Abstract: Pionibacteria are natural inhabitants of the rumen that make up 1.4% of ruminal microflora and produce propionate, a major precursor for glucose production by hepatic gluconeogenesis. Several mechanisms have been suggested for the mode of action of direct-fed bacteria in ruminants include stimulation of desirable microbial growth in the rumen, alteration of ruminal fermentation pattern and end product formation, increasing postruminal nutrient flow, increasing nutrient digestibility and alleviation of stress through enhanced immune response. Propionibacteria have the ability to convert lactic acid and glucose to acetic and propionic acids, reduce the risk of acidosis and increase weight gain and milk production of treated animals. On the other hand, enteric CH4 is the single largest contributing source of greenhouse gases production which causes global warming crisis. Propionibacteria also act to alter the biohydrogenation of polyunsaturated fatty acids in the rumen and increasing the generation of health-promoting fatty acids such as Conjugated Linoleic Acid (CLA). The impact of feeding of propionibacteria on the performance of the ruminant animals has been evaluated but results were inconsistent, this may be attributed to many of factors involved the used bacterial strain and its viability, bacterial inclusion level in the diet, diet composition and frequency of feeding, animal status including age, breed, health and physiological condition. In this review the focus will be on surveying impact of feeding propionibacteria on the productive performance of the ruminants including the effects on nutrients digestibility, rumen activity, blood parameters, milk yield and milk composition.
INTRODUCTION
The global concerns with the antibiotics (e.x. ionophores) utilization as animal growth-promoter encourage the nutritionists to search for alternative safer feed supplements1. In this milieu, utilization of beneficial bacteria in ruminant diets is appearing to be a promising mean for improving feed nutrients utilization and enhance overall of animal’s productivity2-4. There are many bacterial strains have being used as bacterial feed additives but Lactobacilli, Bifidobacteria and Propionibacterium are the most common direct fed bacteria.
Propionibacteria are found naturally in the rumen and make up 1.4% of total ruminal microflora3. Propionibacteria play a vital role in production of glucose (gluconeogenesis), spares glucogenic amino acids and inhibition of hepatic lipid oxidation5. Therefore, they have been used for improving energy metabolism for dairy animals’ especially in transition period from gestation to lactation6. Theoretically, efficiency of propionate as a source of energy in the form of ATP represents 109% compared with glucose7. In addition, the efficiency of propionic acid utilization for the maintenance is 0.86 versus 0.59 for acetate and 0.76 for butyrate7, thus, increasing ruminal synthesis of propionate may increase glucose supply and increase milk and lactose production8,9, weight gain and feed efficiency10,11 and decrease the incidence of acidosis and ketosis12,13.
On the other hand, Propionibacteria as a feed additive may play an important role in reductions of methane (CH4) production by increase competition for hydrogen through producing more propionate in the rumen14,15. Moreover, many of propionibacteria species have antimicrobial activity16-18. Therefore, there inclusion in ruminant diets may reduce CH4 production through their antimicrobial activity and redirect fermentation toward propionate formation.
The impact of feeding of propionibacteria on the ruminant performance and methane production has been evaluated but the results were inconsistent. This may be attributed to many of factors involved the bacterial strain and its viability, bacterial inclusion level in the diet, diet composition and frequency of feeding, animal status including age, breed, health and physiological condition3,4. In this review the focus will be on surveying impact of propionibacteria inclusion in ruminant’s diets on the animal’s productive performance and methane production.
PROPIONIBACTERIA MORPHOLOGY AND ADVANTAGES
Organisms of the genus Propionibacterium are classified as a Gram-positive, slow growing, non-spore forming, non-motile, usually pleomorphic bacteria ranging in size from 0.3 to 1.3 μm in diameter and 1-10 μm in length. Fermentation products from glucose include combinations of propionic and acetic acids and frequently lesser amounts of isovaleric, formic, succinic or lactic acids and carbon dioxide19, Propionibacterium spp. are acid intolerant, anaerobic to aerotolerant organisms which grow best at 30-37°C at a pH near20 7.0. Propionibacteria spp. including (P. freudenreichii, P. jensenii, P. acidipropionici and P. thoenii ) are extensively used by the dairy-food industry as starter cultures for production of Swiss-type cheeses21, commercial production of vitamin22 B12, production of antimicrobial agents such as propionic acid, propionins (antiviral peptides) and bacteriocins which used as preservatives in the food industry23. Propionibacterium strains are also employed as inoculants for silage production24.
