Estimates of losses to owners of livestock from heat range up to $1.5 billion per year with dairy cattle, $1 billion for the pork sector, and $350 million with beef cattle, according to Iowa State University animal scientist Lance Baumgard, who was one of the presenters on a recent webinar titled "Beyond Heat Stress," which was sponsored by Dairy Herd Management magazine.
Although the weather conditions leading to heat stress had not yet established themselves in the Upper Midwest by the early days of June, Baumgard reviewed the tell-tale signs of such stress and described the resulting biological effects that affect dairy cow production and health.
One scientific indication of heat stress is the temperature humidity index (THI), which combines the temperature and humidity at any given time, Baumgard noted. It is not an addition of two numbers but rather the result of a formula, he pointed out.
When the THI reaches the mid to high 60s, it begins to affect dairy cattle, Baumgard stated. He observed that periodic rather than consistent periods of a high THI are likely to have a greater adverse effect on dairy cows. Even parts of Canada can have 40 percent of a year's days with a THI of at least 72, he reported.
The very evident signs of this stress on dairy cows start with more than normal time of standing, followed by having the tongue out, panting, higher respiration rates, dropping of saliva, and drooling, easily leading to the development of acidosis, Baumgard explained. Saliva contains the bicarbonate buffer which helps to control rumen acidosis, he indicated.
Other common reactions to heat stress are changes in eating habits -- slug feeding, sorting, reduced overall intake, and a preference for concentrates over forages, Baumgard observed. He urged caution on the idea of feeding more concentrates as a way to provide more energy in the feed intake.
In addition to those reactions, Baumgard mentioned reduced pregnancy rates, more early term abortions, imbalances with carbon dioxide that affect the blood, and damage to intestinal morphology that result in a loss of the availability of the glucose that is crucial to milk production. Incidents of sore feet and outbreaks of laminitis are also associated with heat stress, he added.
Studies have shown that reduced feed intake accounts for about 50 percent of the loss in milk production during periods of heat stress, Baumgard noted. He said it is also not unusual for dairy cows to lose up to 90 pounds of body weight during such episodes.
To prepare for periods of heat stress, be sure to provide dairy cows with plenty of clean water, Baumgard said. Discuss how to cope with episodes of heat stress with the dairy herd nutritionist before those times arrive, he advised.
Webinar presenter Keith Bryan, a technical support manager for Chr. Hansen, a company that specializes in feed preservatives and additives, stated that dairy cows are subject to a multiplicity of stresses that include the weather, the environment in which they are housed, the pH level of their feeds, and their vulnerability to numerous pathogens and infectious diseases such as dysentery, clostridium, E. coli, salmonella, and cryptosporidium.
Bryan, who had a previous affiliation with Penn State University as a dairy scientist, cited various Chr. Hansen products such as inoculants, probiotics, and yeasts that are designed to improve the acidity traits of stored feeds and rumen fermentation and to provide defenses against some of the stresses that dairy cows face. He said the benefits from the use of one or more of those products are better feed efficiency and digestion of starches along with higher milk production and net income thanks to demonstrated returns of up to four-fold on the cost of the additive ingredients.
In any analysis of animal performance and health, Bryan emphasized that it is crucial to consider profitability in addition to animal welfare, environmental impacts, and food safety. He called for attention to the full cycle of dairy production which involves the production of forages and grains, the chemical and physical traits of the feeds, nutritional value, the environment, and the use of urine and manure as a crop nutrient.