16. Water Consumption of Finishing Lambs Under Heat Stress Conditions.

Abstract

The objective of this study was to evaluate the influence of temperature-humidity index (THI; formula = 0.8 × T(× RH × (T - 14.4) + 46.4); where T = ºC, and RH = relative humidity) on water and feed consumption in feeder lambs. Polypay wethers (initial BW 29 ± 14.3 kg) were allocated to 16 pens (2 lambs/pen). Ad libitum intake was achieved by targeting 10% refusals. Lambs were sheared prior to the start of this study. Water intake was measured using a bucket with a 19 L capacity. Buckets were marked with a line 305mm above the bottom of the bucket. Buckets were filled daily at 0800 hours; The distance between the marked line and remaining water level was recorded at the same time the following day, gallons of water consumed were calculated by difference (pen water intake = (π × r2 × Ind)/ 231). Rainfall was measured daily. Using the same equation, the gallons of rain added were subtracted from the gallons displaced to determine the total amount consumed. Days with precipitation greater than 12.5 mm were excluded. Variables analyzed included feed intake (DMI, kg/d), water intake as a percentage of BW(WIBW), and water intake (WI), both in absolute terms (L/d) and relative to feed intake (L/kg of DMI). The THI was evaluated separately for the minimum (MIN), maximum (MAX), and average (AVG). Data was analyzed using the GLIMMIX procedure of SAS 9.4. Pen was considered the experimental unit, and the model included the fixed effects of THI (both linear and quadratic) and day, as well as the random effects of block, treatment, and pen within treatment. The quadratic term was only maintained for the MIN THI (P < 0.01), whereas it was removed from the AVG and MAX THI (P > 0.10). Water consumption expressed either in L/d, L/kg DMI, or as % of BW increased consistently with rising THI, quadratically for MIN THI (P < 0.01), and linearly for AVG and MAX THI (P < 0.01). Relative water consumption in L/kg of DMI increased from 3.45 to 4.45 L/kg DMI when MIN THI rose from 47 to 77; whereas when MAX THI rose from 65 to 98 water consumption increased from 2.42 to 4.15 L /kg DMI. Lack of water consumption and increase in panting from heat stress could lead to dehydration causing decrease in saliva production and not enough moisture when consuming feed, thus deterring further DMI. Results from the performance evaluation of this trial showed lower energy efficiency utilization than expected which aligns with current findings. This study highlights the necessity of providing lambs with ample shade or cooling areas during periods of the THI exceeding the critical level.