Differences among restriction endonuclease DNA fingerprints of Pennsylvania field isolates, vaccine strains, and challenge strains of infectious laryngotracheitis virus.

Restriction endonuclease fingerprints of infectious laryngotracheitis virus (ILTV) DNA from 13 Pennsylvania field isolates, embryo-propagated and tissue-culture-propagated vaccine strains, and three reference strains were compared. These comparisons were made to evaluate the possible contribution of mutation of ILTV vaccine strains to recent outbreaks of infectious laryngotracheitis (ILT) in Pennsylvania. Six different restriction enzymes were used to generate the fingerprints. Differences in DNA banding patterns were revealed between the currently used ILTV vaccine strains and six of the 13 field isolates. Even greater DNA banding pattern differences were found between the older ILTV reference strains and the vaccine strains. The ILTV DNA fingerprints generated in the present study suggest that at least five different strains of ILTV have contributed to the outbreaks of ILT that have occurred since 1987 in Pennsylvania.     

Physiological aspects of growth promotion in poultry

Growth promotants used in poultry production fall into two categories: those which increase the utilization of food (e.g. antibiotics) and those which have anabolic activity.The mode of action of antibiotics is not certain. Several interacting factors may be involved: altered gut microflora, reduced ammonia production, thinner intestinal walls, reduced epithelial cell turnover and improved nutrient absorption. It has been suggested that antibiotics have a systemic action but evidence of gross physiological change is difficult to find. Thyroid function was not affected after feeding aureomycin but penicillin-fed chickens had a greater plasma growth hormone concentration than control birds. The plasma corticosterone responses to a stressor, corticotrophin, were similar in control and penicillin-fed birds.Goitrogenic substances cause lipid deposition and thyroactive substances improve feather cover but neither consistenly improve growth.Oestrogenic substances tend to stimulate energy consumption and lipogenesis at the expense of protein deposition. Use is made of them to improve carcass quality of capons and turkeys. Androgenic substances have either no effect or depress growth.Growth hormone improves weight gain, increases protein and decreases fat in the carcass. It may be of use in the production of older table birds.     

Control of the bindweeds Convolvulus arvensis and Calystegia sepium in fruit crops

Convolvulus arvensis is the most important species of bindweed in Britain. Established plants spread by means of lateral roots: establishment from seed and fragments of the underground growth is not important. The hormone weedkillers like 2,4-D and MCPA give good control in the year of treatment. With the correct dose and timing there is also good control in the year after treatment. Adding paraquat to 2,4-D reduces the effect in the year after treatment. Repeated annual treatment with high doses of chlorthiamid that prevent shoot growth for the entire season are no more effective against the underground growth than the standard dose of 2,4-D. Calystegia sepium spreads rapidly by rhizomes and stolons. It is more susceptible than C. arvensis to MCPB.     

Effect of daily injections of ACTH on growth and on the adrenal and lymphoid tissues of two strains of immature fowls.

1. The effects of daily injections of ACTH (30 IU/kg) or physiological saline on growth and on adrenal and lymphoid tissues of Rhode Island Red (RIR) and Light Sussex (LS) chickens were compared at 1, 2 and 3 weeks of age. 2. Saline injections retarded skeletal growth in both strains during the 1st week but only affected weight gain in LS birds. 3. Injections of ACTH depressed growth rate, caused adrenal enlargement and deplenished adrenal cholesterol to the same extent in both strains. 4. ACTH caused a greater reduction in bursal size in RIR than in LS birds. Spleen size was reduced by ACTH only in RIR birds. 5. At 2 and 3 weeks the plasma concentrations of corticosterone of RIR birds were greater than those of LS birds. Plasma corticosterone concentrations were within the normal range 24 h after the last injection of ACTH in both strains. 6. Plasma concentrations of growth hormone was unaffected by ACTH treatment in RIR birds, but it was increased in LS birds after 3 weeks of treatment.     

Molecular characterisation of bovine faecal Escherichia coli shows persistence of defined ampicillin resistant strains and the presence of class 1 integrons on an organic beef farm

Antimicrobial use is heavily restricted on organic farms; however, few studies have been conducted to investigate the impact this has on the epidemiology of resistance in pathogenic and commensal bacteria. We investigated the persistence of antimicrobial resistant Escherichia coli within an organic beef herd over a period of 28 months. Faecal samples collected monthly from three calf cohorts and annually from adult cattle and environmental samples, were screened for the presence of ampicillin, apramycin and nalidixic acid resistant E. coli. The prevalence of ampicillin resistance ranged from 27.3 to 40.7% in the annual herd and environmental samplings (n=22-55) and was greater in the calf cohorts, with a peak cohort prevalence of >47% in all 3 years (n=16-18). Apramycin and nalidixic acid resistant E. coli were rare. Pulsed-field gel electrophoresis (PFGE) identified 10 main genotype groups within the herd, with evidence of strain transmission between different livestock groups, animal species and years. Multiple resistance was found in >44% of isolates tested, with ampicillin, neomycin, sulphamethoxazole and tetracycline carriage the commonest phenotype identified. PCR detected the presence of class 1 integrons in <5% of resistant isolates, 6/7 of which were of cattle origin. These data demonstrate that ampicillin resistant E. coli was common on the farm despite restricted antimicrobial use, although strain diversity was low. Persistence of defined genotype groups was observed between years, together with the transmission of resistant strains between different animal species on the farm.