In Côte d’Ivoire as well as in most African countries, there is a growing increase in the demand for animal proteins. To solve this increasing shortage of meat production problem, [1] recommended as solution among many others, the use of small species such as rabbits, which is reported to have the ability in improving meat supply and food security [2]. Indeed, rabbit’s performance is favored by several factors, such as small body size, short generation interval, rapid growth rate, high productive capacity and genetic diversity, which make this animal breeding suitable as meat producing small livestock in developing countries [3]. In addition, rabbits can convert 20% of the protein they eat into edible meat, which is higher than beef (8% - 12%) [4].

However, balanced feeding of rabbits is one of the most important challenges faced by breeding and production programs due to the complex digestion and nature of the diet [5] [6]. Improving feed quality and nutrition could contribute to enhance the rabbit production profitability, as feed has the largest part of the total production cost.

Indeed, rabbits are monogastric mammals that feed on forages, cereal seeds, and compound feeds [7]. Plant and grain-based diets naturally contain phytic acid and several minerals (iron, zinc, calcium, magnesium…). Phytic acid is naturally present in plant-based foods as phytate where it serves as a storage form for phosphorus [8]. However, it is negatively charged at acidic, neutral and basic pH conditions. In consequence, this compound can bind to positively charged molecules in the diet and in endogenous secretions of the gastrointestinal tract, such as digestive enzymes and mucins, thus reducing nutrients digestibility and increasing endogenous nutrient secretion [9]. Indeed, the phytic acid present in the food ingredients acts as an antinutritional factor and can cause mineral deficiency due to efficient chelation of metal ions such as Ca²⁺, Mg²⁺, Zn²⁺ and Fe²⁺, which forms complexes with proteins, thus affecting their digestion and also inhibits some digestive enzymes, such as a-amylase, trypsin, acid phosphatase and tyrosinase [10]. This results in important nutritional deficiencies and real problems of nutrition in a large part of the population in these monogastric animals. Moreover, due to the lack of adequate degradation of phytates in monogastric animals, these compounds are excreted in faeces, which is degraded by the activity of soil microbes, releasing phosphorus in the soil. This phosphorus leads to eutrophication after entering into aquatic bodies. According to various existing methods, notably physical (such as boiling, cooking and autoclaving) and chemical (acid hydrolysis and ion exchange chromatography) to remove phytates decreases the food nutritional value [11]. Therefore, enzymatic hydrolysis using phytases to reduce phytic acid is desirable as it improves the nutritional quality of the food. Indeed, phytases are a great deal to food and feed of non-ruminant animals to make bioavailable P; this clearly translates to recent market trends towards the importance of phytase in the food and feed sectors.

Phytases have a wide distribution in plants, microorganisms, and in some animal tissues [12] [13]. Previous researches have shown that microbial phytases are most promising for a biotechnological application [13] [14]. However, although several scientific reports discussed phytase produced by a diverse range of microorganisms, many of them may not be useful in process development due to the lack of enzyme yields and pH stability at drastic gastrointestinal tract (GIT) conditions, as reported by [15]. Thus, the isolation of new phytase-producing microorganisms, effectively capable of releasing dietary phosphate in the gastrointestinal tract and remaining stable during food processing and storage is a challenge.

In our recent studies on the characterization of the microbial communities of palm wines, traditional spontaneously fermented drinks, we discovered that yeasts populating these drinks produced acid phosphatases [16], most of which after testing for specific substrates have been identified as phytases. Additionally, these yeast strains, containing Saccharomyces cerevisiae and non-Saccharomyces yeasts were able to tolerate and withstand the harsh environment of the gastrointestinal transit and possessed the functional attributes of autoaggregation, coaggregation, hydrophobicity and bile salt hydrolase activity while testedin vitro. Considering that these drinks are consumed with their living microbial content without any toxicity being observed and the limited number of reports on yeast with probiotic and phytase properties used for animal nutrition, we hypothesized that microorganisms of these drinks, particularly the phytase-producing yeasts, could contribute to the reduction in vivo of phytate in phytase deficient organisms such as rabbits and improve the health status.

Therefore, the aims of the present study were to investigate the effects of three phytase producing yeasts on in vivo dephytinization and growth performance in breeds of weanling rabbits. Furthermore, the effects on some blood biochemical parameters and changes in caecal volatiles fatty acids were also studied.