Propionibacteria mode of action: Direct fed Propionibacteria have been used in the ruminant’s nutrition for over 20 years, primarily to improve growth performance, feed conversion and milk production efficiency25. They are administered to animal’s diets in the form of an encapsulated bolus or mixed with the feed. Propionibacteria in the rumen act to convert substrate to propionic acid, this leads to increase propionic acid concentration in the rumen and subsequently in the blood. The increased levels of propionate in the blood lead to increased concentrations of key enzymes in the gluconeogenesis pathway such as pyruvate carboxylase (PC) and phosphoenolpyruvate carboxykinase (PEPCK) in the liver. These enzymes are involved in the gluconeogenesis pathway that converts propionate into glucose. This leads to an increase in available glucose, which may be used by the mammary gland. Within the mammary gland, alveoli secretory epithelial cells increase lactose in the lumen of the alveoli. Lactose is an osmotic regulator of milk production and causes an increase of water in the lumen and thus, an increase in milk production26-28. In addition, propionibacteria serve as an alternate means of hydrogen disposal to ruminal methanogenesis25,29-31. Its well known that, enteric methane (CH4) is a normal product of ruminal fermentation and represents a mechanism to remove H+ and avoid the accumulation of reduced electron carriers during fermentation31. However, enteric CH4 is the single largest contributing source of greenhouse gases which lead to global warming crisis. Hence, substantial efforts are now being directed toward developing strategies to mitigate enteric CH4 emissions. Increasing ruminal synthesis of propionate at the expense of acetate favors reduced CH4 emissions, as propionate is a net H+ sink in the fermentation process32. Recently, the in vitro work of Alazzeh et al.29 identified the ability of P. freudereichii strain T54 to reduce CH4 production, beside their ability to alter the biohydrogenation of polyunsaturated fatty acids33,34 and increasing the generation of health-promoting fatty acids such as conjugated linoleic acid (CLA). It has also been reported that several species of Propionibacteria exert antimicrobial activity and produce antimicrobial peptides that may contribute to a reduction16-18 in CH4.
Propionibacteria impact on feed intake and feed efficiency: Concerning with effect of Propionibacteria addition to ruminants diets and their impact on feed intake and feed efficiency, Swinney-Floyd et al.10 stated that Propionibacterium freudenreichii (P-63) did not affect the dry matter intake (DMI) and feed efficiency in the newly weaned calves. Also, Rust et al.35 reported that the combination of Propionibacterium freudenreichii (PF24) with three different levels of Lactobacillus acidophilus strains did not affect the dry matter intake in finishing cattle but the final live weight was considerably higher for all treated groups compared to the control. Galyean et al.36 found that adding live cultures of Lactobacillus acidophilus strain 45 and (or) strain 51 plus Propionibacterium freudenreichii (PF-24) for growing finishing steers slightly increased daily dry matter intake by 2.4% above the control. Moreover, Huck et al.37 found that heifers fed L. acidophilus for 28 day followed by P. freudenreichii showed greater gain (5.0%) and improved feed efficiency (5.1%) compared with controls. In addition, Allen38 added the Lactobacillus acidophilus and Propionibacterium freudeneichii into the diets of finishing cattle and found that feed conversion improved by 2.4% with insignificant decreased in feed intake. But, there was a trend for feed intake to be numerically reduced by the addition of the microbial preparation. Also, Francisco et al.39 reported that cows fed supplemental Propionibacteria (17/head) showed improved energy balance but lower daily dry matter intake at the first week of lactation, while Ghorbani et al.13 found that dry matter intake was not affected by ruminally cannulated steers supplemented with Propionibacterium (P15) or P15 in combination with Enterococcus faecium EF212. However, Kim and Rust40 found that the addition of Propionibacteria acidipropionici strain (DH42) at rate of 109 CFU/head/day to cattle fed a high concentrate diet decreased dry matter intake and average daily gain, while McPeake et al.41 reported that treated steers with various combinations and concentrations of Lactobacillus acidophilus strains (45 and 51) and Propionibacterium freudenreichii (PF24) had a greater final live weight, average daily gain and dry matter intake than untreated steers. In other studies, Elam et al.42 found no significant differences in dry matter intake. In contrast, Daivis43 found that the treated heifers with mixture of Propionibacteria strains P169 and yeast at level of 5 g/head increased daily feed intake from 9.32 kg to 10.09 (kg/day) without significant differences in feed efficiency. Also, Raeth-Knight et al.44 found that feeding dairy cattle combination of L. acidophilus (LA747), L. acidophilus strains (LA45) and P. freudenreichii (PF24) had no effect on DMI.
