Water: The Frequently Neglected Nutrient in Growing and Finishing Diets

Abstract Text:

The objective of this presentation is to describe water requirements of feedlot cattle and to discuss the effects of water sulfate concentration on water intake (WI). The Recommended Nutrient Allowances for Beef Cattle report was published by the National Research Council (NRC) in 1945 and was revised in 1950, 1958, 1963, 1976, 1984, and 1996 (update 2000).  Water requirements were first described in the 1976 NRC and warranted a separate chapter in 1984. However, in the much aligned 1996 (update 2000) NRC, the discussion of water was relegated to a section in the vitamin chapter.  The findings of Winchester and Morris (1956), describing WI as a function of BW, DMI, and ambient temperature, were used as the basis of the water discussion in the 1976, 1984, and 1996 (update 2000) NRC publications.  Also included in the 1996 (update 2000) revision was discussion of an equation predicting WI by feedlot cattle based on maximum daily temperature (Tmax), DMI, precipitation, and dietary salt concentration (Hicks et al., 1988).  Arias and Mader (2011) developed models predicting WI from several environmental measurements.  Solar radiation (SR, W/m²) and thermal heat index (THI; Thom, 1959; NOAA, 1976) were the most important factors predicting WI during summer; however, Tmax and THI were the best predictors of WI during winter.  Sexson et al. (2012), using a univariate analysis, found that WI from April through October was positively related to all measures of temperature, negatively related to all measures of relative humidity, positively related to wind velocity, negatively related to sea level barometric pressure, positively related to DMI, and negatively related to BW.  A multivariate model predicting WI accounted for 32% of the variation in WI.  Loneragan et al. (2001) and Sexson et al. (2010) demonstrated reduced WI for steers consuming water with > 1000 mg/L sulfate as compared to steers consuming water with < 1000 mg/L sulfate.  The observed reduction in WI associated with increased sulfate concentration was greater during summer months as compared with spring or fall.  Water is described in a separate chapter in the recently released Nutrient Requirements of Beef Cattle, Eighth Revised Edition (National Academies of Sciences, Engineering, and Medicine, 2016).  Equations predicting WI in the eighth revised edition were developed using surface regression of the tabular values published by Winchester and Morris (1956) and include current effective temperature index, as computed from temperature, relative humidity, wind speed, and hours of daylight.

Keywords: Water intake, Water sulfate concentration, Feedlot cattle