Swine behavioral and physiological response to increasing sodium nitrite oral drench administration and resulting tissue residues

Objectives: This study aimed to evaluate the physiological and behavioral responses of pigs administered sodium nitrite, determine an ideal dosing rate by oral drenching of sodium nitrite for depopulation events, and evaluate the nitrite residue present in the ocular fluid and skeletal muscle after sodium nitrite administration. Materials and methods: Four groups of 10 market weight pigs (40 market weight pigs total) and 1 group of 10 sows were used. Each group of market weight animals received a different oral drench dose of sodium nitrite solution (1× [400-441 mg/kg], 2× [800-882 mg/kg], 2.5× [1000-1102 mg/kg], and 3× [1200-1323 mg/kg]) and was observed for distress behaviors. Two market weight animals in each treatment group were implanted with a monitor to measure body temperature, heart rate, and activity levels. The dosing rate with apparent best behavioral and physiological response was applied to the 10 sows and the same behaviors monitored. After death was confirmed, ocular fluid and skeletal muscle samples were collected from the sows. Results: An increased dosage of sodium nitrite greatly reduced the time to distress with a significant linear relationship. A higher frequency of vocalizations and the most frequent spikes in activity levels were observed in the lowest dosing group. No correlation was found between ocular fluid nitrite and skeletal muscle sodium nitrite concentrations. Implications: Oral drenching of sodium nitrite is a viable method for swine depopulation events. Higher doses of sodium nitrite have better welfare associations. Ocular fluid nitrite anion concentrations do not correlate with sodium nitrite skeletal muscle concentrations.