Act now to minimise performance loss to heat stress this summer

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Dairy Cows Grazing Image

With high yielding dairy cows suffering the negative effects of excess heat even at 20°C in direct sunlight or high humidity, and the resulting reduction in feed intake capable of cutting yields by up to 20%, heat stress is a very real threat even during a typical UK summer.

“Cows will start to experience heat stress at a temperature humidity index (THI) as low as 68 (figure 1), which is relatively common during the summer as relatively humidity is often over 80%,” highlights KW nutritionist Dr Anna Sutcliffe.

THI Graph
Figure 1: Temperature Humidity Index (THI) chart for dairy cows (Source: OMAFRA) – click to enlarge

Common symptoms of heat stress include cows that are panting, lethargic, standing rather than lying or with a high respiratory rate (normal is 26-50 breaths/minute). Increased ration sorting, as well as reductions in feed intake or milk yield of 10% or more, are also indicative.

“Cows in late pregnancy (transition) and early lactation (high yielders) are most at risk due to the additional heat generated by the metabolic processes of production,” she adds.

“And research from Scotland’s Rural College (SRUC, formerly SAC) has shown that butterfats can drop from 3.85-3.48% and proteins from 3.27-3.19% when the THI rises by just 10 points, even at levels below the threshold for heat stress. Without taking action to reduce these effects, the impact on income over feed costs (IOFC) this summer could be substantial.”

Importance of water

With high yielding dairy cows drinking up to 150 litres of water each day, good access to clean, fresh water is essential, warns Dr Sutcliffe, particularly as cows attempt to lose heat through evaporative cooling by sweating and panting.

“Make sure there’s at least 15 cm of water trough space for each cow in the group to minimise competition, and check refresh (flow) rates can keep up with demand, especially after milking,” she states. “Feeding a buffer with osmolites and specific herbal-extracts (Equaliser Cool Cow) will improve cow hydration and salt balance.

“Any time stocking density rises can also have a big impact, increasing both the temperature and humidity experienced by the cow. Cows sheltering under a small area of shade, for example, may be out of the sun, but they’ll also be closely packed together, raising the THI and risk of heat stress, particularly when there’s little air movement.”

Dr Sutcliffe’s advice is to choose grazing areas with additional shade whenever heat stress could be an issue, or to consider housing cows during the day and grazing only at night. Collecting yards and feeding areas can be particularly problematic, so consider leaving backing gates alone or splitting the herd to allow cows more space.

Attention to detail

For indoor areas, ventilation should be maximised by opening all vents, replacing solid doors with gates and clearing away any vegetation slowing airflow around the building. Fans installed to increase evaporative cooling must direct air onto the cows to be of benefit, with placement over cubicles useful to encourage lying and rumination.

“Painting over any clear sheets in the roof – particularly if south facing – can be helpful if above an area where cows are unable to move away, such as in tight-packed collecting yards,”she continues. “For new buildings, consider keeping roof lights north-facing and installing roof insulation for summer-housed high yielding herds.

“…it’s vital that ration nutrient density is increased to compensate.”

“The same attention to detail needs to be paid to the ration. Cows will reduce dry matter intake and avoid long fibre to reduce the heat produced by rumen fermentation activity, so it’s vital that ration nutrient density is increased to compensate.”

Adjusting the ration

Start by using only high quality forages or palatable high energy alternatives such as the wheat-gluten moist feed Traffordgold. Including a moist feed (brewers’ grains, draff or Traffordgold) has the added advantage of lowering the forage-to-concentrate ratio (fermenting forage produces seven times more heat than concentrates), whilst still supplying digestible fibre to lower acidosis risk.

Traffordgold image
Traffordgold is a great source of digestible fibre and high quality protein.

“Other high energy digestible fibre feeds to consider include sugar beet feed and soya hulls, both of which can be easily incorporated into a specific summer blend for feeding in the parlour or as part of a mixed buffer feed. Aim to feed 0.75kg/cow of physically effective fibre to maintain rumen function, and consider a live yeast (Vistacell) or rumen conditioner (Acid Buf) to optimise fermentation efficiency.”

Further improve palatability to maintain intakes by adding any of the distillery syrups or molasses-based liquid feeds, such as Molale or Rouxmolflo Plus, which also reduce fibre sorting. Any additional energy density lift needed can come from a rumen-protected fat supplement, whether in the form of a 100% fat to primarily support yield and body condition (Goldenflake) or a high-C16 fat (Butterfat Extra) to also help milk fat production.

“Finally, remember that higher ambient temperatures increase the likelihood of rations heating and spoiling, particularly as intakes drop,” states Dr Sutcliffe. “So mix rations just before feeding out, feed housed cows twice a day and adjust volumes daily to match intake.

“All refusals must be cleared away before offering new feed, and for cows housed full time, feed at least 60% of the ration between 8pm and 8am, as the cows will eat more during the cooler temperatures overnight.”

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