Summer heat stress in cows is known to reduce milk yields and milk quality, reducing the profitability of dairy farms, which is why it is important to find ways to effectively manage it on farms.
Higher producing cows are more sensitive to heat stress
Lactating dairy cows prefer ambient temperatures of between 5 and 25 °C, the “thermoneutral” zone. At ambient temperatures above 26°C, the cow reaches a point where she can no longer cool herself adequately and enters heat stress. Whereas the upper critical limit of the thermoneutral zone for dairy cattle is between 25 °C and 26 °C, the, the temperature-humidity index (THI) is below 72.
Higher producing cows, and thus multiparous cows, are more sensitive to the effects of heat stress compared to lower producing or primiparous cows. As milk yield increases from 35 to 45 kg/d, the heat stress threshold is decreased by 5°C. Recent studies show that modern cows become heat-stressed starting at an average THI of 68 with the levels of stress increasing with increasing THI values.
Higher-producing cows exhibit more signs of heat stress than lower-producing cows because higher-producing cows generate more heat as they eat more feed for higher production. They must get rid of the extra heat generated due to metabolizing more nutrients in the feed. As a result, much of the reduction seen in milk production is due to lower feed intake by the cow. Feed intake in lactating dairy cows starts to decline at around 25°C and drops more rapidly above 30°C. High producing dairy cows also have a higher metabolic heat load produced through processes such as lactogenesis and milk secretion. Consequently, as milk production and metabolic heat production rise genetically, heat stress will increasingly limit the expression of genetic potential in the future.
The stage in the lactation curve at which the cow experiences heat stress is another important factor for the total lactation yield. Cows are less able to cope with heat stress during early lactation and heat stress has the biggest impact during the first 60 days of lactation. This is because cows are in negative energy balance and make up for the deficit by mobilizing body reserves in this early part of lactation. Catabolic processes are associated with heat production.
Summer heat stress in cows affects milk quality
Milk quality is important for producers to earn monetary bonuses through lower somatic cell counts and increased butterfat/protein, increasing farm profitability.
Controlling somatic cell count (SCC) is a year-round challenge for most dairy producers, and hot humid weather intensifies this challenge. Heat stress generally increases the production of free radicals or reactive oxygen species (ROS). This can lead to oxidative stress, which again has been associated with increased SCC in milk.
Results from studies on the impact of heat stress on milk components are inconsistent, however several studies have reported reduced milk fat and protein levels in response to heat stress. Some researches argue that fat yield decreases could be explained by a decrease in forage intake with low fiber levels, and protein decreases could be attributed to reduced DMI and energy intake when the animal is under heat stress. Other research has shown that milk fat depression during heat stress can be linked to depressed rumen health. Therefore, supporting optimal rumen function by nutritional means may help to reduce the negative impact of heat stress on milk fat.
Strategies to mitigate the negative effects of summer heat stress in cows
It is highly important that cows are provided cool water during periods of high temperature. Water is the primary nutrient needed to make milk and cows drink up to 50 percent more water when the temperature-humidity index is above 80. Water should be easily accessible to cows and located in a position such that cows do not have to cross areas of hot sun.
Commercial trial with Anco FIT in cows during summer heat
Gut agility activators, such as Anco FIT and Anco FIT Farm are designed to support the cow to adapt to challenges including heat stress more efficiently by minimising stress reactions including oxidative stress at the cellular level, shifts in the rumen balance and reduced feed intake.
Feedback from a commercial dairy farm with 750 cows in Germany during months where temperatures were recorded above 26°C included that SCC over a period of 3 months were reduced by 13% and milk fat and protein levels increased by 3%. Furthermore, treatments for high SCC were reduced from 5 treatments/week to 1-2 treatments per week. Cows were fed a ration based on corn silage, grass silage, soya and grains, where Anco FIT was added at 30g/cow/day and received a milking concentrate in the milking robot.
It was concluded that feeding Anco FIT to dairy cows during hotter months helped the cows to cope with the heat better and reduce some of the stress reactions that would otherwise impact milk quality and cow wellbeing.