Characteristics and Sodium Pentobarbital Concentrations of Equine Mortality Compost Piles in the Upper Midwest.

Recent changes in rendering availability for chemically-euthanized animals have created a need to explore composting as an equine mortality management method. The objectives of this study were to evaluate equine mortality composting in the Upper Midwest during fall and spring, document sodium pentobarbital concentrations throughout the process, and determine nutrient content of finished compost. During each season, four horses were euthanized by intravenous administration of sodium pentobarbital. Carcasses were positioned at the center of a woodchip and shavings base and covered with a 2:1 mixture of horse stall waste and cattle feedlot waste. Data loggers were placed at 46- and 91cm depths to record pile temperatures every 8 hours. At turning (44-50 days) and trial conclusion (181-216 days), compost piles were sampled for sodium pentobarbital and nutrient composition. Piles contained large bones after 6 months of composting. Sodium pentobarbital remained detectable at trial conclusion (<0.002-1.49 mg kg1 dry matter); however, composting reduced the estimated quantities of sodium pentobarbital by ≥94% (P ≤ .001). Compost from each season met ideal land application values for organic matter (45%-48%), pH (7.3-7.6), and electrical conductivity (3.3-3.4 mm hos cm-1). Low NPK and high C:N ratio (20-30) indicate compost could partially replace synthetic fertilizers when land applied. These findings suggest equine mortality composting is an effective management practice during fall and spring in the Upper Midwest. While remaining sodium pentobarbital residues were minimal, further research is needed to determine environmental implications of composting chemically-euthanized equines.

Forage Characteristics and Grazing Preference of Cover Crops in Equine Pasture Systems.

Cover crops are commonly used to provide environmental benefits and can extend the grazing season, but have not been explored in horse pastures. The objectives of this research were to evaluate forage mass, forage nutrient composition, and preference of annual ryegrass, winter rye, berseem clover, purple top turnip, and daikon radish under horse grazing. Cover crops were seeded in monoculture and mixtures in August 2018 and 2019 as a randomized complete block with four replicates and grazed by four adult horses. Prior to grazing, forages were sampled to determine herbage and root mass and nutrient composition. After grazing, forages were visually assessed for the percentage of removal on a scale of 0 to 100% to estimate preference. Data was analyzed using an analysis of variance and linear regression; significance was set at P ≤ .05. Berseem clover was the lowest producing forage (590 to 1,869 kg ha-1 dry matter; P ≤.001), while minimal differences in herbage mass were observed among the other cover crops. All forages met digestible energy (>2.17 Mcal kg-1) and crude protein (>19%) requirements for idle, adult horses. Berseem clover was most preferred (>73% removal) while turnip and radish were the least preferred (<19% removal; P ≤.001). Winter rye and annual ryegrass in monoculture and when seeded with berseem clover were moderately preferred (20%-68% removal). Placing a priority on preference, berseem clover, annual ryegrass, and winter rye appear to be suitable cover crops to extend the grazing season in horse pastures.