Biomedical subjects

M J Lewis

Publications and source records attributed to M J Lewis.

At least 91 records · Page 5Linked to original sources

PubMed1999

Modification of gibberellin production and plant development in Arabidopsis by sense and antisense expression of gibberellin 20-oxidase genes.

Gibberellin (GA) 20-oxidase catalyses consecutive steps late in GA biosynthesis in plants. In Arabidopsis, the enzyme is encoded by a gene family of at least three members (AtGA20ox1, AtGA20ox2 and AtGA20ox3) with differential patterns of expression. The genes are regulated by feedback from bioactive GAs, suggesting that the enzymes may be involved in regulating GA biosynthesis. To investigate this, we produced transgenic Arabidopsis expressing sense or antisense copies of each of the GA 20-oxidase cDNAs. Over-expression of any of the cDNAs gave rise to seedlings with elongated hypocotyls; the plants flowered earlier than controls in both long and short days and were 25% taller at maturity. GA analysis of the vegetative rosettes showed a two- to threefold increase in the level of GA4, indicating that GA 20-oxidase normally limits bioactive GA levels. Plants expressing antisense copies of AtGA20ox1 had short hypocotyls and reduced rates of stem elongation. This was reflected in reduced levels of GA4 in both rosettes and shoot tips. In short days, flowering was delayed and the reduction in the rate of stem elongation was greater. Antisense expression of AtGA20ox2 had no apparent effects in long days, but stem growth in one transgenic line grown in short days was reduced by 20%. Expression of antisense copies of AtGA20ox3 had no visible effect, except for one transgenic line that had short hypocotyls. These results demonstrate that GA levels and, hence, plant growth and development can be modified by manipulation of GA 20-oxidase expression in transgenic plants.

Arabidopsis↗

PubMed1999

Epidemiology of Streptococcus uberis intramammary infections in a dairy herd.

From 1987 to 1991, almost 36,000 quarter samples of mammary secretion representing 1790 lactations of 510 dairy cows from a research herd were collected for bacteriological examination. The percentage of cows infected with Streptococcus uberis ranged from 12 to 16% of cows/year. S. uberis was isolated from 14.2% of lactations over the 5-year period. The prevalence of S. uberis intramammary infection (IMI) was significantly higher in cows with > or = 4 lactations than in cows with 3 or fewer lactations. Regardless of lactation number, the prevalence of S. uberis was highest before parturition, during early lactation and near drying off. The prevalence of S. uberis infected quarters ranged from 1.3 to 2.3% of quarters/year; the prevalence rate for the 5-year period was 2% of quarters. The quarter prevalence of S. uberis was lowest in cows with < or = 3 lactations, increased significantly with lactation number and was highest in cows with > or = 6 lactations. The percentage of quarters infected with S. uberis varied significantly by year. The majority (95%) of S. uberis IMI were subclinical. The ratio of subclinical IMI to clinical IMI was lowest during early lactation, and increased with days in milk, and with lactation age except for cows in their 5th and 6th lactations. Results of this epidemiological investigation suggest that opportunities exist where suitable control measures could be applied to reduce the impact of S. uberis infections in the dairy herd.

Animals↗

PubMed1999

ATP is involved in myocardial and vascular effects of exogenous bradykinin in ejecting guinea pig heart.

It has recently been reported that bradykinin induces selective left ventricular (LV) relaxation in isolated guinea pig hearts via the release of nitric oxide. Exogenous bradykinin also induces vasodilation, which is only partly due to nitric oxide release. In the present study we investigated the role of adenyl purines on these bradykinin-induced effects. Isolated ejecting guinea pig hearts were studied. LV pressure was monitored by a 2-Fr micromanometer-tipped catheter. ATP concentrations were measured using a luciferin-luciferase assay. Bradykinin (1 and 100 nM) caused a progressive acceleration of LV relaxation together with a transient increase in coronary flow. These effects were inhibited by the nonselective P(2) purinoceptor antagonist suramin (1 microM, n = 6) but were unaffected by the selective P(2x) purinoceptor antagonist pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid (1 microM, n = 6). These myocardial and vascular effects of bradykinin were associated with increased ATP levels in coronary effluent. These data suggest that the selective enhancement of LV relaxation and rise in coronary flow induced by exogenous bradykinin involve endogenous ATP and the subsequent stimulation of P(2) purinoceptors.

