Euthanasia of chickens, young and mature rats, and mice was assessed using chloroform, carbon dioxide and ether. Behavioural patterns were recorded to give some indication of the stress involved. Carbon dioxide induced collapse faster (11.2 +/- 0.4 s) than chloroform (18.9 +/- 0.4 s) or ether (greater than 60 s). With regard to the time taken to death, in carbon dioxide mice had the shortest time (48 +/- 10 s) and mature rats had the longest time (135 +/- 10 s). In chloroform, the only difference was the delayed onset of death (127 +/- 10 s) in the chicken. Behavioural patterns were similar for the chicken in carbon dioxide and chloroform, except for wing flapping, even when unconscious, in carbon dioxide. Chloroform is recommended as more aesthetically acceptable for euthanasia of chickens. Carbon dioxide is recommended for the euthanasia of both rats and mice, considering behavioural criteria. Ether is unsuitable as a euthanasia method as it is dangerous, slow acting and an irritant.

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In one study, 6 cows with high erythrocyte potassium concentrations (HK cows) and 7 with low erythrocyte potassium concentrations (LK cows) were infused with 4.7 ' YO Na,EDTA solution intravenously for 4 h. The immediately observable clinical signs and the sequelae over a period of weeks were recorded and compared. There were no differences in the clinical responses of HK or LK cows to the infusion of NaZEDTA.In a second study, these clinical signs plus those produced experimentally by three other research groups were compared with both the clinical signs of milk fever recorded in three text books and those observed by one of the authors over a period of 25 years in dairy cattle practice. All of the clinical signs of milk fever occurred in the experimental model, but there were extra signs (excessive salivation, excessive lip and tongue actions, and tail lifting) which were not present or recorded in naturally occurring cases of hypocalcaemia.Hypocalcaemia induced in cows by the intravenous infusion of 4.7 ' YO Na2EDTA solution is a reasonably good model for the reproduction of the clinical signs of milk fever, but because of the extraneous signs, and the unusual nature of the subsequent deaths of 3 of 13 cows infused for 4 h, and the death of 1 of 2 cows infused for 4 h daily for 3 days, the model may not be a valid one for periods longer than 4 h in cows.

SummaryThe use of carbon dioxide (C0 2 ) with, and without, oxygen (0 2 ) as a short-term restraint anaesthetic for Wistar rats in which subclinical respiratory disease was endemic, was assessed in 3 separate experiments. In the first, rats were placed in a CO 2 atmosphere generated from solid CO 2 chips in a 70 Iplastic bin, and removed at time intervals ranging from 0 to 120 s after disappearance of the pedal reflex. Eight of 25 rats died, including 2 which were removed immediately the pedal reflex disappeared; it was concluded that CO 2 without O 2 was not a suitable short-term anaesthetic for rats. In a second study, rats were anaesthetized in atmospheres of 50 : 50 and 80 : 20 (C0 2 : O 2 ) provided from commercially available cylinders, in 2 different environments -a 3, 41 glass jar and a 171 plastic bin. Rats became excited in the plastic bin but not the glass jar. Rats in the glass jar displayed visible depression and cessation of whiskers movement significantly more quickly in the 80: 20 (C0 2 : O 2 ) than in the SO: 50 mixture (4'2±0'98s, n=6, and 66·0±4·9s, n=6 vs 13·8±2·77s, n=5 and 152·0±20·8s, n=5, respectively). Rats in the 171 plastic bin lost their pedal reflexes in a mean 41· 5 ± 4· 55 s (n = 11) in the SO : SO mixture and in a mean 30·9 ± 6·38 s (n = 11) in the 80: 20 (C02: O 2 ) group. Those left in the 50 : 50 mixture for 60 sand 180 s after disappearance of their pedal reflexes, recovered these reflexes in 20· 2 ± 0,44 sand 21·5 ± 7· 23 s respectively after removal from the gas. Respiration and heart beat ceased in one rat remaining in the SO : 50 mixture after 13 min 10 s. Received 12 March 1987. Accepted 25 November 1988 No untoward effects occurred in rats left in the 50 : 50 mixture for 180 s after disappearance of the pedal reflex, but 2 died when left for an equivalent period in the 80: 20 mixture. In the third study, examples of the practical use of a 50 : 50 mixture as a short term restraint anaesthetic are described. It was concluded that this mixture was a cheap, safe, and effective means of short-term restraint for rats with subclinical respiratory disease, when the minimal time of exposure to the gases was employed.

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