The effect of different implant programs on beef × dairy steer feedlot growth performance and carcass characteristics.

The objective of this study was to evaluate potency and timing of trenbolone acetate (TBA) administration on live performance and carcass characteristics of beef × dairy steers. A total of 6,895 beef × dairy steers [initial body weight (BW) = 157 ±â€…5.2 kg] were allotted into 30 pens, with pen as the experimental unit. Each pen was randomly assigned one of three implant treatments: 1) Revalor-IS (IS) at d 0, IS at d 80, and Revalor-XS (XS) at d 160 (IS/IS/XS); 2) Ralgro at d 0, IS at d 80, and XS at d 160 (Ral/IS/XS); or 3) Encore at d 0 and XS at d 160 (Enc/XS). Steers were blocked by arrival date, each pen was terminally sorted in three ways at 257 ±â€…22 days on feed and harvested at 329 ±â€…25 days on feed. For live and carcass outcomes, fixed effect of implant treatment and random effect of block was evaluated. Data are reported on a deads and removals out basis. Removals, morbidity, and mortality were similar (P ≥ 0.45). Steers administered TBA prior to d 160 were 5.8 kg heavier (P = 0.03) than Enc/XS steers at d 160. Final BW was not different (P = 0.78). Early administration of a TBA-containing implant resulted in an increased prevalence of bullers [2.40%, 5.18%, 6.86% (for Enc/XS, Ral/IS/XS, and IS/IS/XS) respectively; P < 0.01]. Dry matter intake (DMI) was 2.3% greater (P < 0.01) in steers administered Enc/XS compared to IS/IS/XS; however, DMI as a percentage of BW, average daily gain, and feed efficiency were not different (P ≥ 0.12). Dressing percentage, hot carcass weight, heavy carcass occurrence, Longissimus muscle area, and 12th rib fat thickness were similar among all steers (P ≥ 0.28). Marbling score tended to be greatest for Enc/XS and Ral/IS/XS (P = 0.09). Enc/XS graded a greater proportion of USDA Prime and fewer USDA Select carcasses than IS/IS/XS (P < 0.05). Enc/XS and Ral/IS/XS tended (P = 0.09) to have more USDA Yield Grade (YG) 1 carcasses. While delayed administration or decreased total potency of TBA-containing implants may decrease buller incidence and improve Quality Grade, few differences were observed in live or carcass outcomes.

Bacterial flora of liver abscesses in crossbred beef cattle and Holstein steers fed finishing diets with or without tylosin.

Holstein steers raised for beef production consistently have a higher prevalence and more severe form of liver abscesses than cattle of beef breeds. A study was conducted to compare bacterial flora of liver abscesses collected from multiple abattoirs from 4 groups of cattle, arranged in a 2 × 2 factorial design, consisting of crossbred cattle and Holstein steers, and each group fed a finishing diet supplemented with or without tylosin. A total of 383 liver abscess samples, consisting of 94 and 81 from crossbred cattle and 89 and 119 from Holstein steers fed finishing diets with or without tylosin, respectively, were subjected for anaerobic and aerobic bacterial isolations. The minimum inhibitory concentrations (MIC) of tylosin to the predominant bacterial species were determined. The likelihood chi-square test was performed to assess unadjusted differences in bacterial prevalence proportions between the 2 types of cattle (crossbred and Holstein steers) and feed type (tylosin or no tylosin). There was no interaction between cattle type and tylosin inclusion on the prevalence of any of the bacterial species isolated. Liver abscesses from Holstein steers yielded a higher total number of isolates compared to liver abscesses from crossbred cattle (1060 vs. 788). subsp. was isolated from all abscesses. The prevalence of subsp. was 19.1% and was not affected by the cattle type or tylosin. The prevalence of was higher ( < 0.01) in crossbred cattle (73.7%) compared to Holstein steers (29.8%). Also, the prevalence of was higher in abscesses from tylosin-fed (66.1%) cattle than no tylosin-fed cattle (35%). The overall prevalence of was 25.3% and was similar ( = 0.58) between cattle type, but the prevalence was lower ( < 0.01) in tylosin-fed (16.9%) compared to no tylosin-fed group (33%). Mean MIC of tylosin for and were similar across both cattle types and tylosin inclusion. Although bacterial flora of liver abscesses from Holstein steers appeared to be more diverse than that of crossbred cattle, there was no difference in the prevalence of the and and in fact, prevalence of was higher in crossbred than Holstein steers. Therefore, the difference in bacterial flora is not the likely reason for higher prevalence and severity of liver abscesses in Holstein steers than crossbred beef cattle.

