Recent analysis of TMS data for 2018 has revealed cows were impacted by heat stress for a full six months and fresh cow lactation performance is still affected, says transition specialists Premier Nutrition.

Using the standard temperature humidity index (THI) and 72 THI as a cut-off point, the data recorded heat stress from April to September inclusive and its implications are still impacting metabolic disease incidence, fertility and milk yield.

THI graph
Graph showing humidity by month.

“When cows are hot, they simply stop eating in an effort to cool themselves”, explains Mark Hall, Premier Nutrition’s Transition Manager.  “Unfortunately, the knock-on effects for this drop in nutritional intake, especially if it lasts for a considerable time, is an increased risk in ketosis and acidosis incidences as well as fertility issues and, obviously, reduced milk yield and constituents.”

However, recent work suggests we must also be concerned for the in-calf cow as well as fresh cows.  “Heat stress is a driver for ‘leaky gut’ syndrome.  This is when tight junctions between cells in the gut regress back into the cell, which opens up small gaps and this allows nutrients to ‘leak’ from the gut.  These nutrients are lost in terms of their effectiveness and essentially means the calf is compromised nutritionally in utero as the cow is using everything she has to counter her own heat stress whilst maintaining milk yield.

“The real impact comes post-birth though.  The calf has effectively had to adapt to ‘starvation conditions’ in utero, and when we follow this with
extremely high spec milk powders they struggle to cope with the
insulin levels the high plain of nutrition brings about.  It’s the equivalent of feeding a gourmet meal to a person who has been starved for a period of time, the body does not have time to adapt to the huge change in nutritional status”.

As warmer weather is potentially on the horizon, Premier Nutrition offer the following recommendations to prepare for heat stress:

  • Get the rumen environment right; consider including rumen buffers and balancing for Metabolic Base Ratio to minimise acidosis.
  • Consider fans and air circulation, particularly for dry cows.  Cows also lose key nutrients through sweat inducing acidosis; can you help them to sweat less?
  • Increased water availability is crucial, and it must be as clean as possible with plenty of space to allow drinking.
  • Don’t ignore feed availability, especially for dry cows.  Make sure you push up at least 3 times per day (ideally 4!) and have 0.6m per dry cow at the feed fence.

“It’s really important to prepare as far as possible for heat stress”, Mark adds.  “TMS data is proving that late lactation and dry cows calving in early autumn are not as good as cows calving over the winter and ignoring heat stress is a major factor.  In addition, fresh cow performance is poorer; for cows affected by heat stress, they are typically 2-4 litres below peak lactation and it is impossible to recover this – in other words, they will be underperforming for the entire lactation.”

Premier Nutrition’s TMS system monitors 70,000 transition cows and the data has been independently analysed by the University of Nottingham.