Heat Stress in Dairy Cows
While heat stress has always been a concern in hotter countries such as Australia and the US it has also become more widely recognized in the UK in recent years.
Cows are far better able to deal with cold weather then they are with hot, humid conditions. Heat stress is usually seen when daily temperatures exceed 25C although humidity also plays a significant role. Like humans evaporation is very important in controlling body temperature but high humidity reduces the effectiveness of this.
Heat stress tends to be more severe in larger framed, higher yielding cows. These cows need to eat more and so produce more internal heat. Black cows may also be more susceptible as they absorb more heat and radiate less.
What signs should you be looking out for this summer?
- reduced dry matter intakes and yield
- lethargic cows with an increased rate of breathing
- increased rectal temperatures and some cows will salivate
There may also be knock-on effects such as
- reduced fertility, primarily through a reduction in conception rates (usually seen 6 - 12 weeks later)
- increased acidosis risk, leading to low milk fat percentages and an increased risk of lameness
- ‘summer rise' in bulk cell count
What can you do to minimize the effects of Heat Stress?
- Maintain water supplies. Lactating cows can easily drink 100L of water per day and this may rise to 150L in the middle of summer. Remember cows will preferentially drink after milking and so providing access to water at this time is critical
- Provide shade if possible. In some cases it may be possible to allow cows free access to the cubicle sheds throughout the day
- Alter the TMR if necessary. Increasing the energy density of the ration can be useful (for example including protected fat) although the diet will have to be carefully balance to minimize the acidosis risk.
- In hotter countries farmers use strategies such as positive DCAB rations and misting cows in the collecting yard at milking.