Adenosine Triphosphate↗

PubMed1999

Increased glutathione and glutathione peroxidase in lungs of individuals with chronic beryllium disease.

Reactive oxygen species (ROS) are mediators of chronic tissue damage and fibrosis. Endogenous antioxidants may increase in response to oxidants and reduce tissue injury. We investigated the antioxidant response of the lungs to the chronic release of ROS, as occurs in the immune-specific granulomatous inflammation of chronic beryllium disease (CBD), and compared it with that in healthy controls and individuals exposed to cigarette smoke. The antioxidants superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and glutathione (GSH) were quantitated in lung epithelial lining fluid (ELF) and serum from control subjects (n = 10), cigarette smokers (n = 8), and individuals with CBD (n = 9). GPx activity and extracellular GPx (eGPx) protein were increased in the ELF of subjects with CBD in comparison with that of control subjects and smokers (eGPx in ELF: controls, 1.3 +/- 0.2 microgram/ml, smokers, 1.9 +/- 0.3 microgram/ml, CBD, 3.8 +/- 0.8 microgram/ml; p = 0.002; GPx U/ml ELF, controls 1.4 +/- 0.3, smokers 1.8 +/- 0.4, CBD, 4.5 +/- 1, p = 0.02). Smokers' ELF had higher levels of GSH than that of controls, but CBD patients' ELF contained much more GSH than that of either controls or smokers (p < 0.001). Increases in GSH were correlated with eGPx, indicating similar inducing mechanisms for these antioxidants. Thus, coordinate augmentation of the glutathione antioxidant system occurs in granulomatous lung inflammation.

Adolescent↗

PubMed1999

Evaluation of a postmilking teat disinfectant containing a phenolic combination for the prevention of mastitis in lactating dairy cows.

A trial was conducted for 12 months in a herd of 120 Holstein cows in order to determine the efficacy of a teat disinfectant, which contained a phenolic combination, for the prevention of bovine intramammary infections during lactation. Postmilking teat disinfection was compared to a negative control using a split-udder experimental design. The percentage of quarters newly infected by mastitis pathogens was 45% lower in mammary glands with teats that had been dipped in the experimental teat disinfectant after milking than it was in undipped controls. New infections caused by Streptococcus uberis, Staphylococcus aureus, coagulase-negative Staphylococcus species, and Corynebacterium bovis were significantly lower in mammary glands with teats that had been dipped in the experimental teat disinfectant than in undipped controls. No statistical differences in the incidence of clinical mastitis between treatment groups were observed. No irritation or chapping of teats dipped in the experimental teat disinfectant were observed. The results of this study suggest that the experimental teat disinfectant containing a phenolic combination is an effective postmilking teat disinfectant for use in the prevention of new intramammary infections by both contagious and environmental mastitis pathogens.

Animals↗

PubMed1998

Hyperhomocysteinemia after an oral methionine load acutely impairs endothelial function in healthy adults.

BACKGROUND: Elevated plasma homocysteine is a risk factor for arteriosclerosis, but a cause-and-effect relationship remains to be fully established. Endothelial dysfunction, an early event in the atherogenic process, has been shown to be associated with hyperhomocysteinemia in experimental and human studies. To further establish a direct relationship between changes in plasma homocysteine and endothelial dysfunction, we investigated whether moderate hyperhomocysteinemia induced by an oral methionine load would acutely impair flow-mediated endothelium-dependent vasodilatation in healthy adults. METHODS AND RESULTS: Twenty-four healthy volunteers completed a randomized crossover study in which an oral methionine load (0.1 g/kg) was administered on 1 of 2 study days, 7 days apart. At each visit, plasma homocysteine and brachial artery endothelium-dependent and -independent dilatation were measured at baseline and at 4 hours. To further elucidate the temporal relationship between methionine, homocysteine, and endothelial function, an oral methionine load was administered in 10 subjects on a separate visit, and the time courses of plasma methionine, homocysteine, and flow-mediated brachial artery dilatation were measured at baseline and after 1, 2, 3, 4, and 8 hours. After oral methionine, plasma homocysteine increased from 7. 9+/-2.0 micromol/L at baseline to 23.1+/-5.4 micromol/L at 4 hours (P<0.0001, n=24) and was associated with a decrease in flow-mediated brachial artery dilatation from 0.12+/-0.09 to 0.06+/-0.09 mm (P<0. 05). The time course of the impairment of flow-mediated vasodilatation mirrored the time course of the increase in homocysteine concentration. CONCLUSIONS: Oral methionine loading raises plasma homocysteine and impairs flow-mediated endothelium-dependent vasodilatation. This supports the view that homocysteine may promote vascular disease by inducing endothelial dysfunction.

