In dairy cows, the impact of heat stress can be easily measured, in particular through reduced milk production. Although there is less visibility, fattening cattle suffer just as much as dairy cows in warm temperatures. Detecting the signs of heat stress as early as possible is essential to preserving the herd full production and health potential by adjusting its management, with a particular focus on nutrition.
HEAT STRESS: A STILL UNDERESTIMATED ISSUE IN BOVINE
From 24°C onwards, the animal immediately decreases its feed intake, which then takes several days to stabilize again, even at lower temperatures. The animals increase their respiratory rate and use up energy to dissipate excess heat, which contributes to a significant increase in maintenance needs: this is heat stress.
Susceptibility to heat stress also depends on genetic traits: for example, dark coat breeds suffer more than the light coat ones. Fat layer also plays the role of thermal shield, slowing down the dissipation of heat. Finishing cattle are also more impacted due to their smaller body surface area in proportion to their body weight.
HOW TO ASSESS HEAT STRESS IN BEEF CATTLE
The temperature–humidity index, or THI, is a common indicator of heat stress risk level (Table 1). This means that not only temperature is important but also the air relative humidity level, which exacerbates the effect of temperature. For beef cattle, the heat stress threshold is estimated at 72 (Orange zone in the THI table) (Gatson, et al., 2019). This means that for example, at 50% humidity, cattle suffer from heat stress from 25°C.
By placing a thermo-hygrometer — or new generation of sensors that continuously monitor THI within the barn, — close to the animals, producers can monitor and anticipate heat stress risks.
The negative impact of heat stress is linked to the THI level and to the duration of exposure, both in terms of the number of hours/day and the number of consecutive days of stress.
ANIMAL OBSERVATION IS KEY TO DETECT EARLY SIGNS OF HEAT STRESS
The first visible sign of heat stress is a change of feeding behavior: feed intake is reduced and animals show erratic feeding behavior, feeding at the coolest hours of the day. With more severe conditions (higher THI but also longer periods under high temperature), other signs can appear, including:
• Shallow breathing
• Profuse sweating
• Lethargic behavior
• Increased respiration rate: open mouths and breathing with panting and tongue hanging out indicate more severe heat stress.
CONSEQUENCES ON ANIMAL PERFORMANCES AND HEALTH
If the effect of heat stress in dairy cow is much more monitored, with well-known incidence on dairy production, other methods are necessary to measure its impact in meat cattle. This is possible thanks to new smart farming methods which allow real time individual feed intake monitoring.
For example, at Texas A & M AgriLife Research the implementation of GrowSafe Feed Intake bunks has allowed to show that under heat stress conditions, individual feed intake becomes very unstable. This drop in feed intake is sometimes more difficult to assess at the herd level, as it is very irregular in time from one animal to another. This leads to decreases in growth, which can even lead to negative growth (muscle loss due to low ingestion). Beef cattle weight loss could reach up to 10 kg carcass weight.
In extreme situations, the quality of the meat may also deteriorate (higher pH at the slaughterhouse, which can impair meat ripening). Ultimately, if the animal fails to cool down, this may lead to sudden death (e. g. enterotoxemia and heart failure).
Another, indirectly visible sign of heat stress is acidosis. Several trials performed by Lallemand Animal Nutrition using pH boluses in beef or dairy cows have shown a link between heat stress levels and rumen pH.
In addition to performance and health, fertility is also affected. Bulls show a marked decrease in their fertility, linked to a decrease in the motility and quantity of their semen.
LOOK OUT FOR SIGNS OF REDUCED RUMEN FUNCTION
The following signs can indicate poor rumen function: decreased lying and rumination time, loss of saliva through panting, a reduction in meal frequency and a larger meal size, also known as “slug feeding.” The experts at Lallemand can also help producers measure rumen function on their operation by assessing signs such as manure color and consistency. The presence of undigested grain or cotton seeds, for example, are signs of sub-optimal rumen function, where precious (and expensive) nutrients are not being fully digested by the animal.
STABILIZE THE RUMEN WITH LIVE YEAST
A trial conducted at Texas A & M AgriLife Research Center in 2015 demonstrated that, in a situation of heat stress, the addition of rumen specific live yeast Saccharomyces cerevisiae CNCM I-1077 (LEVUCELL SC) to the diet allows the rumen pH to stabilize, with less daily individual changes, and the cattle to improve their intake. Feed intake was also more regular during the day, while animals not receiving LEVUCELL SC consumed more erratically during cooler periods.
As a result, the average daily gain (ADG) was improved by 50 g /day, and the carcass weight by 5 kg over the fattening period (70 days) with a poorly acidogenic diet.