Effect of bovine respiratory disease during the receiving period on steer finishing performance, efficiency, carcass characteristics, and lung scores.

Bovine respiratory disease (BRD) is responsible for the majority of morbidity, mortality, and production losses occurring in feedlots. This experiment evaluated the effects of BRD incidence on subsequent finishing performance, efficiency, carcass characteristics, and lung scores of steers. Crossbred steers (n = 516) were monitored daily for clinical signs of BRD (BRD attributed morbidity and mortality were 66.5 and 13.2%, respectively). A subset of calves (n = 174) were grouped by the number of times treated for BRD (BRDX) and randomly allocated to finishing pens. The BRDX experimental groups included never treated for BRD (0X; 8 pens) and treated 1 time (1X; 8 pens), 2 times (2X; 8 pens), or 3 or 4 times (3/4X; 8 pens). Arrival BW was not different among BRDX groups (P = 0.17); however, BRDX during the receiving period decreased performance, resulting in BW of 324, 316, 285, and 260 kg for 0X, 1X, 2X, and 3/4X, respectively, at the start of finishing (P < 0.001). Ultrasound estimates, BW, and visual appraisal were used to target a common body composition (average days on feed = 182). With increasing BRDX, days on feed increased linearly (P = 0.002), whereas HCW, DP, rib eye area, QG, and unconsolidated lungs decreased linearly (P ≤ 0.03). These results suggest that with additional days on feed, calves treated multiple times for BRD are able to reach similar compositional endpoints as their untreated cohorts; however, it may not be possible for these calves to reach the same QG and carcass yield.

Effect of copper, manganese, and zinc supplementation on the performance, clinical signs, and mineral status of calves following exposure to bovine viral diarrhea virus type 1b and subsequent infection.

Research has indicated that trace mineral (TM) supplementation may alter immune function and reduce morbidity associated with bovine respiratory disease. The objective of this experiment was to determine the influence of dietary Cu, Mn, and Zn supplementation on the performance, clinical signs, and TM balance of calves following a bovine viral diarrhea virus (BVDV) and (MH) combination respiratory pathogen challenge. Steers ( = 16; 225 ± 20 kg BW) from a single ranch were processed, weaned, and randomly pairwise assigned to either the TM-supplemented (MIN) or the control (CON) experimental treatments. The MIN calves received an additional 150 mg of Cu, 130 mg of Mn, and 320 mg of Zn daily and the CON calves received the basal diet with no additional Cu, Mn, or Zn supplementation. The basal diet contained sufficient Mn and Zn but inadequate Cu based on published nutrient requirements. After 46 d on the experimental treatments, all calves were naturally exposed to a heifer persistently infected with BVDV type 1b for 4 d and then subsequently intratracheally challenged with MH. Data were analyzed using the GLIMMIX procedure of SAS with sampling time serving as a repeated measure and calf serving as the experimental unit. The respiratory challenge was validated via increased BVDV type 1b antibody concentrations, MH whole cell and leukotoxin antibody concentrations, rectal temperatures (TEMP), and subjective clinical severity scores (CS). Calf performance ( ≥ 0.48) was not affected by TM supplementation. Mineral supplementation also did not impact the CS or TEMP of calves ( ≥ 0.53). There was a treatment × time ( < 0.001) interaction observed for liver Cu concentrations. The concentrations of Cu, Mn, Zn, and Fe within the liver; Cu, Mn, and Zn within the muscle; and Cu, Zn, and Fe within the serum were all impacted by time ( ≤ 0.03). Calves receiving the MIN treatment had greater ( < 0.01) liver Cu and Mn concentrations compared with CON calves. In contrast, serum Cu and Fe concentrations were increased ( ≤ 0.05) in CON calves compared with MIN calves. Mineral supplementation did not impact TM concentrations within the muscle ( ≥ 0.38). The supplementation of Cu, Mn, and Zn can improve the Cu and Mn status within the liver and serum of calves in response to a BVDV and MH challenge. When Cu is supplemented to calves receiving a marginally Cu-deficient diet, Cu status within the body is significantly improved.

