Heat Stress and Drinking Water

Considerable research funds have been directed and heat stress in dairy cows in the Northern Hemisphere in recent years. Potential for extreme negative impacts on cows is heightened by housing. This is not to say our cows, exposed to direct sunlight are much better off. Dairy Australia has a section on heat stress and methods of dissipating heat stress under grazing scenarios. My focus is more on just what happens to a dairy cow under heat stress conditions. Heat stress begins for humans at 26c & 40% humidity; for cows, its 22c & 40% humidity.

Reduced feed intake and milk production are notable effects of heat stress, but heat stress can negatively impede reproduction, lameness and immune function. For many years researchers believed reduced intake lowered milk production, however, it is now known changes in the cow’s metabolism also contribute to reduced milk production. Most recent research has highlighted changes in the rumen wall making it more porous and enabling bacteria to be absorbed into the blood stream. This then causes a systemic inflammation due to immune response. Immune response draws on glucose reducing its availability for milk production.

An unfortunate situation for our cows is usually, the highest risk of heat stress also coincides with the highest fibre diet. Fermentation of fibre in the rumen produces extensive heat. Increasing grain feeding during risk periods will reduce dependence on high fibre diets yet sustain, or better, increase energy intake. The cow requires more energy during heat stress apart from milk production because she uses more energy trying to dissipate excess heat from fibre digestion – panting, standing.

Urinary loss of minerals is high due to dramatically increased water intake for cooling. Attention needs to be paid to macro minerals particularly in grain over summer. Likewise, ensure adequate magnesium, niacin and fat soluble vitamins A, D & E. Yeast has research proven benefits in reduction of heat stress effects. Rumensin will increase glucose availability and stabilise rumen pH. Rumination decreases with heat stress increasing risk of low pH.

Reproduction can be reduced simply by body temperature, and lameness induced from long periods of standing trying to access air movement for heat dissipation. Inflammation from immune response to blood bacteria will also hinder conception. Perhaps one of the highest risk times for cows is afternoon milking. Every dairyperson has walked through the yard and knows the humidity is extreme when cows are crowded in the yard. Yard sprinklers are a must.

Heat stress effects linger for months beyond summer heat, both production-wise and physiologically in the cow’s body. Minimisation of heat stress has significant economic benefits.

Water

Clean fresh water would seem an obvious; however, research on farm water supplies tells another story. Before we go down the path of water quality, my experience on farm is supply rate is a major issue. Frequently I see a large number of cows standing around an empty water trough with just a trickle of water flowing into the trough. The cost to milk production, let alone the above impacts on cows’ health, would be staggering. As herds have increased in size, yet the existing water system has not, creates a major bottleneck. Most of the farms I work with have well supplied water troughs immediately after the dairy exit. Research has shown that cows can consume 60% of their water intake at this trough, taking a major load off the paddock trough system.

The first impediment beyond supply issues in water intake is palatability. Exactly the same thing that reduces feed intake. Cows smell everything before they consume it, grass, silage, hay and of course water. High bacteria counts in water will reduce intake simply on taste. This is easy to check as most milk processors will happily test your water for bacteria.

Iron levels in water have been verified as reducing intake somewhere between 4 & 8 ppm. Palatability is implicated here. However, it is also known that iron oxidising bacteria can proliferate in water pipes and troughs when there is sufficient iron in the water – palatability.

These bacteria form slime in pipes and troughs. If levels are low enough, a water softener set up to do so can remove some iron as with calcium and magnesium. The economics of this would need to be assessed. Regular cleaning of troughs is likely the better way, and very necessary as bacteria and a multitude of other organisms and plant-life grow wonderfully in warm water under a summer sun. Chlorination via an injection system will also clean water, however, a reaction/settling tank is necessary for dissipation of residual compounds.

Sulphates in high concentration will reduce water intake. They are also linked to reduced milk fat, diarrhoea, fluid loss and dehydration. Manganese can cause unpleasant taste reducing intake and milk production. Both manganese and iron are known to accumulate in water pipes reducing flow rates. Water borne minerals may also interfere with transition ration DCAD.

Through association with Dr Charlie Elrod who has spent thirty years in water research and its impacts on cow health and production in USA dairy industry and universities, we have access to a water analysis program which takes not just a water test into account, but also dietary minerals, both supplemented and feed sources. We have recently sent water samples from all clients’ farms to the USA and will begin assessment shortly of the combined effects of water and dietary minerals.

John Lyne is a dairy production specialist with Dairytech Nutrition

www.dairytechnutrition.com.au