Another study conducted in Italy on a commercial farm (Consortio Agrario del Nordeste) on Charolais breed cattle showed similar results: + 5% ADG (Figure 1) with an average thermal index THI around 70, and allowed a further understanding of the mechanisms involved. By supplementing the animals with a bolus system, which allows measurement of the ruminal pH in real time (SMAXTEC), this trial indicate that:
• Rumen pH decreases in conditions of heat stress, linked in particular to the strong variations of feed intake and loss of saliva buffering capacity (panting).
• The live yeast helps stabilizes the rumen pH, especially as the animal is in a heat stress condition (Figure 2).
• Thus, ruminal pH is indirectly affected by climate conditions and the use of a ruminant specific live yeast, known for to helps stabilize ruminal pH (rumen modifier), allows the consequences of heat stress on feed intake and growth performance to be minimized.
ANTIOXIDANT SUPPLEMENTATION IS KEY
During heat stress periods, animals face decrease in antioxidant status. For example, level of superoxide dismutase enzyme (SOD) can decrease and pro-oxidant and stress indicator, such as Malondialdehyde (MDA) can more than double (Fike and Saker, 2005).
This is why, ensuring an adequate level of antioxidant solution is important. Nutritionists can choose and combine different sources of antioxidants, either primary or secondary antioxidant. Providing primary antioxidants such as Selenium yeast (such as Alkosel) and natural source of super oxide dismutase (such as Melofeed) helps maintain weight gain of meat type ruminants during heat stress and helps preserve the antioxidant status of animals.
A study conducted on a commercial farm in France, during high temperature and humidity period (July with maximum THI of 80) on Charolais breed cattle shows that animals fed a combination of organic selenium source, ALKOSEL, and SOD source MELOFEED shows a higher body weight (+5.8 kg) compared to control group after 28 days of trial (Figure 3).
In conclusion, heat stress could be underestimated in beef cattle. However, it does represent a challenging period for the animals, affecting feed intake and consequently rumen conditions and efficiency. Heat stress will have short-term consequences, affecting growth performance and health, as well as longer-term consequences in negatively impacting meat quality or fertility. Risk monitoring, planning ahead (e.g. use of adapted feeding strategy) and adapted barn and herd management practices are essential to optimize production and help overcome heat stress challenges in beef.
1. Bouraoui R., Lahmar M., Majdoub A., et al., 2002. The relationship of temperature-humidity index with milk production of dairy cows in a Mediterranean climate. Animal Research, EDP Sciences, 2002, 51 (6), pp.479-491. 10.1051/animres:2002036. hal- 00889824
2. Gatson, G. A., Gunn, P. J., Busby, W. D., Wiegand, B. R., Vander Ley, B. L., & Meyer, A. M. 2019. Effects of dry or wet conditions during the preweaning phase on subsequent feedlot performance and carcass composition of beef cattle. Translational Animal Science, 3(1), 168–171. https://doi.org/10.1093/tas/txy095
3. Perdomo, M.C. et al. 2020. Effects of feeding live yeast at 2 dosages on performance and feeding behavior of dairy cows under heat stress. J. Dairy Sci., Vol. 103 (1) 325 – 339
4. Fike J. and Saker K. Virginia Tech. 2005 Immune function, oxidative stress, and antioxidants in lactating dairy cows.
About Bruno Martin
Bruno Martin is an agriculture Engineer specialized on ruminant nutrition. He has an experience in feed industry, farmers nutrition advising and overall management (comfort, barn engineering, health management). He mainly worked for leading French feed companies (premix, pelleted feed…). He has multiple experiences in formulation, field research, products development (mineral, pelleted feed…) and farming at an international level.
Bruno Martin has a strong expertise nutrition and particularly in acidosis with mainly a practical point of view. He has been working with SMAXTEC © sensors in France and Europe for several years, and had overviewed more than 25 trials in commercial dairy and beef farms with Levucell I1077 (live yeast). These sensors allow to catch numerous data on rumen activity and health (acidosis, estimate of water intake according to rumen temperature drops…). All along these trials, numerous individual animal checking allowed to closely connect rumen parameters with visible signs (feet, nervousness…).
Bruno Martin is involved in several field trials on calves, heat stress, beef production and meat sheep all around Europe… He’s focused on global approach on behavior, feeding and comfort management, meat quality in combination with current Lallemand solutions…
Bruno Martin has been working for more than six years for Lallemand Animal Nutrition as technical support. In his previous jobs, he was a Lallemand customers for years.