Administration, Oral↗

PubMed1998

Epidemic of pediatric deaths from acute renal failure caused by diethylene glycol poisoning. Acute Renal Failure Investigation Team.

CONTEXT: Contaminated pharmaceutical products can result in substantial morbidity and mortality and should be included in the differential diagnosis of deaths of unknown origin. OBJECTIVE: To investigate an outbreak of deaths among children from acute renal failure in Haiti to determine the etiology and institute control measures. DESIGN: Case-control study, cohort study, and laboratory toxicologic evaluation. SETTING: Pediatric population of Haiti. PARTICIPANTS: Cases were defined as Haitian residents younger than 18 years with idiopathic anuria or severe oliguria for 24 hours or longer. Febrile hospitalized children without renal failure were enrolled as control subjects. MAIN OUTCOME MEASURE: The odds of exposure to suspected etiologic agents among cases and controls. RESULTS: We identified 109 cases of acute renal failure among children. The clinical syndrome included renal failure, hepatitis, pancreatitis, central nervous system impairment, coma, and death. Of 87 patients with follow-up information who remained in Haiti for treatment, 85 (98%) died; 3 (27%) of 11 patients transported to the United States for intensive care unit management died before hospital discharge. A locally manufactured acetaminophen syrup was highly associated with disease (odds ratio, 52.7; 95% confidence interval, 15.2-197.2). Diethylene glycol (DEG) was found in patients' bottles in a median concentration of 14.4%. The median estimated toxic dose of DEG was 1.34 mL/kg (range, 0.22-4.42 mL/kg). Glycerin, a raw material imported to Haiti and used in the acetaminophen formulation, was contaminated with 24% DEG. CONCLUSIONS: An epidemic of severe systemic toxicity and deaths from DEG-contaminated acetaminophen syrup occurred in Haiti. Good manufacturing practice regulations should be used by all pharmaceutical manufacturers to prevent such tragedies.

Acetaminophen↗

PubMed1998

Identification and molecular characterization of human T lymphotropic virus type II infections in intravenous drug abusers in the former South Vietnam.

Previous serological studies have demonstrated that some 60% of intravenous drug abusers (IVDAs) in urban areas of the former South Vietnam are infected with HTLV-II. In the present report we have attempted to characterize the viruses using restriction fragment length polymorphism (RFLP) and nucleotide sequence analysis of the provirus long terminal repeat (LTR) region. RFLP analysis of nine samples demonstrated that all were infected with the HTLV-IIb subtype. The HTLV-IIa subtype was not detected. Phylogenetic analysis of the nucleotide sequences demonstrated that the viruses clustered closely with HTLV-IIb isolates present in IVDAs from the New York City area. The present molecular analysis together with the previously reported absence of HTLV-II infection in North Vietnam supports the view that HTLV-II may have been introduced from the United States to this part of Asia by military personnel during the Vietnam conflict.

HTLV-II Infections↗

PubMed1998

Buprenorphine alters ethanol self-administration in rats: dose-response and time-dependent effects.

Buprenorphine is a partial opioid agonist derived from thebaine and has high affinity for mu and kappa opioid receptors. The present study investigated dose-response (0.03, 0.15, 0.3, 3 mg/kg) and time-dependent effects of buprenorphine (1.5 or 4 h post-treatment) on EtOH self-administration in outbred Sprague-Dawley rats. Freely feeding and drinking rats were trained to initiate EtOH self-administration for 1 h daily using the ascending concentration procedure, wherein they were provided with increasing concentrations of EtOH at 2, 5, 7, 9 and 11% (v/v), respectively. Water was concurrently available with each concentration. Animals were maintained on a given concentration of EtOH for 5 days. By day 21, animals began their stabilization on the 11% regimen and remained on this concentration throughout the remainder of the study. EtOH and water consumption were recorded daily at both 10- and 60-min intervals. At 1.5 h post-buprenorphine, all test doses greatly suppressed both EtOH and water intake at the 10-min interval. At the 60-min interval, all but the lowest dose (0.03 mg/kg) significantly suppressed EtOH intake, while only the highest dose (3 mg/kg) suppressed water intake. In contrast to the suppressant profile observed at 1.5 h post-buprenorphine, at 4 h post-buprenorphine the lower doses (0.03 and 0.15 mg/kg) significantly increased EtOH intake while the higher doses (0.3 and 3 mg/kg) continued to suppress intake. None of the doses of buprenorphine altered water intake 4 h post-buprenorphine. The results support previous research demonstrating the utility of low doses of buprenorphine in suppressing behavior rewarded by a non-opioid drug.

