Fighting heat stress in dairy cows with a new holistic concept
Heat-related stress occurs when an animal is no longer capable of naturally eliminating
excess body heat. Heat build-up is caused by external temperatures and a high level of
relative humidity, which overtakes the physiological capacity of thermoregulation
in mammals – also known as evapotranspiration.
This temperature-relative humidity ratio is expressed via the temperature humidity index or THI, which assesses thermal stress levels. For example, a THI of 72 corresponds to a temperature of 22°C at 100% of relative humidity.
Economic losses due to thermal stress are difficult to calculate. However, findings of a study carried out in American cows showed that even when preventative measures were taken against thermal stress (management, equipment), losses still amounted to US$100/cow/year, with 80% of these losses related to production and 20% due to a health expense increase.
It has also been shown that thermal stress during gestation had a negative impact on lactation and therefore subsequent milk yield. Owing to their higher metabolism, dairy cows are more prone to thermal constraints with a THI lower than that seen in humans (Figure 1).
Thermal stress is considered to be moderate when the THI in dairy cows is above 72, while in humans it would be above 80. The thermal comfort zone for a lactating cow varies between 0 and 20°C. As an example, a temperature of 25°C coupled with 50% humidity corresponds to a THI of 72. Dairy cows are therefore very sensitive to heat stress.
Effects of thermal stress
Thermal stress reduces milk yield and its components (drop in milk-fat levels) and
negatively impacts both reproduction and immunity. External signs indicating thermal stress are easy to observe in the herd and include an accelerated respiratory rate, open mouth and mucous ptyalism.
The survival response of a dairy cow facing heat stress is a lower dry-matter intake. Indeed, fermentation in the rumen induces an exothermic reaction. This incremental heat therefore needs to be evacuated in addition to the thermoregulation, due to high external temperatures. There is also a positive correlation between the increase in ruminal temperature (thermoregulation defect) and a higher risk of acidosis.
Causes of rumen acidosis entail a decrease in the quantity of organic matter digested, a reduction in the production of saliva rich in buffer substances (specific glands stimulated during mastication), and a drop in the quantity of sodium bicarbonate available in the blood due to intense breathing.
Moreover, there is an imbalance of ruminal flora at the expense of cellulolytic flora. Feed efficiency is also affected. Heat stress therefore induces the same pathologies as chronic clinical/ subclinical acidosis – health condition is compromised, lameness and fertility disorders occur, and there is a higher culling rate.
Preventing the risk of acidosis
Equipment such as fans or misting systems are increasingly being used on dairy farms confronted with heat stress. Unfortunately, these tools are not sufficient to preserve the dairy yield potential as there is a double rumen-related impact: lower dry-matter intake on the one hand and lower feed efficiency on the other. Feed rations must therefore be adjusted during high-risk periods to reduce these impacts.
Sensory additives for better-being
‘Better-being’ of animals is key for profitable operations. Thorough knowledge of the brain’s ecosystems led Phodé to develop a one-of-a-kind plant-based solution, mainly composed of a specific extract from the Rutacae family that neuromodulates the signalling stress message in the nervous system. As a result, dairy cows perceive less
environmental heat stress and behave normally. In other words, there are fewer changes in feed intake or behaviour.
Phodé has also been working on the third brain – the microbiota – via our essential oils and spices range. Our scientific studies have not only shown the bioregulating action of ruminal fermentation and the production of volatile fatty acids stemming from this, but also the powerful effect that a specific mix of spices could have on buffer substances in the saliva.
Field evidence
The combination of these two sensory solutions were tested in heat-stressed dairy cows in a trial on a farm in Portugal, and included 296 lactating cows. Two study arms were formed according to lactation ranks and stages: mid-lactation primiparous cows and early-lactation multiparous cows.
Daily milk production, feed intake, number of animals as well as lactation stages were recorded. Over the test period, the mean temperature at 05:00 was 17°C and 32°C at 15:00. It was, however, observed that mean temperatures were higher during the supplementation period compared to that of the controls. Before supplementation, cows consumed an average of 22,7kg of dry matter.
Changes were also noted in feed intake during supplementation. Cows in both groups had a greater intake at 05:00 in the morning when the temperature was higher. The neurosensory plantbased solution is an adaptogen, meaning that the treated cows regulate their feed intake according to realtime environmental conditions.
In this trial, it was noticed that the cows would anticipate peak afternoon temperatures, especially when morning temperatures were high, by adapting their feed intake accordingly. Exothermic fermentations therefore mainly occurred at times when the outside temperature was still bearable.
On the contrary, supplementation had no effect on the afternoon ration consumption since temperatures were already too high for the cow to want to risk increasing its body temperature even more. These behavioural results matched those recorded in previous studies lead by Phodé, with similar effects on feed-intake regulation.
A linear regression model, taking into account all recorded parameters, was established to assess the effect of each parameter on the evolution of milk production. It appears that using Phodé’s two sensory additives increased milk production by 0,79ℓ/d and 0,92ℓ/d in primiparous and multiparous cows, respectively. This therefore represents
32 and 35%, respectively, of these variations in milk production.
In conclusion
The two sensory additives described in the article have proven a true interest in maintaining productivity in dairy cows during heat stress; all the more when temperatures are higher during supplementation in both groups.
