Various antibiotic products in poultry production are gradually being banned around the world due to the adverse problems including the antibiotic residues and antibiotic resistance. Tributyrin was a potential alternative to antibiotics. The results of the present study indicated that tributyrin could improve the growth performance by modulating blood biochemical indices and the cecal microflora composition of yellow-feathered broilers. To the best of our knowledge, few studies investigated the effects of tributyrin on intestinal microbiota and its relationship with growth performance in broilers. This will provide a scientific basis for the application of tributyrin in animal husbandry in this post-antibiotic era.
1. Introduction
Sub-therapeutic antibiotics have been extensively used in the poultry industry for nearly 70 years to improve growth performance and disease resistance
[1]. However, due to the rapid emergence of antibiotic-resistant bacteria and its potential threat to human health, an antibiotic ban in animal husbandry has been widely implemented, especially in the European Union in 2006
[2] and China in 2020
[3]. Therefore, there is an urgent need to find safe alternatives with no residual effect in this post-antibiotic era.
Increasing evidence suggests that butyrate is a potential alternative to antibiotics accounted for the fact that it can act as the major energy source of the colon
[4], reduce pathogen colonization
[5][6], improve intestinal barrier function
[7], and exert anti-inflammatory properties
[8]. However, the unpleasant odor and the rapid metabolism of butyric acid have limited its application in the livestock and poultry industry
[9]. To overcome these drawbacks, there is increasing interest in developing butyric acid derivatives. Tributyrin is a triglyceride containing three molecules of butyric acid
[10]. Previous research has shown that tributyrin improved growth performance in
Eimeria maxima-infected broilers
[11]. Moreover, dietary supplementation with 1000 mg/kg tributyrin improved eggshell quality and follicle-stimulating hormone secretion in broiler breeders with different egg-laying rates
[12]. Tributyrin has the ability to converse the pepsinogen into pepsin, thus increasing the activity of the proteolytic enzymes and protein digestion
[13]. A previous study reported that tributyrin increased the growth performance of weaned piglets accompanied with improvement of lipid metabolism and the protein digestibility for decreasing blood urea
[14], a negative indicator of lean gain and feed efficiency
[15]. He, et al.
[16] reported that dietary supplementation with 0.1% tributyrin could efficiently attenuate abnormal lipid metabolism in intrauterine growth retardation piglets.
2. Current Insight Into Dietary Tributyrin for Broilers
Dietary supplementation with tributyrin has been demonstrated to improve animal production performance and disease resistance in monogastrics
[17][18][19] and ruminants
[20]. Notably, the positive effect of tributyrin may be attributed to the production of butyrate, which can promote the proliferation and differentiation of intestinal mucosal cells and improve nutrient absorption and utilization
[21][22]. However, the efficacy of tributyrin as a growth promoter remains a matter of debate. It has been reported that dietary tributyrin administration at 1840 mg/kg increased the ADG, FCR and beneficial bacterial population in Arbor Acres (AA) broiler chickens under an isocaloric feeding regime
[23]. Moreover, diets with a 0.2% mixture of butyric acid glycerides (mono-, di- and tri-glycerides) increased live weight at slaughtering and FCR of Ross 308 female chickens
[24]. In contrast, tributyrate glyceride at 500 ppm or 2000 ppm did not change the ADG or FCR in Ross 308 and Ross 708 broilers; however, it modulated lipid metabolism and reduced abdominal fat deposition
[25]. It found that dietary supplementation with tributyrin increased the final weight and decreased the FCR in the entire phase; however, the difference failed to reach statistical significance. This discrepancy could be due to many factors, including different additions, breed, age, and different experimental conditions.
Blood biochemical indices usually reflect the physiological and metabolic status of animals. Creatinine, urea, and uric acid are widely acknowledged as reliable indicators for kidney function, as they are nitrogenous and protein end products of a catabolic process that are generally excreted by the kidney
[26]. Elevated concentration of these plasma indices indicate kidney damage while decreasing their concentration helps to reduce the development of kidney disease
[27]. In this regard, tributyrin has previously been reported to reduce kidney damage in dairy cows under heat stress by decreasing the concentration of creatinine, aspartate aminotransferase, total bilirubin, and the inflammatory response of immune cells
[28]. The result showed that tributyrin decreased the creatinine during all phases and uric acid levels during the last phase, indicating that tributyrin may have a potent protective effect on renal dysfunction. The mechanisms underlying this protective effect remain largely unknown, warranting further studies. Notably, it found that the uric acid concentration in the TB group was decreased on day 63 due to tributyrin’s previously documented long-term ability to reduce uricase activity
[29]. Moreover, uric acid is a water-soluble antioxidant that inhibits oxidative damage and protects cell membranes and DNA
[30][31]. The decreased uric acid concentration in TB groups contributed to the alleviation of oxidative injury of broilers. It was reported that elevated serum lactate dehydrogenase (LDH) activity together with alanine transaminase (ALT) and aspartate transaminase (AST) could serve as indicators of liver damage
[32]. A previous study showed that the activity of ALT and AST in Japanese quails supplemented with sodium butyrate had no significant effects at day 21 but significantly decreased at day 42
[7]. Consistently, the current study showed that treatment with tributyrin reduced the ALT activity at day 63 and LDH at day 42, suggesting that tributyrin seems to protect the broilers from liver injury during the late phase.
