200. Drinking Water Quality in Brazilian Feedlots and Implications for Trough Water Sampling Procedures.

Abstract Feedlot cattle may consume dozens of liters of water daily, particularly in hot climatic conditions. Therefore, assessing the quality of water provided in feedlot operations is essential to avoid compromising animal performance. Thus, this study aimed to assess drinking water quality in Brazilian feedlots and to determine appropriate sampling procedures for trough water. Eighty-one feedlots were visited across five states. Each feedlot was visited once, and one pen receiving a finishing diet was selected. Three water samples were collected: one from the water inlet and two from the surface of the drinking trough, positioned at equidistant points. All samples were collected in 500-mL plastic bottles, refrigerated, and subsequently frozen. Physicochemical properties and mineral elements of the water were assessed (Table 1). A standardized questionnaire was also used to collect information on water source type, trough cleaning frequency, and other management practices. Descriptive statistics were used to characterize water quality parameters using R software. Spatial variability within the trough was assessed using the maximum critical ratio (MCR) between the two sampling sites. Water sources consisted of wells (66%), surface water (28%), or a combination of both (6%). In most feedlots (52%), troughs were cleaned every two days. Regarding water safety guidelines, Mn exceeded the critical threshold (> 0.05 mg/L) in 2.5% of the water inlets, whereas concentrations in the troughs exceeded this limit in 5% of the operations. Similarly, Fe and total hardness exceeded the maximum limits in 1.2% of the trough samples, whereas they were within safe limits at the source. Considering the alert proximity zone (≤ 20% the limit), the proportion of feedlots approaching the Mn threshold increased from 5% at the inlet to 12% in the trough. Regarding spatial variability within the same trough, pH, electrical conductivity, Fe, and Mn showed low variation between samples, whereas SO4, Mg, Ca, Na, color, total hardness, turbidity, and TDS exhibited considerable variability. Source and trough water met literature-reported limits for key cattle water quality parameters in 98% and 94% of operations, respectively; 95% and 88% fell within the attention zone (≤ 20% the limit). When monitoring water quality, Mn and Fe should be prioritized, as they are most often associated with organoleptic issues. Sampling protocols should include both inlet and trough water. Due to spatial variability within troughs, single-point sampling is inadequate; composite samples are required to represent the water consumed by the herd. For image description, please refer to the figure legend and surrounding text.