Abstract
Probiotics have been used successfully to promote human and animal health, but only limited studies have focused on using probiotics to improve the health of hosts of different age. Canine microbiome studies may be predictive of results in humans because of the high structural and functional similarity between dog and human microbiomes. A total of 90 dogs were divided into three groups based on dog age (elderly group, n = 30; young group, n = 24; and training group, n = 36). Each group was subdivided into two subgroups, with and without receiving daily probiotic feed additive. The probiotic feed additive contained three different bacterial strains, namely Lactobacillus casei Zhang, Lactobacillus plantarum P-8, and Bifdobacterium animalis subsp. lactis V9. Serum and fecal samples were collected and analyzed at four different time points, i.e., days 0, 30, and 60 of probiotic treatment, and 15 days after ceasing probiotic treatment. The results demonstrated that probiotics significantly promoted the average daily feed intake of the elderly dogs (P < 0.01) and the average daily weight gain of all dogs (P < 0.05), enhanced the level of serum IgG (P < 0.001), IFN-α (P < 0.05), and fecal SIgA (P < 0.001), while reduced the TNF-α (P < 0.05). Additionally, probiotics could change the gut microbial structure of elderly dogs and significantly increased beneficial bacteria (including some Lactobacillus species and Faecalibacterium prausnitzii) and decreased potentially harmful bacteria (including Escherichia coli and Sutterella stercoricanisin), and the elderly dogs showed the strongest response to the probiotics; the relative abundance of some of these species correlated with certain immune factors and physiological parameters, suggesting that the probiotic treatment improved the host health and enhanced the host immunity by stimulating antibody and cytokine secretion through regulating canine gut microbiota. Furthermore, the gut microbiota of the elderly dogs shifted toward a younger-like composition at day 60 of probiotic treatment. Our findings suggested that the probiotic treatment effects on canine health and immunity were age-related and have provided interesting insights into future development of probiotic-based strategies to improve animal and human health.
Highlights
Probiotic are defined as “live microorganisms, which confer health effects to the host if administrated in sufficient amounts” by FAO/WHO [1]
No significant difference was detected in the respiratory rate, pulse rate, body temperature, and white blood cell counts between the probiotic and control groups (Figures 1A–C, Table S2), suggesting that the probiotic treatment did not cause any observable adverse physiological effects to the dogs and that it was safe for use in dogs
The results showed that some significant positive correlations were identified between the levels of fecal secretory IgA (SIgA), serum immunoglobulin G (IgG) and body weight with the abundance of Faecalibacterium, Faecalibacterium prausnitzii, Bacteroides, and Bacteroides clarus, while the level of IgG was negatively correlated with the genus Blautia as well as its species Blautia hansenii, Blautia producta, the genus Megamonas, and Ruminococcus torques, and they were positively associated with TNF-α and IL-6
Summary
Probiotic are defined as “live microorganisms, which confer health effects to the host if administrated in sufficient amounts” by FAO/WHO [1]. Probiotics have shown favorable effects on the host’s health including production of antimicrobial substances to inhibit the colonization of pathogenic microbes [2], regulation of host immunity and metabolism, and improvement of intestinal barrier function [3]. Many factors can affect the composition of gut microbiota such as diet, age, disease and gene Among these factors, aging is often associated with gut dysbiosis that is characterized with the reduction of beneficial microbes. This in turn causes negative health impacts like increase in leakiness of the intestinal barrier, excessive secretion of proinflammatory cytokines, and chronic inflammation [7]. The secretory IgA (SIgA) is the dominant antibody type found in mucosal secretions, which could regulate the intestinal microbiota and its development from birth to adulthood [10], and probiotics such as some Lactobacillus can promote the secretion of SIgA to form a protective layer between the mucosa and microbes in host, inhibiting pathogen growth [11]
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