Now here is a quirky fact you may not know
Dairy cows ( Bos Taurus ) only sweat through their noses.
As dairy cows perspire at only 10 per cent of the human rate we have to help them maintain a comfortable body temperature in the hotter summer months.
Cattle dissipate heat primarily through breathing. That is why during the summer months cows’ tongues may be hanging out of their mouths. This is an attempt to increase the volume of air that passes through the airways, maximizing the exchange of heat with the environment.
And they have this very quirky way of wiping the sweat off their noses
To reduce the levels of cow heat stress the trick is to be constantly aware of the weather and what is likely to be coming.
For example a combination of the following can act as a warning
The most useful and practical way to determine how your cows are actually coping with the prevailing conditions and managing their heat load is to check their breathing rate.
Holsteins being black and white have the added burden that black cows feel the heat more and seem to attract more flies that whiter cows. Whereas white cows will suffer sunburn.
Flies seem to more prevalent on black cows
Whilst this much whiter cow sitting next to her didn’t seem to be at all troubled by flies
We have the added complication of the home farm being very steep which means the the cows require extra energy provided via a higher feed intake to walk up and down the hills. Metabolising this extra feed generates more heat aggravating any extra heat stress being incurred from the weather.
The cows are in paddock 3 this week between the morning and the noon milking.
Like this paddock it has a 5 to 6 gradient. That’s almost mountain goat terrain
And they traverse the hills like mountain goats on the walk home
Udders full of milk prior to midday milking
On top of this our cows already have high feed intake because they produce a lot of milk so it goes with out saying higher milk production cows will begin experiencing heat stress before lower producing or dry cows (cows not lactating)
Okay so what do you do?
With wise advice from our nutritionist Dr Neil Moss we adjust the feed by packing the nutrients into smaller volumes of feed that we feed in the dairy.
Our cows get fed a mixture of grains and vitamins and mineral supplements three times daily in the dairy.
On hot days, we put the cows in paddocks where they have access to adequate amounts of shade.
And you need to keep your eyes wide open for the ones in the bushes
High producing cows will often drink 50 per cent more water on a hot day so again it goes without saying they must have access to good quality, cool drinking water
Big troughs and lots of them.
Allowing the cows to take their time their time walking backwards and forwards from the dairy is always a high priority
Cows don’t seem to like hot concrete and will avoid it if the can
Milking three times daily makes it tricky too and our cows are walking backwards and forwards to the dairy during the hottest part of the day. Whilst its hard to modify the times of milking we normally start early ( 4am) so that milking is completed early in the morning before it gets too hot. 
Early starts mean the cows get to the paddock before it gets too hot
We keep the cows close to the dairy for the midday milking and the night time milking (8am) is in the cooler part of the evening. Research says during hot weather,cows prefer to eat at night so we pick the paddock with the highest quality feed for the night feed.
Then we get to the fun part. We have sprinklers set up in the milking yard to cool the cows while they wait to be milked and large fans in the milking shed which helps keep both the people and cows a lot cooler
Cows love to stand under the sprinklers whilst they wait to get milked
The dairy is also protected from the hot sun by two huge Morton Bay figs
Its a challenge but we get better at it every year
For those who like the science – courtesy of Dr Moss
PHYSIOLOGICAL RESPONSES TO HEAT STRESS
Heat stress induces a number of physiological responses by the cow in an attempt to keep body temperatures within normal limits. The following are some of the physiological changes occurring in the cow as heat stress conditions are incurred:
- Respiration rates increase and may reach the stage of panting. In this attempt to increase evaporative cooling, increased amounts of CO2 are exhaled resulting an a decrease in H2CO3 and an increase in blood pH. In response to the decrease in blood pH, the kidney increases resorption of H+ and more HCO3– and cations, primarily sodium, are excreted in the urine.
- Heat stressed cows lose two thirds of their evaporative water loss by sweating and one third by panting. The maximum sweat loss at 95° F is estimated to be 150g/m2 of body surface per hour. Cows lose potassium rather than sodium through sweating.
- Reticulo-rumen motility and overall rate of digesta passage is decreased during heat stress. There also is a change in rumen fermentation with less total volatile fatty acids produced and an increase in the molar percent of acetate.
- Blood flow to the digestive tract and other internal tissues is decreased and flow to the skin surface is increased
- Urine volume generally increases
