Álvaro García
In a previous article (Long-term economic impact of respiratory disease in pre-weaned dairy calves), we examined the long-term consequences of respiratory disease in dairy calves. Pneumonia during the preweaning period is not simply a temporary health problem. Calves that experience respiratory illness early in life often grow more slowly, may reach breeding age later, and frequently produce less milk during their first lactation.
For dairy producers, this means that respiratory disease affects not only treatment costs and mortality, but also the future productivity of replacement animals.
Prevention therefore remains the basis of calf health programs. Adequate ventilation, dry bedding, draft control, vaccination, and systematic health monitoring continue to be the most effective strategies for reducing respiratory disease pressure in calf facilities.
However, growing interest in the calf microbiome has raised an interesting question: can nutrition and microbial interventions help calves better cope with respiratory challenges?
The gut–lung axis
The gastrointestinal tract hosts a vast microbial community that plays a critical role in digestion, immune development, and metabolic regulation. Increasing evidence suggests that this microbial ecosystem also interacts with organs outside the digestive tract.
One of the most interesting examples is the gut–lung axis, a biological connection between the intestinal microbiome and respiratory immune responses.
Microbial fermentation in the intestine produces metabolites such as short-chain fatty acids that can circulate in the bloodstream and influence immune cells in distant tissues, including the lungs. Because of this interaction, nutritional strategies that affect intestinal microbes may also influence respiratory health.
Galacto-oligosaccharides: supporting beneficial microbes
Prebiotics are nondigestible carbohydrates that stimulate the growth of beneficial microorganisms in the intestine. Among these compounds, galacto-oligosaccharides (GOS) have been widely studied. These molecules pass through the digestive tract undigested and are fermented by beneficial bacteria in the lower intestine. As a result, they can:
- stimulate microbial growth
- increase short-chain fatty acid production
- improve intestinal barrier function
- potentially limit pathogen attachment in the gut
Some researchers have suggested that these effects may influence respiratory health indirectly through immune modulation. Another strategy that has attracted attention is microbiota transfer, where microbial communities from healthy animals are introduced into young calves. This approach can include fecal microbiota transfer or rumen microbial inoculation, with the goal of accelerating the establishment of a stable and beneficial microbiome early in life. Studies in several species have shown that transferring microbiota from healthy donors can influence immune responses, reduce the incidence of certain diseases, and in some cases improve growth performance. However, the potential effects of microbiota transfer on respiratory disease in calves have remained unexplored.
A study under high infection pressure
To investigate these strategies, researchers conducted a controlled experiment with 180 Holstein calves raised under conditions typical of veal production systems. In these systems calves are transported from multiple farms and mixed at an early age, creating substantial exposure to respiratory pathogens.
Calves were assigned to four treatment groups:
- control diet
- milk replacer supplemented with galacto-oligosaccharides
- microbiota transfer
- combination of both strategies
The microbiota transfer consisted of rumen fluid and fecal microbial material obtained from healthy donor animals and administered early in the calves’ stay at the facility. Researchers monitored calf growth, clinical health, and several indicators of inflammation in blood and lung fluid throughout the study. Calves receiving galacto-oligosaccharides grew slightly faster than control calves; the improvement in average daily gain was modest but consistent. Interestingly, this advantage persisted even after supplementation ended, suggesting that early dietary interventions affecting the microbiome may have longer-lasting effects on calf metabolism. The improved growth was not clearly linked to improved respiratory health in this study and may instead reflect positive effects on gut function and nutrient absorption.
Respiratory health and immune responses
Despite the improvement in growth performance, supplementation with galacto-oligosaccharides (GOS) did not consistently reduce markers of lung inflammation in this experiment. Clinical respiratory scores increased during the first weeks after arrival, reflecting the high infection pressure typical of systems where calves from multiple farms are transported and mixed at an immature age. These results highlight a critical point: nutritional interventions may improve calf performance even when their effects on specific diseases vary between studies.
Microbiota transfer, on the other hand, influenced several immune indicators. Calves receiving microbial inoculation showed lower circulating white blood cell concentrations and changes in immune cell populations that suggested reduced systemic inflammation. Some indicators of lung inflammation also decreased at certain time points. However, these physiological responses did not translate into measurable improvements in growth performance or clear reductions in clinical respiratory disease.
Researchers also evaluated whether combining both strategies would produce stronger benefits. In theory, providing fermentable substrates such as GOS could support the growth and activity of beneficial microbes introduced through microbiota transfer. In practice, however, the study found little evidence of synergy between the two approaches. The combined treatment did not improve respiratory health or performance beyond the effects observed with each strategy individually.
The practical takeaway
These results highlight both the potential and the limitations of microbiome-based strategies in calf health management. Supplementation with galacto-oligosaccharides improved calf growth performance, suggesting that nutritional support of the gut microbiome may benefit productivity. Microbiota transfer, in contrast, influenced several immune parameters but did not consistently improve calf health or growth under the conditions of this study. Most importantly, these approaches should be viewed as complements to—not replacements for sound calf management practices.
Respiratory disease remains a multifactorial challenge influenced by ventilation, hygiene, nutrition, pathogen exposure, and stress. Supporting the microbiome may eventually become another useful tool, but the fundamentals of calf management remain essential.
The full list of references used in this article is available upon request.
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