At weaning, calves experience a tremendous amount of stress and for a prolonged period of time. Proper nutrition can help alleviate some of the negative issues related to stress. Therefore, it is important to understand how stress impacts the animal and how nutrition can help.

Animals subjected to stress have increased blood concentrations of the hormone cortisol, and cortisol can compromise the immune system. Specifically, cortisol will decrease T-lymphocyte cells, which are involved in cell-mediated immunity.

Cell-mediated immunity is the portion of the immune system responsible for non-specific destruction of pathogens. Therefore, prolonged stress can reduce the animal’s ability to fight infection.

Managing stress with minerals

In order to mount an immune response, energy, protein and certain trace minerals are required, which increases nutrient requirements of the animal. Unfortunately, when calves are under stress, dietary intake is reduced. It has been shown that fasting or feed deprivation can increase cortisol release.

Therefore, the animal now has two issues: Stress has compromised the immune system, and calves are not eating enough to meet the increased nutrient demands of an immune response.

The reduction in dietary intake has been well documented in newly received feedlot calves. Upon arrival to the feedlot, dietary intake can be as low as 62 percent of the intake observed a week later. The National Research Council publication, “Nutrient Requirements for Beef Cattle,” suggests mineral concentrations in stressed calves be increased.

Although research has not definitively confirmed that requirements for essential trace minerals increase during stress, rather this increase in dietary mineral concentration is needed to offset the reduction in intake observed during stressful periods.

Essential trace minerals hold an integral role in the immune system, with copper, zinc and selenium being of particular importance. Chromium is not essential, but it does have some desirable attributes that warrant mention.

Copper

Copper is involved in the production of antioxidants and serves a role in neutrophil function (involved in killing of pathogens). Although reports on the benefit of additional copper for improving immune function vary, the simple fact that it is important for proper function of the immune system warrants consideration when developing mineral programs.

There are research reports indicating that when dietary copper supply and bodily reserves are low, there is a reduction in the ability of the immune system to kill pathogens.

The “Nutrient Requirements of Beef Cattle” publication states a non-stressed calf requires a diet that contains 10 parts per million (ppm) copper. In a stressed calf, copper requirements increase up to 15 ppm.

Copper can be a challenging trace mineral to balance in a diet because of its relationship with iron, molybdenum or sulfur. If these minerals are too high, they can interact with copper and reduce its availability to the animal. For example, when total dietary sulfur intake increases above 0.2 percent, the amount of copper available for the animal decreases by approximately 25 percent.

In some parts of the U.S., water sulfur concentration alone can be high enough to cause this reduction. Therefore, producers in these areas should consult their feed representatives for information regarding the appropriate levels of copper to supplement.

Zinc

Zinc is involved in signals that initiate activity of certain cells in the immune system. Zinc requirements for non-stressed calves is 30 ppm and for stressed calves is up to 100 milligrams per kilogram. Literature focused on zinc’s role in calf health is mixed.

Some reports demonstrate a benefit from supplemental zinc, and some do not. In most cases, animals suffering from zinc deficiency exhibit positive responses to supplemental zinc. Therefore, calves not consuming adequate amounts of zinc are at a greater risk of becoming sick during periods of stress.

Selenium

Selenium plays a role in immune function as it contributes to the production of antioxidants in the body and reduces oxidative tissue damage. Dietary selenium inclusion in diets of non-stressed calves is 0.1 ppm and up to 0.2 ppm for stressed calves.

There are reports that demonstrate additional benefit of supplemental selenium even above 0.2 ppm but, according to the Code of Federal Regulations (21 CFR § 573.920 [2015]), selenium content of a complete feed cannot exceed 0.3 ppm or 3 milligrams per head per day.

In animals fed diets deficient in selenium, improvements in the immune system’s ability to combat pathogens was improved. However, there are data in the literature that would indicate additional dietary selenium does not improve an animal’s ability to ward off infection when the basal diet is sufficient in selenium.

Chromium

Chromium is a trace mineral in which no requirement has been established to date and is typically not included in most commercial mineral supplements. Nevertheless, research has demonstrated that in some cases supplemental chromium can improve animal health and improve glucose utilization.

Supplementing 0.5 milligrams of chromium per kilogram of dry matter increased responsiveness to vaccines in newly received feedlot calves. With that being said, there are numerous reports showing supplemental chromium did not have an impact on animal growth or health.

The differences in response to chromium supplementation between various research reports is likely due to level of stress, basal diet chromium concentration or source.

Impacting profitability

Mineral supplementation programs on the ranch generally focus on the cow, and a good mineral program can positively impact calf performance. In fact, calves generally consume mineral at the same time as the cow. However, their supplemental mineral consumption, as a percent of bodyweight, is approximately 50 percent of that of the cow.

Consequently, mineral status of calves as they go into the weaning season could be marginal. Therefore, whether calves stay on the ranch after weaning for a preconditioning period or go directly to the feedlot, the associated stress will lower intake, which may exacerbate any mineral deficiencies and increase the risk of illness.

If one is concerned about the mineral status of a calf, it is possible to check body mineral reserves with the help of your veterinarian through blood sampling or liver biopsy. (The liver is considered the most accurate site to measure copper, selenium and zinc.) However, one must be cognizant of the condition of the animal in order to properly interpret these values.

Work conducted at New Mexico State University has demonstrated that newly received feedlot calves consuming a diet deficient in essential trace minerals and undergoing weight loss over a 60-day period may have inaccurate liver trace mineral concentrations due to a reduction in liver size.

This change in liver size caused mineral concentration values to actually increase for a period of time – in spite of the fact they were fed a deficient diet (whereas, blood trace mineral concentrations did reflect dietary deficiencies).

In this study, trace mineral concentrations were replenished after 45 days of consuming a high-quality diet with adequate mineral concentrations.

Although we cannot guarantee our calves will not get sick during stressful times, providing cattle with a high-quality mineral prior to and during times of stress will ensure calves have the best chance possible to cope with stress and mount a proper immune response.  

ILLUSTRATION: Illustration by Corey Lewis.