Drinking water intake of grazing steers: The role of environmental factors controlling canopy wetness1

Abstract

Cattle obtain water primarily from the moisture in their feed and from drinking water. On pasture, the moisture content of the diet is influenced by plant tissue water (internal water) and surface moisture (external water), which may include dew, guttation, and intercepted rain, that influence the drinking water requirement. This study investigated the relationship between daily drinking water intake (DWI, L/d) of steers on pasture (19 steers with mean initial BW of approximately 400 kg) and soil and weather factors that are known to affect plant water status (dry matter content) and surface moisture formation and persistence. Daily records of weather conditions and DWI were obtained during 2 grazing seasons with contrasting spring, summer, and autumn rainfall patterns. Plant available water in the soil (PAW, mm) was modeled from actual and potential evapotranspiration and the water-holding capacity of the soil. The DWI averaged over the herd varied among days from 0 to 29 L/d (grazing season mean 9.8 L/d). The DWI on both dry (<0.2 mm rainfall on the corresponding and previous days) and wet (>2 mm) days increased with increasing temperature (mean, maximum, and minimum), sunshine hours, and global radiation and decreasing relative humidity, and the slopes and coefficients of determination were generally greater for wet days. Wind reduced DWI on wet days but had no effect on dry days. The DWI was reduced by up to 4.4 L/d on wet days compared to dry days, but DWI did not correlate with rainfall amount. Increasing PAW decreased DWI by up to >10 L/d on both dry and wet days. These results are all consistent with environmental effects on the water status (dry matter content) of pasture vegetation and canopy surface moisture, the associated effects on grazing-related water intake, and the corresponding balancing changes of DWI. Using the observed relationships with environmental factors, we derived a new model predicting DWI for any soil moisture condition, for both wet and dry days, which included mean ambient temperature and relative humidity and explained virtually all variation of DWI that was not caused by the random scatter among individual animals.

Multivariate analysis of the behavior and physiology of Girolando heifers in pasture

“…Highest water intake by the animals occurred from 9 to 12 h (0.62%) and from 18 to 21 h (0.46%), thus indicating that the animals drank more water in periods of high THI and h, and after greater consumption of forage. Therefore, the results corroborate Sun et al (2014), who reported that water intake is related to environmental temperature, air humidity, pasture moisture content, wind speed, solar radiation and dry matter intake.…”

Model explanation of the seasonal variation of δ18O in cow (Bos taurus) hair under temperate conditions

“…(iii) It influences the amount of water adhering to the leaves from dewrise. (iv) And thus, it also influences the drinking water demand of the animals 15 .…”

“…In the Kohn model, drinking water was calculated by subtracting the other input fluxes from total water demand, which did not reflect the seasonal variation of drinking water intake. We used the models described by Cardot et al 28 for the stall period and Sun et al 15 for the grazing period to estimate drinking water intake as a function of ambient conditions (relative humidity, daily average temperature and precipitation), milk production, and soil water storage (during grazing). The Sun model was modified to consider the influence of body weight (an increase of 1 kg body weight causes 0.1 kg increase in drinking water 14 ).…”

“…Thus, the variation of δ 18 O in hair cannot directly reflect the variation of δ 18 O in precipitation. For instance, drinking water amount can be influenced by precipitation, temperature, relative humidity and plant available water, and also by intake of feed dry matter, crude protein and Na 11–15 , thereby causing a varying contribution of drinking water to total O input flux. The δ 18 O of water in grass, which is the main feed of cattle at pasture, changes hourly with ambient conditions 16 .…”

“…Even δ 18 O of silage water varies with the fluctuation of ambient conditions and the change of exposure time 17 . Furthermore, the intercepted rain and dew in the grass can be ingested by grazing animals, which further increases the complexity of the O input of animals 15, 18 . This suggests that the δ 18 O of daily total feed moisture is a complex variable influenced not only by the ambient conditions but also by feeding time and frequency.…”