Farmers take note of what animals are telling us, AgResearch Grasslands senior scientist Keith Betteridge says.
"They need shade on hot summer days, even from early morning, so replace what you have removed. In return, they will better-distribute excreted nutrients across the farm, stop sulking, grow better and produce more."
A common belief of seeing a cow snoozing under a tree was "If she is sleeping, she is not grazing", resulting in less milk being produced, but a study had found that was not necessarily the case.
Betteridge carried out a three-week trial over summer which showed stock with shade grazed for 35 minutes longer than without.
During the trial, 24 cows were equipped with sensing equipment and divided over four paddocks - two with shade and two without. A GPS collar was fitted so the farmer knew where in the paddock the cows went, along with a motion- sensor monitoring movements such as whether the animals were grazing, standing, walking or lying down. A button temperature-logging sensor inside a piece of rubber bicycle tube was glued to their backs and a rumen sensor was put into four cows to monitor rumen temperature and acidity.
Temperature loggers were installed in one paddock and the highest air temperature recorded during the trial was 31.6 degrees Celsius.
Mean daily temperature ranged from 14-24 deg and the night temperature averaged 14 deg.
"Nevertheless, the average maximum temperature was 10 deg higher in full sun than in the shade. The temperature reading from the cow's back frequently exceeded 50 deg in both groups from 2-3pm," he said.
Cows with shade made good use of it during the day and motion sensors showed that as the midday peak approached cows grazed closer to the trees.
"The greatest revelation was cows with shade still did some grazing during the period of peak temperature. Between 3-6pm, they grazed more than no-shade cows and, overall, grazed 35 minutes longer per day."
Cows with no shade spent more time lying down during the heat of the day and suffered more heat loading, but both groups drank with the same frequency.
Rumen temperature often rose to 40-42 degrees at which time the cow had to have a drink. That was an indicator of heat stress.
"This was not seen in the afternoon, but more typically from 9pm to midnight following the ingestion of their biggest feed of the day from 4pm until sunset."
Planting trees not only provided shade but also soil stabilisation in hill country, extra income and added aesthetic value. Betteridge suggested creating a "magnet" to draw stock away from camping close to the riparian margins of streams so both faecal nutrients and bacterial contaminants were less readily transferred to the water.
"If trees are available then animals will always seek shelter for at least some of the time when the midday sun is hot."