With global temperatures increasing year on year, more animal husbandry professionals around the world are facing the growing challenge of heat stress. In ruminants we see these higher temperatures causing many challenges which can be as severe as reducing the overall production cycle of the animal. Extending the lifespan of a herd is not only economically advantageous but is also beneficial to overall environmental footprint of the farm, so there is a renewed focus on finding solutions that can ensure these animals can tolerate heat more effectively.
Physically reducing the heat burden can be accomplished through barn design, shade provisions, fans, maintaining adequate water supply and feeding the cows during the coolest hours of the day with an adapted diet. However farmers can also look at nutritional approaches to maintain the feed intake, mitigate inflammation and support the resistance of cows to oxidative stress. We spoke to Lallemand Animal Nutrition’s Marie-Valentine Glica, Global Strategic Marketing Manager and Marine Gauthier, Ruminant Technical Development Manager, about the various issues related to heat stress in cows and how Lallemand is developing nutritional solutions to manage this ever-growing challenge.
[Feedinfo] Firstly can you tell us more about the challenge of heat stress and the effects on ruminants. At what temperatures do dairy cows start showing signs of heat stress?
[Marie-Valentine Glica] The optimal temperature for a cow is only 10°C so cows can actually suffer from heat stress from 18°C, especially in some where radiation is stronger. It is also important to consider that humidity plays a big role in heat stress as the air relative humidity level can exacerbate the effect of heat. At the same temperature cows will suffer more from heat if the humidity is high, which is why we use the temperature-humidity index (THI) as common indicator of heat stress risk. The temperature and humidity are not the only parameters to take into account, as the duration of the exposure to high THI is also of importance.
[Marine Gauthier] What makes the situation even more challenging is that cows will not only show significant signs of heat stress such as panting or a high respiration rate. We also observe a reduction of dry matter intake (DMI), which is not easy to detect if the farmer is not measuring it individually. However if you closely observe cows suffering from heat stress, you can notice that rumination is reduced too, more ruminating cows are standing instead of lying down and you may see cows loosing excessive amount of saliva. Heat stress can have big consequences on performance, often seen at the milking parlour by a reduction of milk yield. More seriously it can also increase lameness, losses in body weight and fertility issues.
[Feedinfo] How is the situation different for transition cows? In what ways do they differ from lactating cows when it comes to dealing with heat stress?
[Marie-Valentine Glica] Transition cows will have to face different challenges such as shifting from a forage-rich diet to a lactating diet which is rich in concentrates. In the rumen, we see the passage rate, microbiota and fermentation profiles, rumen pH, and the rumen wall are all affected by heat stress (Bach et al., 2019). As nutritional requirements rise there is a drop in DMI and together with increased oxidative stress, this can translate into lower immunity and higher disease occurrence.In addition, the transition from a high-fibre to high concentrate diet, represents a risk for sub-clinical ruminal acidosis (SARA).
Overall, DMI reduction and the appearance of SARA will increase the negative energy balance at this crucial period. Recent findings show that the consequences of heat stress for peri-partum cows are the same when cows were exposed to hot periods before or after calving or during the whole period (THI > 72). This means that heat stress should be managed carefully during the entire transition period. “The first fan which man can afford, should be placed at the dry cows”.
[Feedinfo] Can you expand more on how heat stress affects milk yield in cows, particularly during the transition period?
[Marine Gauthier] Studies have shown the level of milk loss is linked to both heat stress levels and the duration of exposure. We have seen that only 4 hours exposure/day to low heat stress levels leads to a milk production decrease of 1.1 kg/day. Under heat stress conditions, when the DMI is reduced the foetus exerts pressure on the rumen and reduced rumination occur as the cows divert energy for heat dissipation. The reduced rumination leads to less saliva production, which lowers the buffer capacity and efficiency of the rumen. However, when the transition cow is receiving a transition diet with higher amounts of starch, it needs a fully functional rumen to prevent the risks of SARA. Milk production relies on rumen function, but negative effects can also be expected in the lower gut, with increased risks of inflammation and leaky gut. The cows divert some milk production energy to elicit the immune response, control inflammation, reducing milk potential.
[Feedinfo] Can you elaborate on the link between reduced dry matter intake and the occurrence of uterine diseases in transition cows?
