Article written by Yoav Alony-Gilboa DVM MRCVS CertSHP
As temperatures continue to rise globally year on year, farms are required to tackle heat stress in order to avoid considerable losses. Care should be taken to look at all stages of growth, from day one calves, to adult (both milking and dry) cows.
Heat stress occurs when a cow absorbs and produces more heat than she can lose to the environment.
High ambient temperature, humidity, and exposure to solar radiation, alongside the metabolic heat produced by the cow when digesting feed, will cause cattle to accumulate heat. Dairy cattle will try to “lose heat” by sweating, panting, and standing where cooler air blows over them. When ambient temperature rises above 24°C and relative humidity reaches above 70%, cows will struggle to lose excess heat. The length of exposure to heat stress is also a major factor, and when continuously exposed to mild to moderate heat stress for more than 17 hours, dairy cows will drop yield by an average of 2 kg of milk.
Cows with heat stress become less active, breath rapidly or pant and drool. Their dry matter intake and feed conversion efficiency will drop and as a result so will their milk yield and milk solids (fat and sometimes protein). Heat stressed cows will spend more time standing (to increase their exposed body surface), often in pooled slurry, trying to cool their body and feet. This type of behaviour will predispose them to lameness due to solar ulcers and digital dermatitis. Cows will often bunch together in the coolest place available or lay down in wet areas, thus increasing the chance of mastitis.
Dry cows that have struggled with heat stress during the transition period will often calve early, produce lighter calves, and colostrum low both in quantity and quality. After calving, these cows will be predisposed to ketosis, metritis, and displaced abomasum and often struggle to reach their full milk production potential.
Conception rate drops during times of heat stress. Cows will exhibit oestrus behaviour for shorter periods, resulting in an increased number of “open days”, and higher overall culling rate. Synchronisation protocols and timed insemination might help somewhat to negate this negative effect. Conception rates may continue to be low as follicular development is suboptimal. High twinning rate is also often observed.
Youngstock also suffer with heat stress . Milk fed calves must always have clean water available to them – as milk feeding alone might lead to dehydration and death. As feed conversion efficiency and feed intake drops, care should be taken to reduce heat stress otherwise, animals may fail to achieve their growth targets.
Animals who suffer from or have chronic lung damage because of pneumonia, will struggle more than others to lose heat to the environment via their damaged respiratory system.
Heat stress can be reduced using a combination of means, some will require a capital investment, but some can be achieved at little cost:
• Present animals with high quality feed to reduce metabolic heat production.
• Ensure enough trough space and possibly present the bulk of the feed in the evening, when temperatures drop, and intakes increase.
• Ensure constant, ample supply of fresh, clean water to all age groups.
• When on pasture, ensure water troughs are close by so cows can access easily.
• Provide shade to cows at pasture, or house during the hot hours of the day.
• Reduce stocking density in sheds and ensure ample shade is provided. Insulate roofs where possible.
• Ensure adequate ventilation and a flow of fresh air in sheds.
• “Shower” cows in collecting yards or feed passages and cool the air around them with high pressure misters. When wetting animals, control the amount of water used, and wipe the teats dry before cluster attachment during milking, to reduce the chances of mastitis.
• Use blast fans to ensure fresh air circulation around the animals and help keep feed, beds, and teats dry.
• Fan installation is a financial investment, and these systems will increase running and maintenance costs. However, reducing the level of heat stress is probably a worthy investment on most farms due to both short- and long-term effects described. We would be happy to advise further on ways of reducing heat stress to cows. As no two farms are the same, a bespoke plan should be considered for each farm, get in touch with the Farm Office to find out more.
