Dairy cattle management and housing for warm environments

Heat stress negatively affects the performance, health, and welfare of dairy cattle. Selection for increasing milk yields is lowering the minimum temperature-humidity index at which heat stress starts to depress milk production, and rising global temperatures exacerbates the problem. The average dairy cow in the USA experiences 96 heat stress days during the year if not cooled. Experience and research have shown that management and housing may alleviate the effects of warm environments on dairy cattle. For example, dietary interventions such as feeding melatonin and chromium supplementation may reduce the detrimental effects of heat stress on fertility. An effective strategy is altering the timing of feeding to take advantage of the lower nighttime temperatures. Some cattle are more heat tolerant than others, so breeding values for thermotolerance have been developed. Upgrading the slick-hair gene into high producing Holstein cattle is another approach of making dairy cattle more tolerant of high temperatures. In-vitro produced embryo transfer improves conception rates during heat stress but may be cost prohibitive. Housing design, including cooling systems, is the primary way to reduce heat stress. Fans and water soakers or misters increase evaporative cooling effectiveness. In the USA, there is continuous development in size, number, and position of fans, as well as schedules for soakers. Newer systems are designed to be more energy and water efficient. Tunnel barns and cross-ventilated barns are constructed to help direct cool airflow on to cows. Cooling of heifers and dry cows has been receiving more attention in the last decade. Recent research has shown that cows provided relief from thermal stress during the dry period give birth to heavier and healthier calves, produce more milk during the next lactation and have better immune response during the transition period. Late gestation heat stress of dairy cows also depresses milk production of their daughters and possibly granddaughters. In the USA, economic losses are estimated to be $87 per cow per year if dry cows were not cooled. We discuss various heat abatement strategies including management of feeding, reproduction, genetic selection and housing design and they will continue to receive greater emphasis in dairy production across the USA.