Heat stress in dairy cattle and other livestock under southern African conditions. I. Temperature-humidity index mean values during the four main seasons.

The Livestock Weather Safety Index (LWSI) indicates that in large areas of South Africa and South West Africa/Namibia and for prolonged periods of the year warm conditions are causing heat stress in food-producing animals, especially dairy cattle, thereby hampering their performance. South Africa and South West Africa/Namibia have been mapped according to a modified LWSI, which includes the critical "temperature-humidity index" value for milk production. The importance of heat stress in dairy cattle is discussed relative to such areas.