Evaluation of multiple ancillary therapies used in combination with an antimicrobial in newly received high-risk calves treated for bovine respiratory disease.

Ancillary therapy (ANC) is commonly provided in conjunction with an antimicrobial when treating calves for suspected bovine respiratory disease (BRD) in an attempt to improve the response to a suspected BRD challenge. The first experiment evaluated the effects of 3 ANC in combination with an antimicrobial in high-risk calves treated for BRD during a 56-d receiving period. Newly received crossbred steers (n = 516; initial BW = 217 ± 20 kg) were monitored by trained personnel for clinical signs of BRD. Calves that met antimicrobial treatment criteria (n = 320) were then randomly assigned to experimental ANC treatment (80 steers/experimental ANC treatment): intravenous flunixin meglumine injection (NSAID), intranasal viral vaccination (VACC), intramuscular vitamin C injection (VITC), or no ANC (NOAC). Animal served as the experimental unit for all variables except DMI and G:F (pen served as the experimental unit for DMI and G:F). Within calves treated 3 times for BRD, those receiving NOAC had lower (P < 0.01) clinical severity scores (severity scores ranged from 0 to 4 on the basis of observed clinical signs and severity) and heavier (P = 0.01) BW than those receiving NSAID, VACC, or VITC at the time of third treatment. Between the second and third BRD treatments, calves receiving NOAC had decreased (P < 0.01) daily BW loss (−0.13 kg ADG) compared with those receiving NSAID, VACC, or VITC (−1.30, −1.90, and −1.41 kg ADG, respectively). There were no differences in rectal temperature, combined mortalities and removals, or overall performance among the experimental ANC treatments. Overall, morbidity and mortality attributed to BRD across treatments were 66.5% and 13.2%, respectively. After the receiving period, a subset of calves (n = 126) were allocated to finishing pens to evaluate the effects ANC administration on finishing performance, carcass characteristics, and lung scores at harvest. Ultrasound estimates, BW, and visual appraisal were used to target a common physiological end point for each pen of calves. There were no differences among the experimental ANC observed during the finishing period (P ≥ 0.11). In summary, the use of NSAID, VACC, and VITC do not appear to positively impact clinical health and could potentially be detrimental to performance during the receiving period in high-risk calves receiving antimicrobial treatment for suspected BRD.

The effects of technology use in feedlot production systems on feedlot performance and carcass characteristics.

The objectives of this study were to examine the effects of feedlot production systems with and without the use of a ß-adrenergic agonist compared to an all-natural production program on feedlot performance and carcass characteristics. Crossbred beef steers ( = 336; initial BW = 379 ± 8 kg) were randomized to 1 of 3 treatments in a randomized complete block design (RCBD; 14 steers/pen; 8 pens/treatment). Treatments consisted of an all-natural treatment (NAT), a conventional treatment (CONV), and a conventional treatment with a ß-agonist (CONV-Z). All treatments were fed the same basal diet with NAT cattle receiving no growth promoting technologies. The CONV and CONV-Z cattle were implanted with 40 mg of estradiol and 200 mg of trenbolone acetate (TBA) on d 0 and were fed 33 and 9 mg/kg of monensin and tylosin daily, respectively. The CONV-Z cattle were fed zilpaterol hydrochloride (ZH) at 6.76 mg/kg (90% DM basis) for the last 20 days on feed (DOF) There was no effect of treatment on DMI ( = 0.83); however, CONV-Z steers gained 3.8% faster (1.64 vs. 1.58 kg/d; < 0.01) and were 5.3% more efficient (0.160 vs. 0.152; < 0.01) than CONV steers, and CONV steers gained 32.8% faster (1.58 vs. 1.19 kg/d; < 0.01) and were 26.7% more efficient (0.152 vs. 0.120; < 0.01) than NAT steers. There was a 35.7% improvement in estimated carcass gain (1.29 vs. 0.95 kg/d; < 0.01) and a 32.6% improvement in carcass efficiency (0.126 vs. 0.095; < 0.01) for CONV-Z steers compared to NAT steers. Hot carcass weight was increased by 8 kg for CONV-Z steers compared to CONV steers (394 vs. 386 kg; = 0.05) and 46 kg compared to NAT steers (394 vs. 348 kg; < 0.01). Longissimus muscle area was increased by 3.6 cm for CONV-Z steers compared to CONV steers (92.29 vs. 88.67 cm; = 0.02) and 12.1 cm for CONV-Z steers compared to NAT steers (92.29 vs. 80.16 cm; < 0.01), resulting in a 9.6% unit increase in USDA yield grade (YG) 1 (15.14 vs. 5.52%; < 0.05) and a 21.6% unit reduction in USDA YG 3 for CONV-Z steers compared to CONV steers (30.70 vs. 52.32%; < 0.05). The CONV-Z steers had a lower marbling score compared to the other treatments (432; 0.01), resulting in an 11.7% unit increase (20.70 vs. 9.03%; < 0.05) in USDA Select carcasses compared to CONV steers. The results of this experiment show that CONV-Z and CONV production results in a significant improvement in feedlot performance and USDA YG compared to NAT.

