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Organophosphate-induced delayed polyneuropathy (OPIDP) is thought to result from organophosphorylation of neuropathy target esterase (NTE), followed by an “aging” of the phosphorylated NTE. Prophylactic against OPIDP should thus be achieved by production of an inhibited but “nonaging” NTE. Resolved stereoisomers of ethyl phenylphosphonic acid esters produce two forms of inhibited NTE; in vitro one form ages rapidly and the other only negligibly. The present study examined the in vivo effects of two preparations of incompletely resolved isomers of EPN oxon (ethyl 4-nitrophenyl phenylphosphonate) and its thionate on adult hen brain and spinal cord NTE and the relationship of inhibition and aging to the development of OPIDP. Single doses of the l -(−)-isomers (Preparation A, 7:3 proportion of isomers, or Preparation B, 9:1) caused severe neuropathy after doses which produced 70% aged inhibited NTE and mild effects after 50–60%. Single doses of the d -(+)-isomers produced either equal amounts of aged and unaged inhibited NTE (Preparation A) or predominantly unaged (Preparation B): the amount of aged was never more than 50% and no clinical OPIDP occurred. Doses of d -(+) which produced 50% unaged inhibited NTE were protective: challenge with the highly neuropathic phenyl saligenin cyclic phosphate did not cause OPIDP. All effects are consistent with the two-stage initiation process which requires both inhibition of NTE and subsequent modification of the protein by an “aging” process. Previously reported neuropathic effects of d -(+)-EPN probably reflect a substantial proportion of l -(−)-isomer present in the test material. Neuropathic studies with chiral OP esters should consider the possibility of production of protective unaged inhibited NTE in test animals.

SUMMARY Disease levels in calves were examined using a system which recorded the signs observed from treatment and its cost. The result in cost per sick calf and cost per calf place gave some indication of disease severity i. e. the number and degree of signs observed and their duration. The trials were used to indicate the use of the recording system. The size of the study was not sufficient for a positive assessment of the value of the different feeding and management systems. In trial 2 diarrhoea was much more common (40%) using a machine (M2) which dispensed reconstituted milk powder as fast as it was drunk than with once-a-day (OD) bucket feeding (8%) and calves on a machine (M1) which mixed feed on a two- minute cycle (13%). A high level of respiratory disease was seen in OD calves of trial 3, and this was the main difference seen in trial 4:12 and 13% in once-a-day fed calves (OD and ODC) and 50% in machine-fed (M2) calves. Combining the information from these three trials with that from a previous study showed that OD and twice-a-day bucket feeding produced less diarrhoea than machine feeding (M1, M2). More respiratory disease occurred between entry and five weeks in animals used in a controlled environment house than in a naturally-ventilated monopitch building. More disease occurred in each trial pre-weaning than post weaning (weaning at five weeks). Overall mortality was 1·1 % and the most common diseases experienced up to 12 weeks were respiratory disease (31·2%), diarrhoea (20·1%), eye infections (11·2%) and navel and joint problems (2·2%).

The interaction in vivo of four O-alkyl O-2,5-dichlorophenyl phosphoramidates with neural neuropathy target esterase (NTE) and acetylcholinesterase (AChE) and their ability to cause delayed polyneuropathy in hens has been examined. Previous studies in vitro (Vilanova, Johnson & Vicedo, Pestic. Biochem. Physiol., 28 (1987) 224) had led to the prediction that these compounds would not be neuropathic but, rather, would be prophylactic agents against organophosphorus-induced delayed polyneuropathy. In vivo the effects of these esters on the enzymes differ in 2 respects from effects in vitro: (i) Relative sensitivity of the enzymes was different: thus greater than 50% of brain NTE remained 24 h after an oral dose of 15 mg/kg of the n-hexyl ester while only 10-30% of AChE remained although NTE was the more sensitive enzyme in vitro; (ii) In no case could the inhibited NTE or AChE in autopsy samples from birds dosed with any of the 4 esters be reactivated by treatment with potassium fluoride in vitro: the inhibited enzymes produced by incubation of tissue with the esters in vitro had been reactivatable. Prophylaxis, with therapy in some cases, was required to prevent acute anticholinesterase poisoning when doses were sufficient to cause high inhibition of neural NTE. Inhibition in brain was typically 5-10% more than in spinal cord and 10-15% more than in sciatic nerve. Unambiguous signs of polyneuropathy (Grade 3 or more on an 8-point scale) were not seen in birds observed up to 3 weeks after doses which caused less than 70% inhibition of NTE in brain and spinal cord or less than 60% inhibition in sciatic nerve of pair-dosed birds assayed 24 h after dosing. Doses of 300, 10, 100 and 65 mg/kg, respectively, of the methyl, ethyl, n-butyl and n-hexyl esters caused greater than 70% inhibition of NTE in all 3 neural tissues and neuropathy in the majority of observed birds. Analysis of consolidated dose/response data from 36 assayed and 51 observed birds showed that effects of Grade 3 or more were produced in about 90% of birds when inhibition of NTE was greater than 90% in brain, greater than 85% in spinal cord or greater than 75% in sciatic nerve.(ABSTRACT TRUNCATED AT 400 WORDS)

SUMMARY The degree of calf disease in three groups of calves was studied under different feedings systems. The animals were bucket-fed once (OD) or twice (TD) a day, or ad-libitum machine fed (M1). Various methods of examining the data were considered and it was suggested that the recording system should include some element of disease ‘severity’, i. e. the degree to which signs were present and the duration of the illness. A simple recording system to produce results for on-farm comparison was suggested based on treatments and their costs. This was affected by how long therapy was continued and, in general, more expensive and larger numbers of different drugs tended to be used at the same time in animals which were clinically considered to be more seriously ill. Cost was calculated on the basis of cost per sick calf and cost per calf place. Comparison between the use of OD and TD feeding revealed little difference in level of disease; in the M1-fed animals there was more diarrhoea and respiratory disease. Slightly more disease occurred pre-weaning than post weaning (weaning at five weeks). There was no mortality during the trial.