Lehloenya et al.11 found that treated steers with Propionibacterium strain (169) strain insignificantly increased the intakes of organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF). Also, De Ondarza and Seymour45 reported that supplementation of commercial dairy herd with Propionibacteria freudenreichii (P169) at level of 6×1010 CFU/day/cow increased the dry matter intake under summer heat and humidity condition. On the other hand, Vasconcelos et al.46 found that feeding of feedlot cattle (British and British x Continental steers) with diet supplemented with 1×107 CFU (Low), 1×108 CFU (Medium) or 1×109 CFU (High) of Propionibacterium freudenreichii (strain NP 24) did not affect the final body weight or dry matter intake. While, Weiss et al.47 reported that dairy cows fed Propionibacterium strain P169 at level of 6×1011CFU/day had lower DMI. However, Boyd48 stated that feeding live bacterial inoculant (Bovamine®) at level of 4×109 CFU/h/day of a combination of Lactobacillus acidophilus NP51 and Propionibacterium freudenreichii NP24 to mid lactating Holstein cows during hot weather lead to lower dry matter intake. In contrast, Thompson49 reported that supplementation of Holstein cows with 109 CFU/g of Lactobacillus acidophilus and 109 CFU/g Propionibacterium freudenreichii had no effect on dry matter intake or nutrients digestibility. Also, West and Bernard50 found no effect on dry matter intake by feeding lactating Holstein cows on bacterial inoculants (Propionibacterium freudenreichii strain NP24, Lactobacillus acidophilus strain NP51 and L. acidophilus strain NP45. In addition, Azzaz et al.3 showed significant (p<0.05) increase of all nutrients digestibility coefficients by buffaloes fed rations supplemented with yeast culture+ Propionibacterium (P169) compared with those fed the control ration. Also, the nutritive values of the experimental rations expressed as Total Digestible Nutrients (TDN) and Digestible Crude Protein (DCP) take the same trend of nutrients digestibility coefficients.