Effect of anabolic implants on adrenal cortisol synthesis in feedlot beef cattle implanted early or late in the finishing phase.

Implantation of anabolic steroids to increase growth rate in beef cattle impacts adrenal glucocorticoid production. The mechanism by which combination androgen and estrogen implants reduce cortisol biosynthesis in heifers is not clear. The objective of this study was to identify whether pituitary or adrenal gene expression and liver enzyme activity may contribute to altered serum cortisol concentrations in heifers receiving a combination implant. On d 0 of a 122-d finishing phase, 187 predominantly Angus heifers (361 kg) approximately 14 months old were randomly assigned to one of three implant groups: (1) non-implanted control, (2) implanted at the beginning of the finishing phase (d 0; early implant) with a combination implant (200mg TBA+20mg E2; Revalor 200®), and (3) implanted during the late stage of the finishing phase (d 56; late implant) with Revalor 200®. At d 56, body weight (BW) was greater (P<0.0001) for the early implanted heifers (456 ± 1.9 kg) compared to 437 and 435 (± 1.8) kg for control and late implanted heifers, respectively. Final BW (d 122) was similar between both implanted groups and heavier than non-implanted controls (P<0.0001). Serum cortisol was similar among groups at d 0 (P=0.86) however, by d 28 heifers receiving the combination implant had reduced (P<0.05) serum cortisol concentrations (31.2 ng/mL) compared to controls (49.4 ng/mL) and late (48.2 ng/mL) groups. On d 84 cortisol was similar (P=0.75) among implanted heifers and was less (P<0.01) than non-implanted heifers. Expression of pituitary and adrenal genes involved in glucocorticoid synthesis was evaluated at d 28/29 or 84/85; however, despite decreased serum cortisol in implanted heifers, no change in mRNA expression was demonstrated. Liver CYP3A enzyme activity at d 28/29 was decreased 59% in early implanted heifers compared to control heifers (P=0.01). Additionally, at d 84/85 AKR1C activity was greatest (P=0.01) in control heifers compared to both implanted groups. Data suggest that components of hypothalamic-pituitary-adrenal axis are influenced by exposure to exogenous hormones and this should be recognized when considering cortisol levels as a marker for stress response.

Effects of beef production system on animal performance and carcass characteristics.