Analgesics, Opioid↗

PubMed1998

Syndrome X and endothelial dysfunction.

OBJECTIVE: Syndrome X (angina, normal coronary arteriogram and positive exercise test) remains an enigma with unexplained features and apparent conflicts of evidence. The present study addressed whether (i) the Syndrome is characterised by generalised flow-related endothelial dysfunction, (ii) myocardial thallium201 defects reflect myocardial or microvascular dysfunction, (iii) endothelial dysfunction and its consequences can be improved by oral L-arginine. METHODS: Flow-mediated brachial artery dilatation was measured by ultrasonic 'wall-tracking' in 7 Syndrome X patients, further characterised as having thallium201 defects and no known cause of endothelial dysfunction, and a normal control group. Syndrome X patients entered a 4-week randomised double-blind placebo-controlled cross-over trial of oral L-arginine (7 g twice daily), with brachial artery studies, exercise tests and technetium99 tetrafosmin scans. RESULTS: Flow-mediated dilatation was absent in Syndrome X vs. normal. Stress technetium99 tetrafosmin and thallium201 scans showed similar defects. Flow-mediated dilatation, symptom-limited exercise duration and peak oxygen consumption (VO2max) were increased but rate-pressure-product (RPP) and radionuclide defects were unchanged after L-arginine vs. placebo. CONCLUSIONS: The study supports coronary microvascular rather than myocardial dysfunction and shows loss of flow-mediated dilatation in systemic arteries. Oral L-arginine improved flow-mediated dilatation, exercise capacity and VO2max (by ca. 17%) despite unchanged RPP. The findings support generalised endothelial dysfunction. The arginine effects imply NO-mediated improvement of skeletal muscle perfusion suggesting improved homogeneity of microvascular distribution.

Administration, Oral↗

PubMed1998

Endothelial function is impaired in fit young adults of low birth weight.

OBJECTIVE: Non-insulin-dependent diabetes, hypertension and ischaemic heart disease, with insulin resistance, are associated with low birth weight (the 'Small Baby Syndrome'). Common to these adult clinical conditions is endothelial dysfunction. We tested the hypothesis that endothelial dysfunction could precede their development in those of low birth weight. METHODS: Endothelial function was measured by ultrasonic 'wall-tracking' of flow-related brachial artery dilatation in fit 19-20 year old subjects randomly selected (blind to the investigators throughout the study) from low (< 2.5 kg) and normal (3.0-3.8 kg) birth weight subjects in the 1975-7 cohort of the Cardiff Births Survey and with no known cause for endothelial dysfunction. RESULTS: Flow-related dilatation was impaired in low birth weight relative to normal birth weight subjects (median 0.04 mm [1.5%] [n = 22] cf. 0.11 mm [4.1%] [n = 17], p < 0.05; 0.04 mm [1.5%] [n = 15] cf. 0.12 mm [4.4%] [n = 12], p < 0.05 after exclusion of inadvertently included ever-smokers). CONCLUSION: The findings suggest that endothelial dysfunction is a consequence of foetal malnutrition, consistent with contributing to the clinical features of the 'Small Baby Syndrome' in later adult life.

Adult↗

PubMed1998

Bran: may irritate irritable bowel.

The irritable gut is known to be hypersensitive, and it is reasonable to suspect that patients with the disorder might be hyperreactive to agents that stimulate or irritate it. This appears to be a possible explanation for the adverse effects of bran on hospital patients with this disorder, but we do not yet know how this product affects community IBS sufferers. We cannot ignore the fact that fiber and bran have major beneficial effects in other areas, not least in the reduction of colonic carcinoma. In conclusion, it is probably best to recommend that patients with IBS be left to judge for themselves whether bran helps or exacerbates their symptoms, but there is enough evidence to suggest that the current dogma of routinely treating all IBS sufferers with bran should be challenged. Proprietary sources of fiber, such as ispaghula, may be more appropriate for those IBS subjects (for example, constipated) for whom fiber supplementation is believed justified.

