On an island like Ireland heat stress is an unusual topic to be discussing. However, with increasingly warm summers, heat stress is becoming a more significant challenge for livestock farmers. While the effects on growing animals are often limited to the period of stress, even short episodes of heat stress can have a significant impact on lactating animals and in particular dairy cows, reducing milk production and affecting performance throughout the entire lactation.
Heat stress is influenced by both temperature and humidity, with humidity greatly increasing its effects. Table 1 highlights the Temperature Humidity Index (THI) and the associated risk levels. Direct sunlight can further increase heat load in grazing systems, making effective heat stress management essential for maintaining animal performance and productivity.
Heat stress occurs when the body is unable to cool itself effectively. High humidity significantly increases the risk by reducing the rate at which sweat evaporates from the skin. When the air is saturated with moisture, sweat cannot evaporate efficiently, limiting the body’s natural cooling mechanism and causing body temperature to rise more rapidly.
Collecting yards can become heat stress hotspots during warm weather. Cows standing closely together experience higher temperatures and reduced airflow, limiting their ability to dissipate heat effectively.
How the Cow Responds to Heat Stress:
The majority of heat a cow produces comes from fermentation in the rumen. Higher yielding cows with greater intakes are therefore affected most. Under normal conditions, a cow dissipates this heat into the surrounding environment — but as the THI rises, her ability to do so quickly is reduced and a stress response begins.
The initial response in a dairy cow to heat stress is a reduction in feed intake. This happens because the animal must expend extra metabolic energy to activate cooling mechanisms. However, at this same time the animals’ maintenance requirement can increases by 7% to 30% due to the heat stress. This change in energy balance will reduce milk production and milk constituents. However, this change in energy balance does not explain all the losses in milk production that occur. Changes in metabolism particularly glucose metabolism are at play. Embryo loss and increasing levels of infections e.g. mastitis can also be seen. In an Irish context, embryo loss is a particular concern, given that most spring calving dairy herds at grass are in the last few weeks of the breeding season.
In order to help with heat dissipation cows stand for longer periods. Standing increases an animals’ body exposure i.e. more of the animals’ skin is exposed to moving air which maximises convective heat loss. Equally standing avoids ground heat i.e. reduces the conductive heat absorbed from the warm ground. During periods of heat stress there is a reduction in rumination rate which affects digestion and production of natural rumen buffers. Absorption of nutrients and acids in the rumen are reduced. Blood flow to peripheral area increases and consequently blood flow in core areas (example internal organs and digestive system) is reduced.
Effect On Eating Behaviour During Periods of Heat Stress:
A cow normally eats 9-14 meals per day. However, during periods of heat stress cows eat little during the hot part of the day. Consequently, meals are often bigger, less frequent and often after considerable periods of fasting. This behaviour has significant consequences for rumen function and acidosis risk.
Increase standing reduces an animals’ normal rest time. During hot weather cows often stand close together to avail of shade making it even more difficult for them to dissipate heat. There is also an energy cost to this behaviour. Research shows a higher incidence of lameness associated with increasing periods of standing.
Production losses may not be immediately noticed; however, they can be significant. Post peak lactation cows normally lose 2% of their milk yield per week. During periods of moderate heat stress this can increase to 3-4% per week. While this does not look excessive for high yielding herds these compounds to a few hundred litres for the remainder of the lactation.
Practical Actions A Farmer Can Take Steps To Reduce The Impact:
- Use shaded paddocks and review grazing rotation during peak heat periods
- Ensure water is fresh, plentiful, and easily accessible at all times
- Review milking routines to limit time spent in warm collecting yards
- Increase concentrate levels to offset reduced grass intake
- In indoor confined systems open up sheds to allow air movement- example, use of air conditioning and/or sprinklers
- Add RUMBUFF to support digestive stability through the stress period
How RUMBUFF can help?
RUMBUFF is an ideal buffer for use where heat stress is a concern. It is proven in the toughest environments including across North Africa and the Middle East where heat stress management is not optional, and where product performance is non-negotiable. That same proven efficacy translates directly to the Irish summer, where humid conditions can tip the THI into the alert zone with little warning. The disruption heat stress causes to rumen function, erratic intakes, reduced rumination, and lowered natural buffering are exactly the conditions Rumbuff is designed to address.
For dairy farmers looking to protect milk yield and milk quality through the summer months, RUMBUFF is a proven and cost effective tool for inclusion in their cows diet.
For feedmills, RUMBUFF offers actionable, timely value to your farmer customers who are seeking a clear-cut solution.
Including RUMBUFF in the diet is a key component to keeping cows healthy while also supporting rumen health.
For further information and stockists in your area, please contact your local Inform Nutrition Sales representative.
