PSIX-4 - Comparison of water footprint in roughage-fed and grain-fed beef cattle finishing systems

Beef cattle production has been argued to represent a massive player on water usage given the high water footprint (WF) attributed to the livestock sector. From a water usage mitigation standpoint, at the animal level, manipulation of drinkable water is possible since major differences in water utilization are highly related to diet composition and feed quality. The objective of this study was to evaluate the effects of two cattle finishing systems, grain-finished versus roughage-finished on dry matter intake (DMI), water intake (WI), WF and water use efficiency (WUE) of Angus cattle. Twenty-four steers (385 ± 10.80 kg) were fed either alfalfa only (roughage-finished) or predominantly whole grain (80% corn and 20% alfalfa). Individual DMI and WI were measured for 105 days. Water footprint was expressed as amount of green (rainwater; WFg), blue (surface and groundwater; WFb), and grey (waste; WFgy) water used for feed production and WI of animals, and the sum of all three represents the total WF (TWF). The WUE was calculated as the integral between water used during the experimental period, and then converted into water efficiency as divided by cold carcass weight (CCW). Differences amongst treatments were compared via orthogonal contrast using the GLIMMIX procedure of SAS (version 9.4) with treatment as fixed effect and animals as a random effect. Roughage-fed animals presented significantly higher WI and DMI (P = 0.0005 and P < 0.0001, respectively), 80 kg lighter CCW (P = 0.0005) when compared to grain-finished animals. Grain-finished animals had a lower WFb WFgy, and TWF (P < 0.0001), but a higher WFg (P < 0.0001). Water use efficiency was twice as high for roughage-fed animals. Therefore, for the finishing phase, steers finished on a grains had a lower WF when compared to roughage-fed animals.