Heat stress in dairy cattle can result in costly economic losses for producers. Across the beef, dairy, poultry and swine industries, economic losses from reduced production and reproduction performance as well as increased mortality can reach as high as $2.4 billion annually (St-Pierre, Cobanov, and Schnitkey. 2003).
Heat stress can cause a reduction in feed intake and leaky gut — a condition characterized by a weakening of the intestinal lining, allowing bacteria and pathogens to pass through the gut lining. This results in negative effects on many dairy production factors, some apparent immediately and some delayed. Reduced feed intake and leaky gut during a period of heat stress can ultimately lead to lameness in dairy cattle. These lameness events are generally seen in the fall, even after the temperature has gone down.
In addition, during periods of heat stress, dairy cattle spend more time standing in order to dissipate heat beneath them. This increased standing time can result in additional hoof problems, such as sole ulcers.
Many nutritional strategies to alleviate heat stress have been explored. Dairy producers can help mitigate the negative effects of heat stress by feeding a more nutrient-dense diet in the summer to compensate for the reduction in feed intake. For example, producers could consider replacing some of the fiber in the ration with fat to increase the number of calories the animal is consuming.
Feeding higher levels of performance trace minerals during the summer can also play a positive role in mitigating the negative effects from heat stress and any resulting lameness that may occur.
Economic Cost of Lameness
According to the University of Wisconsin-Extension, the cost of simply treating lameness in cows can range from $90 to $300 USD. While treatment of cow hoof problems is a significant cost to the dairy, lameness also leads to reduced milk yield, reduced fertility and increased risk of culling which can result in considerable economic costs. To put this in perspective, according to Willshire et al. (2009), fertility costs account for 39% of the total annual cost of lameness within a dairy herd, while milk yield and culling each account for 24% and treatment accounts for only 10%.
Additionally, misperceptions about the true prevalence of lameness in dairy operations could be responsible for hidden economic losses. In one study (Whay et al., 2002) dairy producers, when asked, stated that they believed the average prevalence of lameness on farm to be around 5.73%. Following farm evaluations, however, an average prevalence of 22.11% was revealed. This could mean that dairy producers are suffering economic losses from problems they are not even aware of.
Dairy Cattle Lameness: Impacts on Milk Production
These cows don’t just become lame and start producing less milk. They likely have had lower milk production for weeks before they’re identified as lame because inflammation is occurring within the cow before you can physically see that she’s lame using dairy cow locomotion scoring. In addition, as milk production decreases, the risk of a higher somatic cell count increases.
Dairy Cattle Lameness: Impact on Reproduction
Lameness can also negatively impact dairy cow reproduction and the calving interval. When a dairy cow is not cycling properly — not becoming pregnant or potentially losing a pregnancy — it results in a significant economic loss to the dairy. Lame cows will not breed back as efficiently and this will result in increased days open, causing higher feed and reproductive cost to the dairy operation. For example, it costs a dairy operation approximately $4 USD per day for every extra day a cow is open. Lameness can extend the time for a cow to become pregnant by two to six weeks, resulting in an economic loss of $56 to $168 USD per cow over a lactation.
Dairy Cattle Lameness: Impacts on Culling Rates
Once a cow becomes lame, her odds of becoming lame again increase exponentially and cows with a locomotion score of 3 were 8.4 times more likely to be culled from the herd. For example, if a cow gets digital dermatitis, that bacteria stays within the skin and waits for an opportunity to flare up again, so the cow never truly recovers once infected.
According to the National Animal Health Monitoring Service (2007), the average dairy reports a 16% cull rate due to lameness and a 26% cull rate due to reproductive failure. However, it is possible that in a large portion of those culled due to reproductive failure, the reproductive failure was due to lameness.
Trace Mineral Nutrition and Heat Stress Management
Research shows that feeding zinc from performance trace minerals plays a role in maintaining intestinal integrity by strengthening tight junctions during challenges and reducing the incidence of leaky gut and related intestinal inflammation.
During times of stress, more chromium is excreted in the urine, which means supplemental chromium during heat stress can help improve chromium status in dairy cattle. Chromium from performance trace minerals can increase thermal tolerance as well, as it helps to reduce the level of cortisol or corticosterone — involved in regulation of energy, immune reactions and stress responses — in animals. Elevated levels of cortisol or corticosterone cause animals to behave in a hectic manner, expend energy and, ultimately, reduce feed intake. Lowering cortisol and corticosterone levels by feeding diets containing chromium from performance trace minerals can help keep animals calm and more willing to eat during heat stress events.
Chromium is also intimately involved in improving insulin signaling and sensitivity. This is especially beneficial during stress events when insulin sensitivity is generally decreased. Additionally, lowering cortisol and corticosterone levels by feeding diets containing chromium from performance trace minerals can help keep animals calm and more willing to eat during heat stress events. This further decreases the likelihood that the animal experiences a period of decreased insulin sensitivity.
Feeding performance trace minerals to mitigate the negative effects of heat stress in the summer can ultimately prevent lameness from occurring in the fall, helping to maintain milk production and reproductive performance on your dairy herd.
Editor’s note: Dr. Geiger earned his doctoral degree in dairy science – lactation physiology from Virginia Polytechnic Institute and State University. He conducts research and provides dairy technical services to customers globally.