PSXVI-3 Individual Water Use Efficiency in Beef Cattle

Abstract Public opinion has focused on animal agriculture being in competition with growing urban populations for land and water resources. With much of the US in drought conditions, improving water use efficiency is critical for the sustainability of animal agriculture. To date, little has been done to assess water efficiency in cattle. There is evidence for a positive relationship between water intake and DMI, but relationships between water and feed use efficiencies are likely more complex. Our objectives were to understand the magnitude of variation in water use efficiency and make comparisons with feed efficiency, as measured by residual feed intake (RFI). Our study utilized yearling bulls, steers, and heifers (n=745) between the summer of 2019 and the summer of 2021. Individual feed and water intakes were determined using a real-time feed intake system and an In Pen Weighing system (IPW). Water use efficiency, residual water intake (RWI), was calculated similarly to RFI where an expected water intake was determined for the group by regressing average daily water intake on metabolic mid-body test weight and either ADG or DMI. RWI was then calculated as actual daily water intake minus expected daily water intake. The estimation of expected water intake using DMI had a greater R2 than when ADG was used (.36-.51 vs .31-.35). The range in off-test RFI was about one order of magnitude smaller than the range of RWI (e.g., RFI -0.90 to 0.73 kg vs RWI -7.34 to 8.49 L), indicating greater variability in water intake compared with feed intake and a relationship among DMI, ADG, and RWI that needs to be further explored. As animal agriculture strives to be more sustainable, water use efficiency needs to become a common measure and genetic progress needs to be made. There appears to be sufficient variation in the trait to make this feasible.