It is widely acknowledged that commensal gut microbiota plays a crucial role in maintaining host animal’s health and normal physiology
[33]. Accumulating evidence indicates
Firmicutes dominate the cecal microflora in chickens
[34][35]. Nonetheless, the study showed that
Bacteroidetes was the dominant phylum of cecal contents in the TB group, accounting for more than 80%, whereas
Firmicutes accounted for less than 20%, which was consistent with the literature
[36]. Furthermore, LEfSe results showed that the
Bacteroides phylum and its class
Bacteroidia, order
Bacteroidales, species
Bacteroides_barnesiae, were potential biomarkers in the TB group.
Bacteroides are anaerobic gram-negative rods that are considered the major bacteria involved in producing SCFA
[37]. Given that
Bacteroides possess large repertoires of carbohydrate utilization genes
[38], it can be inferred that
Bacteroides can improve the host’s nutrient digestion and absorption through carbohydrate metabolism in tributyrin-treated chickens. Interestingly, a previous study reported the association between beneficial bacteria
Bacteroides in the avian gut and increased growth performance, body weight gain, breast muscle yield and low abdominal fat
[39]. Further research has shown that
Bacteroides were significantly more abundant in the high feed efficiency (low FCR) group
[36], indicating the low FCR and high final weight may be due to the increased
Bacteroides in the TB group.
The genera
Eisenbergiella and
Lachnoclostridium belonging to the
Lachnospiraceae family,
Intestinimonas and
Megasphaera, have been reported to be important butyrate producers residing in the intestinal microbiota
[40][41][42]. The high relative abundance of genera
Eisenbergiella, Lachnoclostridium, Megasphaera and
Intestinimonas observed in the present study indicated that tributyrin strongly helped stimulate the synthesis of butyrate, the preferred energy source for the intestinal epithelial cells
[43]. Additionally, the
Lachnospiraceae family can reportedly degrade starch and nonstarch polysaccharides to produce organic acids
[44], thereby decreasing the expression of virulence factors from pathogens like
Salmonella [45]. Furthermore,
Lachnospiraceae has been documented to be consistently depleted in people with acute colitis, suggesting its beneficial effects on maintaining intestinal homeostasis
[46]. However, a previous study showed high
Eisenbergiella abundance in infected mice, suggesting its association with gut dysbiosis
[47]. There is limited information about the biological function of this genus, especially in birds, therefore needing further explore. Spearman correlation analysis in the study showed that
Eisenbergiella was negatively correlated with FCR, suggesting that the low FCR in the TB group may be attributed to the increased abundance of
Eisenbergiella. Tributyrin treatment was also found to increase
Phascolarctobacterium abundance. A high-fat diet is reportedly more likely to result in an increased abundance of
Phascolarctobacterium [48].
Phascolarctobacterium is a propionate producer, and a decline in the abundance of this genus has been associated with colonic inflammation
[49]. The increased abundance of this genus in the TB group seemed to improve the host immune response to a certain extent.
In conclusion, dietary tributyrin supplementation decreased the FCR during the growth phase and as well as overall. Furthermore, it showed a tendency to increase the final weight. Tributyrin increased the creatine concentrations at the entire period and changed the cecal microflora composition of yellow-feathered broilers on day 63. Furthermore, spearman correlation analysis in the current study showed that Eisenbergiella was negatively correlated with FCR, suggesting that the low FCR in the TB group might be attributed to the increased Eisenbergiella abundance. These findings provided a new insight into the application of tributyrin as a potential antibiotic alternative in broiler industry by modulating the intestinal microbiota composition. Further research should explore the evolution of the cecal microbiota in TB-supplemented broilers and confirm the relationship between the Eisenbergiella and FCR.
This entry is adapted from the peer-reviewed paper 10.3390/ani11123425