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Try out PMC Labs and tell us what you think. Learn More. It is well known that the thermal environment has an integral role in maintaining the health and productivity of cattle. Although cold stress has been identified to negatively influence cattle comfort and productivity, the predominant focus herein has been describing the influence of heat stress on bovines. The impact of heat stress is particularly important due to the changing global environment. Global warming is likely to occur, however, the nature and magnitude of environmental changes, both climatic and non-climatic, are difficult to elucidate.
Therefore a predominant focus on the impact of hot environments on cattle is warranted. This review provides an overview of the dynamic relationship that exists between the thermal environment and bovines. Heat stress and cold stress have a negative influence on cattle welfare and productivity. There have been some studies investigating the influence of cold stress on cattle, however the emphasis within this review is the influence of heat stress on cattle.
The impact of hot weather on cattle is of increasing importance due to the changing global environment. Heat stress is a worldwide phenomenon that is associated with reduced animal productivity and welfare, particularly during the summer months.
Animal responses to their thermal environment are extremely varied, however, it is clear that the thermal environment influences the health, productivity, and welfare of cattle. Whilst knowledge continues to be developed, managing livestock to reduce the negative impact of hot climatic conditions remains somewhat challenging. This review provides an overview of the impact of heat stress on production and reproduction in bovines. The thermal environment can have a negative influence on cattle welfare.
Historically, Ames [ 1 ] defined the thermoneutral zone as the thermal environment where an animal experiences optimum health and maximum productivity. The impact of hot weather on cattle is of increasing importance, particularly in conjunction with the changing global environment. Beyond the direct impact that heat stress has on the health and productivity of animals, the economic impact on livestock producers also needs to be considered. InSt-Pierre et al.
Sackett et al. Given that these analyses were conducted over a decade ago, these estimates may not reflect the current economic impact of heat stress. Furthermore, in conjunction with climate change, it is probable that these estimates are underestimating the economic impact of heat stress on cattle production systems.
For livestock production enterprises, climate change has the potential to alter the thermal environment, which may result in the climate having an increasingly negative impact on the welfare and productivity of cattle. Periods of hot weather are already associated with reduced animal health, reduced reproductive efficiency in both males and females, and decreased feed conversion efficiency [ 46 ].
Therefore, it is likely that climate change will have a considerable impact on the economic viability of animal agriculture worldwide. In spite of this, all animals possess the capacity to adapt to their thermal environment.
Animals are capable of modifying their behavioral, physiological, and morphological characteristics, or a combination of these, in response to the thermal environment [ 7 ]. This review has attempted to provide a rounded overview of the impact that heat stress has on bovines. The effect of climate change is highly variable globally and is largely influenced by geographical location. Cattle and livestock enterprises have the ability to adapt to an increasing mean global temperature, the primary concern, however, is the ability of livestock to cope with climatic extremes, e.
Climate change has the potential to present as i rapid changes in climate over a couple of years or ii as more subtle changes over decades [ 8 ]. However, irrespective of the manifestation of climate change, global warming is likely to have a ificant impact on the stability and sustainability of livestock production worldwide.
Globally, various climate change models are predicting a 1. Furthermore, in southern Australia, the average of consecutive days of heat-stress has increased from two days per heat stress event from toto four days from to [ 10 ]. Numerous species are likely to be negatively impacted by the changing global environment [ 11 ], due to changes in ecosystem microclimates.
Many species have adaptations to cope with short-term climate variability, i. However, these adaptations may not be successful for species survival with the predicted climate change [ 11 ]. Predicting the effect of climate change on livestock is somewhat challenging due to the interrelationships that exist between the animal and its surrounding environment, and the impact of human activity on these relationships [ 8 ]. Irrespective of livestock productions contribution to climate change, animal production needs to increase to satisfy consumer demand.
A challenge regarding the effects of climate change on livestock enterprises is how dependent the enterprise is on the thermal environment and what can be implemented to offset the impacts of increasing temperatures [ 9 ].
The impact of heat load on cattle
The current effect of the thermal environment is estimated by the impact of climatic conditions on animal performance, health, and welfare [ 9 ]. Heat waves are defined as a of successive days, typically three to five, where maximum ambient conditions are above a specific threshold [ 1314 ]. One predicted consequence of climate change is the increased prevalence and intensity of heat waves [ 15 ]. Climatic trends of heat waves differ from summer to summer, and future predictions suggest that the climatic behavior of heat wave events over the years will continue to be varied [ 1617 ]. Although, over the last 50 years there has been a ificant advancement in the ability to predict and forecast climatic events [ 16 ].
This ability to forecast heat wave events has enabled livestock producers to implement mitigation strategies to prepare for forthcoming adverse climatic events. The effects of heat waves on individual cattle are influenced by the intensity and duration of the heat wave.
It is well documented that feedlot cattle can be particularly susceptible to changes in climatic conditions [ 181920 ]. The susceptibility of feedlot cattle to heat load has been emphasized during prolonged heat wave events and where conditions manifest with limited nighttime relief [ 1820 ]. Numerous authors have reported heat wave conditions where cattle, particularly feedlot cattle, have succumbed to heat load, for example:.
February — deaths were recorded in Queensland Australia [ 21 ], with one feedlot reporting deaths [ 22 ] during a heat wave event with high relative humidity and limited air movement. July — deaths were estimated in Western Iowa, [ 23 ], and total deaths for the mid-central US were over cattle [ 24 ].
