not different between the 2 rounds because of the wide ranges in the individual herd costs for disease incidence in each round. In both years of the study, the largest contributor to the total mean annual cost of disease incidence was the cost of death of diseased animals, and this cost accounted for approximately two-thirds of the total mean annual cost in each round. The total mean annual costs of disease prevention in these herds were $11.24 and $11.19 per cow in rounds 2 and 3, respectively. There were wide ranges in both rounds in the amounts of money spent per cow by individual herds for disease prevention. The largest individual cost of disease prevention in each year was the cost of vaccines/drugs, whereas the smallest individual cost in each round was the cost of veterinary services.(ABSTRACT TRUNCATED AT 250 WORDS)

Annual disease incidence in Colorado cow-calf herds participating in rounds 2 and 3 of the National Animal Health Monitoring System from 1986 to 1988.

Thirty-nine and 47 randomly selected Colorado cow-calf operations participated in the National Animal Health Monitoring System (NAHMS) during rounds 2 (October 1986 to September 1987) and 3 (October 1987 to September 1988), respectively. Data on the incidence of disease conditions within each herd were collected by federal and state Veterinary Medical Officers and university veterinarians through monthly visits to the ranches. Annual disease incidence for disease classes and the most frequently reported individual disease conditions were determined and expressed on a per 100 cow basis. The mean annual disease incidences for all diseases in these herds were 48.8 and 47.7 new cases per 100 cows for rounds 2 and 3, respectively. The ranges for herd annual disease incidence were wide in both study years. The enteric disease class had the highest mean annual disease incidence in both years of the study, and this was primarily because of diarrhea of unknown cause in calves. Diarrhea of unknown cause accounted for approximately 25% of all new disease cases in both rounds of the study. The mean annual disease incidences were not different for any disease class between the two rounds. The data indicate that, on the average, diarrhea of unknown cause, pneumonia, dystocia, foot rot (interdigital necrobacillosis), pinkeye (infectious keratoconjunctivitis), respiratory tract infection, death of unknown cause, and nonpregnancy had the highest incidences in these Colorado beef herds during the study period. However, because of the wide variation of the predominant disease problems between herds, a herd's disease history as well as the common disease problems in the geographic area of a herd must be considered in designing a herd health program.

Management practices and their association with reproductive health and performance in Colorado beef herds.

An observational study was conducted to quantify the effects of management practices on reproductive performance and disorders of beef cows. The study population consisted of 44 randomly selected Colorado cow-calf herds monitored for disease and reproductive events as part of the National Animal Health Monitoring System. The managers of the herds were surveyed with a standardized questionnaire to determine specific management characteristics of their operations. Data were analyzed using the random-effects multiple logistic regression model. Outcomes of interest were calving rate, herd incidence rates of dystocia and combined reproductive disorders, and calf mortality rate. A higher calving rate was associated (P less than .01) with a decreased percentage of replacement females in the herd, a shorter breeding season, a smaller herd size, and a lower percentage of bulls being used as yearlings. Incidence rates of both dystocia and combined reproductive disorders were found to be lower (P less than .01) in herds that were fed cottonseed cake as a winter supplement, but higher (P less than .01) in herds that were fed grass hay as a winter supplement. Herds located in the mountains of Colorado had lower (P less than .01) incidence rates of dystocia and reproductive disorders than herds located in the eastern plains. Calf mortality rate was found to be higher (P less than .05) with calving seasons that began earlier in the year. Higher calf mortality rates were associated (P less than .05) with an increased incidence of dystocia, the commingling of cattle on summer range, and smaller herd size.

Effects of androgenizing dairy heifers with ear implants containing testosterone and estrogen on detection of estrus.

Lactating dairy cows in four lots were observed for sexual behavior for 6 mo. One freemartin heifer in each lot was implanted with testosterone propionate and estradiol benzoate to aid in detection of estrus. Blood samples were obtained from androgenized heifers every other week for determination of serum testosterone. The addition of an androgenized heifer to each lot increased the number of mounts and attempts to mount cows, both overall and within observation periods. Thus, the likelihood of detecting a cow in estrus was increased with the addition of the androgenized heifers. Greatest benefit was seen when one or two cows were simultaneously in estrus in each lot. Observational data and serum progesterone concentration of mounted cows indicated that androgenized heifers were selectively mounting open cows displaying estrus, whereas the remaining nonandrogenized cows were less selective with their mounting activity. Serum testosterone increased after heifers were implanted, but testosterone was not related to the proportion of sexual activity. Duration of sexual activity by the implanted heifers was approximately 90 d.

Older drivers: their night fatal crash involvement and risk.

The 1983 Fatal Accident Reporting System (FARS) data and the Nationwide Personal Transportation Study (NPTS) exposure data were used to describe the major problems in night driving that involved older drivers, aged 65 or more, in fatal crashes and to assess their risk. One of the major findings was that the rate of involvement in fatal crashes in darkness of older drivers was much less than for drivers under the age of 25, but greater overall than for drivers aged 25-64. The rate for older females was much less than for older males. Although the overall fatal crash involvement of older drivers is not a serious cause for alarm at this time, the performance of older males does indicate a substantial increase in risk of fatal crash involvement in darkness. These trends can be expected to become more noticeable over the years as a greater proportion of the population in the United States exceeds the age of 65. The older driver crash involvement at night seems to be particularly troublesome for males in multivehicle crashes where they are struck in the side or rear by another vehicle, and single-vehicle crashes where they run off the road on a straight section. Some suggested improvements of the overall night driving environment are discussed.

Effect of Actinomyces pyogenes and gram-negative anaerobic bacteria on the development of bovine pyometra.

Fifteen lactating Holstein cows were used in a trial designed to evaluate the effectiveness of intrauterine inoculation (challenge) of Actinomyces pyogenes (A) alone or in combination with Fusobacterium necrophorum (F) and Bacteroides melaninogenicus (B) to induce pyometra. Cows were assigned to one of five groups: A (n = 3), AB (n = 3), AF (n = 3), ABF (n = 3) or C (control, broth medium alone; n = 3). All cows exhibited estrus 12 or 13 d prior to challenge (Day 0=first day of challenge). During the prechallenge period, the reproductive tract of each cow was palpated per rectum and uterine fluid aspirates for culture and uterine biopsies were also obtained. All cows received an intravenous injection of 5,000 IU of human chorionic gonadotropin (hCG; Day 5) and an intrauterine infusion of 40 ml of 0.7% iodine solution (Day 1). Cows were then inoculated on Days 0, 1 and 2 of the experiment. Sequential palpations of the reproductive tracts, samples of uterine fluid for culture and uterine biopsies were performed for a total of 30 d after the first inoculation. A cow was diagnosed as having pyometra when purulent uterine fluid and a corpus luteum were detected by palpation per rectum. The number of cows that developed pyometra in Group A was 2 of 3, in Group AB 3 of 3, in Group AF 3 of 3, in Group ABF 3 of 3 and in Group C 0 of 3. Cows with pyometra did not exhibit estrus. In 7 of 11 cows, pyometra persisted for more than 21 d. In cows that developed pyometra, the same species of bacteria infused into the uterus were usually recovered one or more times during the postchallenge period. When clinical pyometra was diagnosed, histologic endometritis was invariably present. Histologic endometritis and concurrent isolation of A . pyogenes alone or A . pyogenes with gram-negative anaerobic bacteria occurred in 91.7% of samples during the postchallenge period. Regardless of bacterial treatment, gram-negative anaerobic bacteria were frequently isolated with A . pyogenes during this period.