Editor's Pick 2015, #7:
Dairy production is concentrated in climates that expose animals to less heat stress
Above a temperature threshold, an animal may experience heat stress resulting in changes in its respiration, blood chemistry, hormones, metabolism, and feed intake. Dairy cattle are particularly sensitive to heat stress; high temperatures lower milk output and reduce the percentages of fat, solids, lactose, and protein in milk. In the United States, dairy production is largely concentrated in climates that expose animals to less heat stress.