Heat-tolerant breeds

How the body copes

A heat-tolerant animal loses heat well and makes less of it. Zebu have more and larger sweat glands than taurine cattle, and they sweat more freely. Loose skin, a large dewlap, long ears and a hump give more surface for heat to leave. Short, sleek, light-coloured coats reflect sunlight, while dark skin under the coat protects against the sun. Zebu also have a lower resting metabolism, so they produce less internal heat to begin with.

The slick coat

Some tropical taurine and composite breeds carry a gene variant that gives a very short, glossy coat, known as the slick coat. It was found in the Senepol of the Virgin Islands, the Carora of Venezuela and several Criollo breeds of Latin America. Slick-coated cattle keep their body temperature lower in the heat, and breeders have crossed the slick variant into Holstein lines for hot climates.

What heat does to cattle

Cattle under heat stress eat less, give less milk, grow more slowly and conceive less often. A Holstein cow begins to feel the effect at temperatures many Indian breeds handle easily. That is why tropical dairying has long relied on zebu or zebu crosses, and why Indian breeds became the foundation of cattle farming in Brazil, northern Australia and the American Gulf coast.

Indian breeds in the heat

Tharparkar and Rathi live in the Thar desert, where summer temperatures often pass 45 degrees Celsius. Gir and Kankrej come from the hot, dry west of Gujarat. Ongole and the draught breeds of the Deccan work through the summer before the monsoon. The heat tolerance of these breeds is one reason Indian and international researchers study them, and why their genes are sought by breeders in hot countries.

Worth knowing

• Gir: Gujarat milking zebu, the base of much of Brazil's tropical dairy
• Sahiwal: Dairy zebu kept in hot countries from Kenya to Australia
• Tharparkar: Desert zebu of the Thar
• Red Sindhi: Dairy zebu of Sindh, used in tropical crossbreeding
• Nelore: Brazilian beef zebu from Ongole stock
• American Brahman: Zebu breed of the American Gulf coast
• Senepol: Slick-coated red cattle of St Croix, Virgin Islands
• Bonsmara: South African composite selected for heat

Good to know

• Every breed benefits from shade and clean water in hot weather; heat tolerance is not heat immunity.
• Move and handle cattle in the cool of the morning or evening.
• Watch for open-mouthed panting and drooling, the signs of heat stress.

Sources and further reading

• Zebu on Wikipedia
• Senepol, Wikipedia
• Tharparkar cattle, Wikipedia
• American Brahman, Wikipedia
• Cattle, Encyclopaedia Britannica