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Four tips to tackle heat stress S
BY DR SOPHIE PARKER-NORMAN
ummer months bring often unavoidable heat stress. Heat stress is often spotted by increased respiration rate which is also ac- companied by a drop in dry matter intake (DMI), contributing to reduced production. It is a multifactorial systemic problem and
it is thought that, as well as reduced DMI, shifts in post-absorptive glu- cose and lipid homeostasis may contribute to additional reductions in production. Feeding behaviour is also impacted by heat stress. Dairy cat- tle will usually eat more frequent but smaller meals and spend less time lying. In the rumen we see reduced rumination and altered volatile fatty acid production with a decrease in the acetate to propionate ratio, possi- bly leading to negative impacts on milk fat production. Here are some tips for nutritional approaches: Manage forage inclusion: Fermentation of fibre in the rumen gener- ates a lot of metabolic heat. During heat stress challenges, fibre can be reduced in the ration, but it is important that this is not done to the ex- tent of causing a negative impact on the rumen. Keep an eye on the milk fat to protein ratio. A value below 1.2 indicates that there is not enough fibre in the diet, that acetate production is reduced and therefore there are negative impacts on milk fat production and possibly signs of acidosis.
Meet the energy requirement: The additional energy requirement for a 650kg dairy cow producing 36kg of milk at 35°C vs 15°C is in the re- gion of 22%. That energy gap can be hard to meet, particularly as the cow also has a reduced intake. Feeding an energy-dense rumen-protect- ed fat allows the nutritionist to increase energy density of the ration without impacting rumen fermentation. Don’t forget about protein: Rumen function is not optimal during heat stress. As a result, microbial protein synthesis will also be impacted. Rumen-protected protein sources can be fed to increase contribution of bypass to total metabolisable protein and help to ensure protein require- ments are being met. Watch out for acidosis: When DMI is limited, it may be tempting to in- crease rapidly fermentable carbohydrates. This will work in the short term, but in the long term it can easily lead to acidosis if not managed correctly. Consider using a buffer or pre- or probiotic additive to manage rumen conditions and avoid negative impacts on the fibre-fermenting bacteria. Heat stress is a challenge that is here to stay and could also start to be a more common occurrence in parts of the world where it has previ- ously not been. Management of heat stress will always be difficult, but nutrition has a very important role to play in mitigating losses in produc- tion and health. These nutritional approaches, alongside other manage- ment practices such as housing ventilation, allow the nutritionist to be prepared to weather the challenge during the warmer months.
58 ▶DAIRY GLOBAL | Volume 7, No. 3, 2020
Dr Sophie Parker-Norman is Head of R&D at Volac Interna- tional and is responsible for innovation in animal nutrition.
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