Effects of increasing air temperature on physiological and productive responses of dairy cows at different relative humidity and air velocity levels

Abstract

This study determined the effects of increasing ambient temperature (T) at different relative humidity (RH) and air velocity (AV) levels on the physiological and productive responses of dairy cows. Twenty Holstein dairy cows were housed inside climate-controlled respiration chambers, in which the climate was programmed to follow a daily pattern of lower night and higher day T with a 9°C difference, excluding effects from sun radiation. Within our 8-d data collection period, T was gradually increased from 7 to 21°C during the night (12 h) and 16 to 30°C during the day (12 h), with an incremental change of 2°C per day for both nighttime and daytime T. During each research period, RH and AV were kept constant at 1 of 5 treatment levels. A diurnal pattern for RH was created, with lower levels during the day and higher levels during the night: low (RH_l: 30-50%), medium (RH_m: 45-70%), and high (RH_h: 60-90%). The effects of AV were studied during the day at 3 levels: no fan (AV_l: 0.1 m/s), fan at medium speed (AV_m: 1.0 m/s), and fan at high speed (AV_h: 1.5 m/s). Effects of short and long exposure time to increasing T were evaluated by collecting data 2 times a day: in the morning [short: 1 h (or less) − exposure time] and afternoon (long: 8 h − exposure time). The animals had free access to feed and water and both were ad libitum. Respiration rate (RR), rectal temperature (RT), skin temperature (ST), dry matter intake, water intake, milk yield, and composition were measured. The inflection point temperatures (IPt) at which a certain variable started to change were determined for the different RH and AV levels and different exposure times. Results showed that IPt under long exposure time for RR (first indicator) varied between 18.9 and 25.5°C but was between 20.1 and 25.9°C for RT (a delayed indicator). The IPt for both RR and RT decreased with higher RH levels, whereas IPt increased with higher AV for RR but gave a minor change for RT. The ST was positively correlated with ambient T and ST was not affected by RH but significantly affected by AV. For RR, all IPt was lower under long exposure time than under short exposure time. The combination of higher RH levels and low AV level negatively affected dry matter intake. Water intake increased under all treatments except RH_l-AV_l. Treatment RH_h-AV_l negatively affected milk protein and fat yield, whereas treatments RH_m-AV_m and RH_m-AV_h reduced milk fat yield. We concluded that RH and AV significantly affected the responses of RR, RT, ST, and productive performance of high-producing Holstein cows. These responses already occurred at moderate ambient T of 19 to 26°C.

Effects of increasing air temperature on skin and respiration heat loss from dairy cows at different relative humidity and air velocity levels

“…One might expect that under high ambient T, the RH level may play a role in skin T and hence in skin SHL. Zhou et al (2022) found skin T (averaged from 4 different skin parts) was significantly higher at 60% RH than that at 30 and 45% RH given the same ambient T, causing a larger T difference between skin surface and air at 60% RH, and hence giving a larger skin SHL. Possible reason could be that skin T in previous study was an average skin T measured on 4 different parts, whereas skin SHL in this study was only measured on a small area of the belly (at the location where the ventilated box was placed).…”

“…Each compartment had a volume of 34.5 m 3 and dimension of length × width × height: 4.5 × 2.7 × 2.8 m, as described in detail by Gerrits and Labussière (2015). In each compartment the RH was monitored by one RH sensor (Novasina Hygrodat100, Novasina AG), and the ambient T was monitored by 5 PT100 temperature sensors (Sensor Data BV) evenly distributed over the room at animal height, as described in detail in Zhou et al (2022). The different RH levels were achieved by means of a humidifier (ENS-4800-P, Stulz) or a dehumidifier (Koeltechniek, Nijssen) and the circulating air was heated or cooled depending on the deviation from set-point T, the control mechanism of which can be found in the book of Gerrits and Labussière (2015).…”

“…In addition, in compliance with saving the number of experimental animals (OIE, 2021), the AV_m and AV_h were only combined with the RH_m. More detailed description can be found in the previous study (Zhou et al, 2022). Because of the capacity of the CRC, the ambient T and RH required a time span of 3 h to adjust from one to a new level.…”

“…The microclimate conditions inside the CRC were reported in a previous study (Zhou et al, 2022). Briefly, the daily cyclical T were kept strictly constant according to set points with a deviation smaller than ± 0.50°C.…”

“…When exposure time was long, the cows had a higher skin SHL than under short exposure. This effect is probably caused by the higher skin T at long exposure time (Zhou et al, 2022).…”