Effect of Yeast Type and Dose on Growth Performance and Nutrient Digestibility of Growing Rabbits Fed Maize or Barley

Due to the complex digestive system of rabbits, this species is highly susceptible to enteric diseases and enterotoxaemia  (Rabie et al., 2011). In rabbits, infectious diseases of the digestive system are the principal cause of mortality (Gómez-Conde et al. 2007) and are related to the level of insoluble fiber (NDF) in the diet (Gómez-Conde et al., 2009). Also, different grain types result in varying levels of residual starch concentration in the ileum and modify the energy digestibility coefficient; diets based on barley grain have a higher digestibility compared with maize-based diets (Gidenne et al., 2005). Since feed accounts for the major costs of the total production, improving feed and nutrient quality results in an increased economic viability of rabbit production.

The effect of probiotics on animal production has been well documented (Mingmongkolchai and Panbangred, 2018). However, variable responses to these supplements have been observed in rabbits as a function of type or dose. Oso et al. (2013) and Elmasry et al. (2018) have shown that the effective administration dosages of probiotics vary greatly and are dependent on the level and strains used.

Probiotics have an impact on the intestinal ecosystem by improvement of the intestinal health (Seyidoglu and Peker, 2015) and enhancement of immune responses (Zhang et al., 2019). However, the most beneficial effect of probiotics supplementation is to enhance rabbit performance regarding average daily gain (ADG) and feed conversion ratio.

Therefore, the objective of this study was to evaluate the effects of different levels of Biosaf® and Procreatín7® live yeast on the growth performance and dry matter (DM) digestibility of growing rabbits fed either barley or maize.

The study was carried out at the Laboratory of Microbiology, Department of Animal Science, rabbitry unit of the Chapingo Autonomous University (UACH), Texcoco, Mexico in 2018. Sixty New Zealand White and California growing rabbits (35-38 days old) were randomly allocated in 30 cages under similar housing and management conditions.

Two experimental diets (based on either barley or maize) were formulated to meet the nutritional requirements of fattening rabbits (de Blas and Mateos, 2010; Table 1). Each diet was divided into five equal portions before pelleting at the milling in the unit of UACH (Model of pelletizer Kt1 208): one portion without yeast, one portion supplemented with 0.85 g Biosaf® SC47/kg^-1 (Saccharomyces cerevisiae NCYC Sc47) or 2 g Procreatin®7 kg^-1 (Saccharomyces cerevisiae CNCM I 1077) equivalent to 6.4 ×109 CFU and one portion supplemented with 1.7 g Biosaf® SC47/kg^-1 (Saccharomyces cerevisiae NCYC Sc47) or 4 g Procreatin®7 kg^-1 (Saccharomyces cerevisiae CNCM I 1077) equivalent to 12.8 × 109 CFU/kg. The probiotics were dosed at the same CFUs per gram of substrate, based on the viable yeast concentration determined in the laboratory. The feed was offered once daily at 100 g/kg BW, with free access to clean drinking water through stainless-steel nipple drinkers for rabbits. All rabbits were weighed at the beginning of the experiment (initial body weight; IBW) and the end of the study (final body weight; FBW). The carcass (CW) was weighed hot and with its head. Total body weight gain, total feed intake and feed conversion ratio were determined once a week for growth performance calculation. Feces were collected for 5 days (on days 30 to 35 of each treatment); samples of feces and feeds were dried at 70°C for 72 h and milled to pass a 1-mm screen. The dry matter (DM), organic matter (OM) and ash contents were measured in triplicate using 1-g samples of feeds, feces and caecal contents. The DM was measured by oven-drying at 104°C for 24 h, while ash was determined by burning overnight at 550°C (AOAC 1996). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined according to Van Soest et al. 1991).The apparent digestibility (AD) coefficients for DM, OM, NDF and ADF of the diets were determined according to Equation (1; Safwat et al., 2015).

 

 

 
Where
NI represents the nutrient intake and NE represents the nutrients excreted.
 


Statistical analysis
 
The results were analyzed according to a completely randomized design, using initial body weight as a covariate. A nested treatment arrangement was used with the following factors: grain type (barley or maize) and two commercial probiotics, with three concentrations of probiotic, where the types of probiotics were nested in the probiotic factor (Jung et al., 2008). When the interaction of grain with probiotic was positive, Tukey´s test was applied (Piepho and Edmondson 2018).

