More refined approaches emerging in managing summer heat stress in cattle

Jon Condon, 05/11/2020

WITH summer rapidly approaching and record high temperatures recorded in many cattle areas in Eastern Australia earlier this year, heat stress management in feedlot cattle is again coming into focus – and a recent webinar on the topic provided some useful pointers to what lies ahead.

University of Queensland researcher Dr John Gaughan, a specialist in animal heat stress from the School of Agriculture and Food Science, addressed a recent international webinar on heat stress management in cattle.

Historically, acute heat load events had been reasonably rare, he said, but they had increased substantially over the past ten to twenty years.

“And the other aspect that’s being seen is that they are getting longer. Where previously we might have had a three or four-day heatwave event, now we are seeing heatwaves going five to seven days, and even out to ten days,” he said.

Dr John Gaughan

Regardless of views about climate change, Dr Gaughan said there were definitely changes being seen in the number, and intensity of heatwave events in Australia.

“In some areas it’s getting hotter and drier, other areas cooler and wetter – so there may be a shift over time in where we can effectively feed cattle, in terms of heatload risk,” he responded, to a question from a webinar participant.

“The risk is more from the intensity and frequency of heatwaves rather than gradual temperature change. Cattle will adjust if there was to be a general two degree rise in temperatures, for example. But if a changing climate brings in more heatwave conditions, it will be a bigger issue.”

Dr Gaughan said any casual survey of lotfeeders normally showed that heat stress was among the top three to five risk management concerns they held.

“But when we first started developing heat stress models and management plans ten years ago, it was always number one item on the list. These days it is often ranks lower – often behind things like BRD management or grain prices – because lotfeeders have effective management plans in place for when they do see heat stress events.”

He defined acute heat stress as a sudden, rapid increase in heat load – which may only last a couple of days, or go out to 5-10 days in duration.

“It is these acute events that really cause us the major problems, resulting in physiological challenges, and impacts on production. Typically we are more concerned about these acute events (rather than less severe chronic heatwave events), because these were the ones that cause issues around feedlot cattle and their performance.”

Breed variance

Dr Gaughan said a general consensus, globally, was that Bos Indicus cattle did not actually suffer from heat stress.

“To an extent, that’s true, but we know from our work in Australia and elsewhere, that most breeds, at least some of the time, show a heat stress response – particularly in feedlots.”

“We also know that there is a lot of variation between different Bos Taurus cattle – particularly between British breeds and European. And we know that access to shade plays an important role in reducing the impact of heat stress – at least for some breeds.”

Earlier studies showed there was little difference in rumen temperature among Brahman cattle between groups with access to shade, and those without. In contrast, among Angus cattle, there was definitely a response to shade in body temperature. Somewhere in between was the shade response in Charolais (European bos Taurus) cattle.

This meant that one of the critical things for lotfeeders to consider was understanding how different breeds responded to different conditions they were exposed to.

“We need to know a little more about how these different groups respond,” Dr Gaughan said.

In terms of feed intake, trials showed that regardless of breed, intake would start to decrease as temperatures rose to high levels.

Dr Gaughan said people often assumed that Brahmans did not need access to shade in the feedlot. “While rumen temperature studies show that body temperature does not change greatly with the provision of shade, the reality is that Brahmans do use shade – but they use it quite differently to Bos Taurus cattle,” he said.

“The Angus animal might be in the shade from 8am to 4pm in the afternoon, where the Brahman animal will move in and out of the shade area constantly through the day.”

Monitoring is key

Dr Gaughan told the webinar that monitoring was the key to managing any heat load situation.

“We’re not going to stop a heatwave, or stop heat stress happening. But we have to be able to monitor what we have, and then put strategies in place to reduce the impact of those adverse events,” he said.

Monitoring features typically observed included panting scores, behavioural changes, use of shade or hanging around the water trough, and changes in dry matter intake.

“We also want to look at weather conditions, particularly temperature, humidity, wind speed and rainfall, and also the forecast weather later today, and the next few days,” Dr Gaughan said.

All registered feedlots in Australia had to have in place a heatload management plan, part of which was access to reliable weather data. Almost all Australian feedlots have automated weather stations on site, he said.

Panting score was one of the key tools used to visually assess cattle facing excessive heatload.

“Ideally we would be measuring body temperature and respiration rate, but under commercial conditions that’s almost impossible.”

Some research was being conducted into using so-called ‘sentinel’ animals fitted with monitors within a larger feedlot mob to deliver such data, however.

Dr Gaughan said observations should take into account not only ‘how hot it got today,’ but also ‘how cool it got overnight.’

“It’s not only the maximum temperature that’s important. It’s the minimum temperature reached overnight as well. We all know it is hard to sleep well at night if it is too hot and humid, and we know cattle go through the same thing. They will respond better to a high daytime stress incident if they have had some relief the night before.”

“But if we assess animals first thing in the morning and they already have a panting score of 2, then we know those animals may be in a bit of trouble later on during a hot day.”

The beauty of panting score was that it was visible, easy to use and anybody, including the feedtruck driver, could monitor cattle as they moved around the yard.

Dr Gaughan said some new aspects being developed around this included assessment of breed type, relative to panting score.

