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Essential microbial support: A key component of your calf-rearing program

Kimberley Morrill, David Ledgerwood and Keith A. Bryan for Progressive Dairy Published on 06 November 2019

We often think the weaning period is the only traumatic transition period for calves; however, the entire pre-weaning period consists of many difficult and stressful periods of transition.

Following birth, there are dramatic physiological changes in the gastrointestinal (GI) tract as it develops and matures. The neonate must transition dependency from maternal sources of nutrients to using its own GI tract to break down and absorb nutrients from consumed feed.



Changes within the GI tract begin at birth and continue throughout weaning. Colostrum consumed within the first hours of life stimulates the GI tract, initiating cell proliferation and turnover within the small intestine as well as cessation of macromolecule transport, often referred to as “gut closure.” For the next six to eight weeks, the calf’s GI tract (small intestine and stomach compartments) continue to develop, and the calf begins the process of transitioning to a functioning ruminant. During this time, the proportion of nutrients provided by liquid versus solid feed is constantly fluctuating, and the physical, fermentative and absorptive capacity of the digestive system increases in response to changes in overall digestibility of feedstuffs.

In addition to changes that occur in the GI tract during the first weeks of life, the calf is born with a naïve immune system. When these two factors are combined and stressful events occur, it becomes easy to understand why one of the major causes of calf death is intestinal infection. Understanding the benefits of establishing essential microbial support during the wet, pre-weaning and weaning periods can help us improve GI health, which helps minimize the negative effects of stress, leading to an improvement in overall calf health and performance.

Microbial colonization of the GI tract during early life plays a significant role in immune and metabolic development of calves. Thus, calf production could benefit from modifying the GI microbiota through supplementation of live, microbial-based products throughout the calf rearing process. Numerous studies have demonstrated that probiotic products can positively impact microbial diversity, improve GI tract integrity, and aid natural defenses that modulate the pro- and anti-inflammatory response locally in the GI tract. An increasing number of studies continue to explore the microbial composition of the GI tract, the mucosal immune system and early dietary interventions to improve the health of dairy calves, revealing possibilities for effectively reducing the susceptibility of calves to intestinal infections while promoting growth.

Studies investigating the microbiota of the calf GI tract have reported less diverse bacterial communities at birth that increase in complexity and diversity with age, as a result of GI tract maturation and dietary changes. Furthermore, the use of antibiotics to treat calf diarrhea and respiratory diseases, as well as feeding milk containing residual antimicrobials, negatively impact the intestinal microbiota, thereby resulting in an opportunity for a disproportionate abundance of potentially detrimental microorganisms, i.e. dysbiosis.

Additionally, these studies reported an increase in the prevalence of antimicrobial-resistance genes in the GI tract microbiota of pre-weaned calves. This means we could see decreases in the effectiveness of antimicrobials used to treat pre-weaned calves with infectious diseases because of increases in the abundance of antimicrobial-resistance genes in the early GI tract microbiome.


Small intestine changes in the first 6-8 weeks of life.

Click here or on the image above to view it at full size in a new window.

Besides preserving a healthy microbiota in the GI tract, maintaining effective immune responses that can detect, prevent and eliminate invading pathogens is a key aspect of calf health. The mucosal immune system comprises physical barriers, chemical barriers and pattern-recognition receptors. Physical barriers play a crucial role by preventing the attachment of pathogens present in the intestinal lumen.

The mucosal layer, the first physical barrier, contains mucins that trap a variety of substances and microorganisms. Secretory compounds limit the growth of certain organisms on the mucosal layer. Beneath the mucosal layer, a single layer of epithelial cells, connected by an intracellular junctional complex known as tight junctions, inhibits the movement of macromolecules between the cells.

Similar to lactating cows, if these junctions break down we observe “leaky gut” in calves, where food particles and pathogens can leave the intestinal lumen and enter the circulatory and lymphatic systems. This leaves the calf’s naïve immune system to deal with these insults. Recent studies focused on GI tract development have observed that the first week of life is crucial for the development of the intestinal epithelium and expression of tight junction protein coding genes.

The expression of tight junction protein coding genes can be negatively affected by dietary changes, indicating increased GI permeability (i.e., “leaky gut”). In vitro work using the Transepithelial Electrical Resistance (TEER) assay has demonstrated that the addition of Lactobacillus animalis (LA-51) increased the electrical resistance of “small-intestine”-like Caco-2 cells. When these cells were exposed to Salmonella enterica Typhimurium, the relative TEER decreased (inducing “leaky gut”). Conversely, if LA-51 was also present, the TEER increased and fewer particles were able to translocate across the cells, indicating that LA-51 improved barrier function.


In addition to improvements in barrier function, some probiotics have been shown to be effective inhibiting pathogenic bacteria and fungi in vitro and pathogenic bacteria in vivo. In a Clostridium perfringens type A challenge, calves (10 per group) received one of three treatments: 1. LA-51 and Propionibacterium freudenreichii (PF-24); 2. LA-51, PF-24, Bacillus subtilis and Bacillus licheniformis; 3. Control, no probiotics. All animals were fed their respective treatments for 28 days and were orally challenged with Clostridium perfringens type A on day seven.

Calves receiving probiotic treatments had more normal appearance scores and fecal consistency compared to control calves. Also, the use of probiotics at least doubled the survival rate of challenged calves. In addition to Clostridium perfringens, the combination of LA-51 and PF-24 reduces the prevalence and concentration of E. coli and Salmonella, two pathogens that negatively impact calf health.

The best start for a newborn calf is high-quality, clean colostrum. Feeding colostrum within 4-6 hours after birth provides many benefits to the calf; one that we don’t talk about often is that it facilitates bacterial colonization of the GI tract, promotes colonization of Bifidobacterium and reduces colonization of E. coli. Feeding colostrum also helps stimulate intestinal cell proliferation and turnover.

Throughout pre-weaning and at weaning, daily feeding of a science-based, research-proven probiotic enhances intestinal health by establishing supportive microbiota in the GI tract and aiding in the development of the rumen. It is well established that feeding lactic acid bacteria (LAB) during the pre-weaning phase is associated with improved weight gain after weaning due to a more efficient functioning rumen. In addition to feeding LAB, feeding Bacillus subtilis and Bacillus licheniformis in milk replacer and starter rations led to increased starter intake and average daily gain as compared to calves that did not receive a probiotic.

High calf mortality caused by intestinal infections, as well as increasing pressure to decrease the use of prophylactic antimicrobials, encourage multidisciplinary approaches to improve GI health in wet, pre-weaned and weaned calves. Science-based, research-proven, essential microbial support provides an opportunity to complement current management practices by supporting a healthy lower GI tract, a healthy calf and allowing you to achieve your calf-rearing goals. end mark

David Ledgerwood, M.S., PAS, is a technical service manager for Chr. Hansen.

Dr. Keith A. Bryan is a technical service specialist for silage inoculants and cattle probiotics at Chr. Hansen.

Kimberley Morrill is a Technical Service Manager with Chr. Hansen. Email Kimberley Morrill.