Coming into warmer seasons always brings the potential for heat stress in dairy cattle. Cows produce a lot of heat due to their rumen fermentation activity. In springtime, where days are warm, but nights may still be cold, even though average temperatures seem ok, can lead to such issues.
Whilst ruminants are well adapted to cope with colder temperatures (their thermal-neutral lower limit is around -10⁰C), anything above 25⁰C starts to have a major impact on their welfare and milk yields. Humidity exacerbates the situation, as the animal finds it difficult to dissipate heat via the skin. Heat stress can be manifested as reduced feed intake, increased sweating and panting and poor fertility/conception rates. Sweating increases the need for water intakes, and it is important that clean water is always readily available. ‘Clean’ is defined as not contaminated with algae, bacteria from faecal matter, high nitrates or soil minerals. Cattle have much higher water intake requirements than other mammals, due to their evolution which has resulted in poorer reclamation from their hind gut (hence, the higher water content in faeces).
Severe heat stress (more than 35⁰C) has been shown to reduce feed intake by 35% and milk yields by up to 40%. The reduction in feed intake seen is thought to be an attempt to reduce rumen heat generation from bacterial activity for fibre fermentation, but they still need to produce energy to support themselves and lactation. Hence, heat stress diets have been developed that contain more fat, which has lower heat generation during digestion. In addition, excess protein intakes (generally above 15% of the diet) generate more body heat as this requires more energy to metabolise and excrete the portion that is not used in the body or in milk production. So, the balance between energy generation and protein availability come into sharp focus under heat stress conditions. However, research has shown that intake is not the whole driver of lower milk yields – other physiological factors play a role.
Sweat contains minerals, and such losses must be replaced from the feed, else this is a drain on essential tissue reserves which can affect important balances in tissues and blood. Minerals are needed in every tissue and cell in the body, to maintain water and ion balance that controls muscle contraction and cell function (often referred to as ‘electrolytes’). Potassium, sodium and chlorine are the main components in sweat and must be replaced accordingly to make up any shortfall. Panting causes a reduction in blood bicarbonate levels, which affects pH and essential cellular and organ mechanisms in the body, leading to more losses in urine. Hence, mineral depletion spirals as overheating continues. However, all changes in feed must be done carefully to not unbalance the uptake of other minerals that are essential in the body.
In conclusion, feeding the heat-stressed cow must focus on supplying energy which has a lower heat increment, making sure protein is not in excess and including enough minerals to replace losses in sweat and urine. This will help maintain animal welfare and performance.
Talk to your local Reid’s Dairy Specialist today about the benefits of our mash and the products we can offer to suit your requirements on 1300 REID FEED or enquire here >
Author
Dr Lucy Waldron
PhD RNutr AAS RFellow (Massey)
Head of Nutrition and Technical Services
