HEAT stress in dairy cattle leads to decreased feed intake and decreased milk production.
It is important to know how to recognise heat stress in cattle and also to plan to reduce its impact.
Bos Taurus cattle (Holsteins) have a temperature comfort zone of 4 degrees to 24 degrees, Bos Indicus cattle (Brahmans) 10 degrees to 27 degrees.
Bos Indicus are also better metabolically at offloading and coping with heat stress.
If temperatures are lower than the comfort zone then cows use energy to keep warm.
Temperatures above the comfort zone results in cows using energy to stay cool.
At 35 degrees milk yield can be reduced by 33 per cent and at 40 degrees by as much as 50pc.
The higher producing cattle are at a higher risk from heat stress.
Heat stress is made worse if there is both high air temperature and high humidity.
Humidity above 50pc makes it harder for cattle to evaporate heat off.
Signs of heat stress in dairy cattle: Less active. Seeking shade or wind. Increased breathing rate - sometimes with the mouth open and panting. Sweating and drooling. Agitation and restlessness. Increased thirst - may drink 5 times more than in cooler climates. Weakness, lethargy, stupor, stagger and death.
Management that helps to decrease the risk of heat stress: Changing milking times to the cooler times of the day. Evening milking after 5pm, or at least after 4pm. Changing paddock rotations to allow cows to walk shorter distances over flat ground rather than hilly. Ensure access to shade. Ensure access to cold water in each paddock. Water troughs that are larger will stay cooler longer. Trough water flow rates of 20 litres/cow/hour are recommended and this usually requires water pipe diameters of at least 75mm. Avoid using above ground water pipes (especially black polypipe) as the water can get very hot. Every paddock and the dairy exit should have a water trough. Sprinklers on cows in the yards in hot conditions decreases the risks of heat stress.
Have a look at your farm map and determine now which paddocks fit the requirements above and plan to use these paddocks for hot days.
As physical exercise makes heat stress worse allow cows to walk up to the dairy slowly and leisurely.
As this season is expected to be a long and hot summer some planning and thought now to best enable your cows to cope with heat and humidity can not only result in happier healthier cows but also in limiting the drop in milk production associated with heat.
Until next time, happy milking and a safe and prosperous new year. D
*Sherri Jaques is a practising veterinarian and reproduction adviser in the West Gippsland region of Victoria. All comments and information discussed in this article are intended to be of a general nature only.
Please consult your veterinarian for herd health advice, protocols and/or treatments that are tailored to your herd's particular needs.