Over the last three decades, the research and development of strategies to improve livestock production, to reduce production cost and alleviate the negative environmental impacts of livestock production was of utmost importance for scientists particularly, microbiologists, nutritionists and biochemists. Feed supplementation with either antibiotics or a number of prebiotics and/or probiotics has been exploited to achieve the above objectives [25]. Historically, beneficial microorganisms have been used by humans in agriculture and nutrition. Yeasts are an important source for obtaining products with probiotic activity, either live strains or derivatives of their cell walls. These preparations demonstrated a proven immunosuppressant activity in livestock as well as improvements in gastrointestinal physiology, which contributed to improved production results [26]. In this study, three indigenous yeasts namely S. cerevisiae ADR1B1, Hanseniapora jakobsenii ADR3E1 and Hanseniaspora guillermondii RD3 1, all isolated from palm wines and displaying phytase and probiotic abilities, were tested in rabbit breeding with a purpose of improving conventional feed digestion, growth performance and animal health.

Indeed, phytates represent the major form of phosphorus storage in plants and mainly in cereal grains which are also the main ingredients used in animal feed. They are an organic form of phosphorus poorly utilized by non-ruminant animals such as rabbits, due to the absence of adequate level of phytase in their gastrointestinal tract. This is corroborated by the high rate of this compound present in the faeces of rabbits used as control on which no more than 6% were degraded. The undigested phytates found in faeces had been previously reported to cause eutrophication problems [27] [28] [29]. Contrarily to the control, significant reductions of phytates in the faeces of treated rabbits were observed, with reduction rates between 50% and 75%. Previous studies by [30], using a recombinant strain of Pichia pastoris reduced the phytate content of a wheat-based mixture and a soybean-maize flour mixture by 65.3% and 73.1% respectively. Thus, in addition to considerably enhance the bioavailability of phosphorus, thereby reducing the faecal phosphorus output, phytase producing yeasts are effective in protein digestibility and protein and amino acid utilization due to the breakdown of phytin-protein complexes, as reported by [31]. It is also reported elsewhere that phytase added to diets improves the bioavailability, absorption and concentration of minerals such as copper, zinc, iron, magnesium, phosphorus, calcium, manganese and zinc in plasma, bone and the whole body [31] [32]. Therefore, by improving digestion and nutrients absorption, phytase producing yeasts would exert a positive effect on growth performance and weight gain. This phenomenon was observed on rabbit fed with palm wine indigenous yeasts, on which the weights were significantly increased in comparison to the control. The obtained findings confirmed the previous results reported by studies of [24], who showed that supplementing the rabbit diet with prebiotics improved rabbit growth. The high performance of growing rabbits as a result of indigenous probiotic yeast dietary supplementation may be due to enhancing digestibility and absorption of feed nutrients, resulted in positive anabolic metabolism state, as reported by [33]. Moreover, analysis of the weekly weight gains shows significant differences from the fourth week after weaning of the rabbits, which is consistent with results of [34], showing improvement of rabbit growth between days 43 and 91. The positive effect of probiotics on food utilization and consequently resulting in growth increase was largely demonstrated [35] [36].

For an organism to be considered potentially probiotic, it must be non-invasive, non-carcinogenic and non-pathogenic [37]. Thus, the tested rabbit bloods were analyzed in comparison with the control group, in order to detect any effect of administrated indigenous yeasts on the animal’s health. Serum biochemical parameters analyzed, notably blood glucose, triglycerides, total cholesterol, HDL (high density lipoprotein), LDL (low density lipoprotein), total protein, creatinine, ASAT and ALAT, showed no significant difference between treated rabbit groups and control one. Thus, probiotic yeast strains did not negatively impact rabbits’ health with respect to serum biochemical parameters. Furthermore, the comparison of the recorded parameters averages to the European standards shows no difference for most parameters except for triglycerides concentration. Indeed, this difference would be due to the difference in the composition of the diet offered to the rabbits in Africa and in Europe. However, these results are close to those obtained by [38]. According to some authors, serum biochemical parameters may show differences in animals. This difference would be related to the animals (age, species, strain and sex), environmental conditions, sampling method and analysis method [39] [40].