[Marine Gauthier] Research shows that uterine disease is linked to reduced DMI and altered feeding behaviour before calving (Hammon et al., 2006; Huzzey et al., 2007). Heifers have greater nutrient needs before their first calving because of extensive mammogenesis during late pregnancy. It is possible that the reduction of DMI observed during heat stress affects heifers more than multiparous cows and could explain why heifers seems to be more predisposed to uterine diseases (Menta et al., 2022).
[Feedinfo] How can microbial-based solutions like live yeasts help to address the challenge of heat stress?
[Marie-Valentine Glica] Studies show cows can improve their ability to extract energy from their diet with the addition of the live yeast strain Saccharomyces cerevisiae CNCM I-1077(LEVUCELL SC). Perdomo et al., (2020) showed improvement of feed efficiency with + 130g of milk/kg DMI in lactating dairy cows under heat stress with addition of this live yeast fed at a specific heat stress dosage. The same study also showed the addition of the live yeast improves rumination behaviour by increasing chewing time and reducing time between rumination bouts. It also reduces signs of inflammation with less inflammatory compounds found in the blood of transition cows.
[Feedinfo] Why should the antioxidant status of a cow also be considered when tackling heat stress? How does selenium-enriched yeast contribute to improving antioxidant capacity around parturition in heat stressed cows?
[Marine Gauthier] Heat stress and parturition are both challenging for the body. At a cellular level this stress will be translated into higher production of free radicals that need to be neutralized by the body’s antioxidant system. Maintaining a balanced antioxidant status from the start is crucial to alleviate the negative post-partum consequences of this oxidative stress that will possibly cause increased inflammation, low immune status and decreased milk quality and yield.
We also know that selenium deficiency is linked with increased risk of placenta retention (Harrison et al, 2021), and later, fertility issues, which is why its supplementation is so important during that period. In addition, the selenium cow-calf transfer is an important factor to guarantee robustness of the calf at birth. In neonates, selenium is crucial for the development of the immune system, the thyroid, the hair and other parts of the animal.
However not all selenium sources are equal. Using a source of highly bioavailable selenium will help to enhance the action of this antioxidant. This is because organic selenium provided by selenium enriched yeast is absorbed through the small intestine, following the same enzyme transport system as amino acids (including methionine and cysteine), which improves the bioavailability of the component. In the rumen, inorganic selenium (selenite) is partly reduced into insoluble components that cannot be absorbed in the small intestine.
[Feedinfo] You are also suggesting the use of super-oxide dismutase (SOD) alongside selenium-enriched yeast in heat stressed cows. What makes this such an effective combination? Are there any potential interactions that need to be kept in mind?
[Marine Gauthier] There are several reactions that lead to free radical (reactive oxygen species, ROS) neutralization driven by enzymes. There are 3 different enzymes that act as the first line of defence against oxidative stress, including SOD and glutathione peroxidase (which is selenium dependant). They reduce the production of ROS at the source.
When these ROS are produced, the antioxidant molecules will neutralize them. Because SOD and glutathione peroxidase act at the source, they can neutralize 1,000,000 ROS per 1 molecule, while secondary antioxidants neutralize 1:1. This means feeding both SOD and selenium has been shown to help enhance the activity of the endogenous SOD and glutathione peroxidase.
Our trials show that feeding premium selenium enriched yeast (ALKOSEL), and a supplement rich in SOD (MELOFEED) under high heat stress environment improves antioxidant capacity around parturition and lowers somatic cell counts.
[Feedinfo] With concerns around global temperatures increasing how are companies like Lallemand Animal Nutrition supporting animal husbandry professionals and farmers to assess the impact of heat stress on ruminants?
[Marie-Valentine Glica] We are lucky enough to have many years of data collected from many farms across the world. Our team has used this to develop a tool to predict the impact of heat stress on milk yield and milk quality for dairy cows, dairy sheep and goats, and growth for beef cattle: https://connect.lallemandanimalnutrition.com/en/europe/heat-stress/ . This tool is available to all in the form of an interactive world map representing heat stress risks in various parts of the world and associated production losses. This is just an example of Lallemand’s offering to support our industry partners and end-users in the field. We also offer them access to audit tools that take into account environmental factors such as heat stress and the support of our team of technical experts around the world. Our goal is to help decision making for preventive programs before the summer season hits farms.
Published in association with Lallemand Animal Nutrition