PSIII-13 - Effects of weather, body weight, and feed intake on total and liquid water intake in beef bulls

Abstract: Research conducted in the 1950s to determine water requirements utilized cattle that vary greatly from the animals being raised today. Changes in lean composition and growth rate in young cattle and milk production and mature size in cows have likely altered water requirements. Furthermore, most of the research has been conducted on animals being fed for slaughter, rather than bulls or reproductive females. The objective of this study was to analyze the effect of weather variables, dry matter intake (DMI), and body weight (BW) on total daily water intake (TDWI) in growing beef bulls. Angus (n = 15) and Simmental x Angus bulls (n = 29) with an average initial BW of 362.5 ± 27.0 kg were housed in an open front, monoslope building at the SDSU Cow-Calf Education and Research Facility (CCERF) from November 9, 2021, to March 1, 2022. Bulls were provided with ad libitum access to feed (1.15 Mcal NEg/kg dry matter, 14% crude protein, 52.2% dry matter) and water using the Insentec Roughage Intake Control system (Hokofarm, Marknesse, Netherlands). Feed and water disappearance were assumed to be caused by intake. Water intake was measured in kg; however, the data were converted to L based on a correction factor determined by weighing a known amount of water. Body weights were taken every 28 d to determine ADG and predict daily BW during the duration of the study. Daily weather variables were collected from the South Dakota Mesonet station located 3.86 km from the CCERF. Weather variables analyzed included: average windchill (°C), solar radiation (W/m²), and wind speed (km/h); and minimum, maximum, and average relative humidity (%) and average temperature (°C). R-studio (R-4.1.2.pkg) was used to develop a linear mixed effects model with random intercept and slope used to account for the within subject correlations. Total daily water intake increased with increasing DMI (1.921 L TDWI per kg DMI; P < 0.0001), BW (0.025 L TDWI per kg BW; P = 0.0055), and maximum daily temperature (0.171 L TDWI per 1°C; P = 0.0023). For every 1% increase in the minimum relative humidity, TDWI tended to increase by 0.041 L (P = 0.0616). Warmer wind chill also tended to increase TDWI (0.463 L per 1°C; P = 0.0707). The effects of DMI, BW, maximum daily temperature, minimum relative humidity, and wind chill were predictive of TDWI in growing beef bulls fed during the winter months in South Dakota. This model will be useful for predicting TDWI in growing beef bulls that are raised in areas that experience similar winter weather conditions.