Heat load alleviation in beef cattle: water application during continuous high temperature exposure

Abstract

The live export industry is an integral part of the Australian cattle industry and makes a significant contribution to the Australian economy. Heat stroke has been a major cause of cattle death on long haul sea voyages and has the potential to threaten the viability and sustainability of cattle exports.To mitigate high heat loads on these voyages, it is necessary to implement cooling strategies to lower the temperature of the microclimate surrounding the cattle. The main cooling method used on live export voyages is high pressure hosing but no research has been undertaken to evaluate the efficacy of this or other water application methods. The major focus of this thesis was therefore, to explore heat load mitigation of confined beef cattle. The initial hypothesis was that the application of water onto cattle exposed to a continuous high heat load will reduce the severity of heat stress.As, different breeds of cattle and composites are exported together, the second hypothesis was that different cattle breeds and composites respond differently to heat exposure and to water cooling.Climatic conditions for all three studies were based on the conditions encountered on board a live export vessel travelling from southern Australia to the Middle East (during the northern hemisphere summer). The first study obtained data on changes in the microclimate and responses of Bos taurus cattle (Angus) when water was applied via a hose to cattle maintained in single pens under continuous hot conditions. The results showed that the water application had a positive impact on cattle comfort (respiratory rate reduced by 50 -80 bpm; rectal temperature reduced within an hour after wetting of cattle). The dry-bulb temperature was also reduced following longer duration water applications. The impact of water application on physiological parameters, such as rate of respiration and rectal temperature, was a function of water volume applied and ambient conditions. For all steers mean daily rectal temperatures and respiratory rates were lower (P < 0.01) during thermoneutral conditions than during the 11 days of hot conditions. Four water application methods (hosing, overhead sprinklers, leg sprinklers and misters) were evaluated in the second experiment with the same Bos taurus breed. Volume and frequency of water application was assessed with the cattle were housed in groups (n = 9) on sawdust bedding. Of the four methods evaluated, hosing was the most effective in mitigating the heat load on the cattle. The leg wetting and misting treatments had little to no effect. While not as effective as hosing, overhead sprinklers did afford heat relief and may have advantages for cooling large numbers of cattle at the same time. Bedding had to be removed after it became wet due to increased concentrations of atmospheric ammonia that posed a risk to cattle and human health. IIAs live export ships carry both Bos taurus and Bos indicus cattle, the third experiment investigated the effects of high heat load conditions on three breeds of cattle an...

A Systematic Review of Heat Load in Australian Livestock Transported by Sea

“…For instance, provision of shade will reduce heat gain from solar radiant heat gain; in shipping this is only of relevance where there are open decks and animals may be exposed to direct sunlight. Radiant heat gain from hot metal infrastructure may maintain temperatures so there is little respite for animals housed within; there are currently limited options for cooling the ships other than wetting with cooler water [ 52 ].…”

“…Exact ventilation rates to ensure adequately dry faecal pads have not been determined given these will vary with climate, pen location, ship type and sheep density. The careful management of hosing in cattle pens has also been suggested to improve bedding during times of high heat load [ 52 ].…”

“…Wetting of animals can be used to mitigate high heat loads via lowering the temperature of the microclimate surrounding animals. This approach has been used for cattle in feedlots and on livestock ships [ 52 ]. Wetting has been trialed and has been shown to lower peak body temperatures and hasten recovery from hyperthermia.…”

“…Wetting has been trialed and has been shown to lower peak body temperatures and hasten recovery from hyperthermia. Four water application methods (hosing, overhead sprinklers, leg sprinklers, and misters) were evaluated by Tait [ 52 ] in a CCR experiment with B. taurus cattle, and high-pressure hosing was found to be the most effective. It is unknown how practical water spray cooling would be on-board ships or how effective it would be for sheep.…”

“…Wetting has the effect of increasing local humidity, causing undesirable wetting of the faecal pad and wetting the fleece of sheep which will only slowly dry in humid conditions. For these reasons, wetting has not been further explored for preventing harmful heat load in transported sheep but is considered to be a useful approach for cattle [ 52 ].…”