Wetting and the physiological responses of grain-fed cattle in a heated environment

Abstract

A controlled crossover experimental design was used to determine the effect of altered water sprinkling duration on heifers subjected to heat stress conditions. Heifers were subjected to 3 days of thermoneutral conditions followed by 3 days of hot conditions accompanied by water sprinkling between 1300 and 1500 h (HOT1–3). Then on the following 2 days (HOT4–5), environmental conditions remained similar, but 3 heifers were sprinkled between 1200 and 1600 h (WET) and 3 were not sprinkled (NONWET). This was followed by a 1-day period (HOT6) in which environmental conditions and sprinkling regimen were similar to HOT1–3. Rectal temperature (RT) was collected hourly, and respiration rate (RR) was monitored every 2 h on HOT Days 2, 4, 5, and 6. Dry matter intake and rate of eating were also determined. Sprinkling reduced RR and RT (P < 0.01) of all heifers during HOT1–3. During HOT4–5, WET heifers had lower (P < 0.05) RT than NONWET from 1300 to 700 h and lower RR from 1400 to 2000 h. Dry matter intake of NONWET heifers was reduced by 30.6% (P < 0.05) during HOT4–5 and by 51.2% on HOT6. On HOT4–5 the dry matter intakes of WET heifers were similar to intakes under thermoneutral conditions. During HOT6, RT was again reduced following sprinkling in all heifers. Comparison of RT and RR of NONWET and WET heifers on HOT1–3 v. HOT6 revealed that under similar environmental conditions, NONWET heifers had increased RT, partially due to carry-over from HOT4–5. However, NONWET heifers had 40% lower feed intake but tended to have lower RR on HOT6 v. HOT1–3. Only RR of WET heifers was greater on HOT6, possibly a result of switching from a 4-h back to a 2-h sprinkling period, while maintaining a 62% greater intake (5.80 v. 3.58 kg/day) than NONWET heifers during this time. Results suggest that inconsistent cooling regimens may increase the susceptibility of cattle to heat stress and elicit different physiological and metabolic responses.