Comparison of ketamine-xylazine, ketamine-xylazine-butorphanol, and tiletamine-zolazepamxylazine-butorphanol as intramuscular anesthetic combinations for neutering procedures in registered free-roaming cat colonies

Abstract

Background: Free-roaming cats (FRCs) represent a growing welfare and ecological concern, and Trap-Neuter-Return (TNR) programmes rely on safe, field-adapted anesthetic protocols. The purpose of this study is to compare three injectable protocols used in a high-volume TNR setting to improve quality of awaken and reduce isoflurane reliance. Methods: Sixty-three colony cats randomly assigned to one of three intramuscular protocols: ketamine-xylazine (KX), ketamine-xylazine-butorphanol (KXB) and tiletamine-zolazepam- xylazine-butorphanol (ZXB). Sedation depth at 10 min was scored with a validated multiparametric scale, and cats were classified as having no, mild, moderate, or deep sedation. Pain was assessed postoperatively using the Feline Grimace Scale and The Glasgow Composite Measure Pain Scale. Data were analyzed using ANOVA, χ² tests, odds ratios and an exact binomial test (α = 0.05). Results: Surgical duration did not differ between protocols (p = 0.582). In contrast, recovery was protocol-dependent, KXB produced significantly faster onset of awakening and shorter timer to sternal recumbency than KX and ZXB (p = 0.0247 and p = 0.0076, respectively). At 10 minutes, deep sedation was most frequent with KX (90.9%), followed by ZXB (66.7%) and KXB (47.8%), with a significant association between protocol and sedation depth (p = 0.008). Cats receiving KX were 10.9 times more likely to achieve deep sedation than those given KXB (p = 0.003). Isoflurane supplementation was required most often in the ZXB group, followed by KXB and least in KX. Sex and body weight were not associated with sedation depth. All cats were pain-free on both scales; this complete absence of pain was statistically significant (p = 0.0395; 95% CI: 0.9536-1.000). Conclusions: In a TNR field context, KX provided the most reliable deep sedation with minimal need for inhalational supplementation, whereas KXB offered faster recoveries at the expense of lighter anesthesia, and ZXB produced intermediate sedation but frequently required isoflurane. All three protocols ensured effective analgesia in this FRC population.