Hahn [ 20 ] reported the loss of feedlot cattle in central Nebraska over a heat wave that had three spikes in thermal lo.
February — cattle died in southwestern New South Wales with deaths occurring after a rainfall event where climatic conditions presented high relative humidity and high overnight ambient temperature [ 22 ]. Traditionally, the impact of hot weather has been referred to as heat stress. Buffington et al.
This is somewhat misleading as the term heat stress by definition refers to the combination of environmental conditions alone without consideration of animal factors [ 2128 ]. However, factors, such as genotype, coat type and coat color, diet type and diet composition, body condition, i. Animals that are adapted to a hot climate generally exhibit reduced growth and reproductive efficiency [ 29 ], which is associated with the adaptive mechanisms that ensure survival [ 30 ].
In extensive grazing systems, it has been identified that climatic constraints are not the only factor that negatively influences livestock production. The indirect effects of climate change will also influence pasture resources [ 31 ], potentially depriving grazing animals of nutrient requirements. Similarly, the changing climate may also result in droughts, ultimately resulting in feed and water scarcity for grazing animals.
These situations can be associated with a decrease in growth and reproductive efficiency in livestock [ 32 ]. Furthermore, these animals may also be required to walk long distances under high solar lo to find feed and water, imposing locomotor stress on grazing animals [ 33 ]. Therefore, it is important to consider the impact of multiple stressors on livestock, this is particularly important to consider in conjunction with climate change, as it is unlikely that animals will be exposed to a single stressor. Numerous sheep and goat studies have evaluated the impact of multiple environmental stressors heat, nutritional, and walking on production, reproduction, and ability to cope with stressful conditions [ 3234353637 ].
These studies have identified that when these species are exposed to a single stressor, they are able to effectively cope without altering normal body functions [ 38 ]. However, when these animals are exposed to two or more stressors simultaneously, the combined stress has a negative influence on growth [ 3738 ] and reproduction [ 3436 ]. As a result, the adaptive capability of the animals is reduced, and there is an inability to maintain normal homeothermy [ 3235 ].
Although the concept of multiple stressors is becoming a focal research topic in small ruminants, the impact of multiples stressors has not been adequately researched, and as such, there is no information on large ruminants. Therefore, it is essential to explore the impact of multiple stressors on both dairy and beef cattle, particularly in conjunction with the changing global environment. Figure 1 depicts the proposed hypothetical model describing the concept of multiple stressors in cattle. The generation of baseline information is vital as this will allow for the development of appropriate amelioration and adaptive strategies to support livestock production systems.
Schematic highlighting the concept of multiple stressors on cattle adopted and modified from Sejian et al. Animal responses to environmental stressors have been investigated for some time, and although knowledge continues to be developed, managing livestock to reduce the negative impact of hot weather remains challenging [ 1820 ].
Reductions in dry matter intake DMIgrowth, feed conversion efficiency [ 253940 ], reproduction [ 41 ], milk production and milk quality [ 4243 ], are commonly observed when cattle are exposed to thermal stress. Quantifiable measures, such as physiological, behavioral, and biological responses to heat load have been identified as indicators of heat load. Physiological responses to heat load include increased sweating rate [ 14 ], respiration rate, breaths per minute [ 44 ], panting score [ 45 ], and body temperature [ 46 ].
Behavioral responses include alterations to posture, including increasing the proportion of time standing, increased duration in shaded areas or increased shade seeking, including shade provided from other animals, and body splashing at water troughs [ 47 ]. Biological markers in the blood are also indicators in determining the level of stress an animal is under [ 48 ]. Heat production has a positive relationship with feed intake in ruminants, and it has been shown that heat production is closely associated with feeding time [ 50 ].
As ambient heat load increases and DMI decreases there is a reduction in metabolic heat production [ 50 ]. During hot weather, cattle compensate for the hotter conditions by last smaller meals, more frequently, and shifting feed intake to cooler parts of the day [ 405354 ]. However, the ambient temperature at which DMI begins to decline is influenced by diet type and composition specifically diets with a greater proportion of roughage exhibit more rapid reductions in Day [ 55 ].
Variations in DMI are also influenced by breed genotypeproduction status, health status, body condition, and days on feed. Water is available to hot in three forms, free drinking water, water in feed, and water produced via oxidation of organic compounds or metabolic water [ 56 ]. Water requirements of cattle are influenced by ambient conditions, diet type, breed genotypeweight, and physiological functions [ 57 ].
Daily water intake is also influenced by a of body functions, including the regulation of core body temperature, growth and development, lactation and reproductive functions, digestion and metabolism, and hydrolysis of proteins, fats and carbohydrates [ 58 ]. Water intake is linked to DMI, with both feed intake and feed type influencing water intake [ 59 ]. Furthermore, water intake is influenced by the need of water gained from drinking, eating, via metabolic water, and the load of water lost per unit time through respiration, sweating, faces, urine, and lactation [ 60 ].
Arias and Mader [ 57 ] reported that feedlot cattle finished in the summer consumed However, an increase in water intake may also be a reflection of ruminants attempting to compensate for heat lo, particularly in un-shaded grazing systems [ 61 ]. Digestion and absorption processes carried out by the animal are affected by the thermal environment. Primarily, during heat load, absorbable nutrients are diverted from growth and development and directed to maintaining homeostasis [ 62 ].