Animals fed with maize had a higher FBW than those fed with barley (Table 2); they also showed higher weight gain and CW. The feed conversion rate, the total and daily feed intake and the ADG were different (p < 0.05) for both types of grain. Apparent digestibility coefficients of the nutrients are reported in Table 3. The maize or barley diets had similar apparent digestibility; (dry matter; organic matter and acid detergent fiber); but maize diets have a higher neutral detergent fiber apparent digestibility (NDFAD), this change might explain the difference in the performance of the rabbits fed with maize. These results  are different from those obtained by Gidenne et al., (2005), who found no impacts of grain type on the dry matter or organic matter apparent digestibility values of 50-day-old rabbits, while in young rabbits, the maize diet reduced the DMAD and OMAD values compared with the barley diet, which is a result of the higher ileal starch concentration, related to the quantity of resistant starch present in maize. The same authors show that the extrusion of maize increases ileal starch digestion. In our work, the pelleting of the feed could have had a similar effect on the extrusion of maize starch, increasing the OMAD levels. Additionally, maize diets have a high NDFAD, resulting in a high hemicellulose concentration; this change in digestibility might explain the difference in the performance of the rabbits fed with maize. Generally, diets with a high quantity of fiber result in increased growth and ADG levels (Gidenne et al., 2004; Bovera et al., 2012). In other studies, feed efficiency increased linearly (P < 0.001) with increasing NDSF inclusion (Gómez-Conde et al., 2009).





Supplementation of both kinds of S. cerevisiae increased (p < 0.05) the performance (FBW, TWG, CW and FCR) of the rabbits (Table 4). These results agree with  Falcão-e-Cunha et al. (2007), who found that probiotics supplementation improved growth performance characteristics. Das et al., (2002) and Bhatt et al. (2017) showed that in rabbits, the probiotics enhance ADG and FCR levels, with a decrease in mortality rate. Ezema and Eze, (2012) recorded higher (p < 0.05) TWG levels for rabbits fed on bioactive yeast (probiotic) at 0.12 g yeast (Saccharomyces cerevisiae)/kg of diet than for rabbits supplemented with either 0.08 or 0.16 g yeast/kg diet. According to EFSA, (2012), there is a significant improvement in total body weight of rabbits fed diets supplemented with Actisaf SC47, along with an improved feed conversion ratio  (p < 0.05) and reduced mortality (p < 0.05) when compared to untreated animals. The effect on the FCR is related to the increase in TWG and DWG, without altering the feed intake. The results of this experiment show that animals receiving probiotics have the same feed intake (p > 0.05) as control animals. The positive effect of S. cerevisiae on animals can result from a direct nutritional effect; alternatively, they act as bioregulators of the intestinal microflora, enhancing the host’s natural defenses (Jawhara et al., 2012). One of the most important results of this work is the change in CW; supplementation with S. cerevisiae resulted in significant increases in CW (p < 0.05). Ahmed et al., (2019) obtained a similar result with rabbits, using 4 g/kg of SC. In other species (ruminants), the inclusion of yeast in the diet resulted in differences in carcass quality and the proportion of “Premium Choice” carcasses increased with increasing levels of yeast in the diet (Ovinge et al., 2018). According to Elghandour et al. (2019) supplementation with S. cerevisiae could have metabolic effects and results in immunomodulation, changes in intestinal microbiota and the removal of oxygen.



The supplementation of high levels of Procreatin®7 or Biosaf SC47 to the maize or barley diets increased the OMD, DMD, NDFD and ADFD (p < 0.05; Table 5). The desirable effects of yeast found here could be related to the higher level of yeast found in the caecum of supplemented animals. In contrast to the rumen, the caecum is a more strictly anaerobic compartment (Kimsé et al., 2012). As a result, both kinds of S. cerevisiae increased the DMAD, OMAD and NDFAD levels. Ewuola et al., (2011) reported positive effects on DM, protein and crude fiber digestibility due to the administration of S. cerevisiae (125,000 million cfu) and Saccharomyces boulardii (30,000 million cfu). Additionally,  Ghazanfar et al. (2015) suggested significant effects (p < 0.05) on dry matter (DM), organic matter (OM), crude protein (CP), as well as NDF and ADF digestibility. Our data support the findings of Ghazanfar et al. (2015), who showed that NDF and ADF digestibility were improved in yeast-supplemented groups. Chaucheyras-Durand et al. (2016) revealed the in vitro potential of probiotic yeasts to enhance the growth and activity of fiber-degrading rumen microorganisms. Elghandour et al. (2019) showed that the addition of live yeast to animal rations can alter the digestion of dietary components. Similarly, