Maintaining healthy hogs and increasing production is important to the pork industry, consumers, and the economy. Many strategies are employed by the pork industry to increase production. One common strategy involves weaning piglets at approximately 21 days of age in order to allow for more piglet litters per sow each year [1
]. While weaning piglets at early ages shortens the time-period when the sows are out of production, performance of the piglets can be negatively affected. Weaning piglets early is challenging because their digestive and immune systems are not yet fully mature [2
]. Consequently, piglets are more susceptible to infections and gastrointestinal (GI) issues. One GI disease that piglets are prone to develop, particularly when they are weaned before four weeks of age, is post weaning diarrhea (PWD). PWD leads to anorexia, growth inhibition, and death of piglets and therefore is an important issue with economic consequences to the swine industry. To avoid post-weaning diarrhea, antibiotic growth promoters have been included in piglet diets; however, antibiotic growth promoters are potentially linked to the emergence of antibiotic resistant bacteria [3
]. Therefore, alternatives to antibiotic growth promoters that maintain piglet health and boost immunity are being sought [4
In swine, nutrients consumed during gestation and lactation has been shown to be key to the viability and health of offspring. Alexopoulos et al.
] reported that supplementation of sow diets with probiotics during gestation and lactation has been shown to lead to increased body weights and reduced incidences of diarrhea in their offspring. To promote the health of weaned pigs and protect against PWD, it is important that the gut be colonized by beneficial bacteria and that strong intestinal/mucosal immunity develops. Beneficial bacteria, like bifidobacteria and lactobacilli can stimulate the immune system, inhibit the growth of pathogens, and reduce the incidence of diarrhea and constipation in pigs [6
]. Research has shown that a mother’s diet has the potential to positively affect the overall health of her offspring and contribute to development of their offspring’s immune systems. For example, breastfed infants of mothers who consumed probiotics had fewer gastrointestinal issues such as diarrhea [8
]. In this study, we sought to evaluate whether supplementation of feeding system with oat would lead to changes in the levels of probiotics in milk. The objectives of this study were to investigate the impact of feeding oat on the population of bifidobacteria and to evaluate their probiotic potential.
Hog production is an important industry to the US and worldwide market. Post weaning diarrhea is responsible for major economic losses due to mortality, morbidity, decreased growth rate, and cost of medication [13
]. PWD is a multifactorial disease that can be caused by many different agents. Several pathogens that cause diarrhea include Lawsonia
ssp., coronaviruses, and transmissive gastroenteritis viruses [4
]; however, in the swine industry, the most common cause of post-weaning diarrhea is enterotoxigenic Escherichia coli
To avoid post-weaning diarrhea, antibiotic growth promoters have been included in piglet diets. However, antibiotic growth promoters are known to suppress beneficial organisms in the gut and, because of a possible link to the emergence of antibiotic resistant bacteria, there is a push to phase out or eliminate their use in swine production [16
]. Intestinal microflora is a key contributor to intestinal health. Among probiotic genera, bifidobacteria are one of the predominant bacterial groups existing in the animal and human intestine [17
] and are believed to play a beneficial role in maintaining the health of the host.
Our study showed that the inclusion of oat diet increased the bifidobacterial population more than lactobacilli. The possible explanation for this could be that oat contains oligosaccharides that function as prebiotic for the bacterial growth including bifidobacteria [18
]. Tuohy et al.
] reported that bifidobacteria as specialized oligosaccharides-degrading bacteria. These bacteria have a broad range of glycolytic enzymes and carbohydrate uptake channels with high affinity for prebiotic oligosaccharides and their composite sugars. These prebiotics could have served as a growth-promoting factor for bifidobacteria [19
]. This is further confirmed by Hinz et al.
], who also reported that bifidobacteria play an important role in degradation of oligosaccharides. Consistent with our findings, a study conducted by Connolly et al.
] showed that oat flakes increase bifidobacteria populations in vitro
, which also suggest that oats have prebiotic properties. Additionally, using culture, isolation, sequencing, and fingerprinting methods, Jost et al.
] demonstrated that the same probiotic bacteria are found in the feces of mothers and offspring as well as in mother’s milk, suggesting that the probiotic bacteria travel from mother’s gut into milk. Therefore, in our study, one can speculate that the diet containing oat led to increased bifidobacteria in the intestine of the sows and that these bacteria travelled to the milk.
The principle criterion for selection of a good probiotic is to overcome physiological barriers through the stomach (acid pH) and small intestine (bile salt) in order to arrive in the large intestine in a viable physiological state [23
]. In addition, these probiotics should adhere to the intestinal mucosa, possess antimicrobial properties, and should not have transmissible antibiotic resistance genes [24
]. Acid and Bile tolerance are considered to be an important characteristic of probiotic strains. This tolerance supports survival and growth of probiotics and thus allows probiotics to exert their beneficial effects in the gastrointestinal tract [24
]. Yun et al.
] reported the survivability of Lactobacillu
s strains isolated from pig feces at 1% (w/v) bile, which is the condition found in the stomach and intestine. All the isolates tested in our study were able to survive at 2.0% (w/v) bile concentration. However, bile salt tolerance usually varied among the strains of bifidobacteria [27
It has been reported that probiotic strains, and particularly bifidobacterial strains, have lower acid tolerance system, with the exception of B. animalis
]. However, probiotic strains may have adaptive capabilities to survive in acidic conditions, allowing the strains to improve recovery and to continue growth. Despite having a slightly low bacterial count (Log CFU/mL), growth of isolates were not affected following 90 min exposure to pH 2.5 when further grown in pH 6.5 MRS broth. The basic requirement for probiotics to exert expected positive effects is to be viable. Similarly, all the isolates were capable of surviving and growing at pH 2.5 and 1% (w/v) bile salt, which are the conditions, found in the stomach and intestine. All the tested isolates survived well in low pH (2.5) and showed a similar growth trend. Acid tolerance response (ATR) may have developed in these isolates after the exposure of cells to low acid (pH 2.5), which might account for the isolates’ good growth after the recovery period [29
Aggregation properties of probiotic bacteria indicate that they can adhere to mucosal surfaces that will have prolonged survival in the body of the host. This property of probiotics bodes well for the use of probiotics and could be promising candidates for use in animal feed or to develop functional foods [30
]. Ibrahim et al.
] studied several bifidobacterial strains and classified them into autoaggregation sensitive (≥70%), moderate (20%–60%), and resistant groups (<20%) similar to our classification of high, medium and low autoaggregation behavior. In the present study, all the isolates also showed a clear zone of inhibition against E. coli
O157:H7. From these observed zones, it is apparent that these isolates possess antimicrobial properties.
The determination of antibiotic susceptibility of intestinal microorganisms is another important criterion for selecting an organism as a probiotic. Agaliya and Jeevaratnam [31
] reported the resistivity of L. plantarum
isolated from fermented olives towards gentamicin (10 μg/disc) whereas strains were sensitive to ampicillin (10 μg), chloramphenicol (30 μg), and erythromycin (15 μg). Argyri et al.
] also reported the resistivity of various lactic acid bacteria strains to ampicillin, chloramphenicol, erythromycin, and gentamicin when concentrations were used above MIC values set by EFSA. High resistance rates were observed with low-level kanamycin (30 μg) and gentamicin (15 μg) for 100% of the tested strains of Bifidobacterium
spp., similar to our results. However, tested strains were sensitive to high-level of kanamycin (1000 μg) or gentamicin (500 μg,) using the disc diffusion method [32
]. Similarly in another study, Bifidobacterium
spp. isolated from dairy and pharmaceutical products were resistant to gentamicin (MIC = 0.5 μg/mL), and susceptible to chloramphenicol (MIC = 2 μg/mL), erythromycin (MIC = 0.5 μg/mL), and ampicillin, (MIC = 4, μg/mL) [33
]. In cases of co-administration with antibiotics to prevent and treat intestinal disorders, probiotics should be resistant to certain antibiotics in order to survive in the gastrointestinal tract [34
]. However, the use of antibiotic-resistant probiotic strains is still a controversial subject as antibiotic-resistant genes could transfer to the other bacteria present in the host gastrointestinal tract [35
]. In addition, if such probiotic bacteria are added to different feed products, they could contribute to a potential source for the spread of antibiotic-resistance genes [33
]. Therefore, it is still a debatable subject whether one should select antibiotic-resistant or sensitive strains. Thus, more work is needed to address the potential impact of antibiotic-resistant bacteria to the host.