Milk Replacer

Heat Stress: Seasonal Feeding When Temperatures Climb

Animal : Calf

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Purina Animal Nutrition

While you are enjoying a pleasant spring or summer day, your calf may be experiencing heat stress. When the air temperature reaches 75°F, calves may begin to experience physiological signs of heat stress. Prolonged heat stress in calves can reduce feed intake and average daily gain (ADG) and may even compromise the immune system.1
It’s important to adjust both nutrition and management practices to help minimize the impact of heat stress on your calves.

Consider a seasonal milk replacer

Calves require the same nutrients in moderate weather and hot weather, yet calves undergoing heat stress often have reduced appetites and consume less milk replacer and starter. With this in mind, it’s important to feed a milk replacer that will encourage intake.
The balance between fat and protein levels in the milk replacer plays a key role in encouraging intake. Excessively high fat levels (above 20%) can suppress starter intake and result in calves with poorer feed efficiency that may not meet growth and breeding benchmarks in an economical timeframe.2
Milk replacer with a lower fat percentage does not necessarily mean it’s a low-energy product. For example. LAND O LAKES® Cow’s Match® WarmFront® calf milk replacer contains just 10% fat, yet it provides similar energy per pound to a milk replacer that contains 20% fat.  

Table 1 illustrates the minor differences in energy content of milk replacers at different fat levels according to the NRC, compared to the energy level equivalent in Land O’Lakes Animal Milk Solutions’ formulations.
The amount fed also plays a big role in providing the necessary energy to heat-stressed calves. Feeding a full potential diet (minimum 2.5 pounds of milk solids in 8-12 quarts of milk or milk replacer daily) means calves still get the required amount of energy, even if the fat level in the milk replacer is low. It’s important to focus on feeding more total calories to the calf rather than on feeding a high-fat diet.
LAND O LAKES® Cow’s Match® WarmFront® calf milk replacer helps support calves during heat stress via a unique combination of carbohydrates that provide ready energy needed for growth, immune system support, and increased respiration for cooling in warm weather.
LAND O LAKES® Cow’s Match® WarmFront® calf milk replacer contains:
  • An enhanced fatty acid formula made up of medium chain triglycerides and omega-3 fatty acids, which makes the fat in milk replacer more like milk fat.
  • L-carnitine which helps utilize fat more efficiently by the calf compared to traditional fat sources.
  • Balanced amino acids to support optimal calf growth.
  • Essential oils to optimize digestibility and nutrient absorption, enhance palatability, and assist with milk replacer and starter intake.
  • Organic trace minerals, a more bioavailable form of trace minerals, to support immune function.
  • Probiotics to support an optimal gut microbiome by breaking down nutrients and addressing health challenges.
  • Prebiotics to support immune health by feeding the good microorganisms.

LAND O LAKES® Cow’s Match® WarmFront® calf milk replacer is also available with a coccidiostat to help control coccidiosis and ClariFly® to assist with fly control management.

  • ​Switch to LAND O LAKES® Cow’s Match® WarmFront® calf milk replacer with ClariFly® 30 days prior to flies appearing.
  • Switch to LAND O LAKES® Cow’s Match® ColdFront® calf milk replacer without ClariFly® when cold weather restricts fly activity.
  • Always offer calves free-choice water during warm weather.

Hydrate with electrolytes

Sweating and panting during heat stress results in loss of water and electrolytes, particularly potassium. If untreated, dehydration in calves can lead to anorexia, weaken the immune system, and even lead to death if conditions become extreme. Electrolytes can be an excellent source of hydration as well as extra calories. Always feed electrolytes in addition to free-choice, low sodium (< 50 ppm) water.
A more dilute solution is needed when using electrolytes to rehydrate heat-stressed calves, compared to scouring calves. Since the purpose of the solution is to replace lost water, it is important to use either an iso- or hypotonic solution (<300 mOsm/L). A hypotonic solution is different from a hypertonic solution which is used to address electrolyte loss due to scours.

