Abstract
Simple SummaryThe severity of heat stress issues on dairy cows will increase as global warming progresses. Fortunately, major advances in environmental management, including fans, misters, sprinklers, and cooled waterbeds, can attenuate the effects of thermal stress on cow health, production, and reproduction. These cooling systems were, however, tested in subtropical areas and their efficiency in northern regions is uncertain. This article assesses the potential of existing technologies to cool cows in humid continental climates through calculation of heat stress indices.Heat stress negatively affects the health and performance of dairy cows, resulting in considerable economic losses for the industry. In future years, climate change will exacerbate these losses by making the climate warmer. Physical modification of the environment is considered to be the primary means of reducing adverse effects of hot weather conditions. At present, to reduce stressful heat exposure and to cool cows, dairy farms rely on shade screens and various forms of forced convection and evaporative cooling that may include fans and misters, feed-line sprinklers, and tunnel- or cross-ventilated buildings. However, these systems have been mainly tested in subtropical areas and thus their efficiency in humid continental climates, such as in the province of Québec, Canada, is unclear. Therefore, this study reviewed the available cooling applications and assessed their potential for northern regions. Thermal stress indices such as the temperature-humidity index (THI) were used to evaluate the different cooling strategies.
Highlights
The physiological and behavioural controls of dairy cows attempt to maintain a constant body temperature by regulating their thermal energy balance, so that heat input through metabolism equals heat loss to the environment
The selection of cooling systems to improve cow health and performance without worsening ambient conditions under a humid continental climate can differ from areas that are more arid
Shade, roof insulation, circulation fans, tunnel ventilation, and water-cooled mattresses are the practical cooling strategies that should be considered under a humid continental climate
Summary
The physiological (e.g., respiration rate) and behavioural (e.g., resting pattern) controls of dairy cows attempt to maintain a constant body temperature by regulating their thermal energy balance, so that heat input through metabolism (maintenance, exercise, growth, lactation, gestation, and feeding) equals heat loss to the environment (by conduction, convection, and evaporation). Cow health, production, and reproduction performance are reduced under heat stress [1,2]. Feed intake begins to decline at air temperatures of 25–26 ◦ C in lactating cows [3] as reducing dry matter ingestion is a way to decrease heat production in warm environments [4]. The reduction of dry matter intake for heat-stressed cows is about 10 to 15% relative to cooled cows [5]. Cows under heat stress have elevated respiration and sweating rates, which results in greater body fluid losses that increase maintenance requirements to control dehydration and blood homeostasis [4]
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