Colonic Diseases, Functional↗

PubMed1998

Pain comparison after subcutaneous administration of single-dose formulation versus multidose formulation of epogen in hemodialysis patients.

Subcutaneous (s.c.) injection is an approved route of administration for recombinant human erythropoietin (epoetin alfa). However, pain at the injection site with the single-dose formulation has limited its use. With the recent development of a multidose formulation containing benzyl alcohol as a preservative, anecdotal reports have emerged that suggest this product causes less stinging. Using a randomized, triple-blind, placebo-controlled crossover design, this study compared pain perception, intensity, and duration after s.c. injection with a multidose formulation versus single-dose formulation using visual analogue (VAS) and verbal descriptive pain scales (VDS). Twenty-eight hemodialysis patients received s.c. injections of placebo (normal saline) in one arm and either the multidose or single-dose formulation in the opposite arm. One week later, the subjects again received placebo in one arm and the other epoetin alfa formulation in the opposite arm. The VAS and VDS measurements were obtained at time 0 and then every 5 minutes for a period of 30 minutes. Results showed a statistically significant difference in pain perception between formulations at times 0, 10, and 15 minutes for both the VAS and VDS. In conclusion, there was a significant difference in pain perception between formulations with the multidose formulation causing less pain than the single-dose formulation. However, it should be noted that several patients reported no pain with the single-dose formulation. This indicates that individual patient response could be considered when deciding which formulation to use, although it may be difficult to implement an error-free distribution and administration system using the two different formulations.

Adult↗

PubMed1998

Influence of clinical mastitis during early lactation on reproductive performance of Jersey cows.

The purpose of this study was to determine the influence of clinical mastitis on reproductive performance of high producing Jersey cows. Cows (n = 102) with clinical mastitis during the first 150 d of lactation were evaluated. Groups were balanced according to lactation number and days of lactation and sub-divided as follows: group 1, clinical mastitis before first artificial insemination (AI) (n = 48); group 2, clinical mastitis between first AI and pregnancy (n = 14); group 3, clinical mastitis after confirmed pregnancy (n = 40); and group 4, control cows (n = 103) with no clinical mastitis. No differences in reproductive performance were detected because of milk production or mastitis caused by Gram-positive or Gram-negative pathogens. The number of days to first AI was significantly greater for cows with clinical mastitis before first AI (93.6 d) than for all other groups (71.0 d). Artificial inseminations per conception were significantly greater for cows with clinical mastitis after first AI (2.9) than for cows with clinical mastitis before first AI (1.6), cows with no clinical mastitis, or cows with clinical mastitis after confirmed pregnancy (1.7). The number of days to conception for cows with clinical mastitis after first AI (136.6 d) was significantly greater than that for control cows and that for cows that developed clinical mastitis after confirmed pregnancy (92.1 d). Clinical mastitis during early lactation markedly influenced reproductive performance of Jersey cows.

Animals↗

PubMed1997

A novel SNARE complex implicated in vesicle fusion with the endoplasmic reticulum.

Intracellular vesicular traffic is controlled in part by v- and t-SNAREs, integral membrane proteins which allow specific interaction and fusion between vesicles (v-SNAREs) and their target membranes (t-SNAREs). In yeast, retrograde transport from the Golgi complex to the ER is mediated by the ER t-SNARE Ufe1p, and also requires two other ER proteins, Sec20p and Tip20p, which bind each other. Although Sec20p is not a typical SNARE, we show that both it and Tip20p can be co-precipitated with Ufe1p, and that a growth-inhibiting mutation in Ufe1p can be compensated by a mutation in Sec20p. Furthermore, Sec22p, a v-SNARE implicated in forward transport from ER to Golgi, co-precipitates with Ufe1p and Sec20p, and SEC22 acts as an allele-specific multicopy suppressor of a temperature-sensitive ufe1 mutation. These results define a new functional SNARE complex, with features distinct from the plasma membrane and cis-Golgi complexes previously identified. They also show that a single v-SNARE can be involved in both anterograde and retrograde transport, which suggests that the mere presence of a particular v-SNARE may not be sufficient to determine the preferred target for a transport vesicle.

Amino Acid Sequence↗

PubMed1997

Regulation of left ventricular relaxation in the isolated guinea-pig heart by endogenous endothelin.

