The effects of heat stress are estimated to cost the U.S. dairy industry more than $897 million in lost performance — even when heat abatement systems are used.
Adjusting nutrition, feeding practices and cooling strategies can help reduce these losses while maintaining rumen function and performance.
"When cattle are stressed because of high temperatures and humidity, producers can see reductions in dry matter intake, milk production and reproduction," said Anthony Hall, technical services, ruminant, with Lallemand Animal Nutrition. "While we can't control the weather, producers can change how they help their herds manage this challenging time."
Dairy cattle can be considered "heat stressed" when the temperature/humidity index is 72 or above, which corresponds to 72°F at 100% humidity or 82°F at 20% humidity. However, research has shown that high-producing and early-lactation cows have lower thresholds, Hall noted.
Once heat stress occurs, cattle begin to divert energy from body maintenance, growth and/or milk production. Then, producers can see such effects as: increased respiration rate, decreased milk production, lowered feed intake, reduced reproduction, increased risk of lameness and higher rates of culling.
"Some of these effects point to impaired rumen function, which we know can occur during all sorts of challenging environments, including — but not limited to — high temperatures and humidity," Hall said. "Heat stress is so important to herd health and productivity that producers should address it from every angle. Optimizing rumen function can help a cow combat heat stress from the inside out."
In fact, impaired rumen function can add to another common health challenge: sub-acute ruminal acidosis, which occurs when the rumen environment spends three hours or more below a pH of 5.8 during a 24-hour period. Adding an active dry yeast probiotic — like Saccharomyces cerevisiae CNCM I-1077 — can improve rumen function and increase fiber digestion for all life stages of both beef and dairy cattle, Hall said.
"When heat stress occurs, normal rumen function is disrupted. This worsens the already significant effects of heat stress in dairy cattle," Hall said. "Continued research into the positive effects of active dry yeasts offers support for including probiotics as part of a heat abatement strategy."
Long-range summer forecasts call for average to above-average temperatures for nearly all of the U.S. While it may be unknown how high the mercury will rise in the coming months, dairy farmers do know that much warmer weather is just around the corner and that their cows will have to deal with the effects of heat stress.
"Hot weather reduces feed intake and rumination, dragging down animal performance. This condition is often made worse because cows are prone to potassium deficiencies during heat stress," explained Dr. Elliot Block, research fellow with Arm & Hammer Animal Nutrition.
Dairy producers don't have to let heat stress gain the upper hand. Block said there are nutritional steps that can be taken to optimize milk production in a herd before temperatures climb, including:
1. Focus on potassium. Potassium is a key dietary consideration, and including supplemental dietary potassium in lactating cow rations is a recommended part of a proactive heat abatement plan.
* Potassium is the number-one mineral in milk, even more so than calcium, yet potassium is the main component of sweat, and cows lose it quickly through increased perspiration and urination during heat stress.
* Due to reduced feed intake, heat-stressed cows ruminate less and, therefore, generate less saliva, which also reduces salivary bicarbonate content. These reductions, along with the decreased amount of saliva entering the rumen, make the heat-stressed cow much more susceptible to subclinical and acute rumen acidosis.
* Fresh cows require higher levels of dietary potassium. Research shows that cows are often potassium deficient for the first 10 weeks of lactation, even when potassium is fed at National Research Council-recommended levels.
* Feeding supplemental potassium is critical to replace what's lost.
* University research shows that increasing dietary potassium levels can also boost fat-corrected milk production by more than 8 lb. per day.
2. Benefit from buffers. Buffers seem to have become the forgotten tool of basic dairy nutrition, Block said. Not only is adequate inclusion of buffers in the ration important for maintaining milk component production, but they are key factors in combating the effects of heat stress.
Buffers help stabilize rumen acids, increasing feed intake and improving rumen performance for enhanced productivity. Cows need this assistance throughout the year, but especially during periods of heat stress.
Today's diets include more fermentable carbohydrates — which require more buffering, not less. Rations also minimize fiber and rely more on microbial protein and fermentation than in the past. In addition, variation in feed ingredient quality plays a significant role in ration performance.
The key is to feed buffers at recommended levels. "There's been a downward trend in ration buffer inclusion rates, to the detriment of cow performance," Block said. "To increase animal success, include buffers at proper levels."
3. Tap into yeast culture advantages. Be sure that rations include proper levels of yeast culture. Research in California found that feeding yeast culture improved daily milk yield by 2.6 lb. per cow during heat-stressed conditions.
"Don't wait until hot weather hits to evaluate your ration and formulate it for higher levels of these key feed ingredients," Block said.
Manage high-producing and fresh cow diets to include 1.7-2.0% potassium and ensure that rations are formulated to include adequate buffering and recommended levels of yeast cultures to help maximize production and improve cow starts during periods of heat stress this summer.