1. Where Cattle Release Body Heat on Hot Days
On hot summer days, heat builds up inside a cow’s body. Like humans, cattle sweat to release this heat. Moisture evaporates at the boundary between the skin and hair, carrying heat away and cooling the body [1]. When temperatures exceed about 30°C (86°F), sweating is said to account for approximately 85% of the heat escaping from the body. However, this 85% figure applies specifically to high-temperature conditions and is not a constant number [1].
Guidelines from Kagoshima Prefecture in Japan explain that the comfortable temperature range for dairy cows is 4–24°C (39–75°F). Milk production begins to drop when temperatures exceed 21°C (70°F) and falls sharply above 27°C (81°F). In heat, it becomes harder to release body heat, causing body temperature and breathing rates to rise [10]. These figures are guidelines for dairy cows, and numbers vary by institution for beef cattle. Despite the physical burden of heat, cattle are a major industry in northern Australia. What makes heat-resistant cattle different?
2. How Zebu Cattle's Large Sweat Glands and Lower Heat Production Help Them
Northern ranches are home to "humped cattle" (Zebu) of Indian origin. The Brahman is one breed within this group, and its ancestors evolved in hot, humid environments [1]. A study of 319 female cattle in the southeastern United States found that groups with over 75% Brahman genetics had the largest sweat gland areas. Brahman sweat glands were reportedly large and located close to the skin surface [1]. Since sweat glands are organs that produce sweat, this means their heat-releasing apparatus is larger. Note that this research measured cattle in the United States, not Australia.
Additionally, a review of research states that low metabolic heat production (the amount of heat created inside the body) is another reason Zebu cattle are heat-resistant [3]. It is thought that two factors overlap: a strong ability to release heat and a low amount of heat produced. A 2020 study of female cattle on pasture also found that groups with Brahman genetics had clearly superior ability to regulate body temperature when heat stress was moderate to high [2]. Do these cattle have other traits suited to the north?
3. How the Coat and Tick Resistance of Zebu Cattle Suit the North
According to a research review, the coat of Zebu cattle is said to release heat easily and absorb less heat from sunlight [3]. This is like wearing thin clothes in summer, but the coat is part of the body and cannot be removed. Another issue in hot lands is ticks that attach to cattle. It has been widely confirmed that Zebu-type cattle have higher resistance to ticks and the pathogens they carry than European-type cattle [7].
Thus, Zebu cattle have bodies adapted to both heat and ticks. Yet, they were not welcomed from the start. Why?
4. Why Zebu Cattle, Once Seen as Inferior, Became the Mainstay of Northern Ranches
In 1933, CSIR (later CSIRO) imported Zebu cattle to Queensland as a research institution. At the time, many ranch owners reportedly viewed humped cattle as inferior [4]. In 1941, a person named Kelly described crossbreeding experiments with Zebu as "the most valuable experiment" [4]. Widespread adoption began in the 1960s, when government agricultural researchers actively conducted campaigns [5].
As a result, the share of Queensland’s cattle with Brahman genetics was less than 15% in 1965 but reached 60% in 1981 [4]. This means the percentage more than quadrupled in about 16 years. In 2001, the profit this change brought to the state’s cattle industry was estimated at 8.1 billion Australian dollars [5]. Researchers established a facility in Belmont near Rockhampton in the 1950s to study adaptation to the tropics and breed tropical hybrids [4]. A 2017 article estimates that about half of Australia’s roughly 26 million cattle have Brahman genetics, and over 70% of bulls working north of the Tropic of Capricorn are Brahman. However, this is an estimate from that article and may not reflect current statistics [6]. If cattle are heat-resistant, do they not need shade?
5. Why Even Heat-Resistant Cattle Need Shade
A study at a University of Queensland holding facility examined 12 Angus, 12 Charolais, and 12 Brahman cattle over 154 days. As it got hotter, the score for "panting" (open-mouthed breathing) increased in all groups. The increase was smallest for Brahman cattle with shade (0.13) and largest for Angus cattle without shade (0.71) [9]. A simple comparison shows a difference of about 5 times. This study concludes that shade is important regardless of breed. Even for heat-resistant breeds, having shade reduces the burden on the body [9].
Meat & Livestock Australia (MLA) explains that Zebu cattle are more heat-resistant than European types, that cattle with lighter coat colors tend to be stronger, and that fatter cattle tend to be weaker. There are individual differences within breeds [8]. Heat management for cattle involves both selecting breeds and creating shade. Can we verify this mechanism with everyday objects?
6. A Home Experiment: Cooling by Sweat Evaporation and Heat from the Sun
Try this: Wet the back of your hand with a little water and fan it. It feels cool because the water takes heat away as it evaporates. Cattle sweat works the same way to cool their bodies.
Try this: On a sunny day, place white paper and black paper in the sun for about 10 minutes, then touch them to compare. This gives a clue about how much heat from sunlight is received. Before touching, check whether it feels hot. If left too long, the paper will become hot. Since cattle hair and paper are completely different, you cannot directly apply the results to cattle.
For those who want to know more, CSIROpedia’s "Cattle for the tropics" (Source [4]) is an entry point for reading about the introduction in 1933 and breed development (in English).