Feed LAND O LAKES® Electrolyte Base at a diluted dose for calves experiencing heat stress. The highly palatable formula will encourage water consumption.

If calves are still eating their full milk ration, and they are provided with free-choice low sodium (< 50 ppm) water, there is no concern about overfeeding diluted electrolytes (< 300 mOsm/L). In addition to supporting calves already undergoing heat stress, feed electrolytes prophylactically when temperatures are predicted to rise.

Heat stress and colostrum

Stress events, including heat stress, cause cortisol levels in animals to rise. Research has shown that when calves have elevated cortisol levels, they absorb colostral IgG less efficiently and are at greater risk of failure of passive transfer of immunity.3 Calves born to heat-stressed dams have also been shown to have reduced efficiency of IgG absorption.4
When heat stress occurs, the role of maternal colostrum or colostrum replacer becomes more important. In addition to providing essential antibodies, including IgG, maternal colostrum, or colostrum replacer can also help hydrate a heat-stressed calf. Feeding newborn calves 4 quarts of high-quality, warm maternal colostrum or colostrum replacer within 1 hour of birth and repeating 12 hours later (ad libitum) will help with hydration.
When high-quality maternal colostrum is not available, feeding LAND O LAKES® Bovine IgG Colostrum Replacer is the best alternative to ensure the calf consumes ample nutrition and antibodies, including IgG, to help support her naïve immune system.

Support the gut microbiome during heat stress

 A healthy gut microbiome is important to support a calf’s immune function and to help her fight pathogens. As calves try to dissipate heat, blood flow shifts away from the gut towards the skin. If the attempt to dissipate heat is prolonged, it may result in hypoxia of the gut tissue, which can lead to “leaky gut” or increased permeability of the gut wall. Leaky gut can contribute to poor nutrient absorption as well as increase the risk of infection by pathogens and subsequent bacterial infection.

Support the gut microbiome with:

 Adjust calf management protocols

Calf management also plays a critical role in reducing heat stress. Always provide fresh, clean, free-choice water and keep buckets in a shaded location within the hutch or pen. Clean and sanitize water and milk pails frequently to help prevent algae, mold, and bacteria growth. Replace calf starter daily as feed can spoil in high heat.
Adjust feeding times to avoid the hottest times of the day when calves are less likely to eat. Consider three times a day feeding to provide more nutrition throughout the day. If feeding twice a day, feed at night and early morning or as close to 12-hour intervals between feedings as possible.
Also, consider adjustments to hutch location and management to maximize calf comfort and reduce heat stress. Open all hutch vents and doors and raise the back of the hutch to increase airflow. Reposition hutches to take advantage of air movement and provide shade. For indoor housed calves, fans are a great option to increase airflow and dissipate heat. Research has shown that running fans from 8 a.m. to 5 p.m. can improve average daily gain by 23% and increase feed efficiency by 20%.5

Contact your local calf specialist or visit to learn more.

1 O’Brien MD, Rhoads RP, Sanders SR, Duff GC, Baumgard LH. Metabolic adaptations to heat stress in growing cattle. Domestic Animal Endocrinology. 2010;3886-94. 
2 LOL CT-01-07
3 Stott GH, Wiersma F, Menefee BE, Radwanski FR. Influence of environment on passive immunity in calves. Journal of dairy Science. 1976 Jul 1;59(7):1306-11.
4 Laporta J, Fabris TF, Skibiel AL, Powell JL, Hayen MJ, Horvath K, Miller-Cushon EK, Dahl GE. In utero exposure to heat stress during late gestation has prolonged effects on the activity patterns and growth of dairy calves. Journal of Dairy Science. 2017 Apr 1;100(4):2976-84.
5 Hill TM, Bateman HG 2nd, Aldrich JM, Schlotterbeck RL. Comparisons of housing, bedding, and cooling options for dairy calves. J Dairy Sci. 2011;94(4):2138-2146.