The objective of this study was to evaluate conventional (CONV) and natural (NAT) beef production systems from annual pasture through finishing through grazing. Beef steers (n=180, initial BW=250±19 kg) were assigned randomly to 2 treatments in the pasture phase. Steers were implanted with 40 mg of trenbolone acetate (TBA), 8 mg estradiol, and 29 mg tylosin tartrate (CONV), or received no implant (NAT). Steers on the 2 treatments grazed wheat or cereal rye for 109 d. Conventional steers had an 18.5% improvement in ADG (1.22 vs. 1.03 kg/d, P<0.01) and a heavier final BW (385 vs. 366 kg, P<0.01) compared with NAT steers. Following the pasture phase, steers (n=160 steers, 5 steers/pen, 8 pens/treatment) were assigned to a 2×2 factorial in the feedlot phase. Production system (NAT vs. CONV) was maintained from the pasture phase, and the second factor was 7 vs. 12% low-quality roughage (DM basis, LOW vs. HIGH). During finishing, CONV steers were given 120 mg of TBA and 24 mg estradiol at processing, fed monensin and tylosin, and fed zilpaterol hydrochloride for the last 20 d of the experiment. There were no program×roughage level interactions (P>0.07). The CONV steers ate 6.9% more feed (11.8 vs. 11.0 kg/d, P<0.01), gained 28.4% faster (1.90 vs. 1.48 kg/d, P<0.01), and were 24.2% more efficient (0.164 vs. 0.132, P<0.01) compared with NAT steers. The LOW steers had greater G:F (0.153 vs. 0.144, P<0.01) compared with HIGH steers. There was a 28.3% improvement in estimated carcass weight gain (1.36 vs. 1.06 kg/d), 18.6% improvement in carcass efficiency (0.115 vs. 0.097, P<0.01), and 21.6% improvement (1.52 vs. 1.25 Mcal/kg, P<0.01) in calculated dietary NEg for CONV compared with NAT steers. Hot carcass weight was increased by 62 kg (424 vs. 362 kg, P<0.01) and LM area was increased by 16.9 cm2 (100.9 vs. 84.0 cm2, P<0.01), decreasing USDA yield grade (YG, 3.09 vs. 3.54, P<0.01) for CONV steers compared with NAT steers. Natural steers had a greater percentage of carcasses in the upper 2/3 of USDA Choice grade (48.7 vs. 18.7%, P<0.01), a greater percentage of YG 4 and 5 carcasses (25.4 vs. 9.3%, P<0.01), and a greater percentage of abscessed livers (39.6 vs. 10.5%, P<0.01) compared with CONV steers. The results show that CONV production results in more rapid and efficient production that resulted in heavier carcasses with superior YG and desirable quality grades with both roughage levels.

Growth and Development Symposium: Impacts of inflammation on cattle growth and carcass merit.

Inflammation caused by bovine respiratory disease (BRD) continues to be one of the greatest challenges facing beef cattle producers and feedlot managers. Inflammation decreases DMI, ADG, and G:F in feedlot calves, decreasing growth rate and increasing days on feed, which results in economic losses during the feeding period. During the past decade, marketing of feedlot animals has changed from selling cattle on a live basis to a grid-based marketing system. When cattle are marketed on a live basis, the economic effects of BRD stop at increased health cost and decreased feedlot performance, carcass weight, and death loss. However, when cattle are marketed in a grid-based system, inflammation has the potential to also affect carcass cutability and quality. The effects of inflammation on feedlot cattle in regards to performance are well understood; however, specific effects on cattle growth and ultimately carcass merit are not as well described. Recent studies in feedlot cattle have indicated that the incidence of BRD decreases both HCW and marbling; however, mechanisms are not understood. Research in other species has demonstrated that during the acute phase response, pro-inflammatory cytokines promote skeletal muscle catabolism to supply AA and energy substrates for immune tissues. Further, during this early immune response, the liver changes its metabolic priorities to the production of acute phase proteins for use in host defense. Together these dramatic shifts in systemic metabolism may explain the detrimental effects on performance and carcass traits commonly associated with BRD in feedlot calves. Moreover, recent studies relative to human health have revealed complex multilevel interactions between the metabolic and immune systems, and highlighted inflammation as being a significant contributor to major metabolic diseases. The objective of this paper is to review data to help explain the economical and physiological effects of inflammation on cattle growth and carcass merit.

Alternative cerebrospinal fluid tests to diagnose neurosyphilis in HIV-infected individuals.

OBJECTIVE: To identify alternatives to the CSF-Venereal Disease Research Laboratory (VDRL) test for the diagnosis of neurosyphilis in HIV-infected individuals. METHODS: CSF fluorescent treponemal antibody (FTA) reactivity and % CSF lymphocytes that were B cells in fresh and frozen samples were determined for 47 HIV-infected cases with syphilis and 26 HIV-infected controls. As for serum, CSF fluorescent treponemal antibody reactivity > or =2+ was considered positive. Based on the results in controls and cases with normal CSF measures, cut-offs for elevated CSF B cells were proposed to be > or =9% in fresh and > or =20% in frozen samples. Neurosyphilis was defined as a reactive CSF-VDRL. RESULTS: CSF-FTA-ABS (absorbed) and CSF-FTA (unabsorbed and undiluted) were 100% sensitive for the diagnosis of neurosyphilis. Elevated % CSF B cells in fresh and cryopreserved samples was specific (100%) but not sensitive (40 and 43%) in post hoc analyses. The results of CSF-FTA and assessment of % CSF B cells together allowed 16% of cases with pleocytosis but nonreactive CSF-VDRL to be diagnosed with neurosyphilis and 26% to be diagnosed as not having neurosyphilis. CONCLUSION: When the CSF-VDRL is nonreactive, CSF-FTA and % CSF B cells may help exclude or establish the diagnosis of neurosyphilis.

