Comparison of carbon dioxide and argon euthanasia: effects on behavior, heart rate, and respiratory lesions in rats.

In this study we compared rat (n = 16) responses to euthanasia with either gradual-fill CO(2) or rapid induction argon gas by evaluating the animals' heart rate via radiotelemetry, behavior, and vocalizations. We also evaluated the histologic effects of the gases. Rats were placed in an open test chamber 24 h before the start of the experiment. During baseline tests, rats were exposed to oxygen to evaluate the effects of the noise and movement of gas entering the chamber; 1 wk later, rats were euthanized by gas displacement with either 10%/min CO(2) or 50%/min argon gas. Rats tended to have higher heart rats and were more active during the baseline test, but these parameters were normal before the euthanasia experiment, suggesting that the rats had acclimated to the equipment. Heart rate, behavior, and ultrasonic vocalizations were recorded for 2 min after gas introduction in both groups. All rats appeared conscious throughout the test interval. The heart rates of rats exposed to argon did not change, whereas those of rats exposed to CO(2) declined significantly. Unlike those exposed to CO(2), rats euthanized with argon gas gasped and demonstrated seizure-like activity. There were no differences in the pulmonary lesions resulting from death by either gas. Our results suggest that argon as a sole euthanasia agent is aversive to rats. CO(2) using a 10%/min displacement may be less aversive than more rapid displacements. Future research investigating methods of euthanasia should allow sufficient time for the rats to acclimate to the test apparatus.

Effective and safe anesthesia for Yorkshire and Yucatan swine with and without cardiovascular injury and intervention.

The goal of this study was to identify an injectable anesthetic protocol that provides sedation sufficient for peripheral vascular catheterization, intubation, and transport while minimizing cardiovascular changes in Yorkshire and Yucatan pigs with and without cardiovascular injury and intervention (CI). Phase 1 examined the safety and efficacy of acepromazine-ketamine, diazepam-ketamine, midazolam-ketamine, and medetomidine-ketamine in 5 healthy Yorkshire pigs. For each drug combination, we obtained multiple measurements of heart rate, blood pressure, respiratory rate, temperature, sedation score, ability to catheterize and intubate, and recovery score. Phase 2 evaluated and refined the dose of the most effective Phase 1 anesthetic combination (midazolam-ketamine) in healthy and CI Yorkshire pigs (n = 53 trials). Phase 3 mirrored Phase 2 but tested midazolam-ketamine in healthy and CI Yucatan pigs (n = 34 trials). Midazolam (0.5 mg/kg)-ketamine (25 to 27 mg/kg) was the most effective anesthetic combination in healthy Yorkshire pigs, but this dose was less effective in healthy Yucatan pigs and CI Yorkshire and Yucatan pigs. Midazolam-ketamine resulted in tachycardia and apnea more frequently in CI pigs than healthy pigs. This combination also caused vomiting in one CI Yucatan pig. Overall, midazolam-ketamine provided safe and effective sedation for catheterization and intubation of both healthy and CI pigs. This study suggests Yucatan pigs may require a higher dose midazolam-ketamine to achieve the same level of sedation as that in Yorkshire pigs. Although anesthetic complication rates were higher in CI pigs, our results indicate that midazolam-ketamine can be safely used for sedation of both pig breeds with and without CI.

Infertility in CFW/R1 mice associated with cystic dilatation of the bulbourethral gland.

A third of male inbred CFW/R1 mice in a breeding colony developed subcutaneous, bilateral, perineal masses determined to be cystic bulbourethral glands. The masses developed in mice between 4 and 15 months of age. After development of these perineal masses, diseased males were unable to produce offspring. Gross examination revealed the masses impinging on the scrotum and displacing the testes into the inguinal canal. The perineal masses were paired, membranous, translucent cysts, 6 to 10 mm3, attached to the bulbocavernosus muscle and connected to the pelvic urethra by way of a non-patent duct. The cysts contained a clear to tan, minimally cellular, viscous fluid with high mucus content, as documented by examination of Wright Giemsa-stained cytologic preparations. Histologic examination of hematoxylin and eosin-stained sections revealed cystic tubuloalveolar glands surrounded by striated muscle and lined by a single layer of pyramidal cuboidal to columnar epithelial cells with pale, basophilic, lacy cytoplasm and round, basal, condensed nuclei. These gross and histopathologic findings were consistent with cystic dilatation of the bulbourethral gland.