98 Growth and mineral content of tall fescue grown in manure extracts from horses fed varying trace mineral sources and levels

Abstract

Horse manure spread on pasture can provide nutrients and minerals to plants, but the effect of horse diet on fecal mineral availability to plants is unknown. This study's objective was to determine if the amount and source of trace minerals (TM) fed to horses would affect the growth and mineral content of plants grown hydroponically in manure extracts. Nine horses were used in a replicated 3 × 3 Latin square design for the study's feeding portion. Horses had ad libitum access to forage and were fed a protein pellet containing one of 3 dietary treatments: a low TM treatment with no added TM (CON) or industry relevant TM level treatments with TM added as either organic TM (ORG) or inorganic TM (ING). Added TM were Co, Cu, Mn, Se, and Zn at equivalent amounts for ORG and ING. There were 3 21-d feeding periods, including a 5-d washout; each horse received each treatment. Feces were collected on d 21 of each period. Manure extracts were made from each horse by mixing wet feces with distilled water (30 g DM/L), incubating for 20 h, and straining. Extracts were combined by treatment and TM concentrations reflected dietary levels, with ING and ORG being similar and greater than CON. Manure extracts, distilled water/negative control (WAT) and Steinman's nutrient solution/positive control (NUT) were applied as liquid treatments. Tall fescue seeds were germinated in a growth chamber, and seedlings transferred to rockwool in pans (40 seedlings/pan) on d 9. Pans were randomly assigned to treatment with 4 replicate pans/treatment. Plants were grown in an environmentally controlled room, and watered with the liquid treatment to keep fluid amount consistent in the pans. Plant height was recorded every 10 d. At the experiment's end (d 41), plants were harvested to determine plant DM biomass and TM content using ICP-MS. Biomass, final height and TM data were analyzed using ANOVA and growth rate data were analyzed using regression and orthogonal contrasts. The NUT and ORG plants had greater final DM biomass and height compared with WAT plants, while ING and CON were intermediate ( P < 0.05). Growth was quadratic for WAT, with a plateau in growth at d 25. Growth in the remaining treatments was linear and rate was greatest for NUT, followed by ORG, lowest in CON, and ING did not differ from ORG and CON ( P < 0.05). Cu and Mn was greatest in NUT ( P < 0.05). Zn was lower in WAT compared with all treatments ( P < 0.055) and Co and Se were not different among treatments ( P > 0.05). The level and source of TM in horse diets affected plant availability of nutrients in the manure, which can influence pasture growth and composition.