Keeping your cows cool

Every living creature has an ideal environmental temperature zone in which they will thrive, referred to as the thermo neutral zone (TNZ). For you and I, it will most likely be in the range of 23-30˚C, sitting under the shade of a palm tree on the beach in Fiji, cocktail in hand. For lactating dairy cows, their TNZ is considered to be in the range of -5 to 25˚C, excluding wind chill and humidity.

Our girls will be quite comfortable when ambient temperatures fall within this range, but health and production can suffer greatly as we move outside the TNZ. We also need to remember that each cow carries around her own little internal portable heater, commonly called a rumen.


Things are heating up

As summer temperatures rise cows are trying to keep their core body temperature in and around 39˚C. They have what is referred to as ‘metabolic heat’ coming from rumen fermentation and walking activity. On top of that, they are taking on board ‘environmental heat’ from humidity, direct sunlight and body heat transfer in the dairy. As environmental heat increments begin to rise, our cows have to work harder and spend more energy to remain comfortable.

Watching out for heat stress

There are heat stress matrices that have been developed to illustrate the relationship between ambient temperature and relative humidity. These matrices then provide a Temperature-Humidity Index (THI) to indicate the level of heat stress likely to be encountered, which can be used to implement management strategies.

From this work and our experience, when ambient temperatures rise above 24˚C and relative humidity is more than 50%, we notice cows reduce grazing time to seek shade, respiration rates rise and dry matter intake (DMI) begins to fall. We often think that reduced DMI is mostly from reduced pasture availability and quality, but don’t rule out the effects of heat stress.

On New Zealand dairy farms, we don’t encounter extreme heat stress that can become life threatening to cows, but THI will increase enough to reduce DMI and milk production.

Cows with increased respiratory rate – they’re trying to offload heat - spend less time ruminating and often have reduced rumen motility. This can lead to SARA, reduced immune status, and greater susceptibility to mastitis and lameness.

How to beat heat stress

  • Always provide plenty of shade, clean drinking water and consider using sprinklers to help cool your girls in the yard at the dairy.
  • Offer main grazing feeds early in the morning or at night when the cows have off-loaded some heat units and are more comfortable and so are likely to graze aggressively.
  • Feed high quality silage or hay to aid rumen fill, as this is the best way to stabilise rumen pH.
  • Provide glucose precursors in the form of starch, with preference for slowly degrading starches, as cows with increased respiration rates will be burning blood glucose for maintenance, which reduces availability for milk synthesis.

Keep your girls cool in the summer months and you will realise the benefits of healthier, more productive cows.


Talk to your Ingham Dairy Nutrition Specialist about a FREE plan for maintaining production through summer.   

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