At times, Bos Taurus and higher Bos Indicus cattle might be in the same pen, and across the feedlot. As a result, a panting score model was developed across five basic breed types, from 100pc British Bos Taurus, 100pc Euro Bos Taurus, and 25-50pc indicus, 50-75pc indicus, and 75-100pc indicus.

Under the five-point model, different breed types hit threshold point at different heatload stages, allowing feedlot managers to assess individual pens, and make management decisions about how each group is treated in terms of a heatload or heat stress event.”

“With this, we want to be able to predict the probability of a heat stress event, pen by pen. If we can predict the probability, then we have some way to manage it – proactively, rather than reactively.”

Another project was looking at whether panting scores could adequately be predicted for a given group of cattle, at a later point in time. Risk assessment models had been developed.

“The way people are starting to think about using this is to assess pens where we have multiple breeds, but also to know that not every pen in the feedlot is going to be affected the same way with a heatload event. We can then manage the animals quite differently.”

He said the longer that animals were exposed to extreme conditions, the more susceptible they became. Thus the accumulated heat load index was a better indicator than single point heat load index on what was happening.

Productivity impacts

Dr Gaughan spent some time looking at productivity impacts from heatload events.

“We know there are breed effects, dietary effects and heat load effects on things like dry matter intake. Interestingly we do not see much reduction in feed intake under commercial feedlot conditions until a heat load index gets pretty high – around 96. That tells us that cattle are fairly robust in many ways, and as long as they have that ability to cool-off at night, then feed intake is maintained.”

“But as we go from low levels to high levels of heat stress, feedlot studies show we start to lose some efficiency, in terms of feed intake and energy intake.”

Impacts differed from chronic to acute heat stress events, studies showed.

“As summer goes on, minor increases in temperature lead to some reductions in feed intake over time. But it is nothing too bad – cattle drop down and come back up again. But when there is an acute event, the key is that after the animals drop their feed intake significantly, it takes a month to get back up to original intake levels again,” Dr Gaughan said.

Not only was growth rate lost for 20-25 days, but the ability to convert fed was compromised. Similar patterns are seen with average daily gain, which can drop to near zero.

“What this means is that the feedlot operator is losing money,” Dr Gaughan said. “The challenge is how do we maintain cattle on feed during these heat periods, and also how (or can) we get them back up onto feed again more quickly afterwards.”

Evidence of carcase impact after heatload events was highly variable, studies had shown.

“We’ve done studies where we’ve seen absolutely zero impact of heat stress on carcase quality, but other studies have shown significant impact. Again it may come back to whether it was a chronic or acute heatload event, and whether the animal has time to recover from the event before slaughter. Quite often they will recover, but do so by being less efficient, so we see a big increase in feed usage to get the same gain.”

He said lotfeeders were not going to be able to stop heat stress events or animals reducing their feed intake, but research was focussing on what could be done through nutrition, for example, to help animals recover more quickly.

“But we still need to know more about heat stress impact on ADG and feed efficiency, and trying to better understand breed effects. There’s still a lot of work to be done in this area.

“When I first started to look at heat stress in cattle the late 1990s, I was told we already knew everything we need to know about heat stress in cattle. Twenty odd years later, and we are still making important discoveries.”

Future directions in shade provision

Discussing what was on the horizon in his field of research, Dr Gaughan said it was ‘all about animal welfare.’

“We are really moving down this track fairly quickly. I’ve been asked a number of times about shade, which is not compulsory in Australian feedlots. Having said that, some local government authorities will no longer issue feedlot application approvals unless shade is included.

Currently, around 88pc of all feedlot cattle in Australia had access to shade, and most of the remainder were in mild areas where it was not necessary.

“Having said that, there is a really strong push from the animal welfare groups, parts of government, and also parts of the cattle industry, to mandate shade use in feedlots – and in some cases, in grazing situations as well,” Dr Gaughan said.

“Where Bos Taurus cattle are being fed in feedlots, then there is a strong push to make that shade mandatory.”

He said one of the features of the grainfed industry was that industry bodies like ALFA and MLA were ‘really proactive,’ getting out there are doing things before government steps in and tries to mandate over issues like shade.

“But there is no doubt that there will be more emphasis on heat load management into the future,” he said.

“Heat stress events are becoming slightly more frequent, but the important point from a management perspective is that they are becoming more intense – we are getting much hotter periods that are lasting longer.”

“Were never going to be able to eliminate heat stress. But we can reduce the effects by using shade, so long as it is designed correctly. There’s also a lot of nutritional interventions including the use of supplements which have potential to really impact animals – particularly in this period of time when they are in recovery after heat load.”

“Nutritional intervention is going to be a critical thing, one we get other factors in place, like shade, and placement and design of feedlots to ensure maximum airflow, the use of heat-tolerant breeds. A lot of work is being done in identifying the genes for heat tolerance in Bos Taurus type cattle, for example.”

During questiontime, a listener asked about economic impact on feedlots from heatwave events.

“We don’t have any economic data on a particular heatwave event,” Dr Gaughan said.

“But what we do know is that heat over the summer months reduces productivity by between $20 and $50 per animal, on average. If it is a mild summer it will be quite low, but a hot summer higher,” he said.

The webinar was hosted by animal health company Phibro, which produces and markets a feed additive called OmniGen AF, which carries claims around heat stress mitigation and recovery.


  • Editor’s note: Come back tomorrow for more news from ALFA on feedlot shade developments





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