88 Exploring equine mortality composting

Abstract

Composting is an environmentally friendly, economical, and bio secure method for livestock mortality disposal. Recent changes in availability of rendering for chemically-euthanized animals has created a need to explore composting. The objectives of this study were to demonstrate successful equine mortality composting in the winter and document sodium pentobarbital concentrations throughout the process. The authors hypothesized composting would degrade carcasses and reduce pentobarbital concentrations. On 26 September 2019, 4 horses (451 ± 36 kg) were euthanized for terminal medical reasons by intravenous administration of sodium pentobarbital (88 ± 2 mg/kg; Fatal-Plus, Vortech Pharmaceuticals, LTD, Dearborn, MI). Carcasses were transported immediately to a private composting site. Four separate compost piles were constructed on a 6.1- by 27.4-m concrete pad. Each pile consisted of 46 cm of playground woodchips, 8 cm of dry pine shavings, a horse carcass, and 61 cm of a 2:1 mixture of horse stall waste and cattle feedlot waste. Data loggers were placed at 46- and 91-cm depths to record pile temperatures every 8 h. Compost piles were topped with manure mixture at d 9 to cover cracks, turned at d 50 when pile temperatures were ≤54.4°C, and concluded on d 216 following approximately 5 mo. of curing (≤43.3°C). On d 50 and 216 piles were cut into 3 mirrored cross sections and subsampled (n = 36) to form one composite sample per cross section. Samples were analyzed for sodium pentobarbital (on an “as is” basis) and nutrient content. Carcass degradation was scored on a subjective scale (1 = discernable carcass, 5 = few large brittle bones). Pentobarbital concentrations were compared using a 2-way ANOVA with cross section and day as fixed effects. P-values < 0.05 were considered significant. Three piles received a carcass degradation score of 2 at d 50 with soft tissue, hair, and hide present. By d 216, all piles received scores of 3 (n = 2) or 4 (n = 2) with some hide and large bones remaining. Pentobarbital concentrations declined between d 50 and d 216; however, remained detectable at d 216. On average, pentobarbital concentrations tended to be higher (9.05 mg/kg) at the center of the compost pile on d 50 (P < 0.05); however, on d 216 concentrations were similar (0.432 to 0.735 mg/kg; P > 0.05) among cross sections. While pentobarbital concentrations at d 216 were minimal, further research is needed to determine environmental implications of composting chemically-euthanized equines. These findings suggest mortality composting is an effective method for disposing of equine carcasses.