Can Probiotic Supplements Reduce Beef Calf Stress?

Background

Beef cattle are exposed to different stresses that can compromise their health and productivity. Traditionally, antibiotics have been used to treat disease and as preventative agents, especially during times of high stress, such as weaning. With the rise in antimicrobial resistance, other strategies are being explored to improve the health of calves by reducing stress and ultimately reducing the reliance on antibiotics.

One emerging area of interest is the use of beneficial bacteria, known as probiotics or “psychobiotics,” to influence both gut health and stress-related physiology. While most probiotic research in younger animals has focused on dairy calves and requires daily feeding, beef operations need low-labour, economical approaches. Early-life administration of a bovine-derived lactic acid bacteria probiotic offers a potentially practical tool, but its effects on stress resilience and overall calf development remain unclear. Understanding whether early microbial interventions can support calf health is important for improving well-being and supporting productivity in beef herds.

Objectives

• Evaluate the effects of a probiotic cocktail of lactic acid bacteria supplemented early in life to beef calves and analyze the potential alleviation of stress during the stressful weaning process.
• Estimate the densities and proportions of beneficial bacteria.
• Evaluate changes in immune function, health status and growth.
• Measure metabolic markers related to stress.
• Explore behavioural changes, including activity levels and temperament.

What they did

Researchers randomly divided 32 crossbred beef calves into two groups at spring processing (2 months of age). One group was supplemented with two doses of the probiotic cocktail at spring processing. The other group received a saline solution as a control. Body weight and numerous samples were collected from the day of the first inoculation to 14 days after they were abruptly weaned. Data included:

• Blood samples to assess immune function and stress-related markers like cortisol, serotonin and haptoglobin
• Fecal samples to determine whether the probiotic successfully established long-term
• Behavioral responses of calves to stressors such as handling
• Pedometers were used to monitor calf activity (i.e., steps taken, lying and standing durations) in response to abrupt weaning

What they learned

Immune and stress responses: As expected, abrupt weaning significantly increased numbers of monocytes (an immune cell). The probiotic group showed no significant differences in their immune cell counts compared to the control group, suggesting no significant effect on immune function.

Plasma cortisol (a stress hormone) was lower, and serotonin (a mood-boosting hormone) was higher in the probiotic group than the control group, suggesting the probiotic may have helped mitigate stress responses. Control calves showed lower concentrations of amino acids required in stress signaling and responses, suggesting that control calves may have experienced more stress and needed to use more of these amino acids to mitigate its effects.

Behavior and reactivity: The probiotic treatment did not affect the temperament of calves in the chute or the speed at which they exited the chute. Post-weaning activity levels such walking, lying and standing time did not show major differences between the groups.

Calf growth: Average daily gain and body weight was unaffected by the probiotic treatment.

Fecal bacterial densities: The probiotic treated calves did not have greater numbers of lactic acid bacteria in their feces compared to the control calves, but it may have existed in other regions of the gut.

what it means

Use of a lactic acid bacteria probiotic cocktail helped alleviate some physiological stress biomarkers in beef calves, although there were no observed effects on immune function, behaviour or growth. The gut microbiome is complex and competitive. This makes it difficult for a single dose of probiotics to establish a significant population. Giving the probiotic at birth, before the gut microbiome has fully established, may have had a greater benefit on stress, immunity and growth.