5-HT2 receptor antagonism reduces hyperactivity induced by amphetamine, cocaine, and MK-801 but not D1 agonist C-APB.

The hyperlocomotion induced by the noncompetitive NMDA antagonist MK-801 (0.3 mg/kg SC) in mice was attenuated by the nonselective 5-HT2 antagonist ritanserin (0.12 and 0.25 mg/kg SC) and by the 5-HT2A selective antagonist MDL100907 (0.05 and 0.1 mg/kg SC). SB242084 (0.25-1.0 mg/kg), a selective 5-HT(2C) antagonist, had no effect on MK-801-induced hyperactivity. These same doses of ritanserin and MDL100907 reduced the hyperactivity induced by cocaine (10 mg/ kg). Amphetamine (2.5 mg/kg SC) induced hyperlocomotion that was also attenuated by ritanserin (0.064).25 mg/kg SC). The hyperlocomotion induced by the D1 agonist C-APB (1.0 mg/kg) is not altered by pretreatment with ritanserin or MDL100907. This suggests that compounds that increase locomotor activity via indirectly increasing dopaminergic activity (either by increased release or blockade of reuptake) require the activation of a 5-HT2A receptor. Activity of compounds that act directly at the postsynaptic dopamine receptors such as C-APB is not dependent on such a mechanism. This suggests a selective involvement of 5-HT2A receptors but not 5-HT2c receptors in the mediation of the behavioral effects of compounds that increase synaptic concentration of dopamine but not directly acting agonists. This implies that the 5-HT2A receptors modulate elevation of extracellular dopamine, not the postsynaptic sensitivity of dopamine neurons.

Resolution of serum and cerebrospinal fluid abnormalities after treatment of neurosyphilis. Influence of concomitant human immunodeficiency virus infection.

BACKGROUND AND OBJECTIVES: Little is known about resolution of serum and cerebrospinal fluid abnormalities after neurosyphilis treatment, especially in patients infected with human immunodeficiency virus (HIV). GOAL: To examine the time course of resolution of these abnormalities. STUDY DESIGN: Case series of 22 patients with neurosyphilis (13 infected with HIV) with reactive cerebrospinal fluid Venereal Disease Research Laboratory test who underwent at least one lumbar puncture after treatment. RESULTS: Resolution of all serum and cerebrospinal fluid measures was slower in patients infected with HIV. Serum and cerebrospinal fluid abnormalities resolved in most patients not infected with HIV by 30 weeks, and all met Centers for Disease Control and Prevention criteria for cure. One patient infected with HIV failed therapy by Centers for Disease Control and Prevention criteria, and three others had persistent pleocytosis. CONCLUSIONS: HIV-infected patients with neurosyphilis have slower resolution of serum and cerebrospinal fluid abnormalities after therapy. This observation may suggest impaired clearance of Treponema pallidum from the central nervous system.

Physicians' experience with the acquired immunodeficiency syndrome as a factor in patients' survival.

BACKGROUND: Previous studies have found that patients with the acquired immunodeficiency syndrome (AIDS) who are admitted to hospitals that admit many such patients have lower mortality rates than patients in hospitals with less experience with AIDS. We examined the relation between physicians' experience with AIDS and the survival of their patients with AIDS. METHODS: We studied 403 adult male patients enrolled in a staff-model health maintenance organization in whom first AIDS-defining illnesses were diagnosed from 1984 through mid-1994; we determined that these illnesses met the 1987 case definition of the Centers for Disease Control. We defined three levels of experience for the patients' 125 primary care physicians according to their experience with AIDS during residency training and the cumulative number of patients with AIDS they had cared for in their practices. RESULTS: The median survival of the patients of physicians with the least experience in the management of AIDS was 14 months, as compared with 26 months for the patients of physicians with the most experience (P<0.001). Controlling for the severity of illness and the year of diagnosis, we found that the patients cared for by physicians with the most experience had a 31 percent lower risk of death than the patients cared for by physicians with the least experience (P<0.02). Among 244 patients with an AIDS-defining illness diagnosed from 1989 through 1994, after adjustment for the CD4+ cell count and the severity of illness, the risk of death was 44 percent lower for patients of the most experienced physicians than for patients of the least experienced (P<0.02). CONCLUSIONS: The experience of primary care physicians in the management of AIDS is significantly associated with survival among their patients.