Propionibacteria impact on ruminal fermentation: The rumen is a dynamic and continuous-culture type fermentation container with a highly complex and competitive microbial ecosystem within, yet the rumen microbial ecosystem represents and facilitates a classic symbiotic association between the microbes and the host animal. Propionibacteria represent a good example for relation between the microbes and the host animal. In this concern, Kim et al.51 fed Propionibacterium acidipropionici, strain DH42 at levels 0, 107, 108, 109 and 1010 CFU to steers fed high concentrate diet. They concluded that P. acidipropionici may alter ruminal metabolism toward less production of acetate and butyrate but more propionate with no effect on rumen pH, lactate or branched-chain fatty acids. In contrast, Akay and Dado52 reported that Propionibacterium P5 increased the in vitro total VFA's, propionate, acetate, butyrate and valerate at all experimental inclusion levels (103, 106 and 109 CFU mL–1). In this concern, Ghorbani et al.13 found that steers received diet supplemented with Propionibacterium P15 (P15) at level of 1×109 CFU g–1 did not show any change in ruminal pH, total VFA, propionate, iso-butyrate and iso-valerate concentrations or the acetate:propionate ratio. Also, Yang et al.53 found no significant effect on the in vitro pH, acetate, propionate, butyrate or total VFA's concentration or acetate/propionate ratio when Propionibacterium P15 at level of 1×109 CFU g–1 was tested. Moreover, Stein et al.8 reported that Holstein cows supplemented with Propionibacteria strain 169 at level of 6×1011 CFU/day for 30 week postpartum showed reduction in ruminal pH and greater ruminal propionate production which leads to decrease ruminal acetate/propionate ratio. However, the molar percentage of ruminal acetate and butyrate were not affected by the treatment. In addition, Raeth-Knight et al.44 stated that Holstein cows treated with L. acidophilus and P. freudenreichii did not show any change on their ruminal total VFA's and ammonia concentrations. While, Lehloenya et al.11 found that feeding Propionibacterium strain P169 and yeast culture (XPY) increased molar proportion of propionate (by 9.7%) but decreased molar proportion of acetate and acetate: propionate ratio compared to control steers. They suggested that feeding P169 alters ruminal metabolism toward increased propionate without affecting feed intake or ruminal kinetics. Also, Weiss et al.47 reported that dairy cows fed the Propionibacterium strain at a rate of 6×1011 CFU/day had lower concentrations of acetate but higher concentrations of propionate and butyrate than control. On the other hand, Thompson49 reported that supplementation of Holstein cows with 109 CFU g–1 of Lactobacillus acidophilus and 109 CFU g–1 Propionibacterium freudenreichii had no effect on rumen kinetics, pH, acetate, propionate, butyrate and acetate/propionate ratio.
Propionibacteria impact on animal’s blood metabolites: In ruminants, Francisco et al.39 found that feeding dairy cows on propionibacteria 169 at level of 6×1010 CFU/cow during the first 12 week postpartum did not influence concentrations of glucose and cholesterol in cow’s blood plasma. Similarly, Ghorbani et al.13 found that steers received diet supplemented with Propionibacterium P15 at level of 1×109 CFU g–1 did not show any change in blood glucose. Also, Lehloenya et al.54 stated that blood plasma glucose concentrations of cows received supplemented diets with Propionibacterium strain P169 were not changed compared to control cows. Moreover, Daivis43 found no significant effect of Propionibacteria strains P169, P5 and yeast supplementation on plasma glucose and insulin concentrations of Angus× Hereford heifer’s blood. In addition, Aleman et al.9 studied the effect of feeding primiparous Holstein cows at two levels of Propionibacteria (high dose, 6×1011 CFU/head/day and low dose, 6×1010 CFU/head/day) on metabolic indicators during lactation. They found that plasma glucose levels reach 67.9 mg dL–1 in low-dose P169 treated cows, which represent 6-9% greater plasma glucose than high-dose P169 treated and control cows, respectively. In contrast, Weiss et al.47 found that plasma concentrations of glucose and β-hydroxybutyrate (BHB) of dairy cows were not affected by P169 treatment. Similarly, Boyd48 found no significant effect on concentration of serum glucose by feeding mid lactating Holstein cows on a combination of Lactobacillus acidophilus NP51 and Propionibacterium freudenreichii NP24) at level of 4×109 CFU/head/day. Also, Thompson49 reported that supplementation of Holstein cows with 2×109 CFU/day of Lactobacillus acidophilus and 2×109 CFU/day of Propionibacterium freudenreichii had no effect on the blood metabolites: glucose and β-hydroxybutyrate. In addition, West and Bernard50 reported that serum glucose content was not altered by similar treatment. In addition, Azzaz et al.3 showed no significant differences among buffaloes fed rations supplemented with yeast culture+Propionibacterium (P169) and buffaloes fed the control rations in the overall means of plasma glucose, ALT, AST, total lipids, total protein, albumin, globulin concentration and albumin/globulin ratio.