OBJECTIVE: TO examine the effects of endogenous endothelin-1 on cardiac contraction in the isolated heart using endothelin receptor antagonists. METHODS: Isolated ejecting guinea-pig hearts were perfused with Krebs buffer (1 microM indomethacin) at 37 degrees C, constant loading and heart rate, and high-fidelity left ventricular pressure was monitored by an apical 2F Millar catheter. The effects of the following interventions on left ventricular performance and coronary flow were determined: (a) no treatment (i.e., time controls) (n = 8); (b) the specific ETA receptor antagonist, BQ123 (1 microM, n = 8); (c) the specific ETB receptor antagonist, IRL 1038 (0.1 microM, n = 4; 1 microM, n = 6); (d) exogenous endothelin-1 (0.01 nM, n = 6; 0.1 nM, n = 6); (e) the specific ETB receptor agonist, BQ3020 (5 nM, n = 8). RESULTS: All parameters were stable in control (untreated) hearts. BQ123 induced progressive acceleration of early left ventricular pressure decline and a fall in left ventricular end-diastolic pressure with no effect on peak left ventricular pressure, dP/dtmax, stroke volume or coronary flow. IRL 1038 had no effect on any of these parameters. In contrast, exogenous endothelin-1 exerted potent vasoconstrictor effects associated with a fall in peak left ventricular pressure, dP/dtmax and stroke volume. Similar changes were observed with BQ3020. Concentrations of endothelin-1 < 0.1 nM, which had no vasoconstrictor effect, produced no change in LV function. CONCLUSIONS: These data indicate that basal intracardiac release of endothelin-1 significantly delays LV relaxation in the isolated guinea-pig heart, but has no effect on coronary flow. The contrasting effects of endogenous endothelin-1 (elicited by BQ123) and exogenous endothelin-1 are likely to reflect differences in their site of action and in their effective concentrations at these sites.

Animals↗

PubMed1997

Parental perceptions of barriers to childhood immunization: results of focus groups conducted in an urban population.

The current US immunization rates for 2 year olds are approximately half of the goal set for the year 2000. Research studies have focused primarily on the perception of health care providers in the identification of barriers and benefits to childhood immunization. While health care providers are an important part of the immunization delivery process, the perceptions of parents are also important. In this study, qualitative methods were used to explore perceived parental barriers to childhood immunization delivery. Twelve focus groups comprising White, African-American, Hispanic, urban and non-urban people were conducted at a variety of sites, including clinics, churches, schools and work sites. The results indicated that time off from work, access to well-child care and difficulty understanding the complexity of the immunization schedule were seen as barriers to adhering to an immunization schedule. Participants emphasized problems in taking time off from work to get immunizations, sometimes without pay, and expressed fears that doing so would jeopardize promotions and raises. While some of the parental perceptions were similar to those identified in studies of health care providers in the literature, many were not. This study emphasizes the importance of gathering information from parents as well as from health care providers.

Attitude to Health↗

PubMed1997

Antibiotic residues and prevalence of mastitis pathogen isolation in heifers during early lactation following prepartum antibiotic therapy.

The present study was conducted to determine if antibiotic treatment of heifer mammary glands earlier in the prepartum period reduced the occurrence of residues in milk without compromising efficacy in treatment of intramammary infections. Heifers were assigned randomly to two groups: 1. untreated negative control (n = 42); and 2. intramammary infusion of 200 mg cephapirin sodium (n = 40) 14 days prior to expected calving. Mammary secretions were collected before treatment and during early lactation, and were analyzed for residues by the Bacillus stearothermophilus disc assay. Only four of 127 samples (3.1%) obtained from cephapirin-treated mammary glands at 3 days after calving were positive for residues and most (three of four) were from a heifer that calved within 3 days of treatment. Mammary secretions were also collected before treatment, and at 3 and 30 days after calving for microbiological evaluation. For untreated control heifers, mastitis pathogens were isolated from 67.3% of samples obtained from mammary glands 14 days prior to expected calving, 55.6% obtained 3 days after calving and 36.4% of samples obtained 30 days postpartum. A similar percentage of samples (63.8%) was positive for mastitis pathogens at 14 days before expected calving prior to antibiotic treatment. However, only 15.1% of samples obtained at 3 days after calving and 7.9% of samples obtained 30 days postpartum from mammary glands of antibiotic-treated heifers contained mastitis pathogens. Coagulase-negative staphylococci were isolated most frequently. Intramammary infusion of antibiotics earlier in the prepartum period markedly reduced the occurrence of residues in milk during early lactation without affecting efficacy.

Animals↗