Neurologic Manifestationsof HIV Infection Without AIDS:Follow-UP of a Cohortof Homosexual and Bisexual Men.

To identify neurological abnormalities in HIV infection, 159 HIV-seropositive men without AIDS and 76 seronegative controls underwent standardized general and neurological examinations, lumbar puncture (LP), neuropsychological (NP) assessment, and brain magnetic resonance (MR) imaging. History, physical, and laboratory evaluations were repeated every six months. NP tests (all subjects) and MR imaging (seropositives only) was repeated every 6-12 months; LP (seropositives only) was repeated yearly. Mean follow-up was 24.6 months. Neurological abnormalities, most related to hearing, were seen in 60 (38.2%) of 157 seropositives and 23 (30.3%) of 76 controls at baseline (p = NS). During follow-up, 43 (31.6%) of 136 seropositives had persistent hearing abnormalities compared to 9 (14.1%) of 64 seronegatives (p = 0.008). Seven HIV-seropositives developed peripheral neuropathy; this was more common among those with hearing abnormalities (p = 0.03). HIV-seropositives performed less well on NP tests than controls, but overall performance did not decline. Worsening brain atrophy by MR imaging or cerebrospinal fluid abnormalities are more common in HIV-seropositives than seronegatives and may share a common mechanism with peripheral neuropathy. Further study is needed to determine whether these abnormalities portend more serious neurological disease.

Poverty and HIV seropositivity: the poor are more likely to be infected.

We analyzed demographic and behavioral risk factors for HIV seropositivity using data from 3601 clients of the main HIV counseling and testing clinic for high-risk people in Seattle, Washington, USA. Clients with lower income were found to be more likely to be HIV seropositive, before and after controlling for other demographic and risk factors with logistic regression. This result supports the hypothesis that the impoverished are at increased risk for HIV infection due to the physical and social circumstances in which their poverty places them. These may include poor access to risk-reduction information and less support for implementation of risk-reduction strategies.

Nucleotide sequence preservation of human leukemic mitochondrial DNA.

Nucleotide sequence variation in mitochondrial DNA isolated from human leukemic cells has been analyzed by recombinant DNA techniques. Three hundred eighty-seven independent recombinant DNA clones, each containing one of three defined segments of mitochondrial DNA isolated from the neoplastic cells of four leukemic patients, were analyzed. Partial nucleotide sequence determination of the 387 clones yielded a total of 81.7 kilobases of nucleotide sequence information. The only evidence of within-individual nucleotide sequence divergence consisted of three clones containing deletions of one or two nucleotides in one mitochondrial DNA region. These clones were three of 113 independent clones isolated from a patient with acute lymphocytic leukemia. The low level of nucleotide sequence divergence in the mitochondrial DNA population of neoplastic cells from individual leukemic patients suggests that a mechanism or mechanisms exist that limit the development of nucleotide sequence divergence in mammalian mitochondrial DNA. The results further suggest that this mechanism does not appear to be abrogated by neoplastic transformation in leukemic patients.

Mosaicism in amniotic fluid cell cultures: classification and significance.

The last decade has witnessed increasing application of human cytogenetic technology to prenatal chromosome analysis. However, unlike the rather uniform peripheral blood T-lymphocyte system which has provided most of our experience in human cytogenetics, long-term amniotic-fluid cell cultures display extreme cellular heterogeneity and disproportionate growth of certain cell types as a consequence of clonal amplification. When they enter cell culture, many of these cells are approaching the terminal stages of their respective, life spans and may have accumulated chromosomal aberrations. Concern about the possibility of true fetal mosaicism seems warranted chiefly in situations were multiple colonies display potentially viable aberrations. Clonal analysis, preferably of multiple clonal types, and attention to details of clonal morphology are likely to minimize diagnostic errors and undue apprehension resulting from mosaicism in amniotic-fluid cell cultures.