On the time when heat load becomes equal during the exposure to hot environments where only the air speed is different

In smallholder dairy farms (SDFs), farmers often build cowsheds using local materials and based on self-accumulated experience without due consideration to reducing the risk of heat stress. This study aimed to characterise the heat stress abatement strategies and microclimate within SDF cowsheds from four typical dairy regions of Vietnam (south lowland, south highland, north lowland and north highland) and identify the housing parameters most associated with the microclimate. The study was conducted on 32 SDFs (eight SDFs per region) in autumn 2017. Twelve housing management variables, illustrating cowshed design and heat stress abatement methods of each SDF, were collected. Six microclimate parameters, collected within the cowshed, were temperature (AT), humidity, air speed (AS), heat load index (HLI), Temperature-humidity index (THI) and accumulated heat load units (AHLU) during a day (06:00 h to 18:00 h). Factor analysis and cluster analysis was applied to group cowsheds of SDFs into clusters where SDFs in the cluster had the same cowshed characteristics. Multivariable linear models were applied to define the parameters most likely to inform future research into heat stress mitigation on SDF. Averaged from 08:00 h to 18:00 h, microclimate inside the cowsheds was considered hot (HLI > 79) in the highland and very hot (HLI > 86) in the lowland regions. Cows in the lowland regions accumulated high heat load (AHLU > 50) by 18:00 h. Cowsheds of SDFs varied widely and grouped into seven cowshed types, but no type was more effective than others in reducing heat stress conditions within cowsheds. Using roof soakers together with fans decreased AT and HLI by 1.3 °C and 3.2 units, respectively, at 14:00 h compared to 11:00 h. Each 100 m increase in altitude was associated with decreases of 0.4 °C in AT, 1.3 units in HLI and 0.8 units in THI (p < 0.001). Each meter increase in the eave height of the cowshed roof was associated with decreases of 0.87 °C in AT, 3.31 units in HLI and 1.42 units in THI, and an increase of 0.14 m/s in AS (p < 0.05). The cowshed parameters that should be prioritised for future research into the amelioration of heat stress in SDF cows include using the roof soakers together with fans, increasing altitude, eave roof height and floor area per cow.

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Additional Clothing Increases Heat Load in Elite Female Rugby Sevens Players

International Journal of Sports Physiology and Performance ◽

10.1123/ijspp.2020-0620 ◽

2020 ◽

pp. 1-8

Author(s):

Mitchell J. Henderson ◽

Bryna C.R. Chrismas ◽

Christopher J. Stevens ◽

Andrew Novak ◽

Job Fransen ◽

...

Keyword(s):

Heat Load ◽

Perceived Exertion ◽

Sweat Rate ◽

Training Session ◽

Rating Of Perceived Exertion ◽

Compression Garments ◽

Wet Bulb Globe Temperature ◽

Parallel Group ◽

Globe Temperature ◽

Hot Environments

Purpose: To determine whether elite female rugby sevens players are exposed to core temperatures (Tc) during training in the heat that replicate the temperate match demands previously reported and to investigate whether additional clothing worn during a hot training session meaningfully increases the heat load experienced. Methods: A randomized parallel-group study design was employed, with all players completing the same approximately 70-minute training session (27.5°C–34.8°C wet bulb globe temperature) and wearing a standardized training ensemble (synthetic rugby shorts and training tee [control (CON); n = 8]) or additional clothing (standardized training ensemble plus compression garments and full tracksuit [additional clothing (AC); n = 6]). Groupwise differences in Tc, sweat rate, GPS-measured external locomotive output, rating of perceived exertion, and perceptual thermal load were compared. Results: Mean (P = .006, ) and peak (P < .001, ) Tc were higher in AC compared with CON during the training session. There were no differences in external load (F4,9 = 0.155, P = .956, Wilks Λ = 0.935, ) or sweat rate (P = .054, Cohen d = 1.09). A higher rating of perceived exertion (P = .016, Cohen d = 1.49) was observed in AC compared with CON. No exertional-heat-illness symptomology was reported in either group. Conclusions: Player Tc is similar between training performed in hot environments and match play in temperate conditions when involved for >6 minutes. Additional clothing is a viable and effective method to increase heat strain in female rugby sevens players without compromising training specificity or external locomotive capacity.

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Ability of wild rabbit, Oryctolagus cuniculus, to lactate successfully in hot environments explains continued spread in Australia

Wildlife Research ◽

10.1071/wr17177 ◽

2018 ◽

Vol 45 (3) ◽

pp. 267 ◽

Cited By ~ 3

Author(s):

B. D. Cooke ◽

M. Brennan ◽

P. Elsworth

Keyword(s):

Heat Load ◽

Limiting Factor ◽

Lactation Period ◽

Wild Rabbit ◽

Adaptive Responses ◽

Mediterranean Habitats ◽

Body Reserves ◽

European Rabbits ◽

Selection For ◽

Hot Environments

Context European rabbits evolved in Spain and Portugal and are adapted to winter-rainfall Mediterranean habitats. On introduction into Australia in 1859, wild rabbits quickly colonised similar habitats across the southern two-thirds of the continent. However, over the past 40 years, they have spread further into monsoonal savanna habitats in northern Queensland. Aims To explain this, we considered adaptive responses of wild rabbits to hot conditions, particularly potential mechanisms for reducing the heat load of lactation, which has been identified as a likely limiting factor. Methods We analysed data from captive wild rabbits to identify mechanisms that could potentially reduce lactational heat load, and obtained data from shot samples of wild rabbits from northern Queensland to determine which of these might be most important in the field. Key results Rabbits spread food intake evenly across the 20-day lactation period and under hot conditions, captive wild individuals used body reserves to meet energy requirements for lactation, which is more energy efficient than converting digestible foods to milk. Conclusions This strategy reduces the heat load of lactation, enabling rabbits to suckle young successfully under hot conditions, but it comes at a cost. Rabbits need extra body reserves before breeding and need to regain those reserves between litters. Implications The slow spread of rabbits into Australia’s monsoonal savannas is likely to continue, given the rabbit’s reproductive flexibility and further natural selection for breeding in this environment.

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