Date Full Report Received03/11/2011
Date Abstract Report Received03/11/2011
InvestigationInstitution: University of Guelph
Primary Investigator: Tina Widowski
Co-Investigators: Teresa Casey-Trott, Suzanne Millman, Stephanie Nykamp, Patricia Turner
Funded ByNational Pork Board
Timely euthanasia of low birth weight and compromised piglets prevents unnecessary suffering, provides littermates with a greater chance at success, and offers some economic benefits by reducing continued care and feed costs. Blunt force trauma (BFT) remains the most commonly practiced method for euthanasia of piglets; but the effectiveness of the technique is significantly limited by the size of the piglet, and is not recommended for piglets greater than 12 lbs. When properly performed BFT has been shown to be humane, although it may not be aesthetically or emotionally acceptable for many stock people. Therefore alternative euthanasia methods for piglets are being investigated. Ideally, an alternative should be consistent, humane, aesthetically acceptable, and capable of being used effectively for piglets from birth through the start of nursery phase. Previous investigation (NPB Project #06-165) of a pneumatic non-penetrating captive bolt gun (NPCB) powered by an air compressor showed promise but the design required some modification to ensure consistency. The project reported here investigated the effectiveness of the modified design for euthanasia of newborn piglets and its potential to be used on larger piglets up to 9 kg. (20 lbs).
The present study consisted of two trials. In Trial 1 we tested the effectiveness of the NPCB on 100 suckling piglets that were less than 3 days of age (average weight 1.04 kg ± 0.03 SE) using reflexes that indicate signs of consciousness, duration of neuromuscular spasms (leg paddling) and time to cardiac arrest. We also determined the degree of brain damage by macroscopic scoring of damage at gross necropsy, and by CT scans performed by a veterinary radiologist and microscopic examinations of the brain by a veterinary pathologist on a sample of piglets. Ten stock people (10 piglets each) from 4 different farms performed the euthanasia.
All 100 piglets were immediately rendered insensible without return to consciousness. On average, leg movements ceased in 229 sec (± 9.2 SE). Only five piglets (5%) required a secondary step due to prolonged presence of a heartbeat; all other piglets reached full cardiac arrest in 444 sec (± 18.7 SE). From CT scans, skull fracture displacement averaged 6.2 mm (± 0.07 SE) and severe hemorrhage was reported in 50% of the piglets scored. From macroscopic scoring, moderate to severe damage was found in all piglets. Microscopic analysis reported moderate hemorrhage on the brain surface in 70% of the piglets scored as well as moderate hemorrhage within the brain tissue in 50% of the piglets scored. These results indicated that method was highly effective for euthanasia of the neonate piglets and that its effectiveness on larger weight classes should be investigated.
In Trial 2, 5 piglets were selected from each of four weight classes (n=5: 3, 5, 7, and 9 kg). All piglets were anaesthetized prior to application of the NPCB. Piglets were monitored for rhythmic breathing, leg spasms, and heartbeat. Port-mortem CT scan, macroscopic, and microscopic scoring analyses were completed for all 20 piglets to assess the amount of brain damage and to compare it with that found in the neonates. Of the 20 piglets tested, one required an extra shot due to the presence of rhythmic breathing. Breathing was immediately absent in the remaining 19 piglets. Leg spasms ceased on average in 148 sec (± 12.4 SE). A secondary step was required for one piglet due to sustained presence of a heartbeat. All other piglets reached full cardiac arrest in 371 sec (± 17.9 SE). From post-mortem CT scan analysis, fracture displacement averaged 9.38 mm (± 0.84 SE) and mild hemorrhage severity was reported in 65% of the piglets. From macroscopic scoring, moderate to severe damage was reported in > 90% of piglets.
Comparisons between the neonatal and larger anesthetized piglets indicated that duration of leg spasms was significantly shorter in the larger anaesthetized piglets (p< .001); but time to full cardiac arrest was not different. Results of CT scans and microscopic scoring indicated that brain hemorrhage was significantly less severe in the larger, anaesthetized piglets but that skull fracture displacement was significantly greater (p=.019).
The results form Trial 2 indicated that the NPCB can effectively induce cardiac arrest in piglets up to 9 kg and that it caused brain lesions known to be associated with loss of consciousness in Trial 1. The next stage of research will be testing the effectiveness of the NPCB on conscious piglets. Due to the size of the piglets within the next trial (up to 9 kg), a restraint device will also be designed to ensure the safety of the operator and the piglet.