This presentation was prepared in 2020 as Calf Note #219 and was adapted to Tech Seminar #03.
Click here for video transcript
Summary
In Calf Note #219, Calf Management in Summer, Part 1, Dr. Jim Quigley explains how heat stress affects young calves and why understanding their physiology is essential for maintaining performance and future productivity. He reviews thermoneutral zones (TNZ), upper critical temperature (UCT), and Temperature-Humidity Index (THI), noting that calves generally begin to experience heat stress at a THI of about 78–82 (≈80 as a practical guideline). Signs of heat stress include increased respiration rate, elevated body temperature, reduced feed intake, increased water consumption, and metabolic and hormonal changes that ultimately reduce growth and increase maintenance energy needs. Although calves are somewhat more heat tolerant than adult cows—due to greater surface area, lower rumen fermentation, and highly digestible diets—they are still vulnerable, especially without adequate nighttime cooling. Research shows that proper heat abatement strategies involving nutrition, housing, airflow, shade, and bedding can significantly reduce heat stress and improve calf health and efficiency.