Date Full Report Received11/04/2020
Date Abstract Report Received11/04/2020
InvestigationInstitution: Carthage Veterinary Service
Primary Investigator: Aaron Lower
Co-Investigators: Gustavo de Sousa e Silva, Joseph Connor, Beau Peterson, Youngsoo Lee
Funded ByNational Pork Board
It is critical to develop feasible mass euthanasia technology that is humane, economical, safe, and less labor intensive. Microencapsulated sodium nitrite (meSN) feral swine bait has been developed and marketed by Animal Control Technologies Australia (ACTA) as a feed-based toxicant for feral swine control. This technology has not been applied to commercial swine in confinement barns, just feral swine. Sodium nitrite is a chemical commonly used in low concentrations as a preservative in processed meats. If consumed at high doses, sodium nitrite can convert hemoglobin to methemoglobin that is unable to transport oxygen in the blood. The reduced oxygen carrying capacity of the blood depletes the brain and tissues of oxygen, causing unconsciousness and death. Previous pilot trials showed that SN can effectively euthanize swine, however, has been difficult to achieve reliable ingestion when SN is added to commercial feed due to palatability issues.
110 early nursery weight pigs (6.2 kg average weight) were randomly allotted to one of the 11 treatments (one treatment per pen, 10 pigs per pen). Granular form SN (un-encapsulated) salt and microencapsulated SN were the two sources of SN used in the feeds. There were three different feed flavors or taste suppressor combinations. Dried molasses at 4.4% inclusion was the first feed flavor. Vanilla at 0.1% inclusion was utilized as the second flavor. A bitterness taste suppressor at 0.2% inclusion was utilized as the third treatment. The dosage of SN was targeted at 20 grams of SN/100kg of pig at 2 lbs offered per pig. The resulting concentration was 2.2% SN per kg of feed. The dosage of SN in the water was targeted for an intake of 20g of SN per pig with an intake estimation of 0.25 gallons per pig.
2 Feed + SN
3 Feed + SN + Molasses
4 Feed + SN + Taste suppressor
5 Feed + SN + Flavor
6 Feed + meSN
7 Feed + meSN + Molasses
8 Feed + meSN + Taste suppressor
9 Feed + meSN + Flavor
11 Water + SN
Feed was removed 24 hours prior to offering treatments. The water treatment pens had water removed also 24 hours to trial start. Pigs were offered their respective treatments for 3 hours of ab libitum consumption.
Of the feed treatment groups, 53 of 80 pigs (66%) were euthanized by SN. Each feed treatment resulted in a range of 50-80% mortality regardless of treatment. 63% of the pigs vomited during the feed treatment. The average time to death was 2 hours and 12 minutes. The earliest pig died at 1 hour and 13 minutes and latest pig at 3 hours. The water treatment group (Group 11) failed to induce clinical signs or mortality. Average feed consumption was 0.14 kg/pig. Pigs on averaged consumed 0.49 g of SN per kg of body weight with a range of 0.20 to 1.09 g of SN per kg.
General timeline of clinical signs:
• 0-45 minutes: good feed intake
• 45-75 minutes: stop eating and huddle
• 75 minutes: start to observe vomiting. Progresses to ataxia and palor and then lateral recumbency.
• 90 minutes: earliest mortality. Most were 90-180 minutes.
All feed formulations performed similarly, with only a 30% mortality rate range between treatments. This method of euthanasia is promising for use in constrained circumstances for depopulation, however, it did not achieve 100% mortality in this trial. It is imperative that pigs receive a bolus of SN for a lethal amount. Increasing the inclusion rate may increase the mortality rate but at the risk of pigs being averse to consume the product. It would also be recommended that pigs have uncompetitive access to consume feed when SN feed is administered.
There were minor differences in intake and mortality between the following groups (meSN versus SN, molasses versus vanilla versus taste blocker groups, unflavored meSN and SN versus flavored and taste blocker). The flavorings and taste blockers did not improve intake and mortality in comparison to feed with meSN and SN by itself.
Pigs were averse to consuming water with SN solubilized. There was minimal intake and no clinical signs.
Sodium nitrite is a viable option for mass depopulation in constrained circumstances. It euthanized between 50-80% of the pigs when offered to commercial swine in this study. Further development is needed to increase the euthanasia rate of pigs, speed up time to death, and decrease the percentage of pigs that vomit.
For further questions or information on this study, please contact:
Aaron Lower, DVM