Like serum biochemical parameters, hematological parameters analyzed were not significantly different regarding red blood cells, hemoglobin and hematocrit, excepted for the rabbits fed with H. Jakobseni ADR3E1, which hematological parameters were higher than the control. Indeed, according to [41], the level of red blood cells, hemoglobin and hematocrit would increase when yeast probiotics were added to the rabbit’s diet. On the other hand, Chebab [42] studies showed a decrease in these blood parameters with the use of lactic acid bacteria probiotics. These recorded differences would be related either to the genetic and physiological characteristics of the rabbit, or to an effect exerted by the probiotic, or to a diet which is not balanced both qualitatively and quantitatively. Furthermore, the results obtained are consistent with the normal values referenced. Thus, the probiotic strains used would not cause anaemia in the treated rabbits. As for the leukocyte formula, the results obtained also showed no difference in the white blood cells and lymphocytes of treated rabbits compared to the control. Similar results were observed in the study of [41]. Furthermore, the results obtained were within the normal leukocyte range. Thus, the values obtained are not indicative of acute and chronic infection.

Microbial fermentation of the feed occurs in the caecum to ensure nutrient supply [43] [44]. The products of fermentation are important to the rabbit because the VFAs produced are an energy source for the host. The production of VFAs covers the maintenance energy requirements of rabbits [45] [46]. The concentration of VFAs produced by the different groups of treated rabbits varied significantly compared to the control group, and this finding is consistent with that of [47]. This variation can be related according to [48] to the animal age, the level of ingestion and the quality of the diet, especially the concentration of rapidly fermentable fiber [46] [49]. Gong et al. [50] observed a significant decrease in total VFA production in the rabbit group fed with a yeast-supplemented diet, which is in agreement with results obtained while rabbits were fed with H. jakobseni ADR3E1. This yeast strain can contribute to ferment in rabbit caecum foregut-undigested materials, volatile fatty acids, ammonia nitrogen, vitamins and other nutrients. Thus, the yeast strain ADR3E1 would promote the digestion of nutrients in the stomach before their arrival in the cecum. The volatile fatty acids can be rapidly absorbed in the intestine and can then provide 40% energy to maintain adult rabbits, in which butyric acid is a direct source of energy to hindgut, whereas acetic acid creates cholesterol and fat metabolism in the liver in metabolism, as reported by [51]. However, other researchers have reported an increase in VFA [52] [53], which can be associated with low amount of fermentable sugars available in the cecum.

The multivariate analysis achieved to classify the indigenous phytase producing yeasts tested regarding the various parameters analyzed led to three distinct clusters, with Hanseniaspora jakobsenii ADR3E1 displaying the best positive effect on rabbits growth performance and health. Usually, yeast strains, more well-known in their use as probiotics belonged to the genera Saccharomyces, Kluyveromyces, Hansenula, Pichia and Candida and within these genera, species S. boulardii, S. cerevisiae, K. fragilis, K. lactis, C. saitoana and C. pintolopesii [54] [55] [56] [57]. In addition, the most prominent yeast used as a feed additive in livestock is S. cerevisiae because of its richness in digestible proteins, vitamins (vitamin B6, thiamin, biotin, riboflavin, nicotinic acid and pantothenic acid), magnesium and zinc as reported by [58]. However, in this study, H. jakobsenii, which remains an almost unknown yeast, exhibits greater efficacy than S. cerevisiae from the same origin as it, following its supplementation to the rabbit’s diet. This finding is of capital importance for the characterization of this strain and an important contribution in the study of its technological potential and its exploitation in the improvement of animal’s diets in general. If some species of the genus Hanseniaspora, notably H. osmophila, H. uvarum [59] are well known for their probiotic potentials, this is not the case for the species H. jakobsenii, the isolation and identification of which are still recent [60]. The fact remains that this species has enormous potential that deserves to be elucidated. Indeed, its prowess in improving the growth performance and health of rabbits make it a good candidate to consider in the development of food supplements for animals.

The dietary supplementation with three palm wine indigenous phytase producing yeasts (H. jakobsenii, H. guillermondii and S. cerevisiae) increases weekly weight gain, growth performance and digestibility in rabbits. Serological data also showed that yeast supplementation did not alter the blood parameters assessed. Based on the findings, it is recommended to supplement rabbit diet with H. jakobsenii which displayed the best potentialities to enhance growth performance and health status.

This work was financially supported by the International Foundation for Sciences (IFS) under the grant number E/5669-l.

The authors declare no conflicts of interest regarding the publication of this paper.

Celaire, N.K.M., Francine, A.M.D., Moussa, K., Marcellin, D.K. and Theodore, D.N. (2022) Effect of Indigenous Phytase-Producing Yeast Cultures on Growth Performance, Digestion and Health of Rabbits (Oryctolagus cuniculus). Advances in Bioscience and Biotechnology, 13, 73-91. https://doi.org/10.4236/abb.2022.132003