By Bruno Martin, Ruminants Technical Support Manager, Lallemand Animal Nutrition
Heat stress : a still underestimated issue in bovine
In dairy cows, the impact of heat stress can be easily measured, seeing lower milk production, less feed intake and many more variations from their typical behaviors, however, in beef cattle the signs of heat stress are much less visible. Although there is less visibility, fattening cattle suffer just as much as dairy cows in warm temperatures. From 25° 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. 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.
In addition, bulls show a marked decrease in their fertility, having a decrease in the motility and quantity of their semen.
For example, over the last two years in France, on average, the temperatures for 30% of the days from June to August were above the acceptable threshold for fattening cattle (determined on the basis of a THI index combining both temperature and hygrometry; Lallemand Animal Nutrition survey).
Various trials carried out by Lallemand Animal Nutrition have demonstrated 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). 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).
Stabilizing the rumen for better stress management
A trial conducted in Texas (Texas A & M AgriLife Research Center, Lallemand Ruminant Center of Excellence) demonstrated that, in a situation of heat stress, the addition of a specific ruminant live yeast Saccharomyces cerevisiae CNCM I-1077 (LEVUCELL SC) to the diet allows the rumen to stabilize (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 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 stabilizes the rumen pH, especially as the animal is in a heat stress condition (Figure 1).
- Thus, ruminal pH is indirectly affected by climate conditions and the use of a ruminant specific live yeast, known for its stabilizing effects on ruminal pH (rumen modifier), allows the consequences of heat stress on feed intake and growth performance to be minimized.
How to face heat stress in practice ?
Some simple adaptation measures can be put in place for the herd when the hot months are in sight:
- Check the flow of water tanks as they are very often insufficient. As temperatures increase, water consumption also rises.
- Check sodium intake. Generally it is advisable to increase this contribution beyond the strict requirements, this in order to stimulate water intake. In Europe, an intake of 30 to 50 g / day is recommended. Also check potassium intake especially for high-grain rations (optimum intake 14 g / kg dry matter, minimum intake 8 g / kg DM).
- Ventilate the building at best as possible by creating a draft. Low openings for refreshing animals are very useful. Provide some shade.
- Concentrate the ration to limit the effects of feed intake reduction:
- At 27°C – decrease in feed intake of 4% = potential growth loss 100 g approximately.
- At 30°C – decrease in feed intake of 10% = potential growth loss 300 g approximately.
- At 35°C – decrease in feed intake of 28% = potential growth loss 800 g approximately.
The use of fats appears quite interesting in this situation.
- Implement an early insect repellant strategy. Flies cause a decrease in rumination.
- Feed live yeast LEVUCELL SC in “reinforced” dose as soon as the ambient temperature increases. By stabilizing the rumen pH and feed intake, LEVUCELL SC will maintain the growth potential.
- Carefully monitor the heating of the ration at the trough. A trial on farmed heifers revealed an 11% decrease in intake with a ration that was heating (Dr. Kung- University of Delaware). If the ration heats, try to spread and push it more frequently. However, the most effective method is to treat the silage at harvest with a silage inoculant containing Lactobacillus Buchneri 40788 at a rate of at least 300,000 CFU / g.
- Distributing the ration at the coolest hours of the day also promotes consumption.
Finally, considering longer-term planning, keep in mind that the increase in ambient temperature and the increasing variability are detrimental to fattening cattle. It is advisable to plan buildings design accordingly. Easy access to water with a drinking trough for up to 10 animals is recommended. If fans and foggers may appear today as an unnecessary luxury for beef cattle, they however, they may appear to be vital in the near future.