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      The Impact of Heat Load on Cattle

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          Abstract

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          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.

          Abstract

          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.

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          Most cited references153

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          Effects of heat stress on postabsorptive metabolism and energetics.

          Environmental-induced hyperthermia compromises efficient animal production and jeopardizes animal welfare. Reduced productive output during heat stress was traditionally thought to result from decreased nutrient intake. Our observations challenge this dogma and indicate that heat-stressed animals employ novel homeorhetic strategies to direct metabolic and fuel selection priorities independent of nutrient intake or energy balance. Alterations in systemic physiology support a shift in carbohydrate metabolism, evident through changes such as basal and stimulated circulating insulin levels. Hepatocyte and myocyte metabolism also show clear differences in glucose production and use during heat stress. Perhaps most intriguing, given the energetic shortfall of the heat-stressed animal, is the apparent lack of fat mobilization from adipose tissue coupled with a reduced responsiveness to lipolytic stimuli. Thus, the heat stress response markedly alters postabsorptive carbohydrate, lipid, and protein metabolism independently of reduced feed intake through coordinated changes in fuel supply and utilization by multiple tissues.
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            Effects of heat stress and plane of nutrition on lactating Holstein cows: I. Production, metabolism, and aspects of circulating somatotropin.

            Heat stress is detrimental to dairy production and affects numerous variables including feed intake and milk production. It is unclear, however, whether decreased milk yield is primarily due to the associated reduction in feed intake or the cumulative effects of heat stress on feed intake, metabolism, and physiology of dairy cattle. To distinguish between direct (not mediated by feed intake) and indirect (mediated by feed intake) effects of heat stress on physiological and metabolic indices, Holstein cows (n = 6) housed in thermal neutral conditions were pair-fed (PF) to match the nutrient intake of heat-stressed cows (HS; n = 6). All cows were subjected to 2 experimental periods: 1) thermal neutral and ad libitum intake for 9 d (P1) and 2) HS or PF for 9 d (P2). Heat-stress conditions were cyclical with daily temperatures ranging from 29.7 to 39.2 degrees C. During P1 and P2 all cows received i.v. challenges of epinephrine (d 6 of each period), and growth hormone releasing factor (GRF; d 7 of each period), and had circulating somatotropin (ST) profiles characterized (every 15 min for 6 h on d 8 of each period). During P2, HS cows were hyperthermic for the entire day and peak differences in rectal temperatures and respiration rates occurred in the afternoon (38.7 to 40.2 degrees C and 46 to 82 breaths/min, respectively). Heat stress decreased dry matter intake by greater than 35% and, by design, PF cows had similar reduced intakes. Heat stress and PF decreased milk yield, although the pattern and magnitude (40 and 21%, respectively) differed between treatments. The reduction in dry matter intake caused by HS accounted for only approximately 35% of the decrease in milk production. Both HS and PF cows entered into negative energy balance, but only PF cows had increased (approximately 120%) basal nonesterified fatty acid (NEFA) concentrations. Both PF and HS cows had decreased (7%) plasma glucose levels. The NEFA response to epinephrine did not differ between treatments but was increased (greater than 50%) in all cows during P2. During P2, HS (but not PF) cows had a modest reduction (16%) in plasma insulin-like growth factor-I. Neither treatment nor period had an effect on the ST response to GRF and there was little or no treatment effect on mean ST levels or pulsatility characteristics, but both HS and PF cows had reduced mean ST concentrations during P2. In summary, reduced nutrient intake accounted for just 35% of the HS-induced decrease in milk yield, and modest changes in the somatotropic axis may have contributed to a portion of the remainder. Differences in basal NEFA between PF and HS cows suggest a shift in postabsorptive metabolism and nutrient partitioning that may explain the additional reduction in milk yield in cows experiencing a thermal load.
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              Black Globe-Humidity Index (BGHI) as Comfort Equation for Dairy Cows

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                Author and article information

                Journal
                Animals (Basel)
                Animals (Basel)
                animals
                Animals : an Open Access Journal from MDPI
                MDPI
                2076-2615
                06 June 2019
                June 2019
                : 9
                : 6
                : 322
                Affiliations
                [1 ]School of Agriculture and Food Sciences, The University of Queensland; Gatton, QLD 4343, Australia; a.wallage@ 123456uq.edu.au
                [2 ]School of Environmental and Rural Science, University of New England, Armidale, NSW 2350, Australia; csteel5@ 123456une.edu.au (C.C.S.); Jarrod.Lees@ 123456une.edu.au (J.C.L.)
                [3 ]Indian Council of Agricultural Research (ICAR)-National Institute of Animal Nutrition and Physiology, Adugodi, Bangalore 560030, India; drsejian@ 123456gmail.com
                [4 ]Department of Animal Science, University of Nebraska, Lincoln, NE 68588, USA; tmader12@ 123456msn.com
                [5 ]Mader Consulting, Gretna, NE 68028, USA
                Author notes
                [* ]Correspondence: angela.lees@ 123456une.edu.au (A.M.L.); j.gaughan@ 123456uq.edu.au (J.B.G.); Tel.: +617-5460-1036 (J.B.G.)
                Author information
                https://orcid.org/0000-0003-4898-2843
                https://orcid.org/0000-0002-8224-4521
                Article
                animals-09-00322
                10.3390/ani9060322
                6616461
                31174286
                b46d87db-3f45-4f66-8aaa-7e2500fd8ef6
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 17 April 2019
                : 31 May 2019
                Categories
                Review

                cattle welfare,climate change,heat load,heat stress,mitigation techniques,multiple stressors,production,reproduction,thermotolerance

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