Propionibacteria impact on animal’s milk yield and milk composition: In lactating ruminants, Francisco et al.39 found that feeding dairy cows on propionibacteria 169 at level of 6×1010 CFU/cow during the first 12 week postpartum did not influence daily milk yield or 4% fat corrected milk production. In addition, Stein et al.8 found limited positive responses in milk yield to Propionibacteria supplementation for multiparous cows in early lactation. Similarly, Raeth-Knight et al.44 found that supplementing mid lactating dairy cows with Lactobacillus acidophilus and Propionibacteria freudenreichii had no effect on milk yield or milk components. In contrast, Lehloenya et al.54 reported that daily milk and 4% FCM production for cows fed propionibacteria strain P169 (6×1011 CFU/head/day)+ 56 g/head of yeast were 9-16% greater than the control during mid lactation (9-30 weeks). Also, milk protein and SNF percentages and yields increased in treatments compared to control. In addition, De Ondarza and Seymour45 stated that inclusion of propionibacteria in the diet increased (p<0.05) milk production, especially in early lactation and in older cows. However, the production of 3.5% fat-corrected milk and milk protein percentage were not affected by P169 supplementation. Moreover, Weiss et al.47 found that cows fed the Propionibacterium strain P169 2 weeks before calving to 119 postpartum at rate of 6×1011 CFU/cow/day had comparable milk yield and composition as the control cows. Concentrations and yields of milk fat, milk protein, yield of energy corrected milk were greater (p<0.05) during the first week of lactation. Additionally, Boyd48 found no significant effect on milk yield, energy corrected milk and milk fat percentage by feeding mid lactating Holstein cows with combination of Lactobacillus acidophilus NP51 and Propionibacterium freudenreichii NP24) at level of 4×109 CFU/head/day. Similarly, Thompson49 found that supplementation of dairy cows with Propionibacterium freudenreichii had no significant effects on milk production, milk components or milk fatty acids profile compared to control cows. While, West and Bernard50 found that supplementation of Holstein cows with 1×109 CFU/day of Lactobacillus acidophilus and 2×109 CFU/day of Propionibacterium freudenreichii increased significantly their yields of milk fat, FCM and energy-corrected milk than cows of control. Also, efficiency of milk production (defined as energy-corrected milk yield per unit of DMI) was greater for cows fed bacterial inoculants compared with control cows. However, the effects of treatment on milk fat percentage or milk protein yield or percentage were not significant. In addition, Azzaz et al.3 showed that milk yield and 4% fat corrected milk (FCM) yield were significantly higher for yeast culture+Propionibacterium (P169) treated buffaloes compared to control. Also, the percentages and yields of milk fat, protein, lactose, Total Solids (TS) and Solid Not Fat (SNF) take the same trend of milk productivity.
CONCLUSION
It could be concluded that, propionibacteria as feed supplements can play a vital role in enhancement of ruminant's productive performance through:
| • | Improving energy metabolism for dairy animals’ especially in transition period from gestation to lactation as Propionibacteria have important role in production of glucose (gluconeogenesis), spares glucogenic amino acids and inhibition of hepatic lipid oxidation |
| • | Increasing ruminal synthesis of propionate which led to increase glucose supply to mammary gland and consequently increase milk and lactose production |
| • | Increasing weight gain and feed efficiency |
| • | Decrease the incidence of the metabolic disorders like acidosis and ketosis |
| • | Mitigate enteric CH4 emissions and consequently reduce the production of single largest contributing source of greenhouse gases which lead to global warming crisis |
SIGNIFICANCE STATEMENT
This study discover the possibility of using propionibacteria as feed supplements for enhancement of ruminant's productive performance and environment protection through mitigate farm animal's CH4 emissions. This study will help the ruminant animal's breeders to: (1) Use propionibacteria as alternative for harmful antibiotics (e.x. ionophores) in their animal's diets and (2) Reduce their animals feeding cost to become at the minimum and maximizing their profits.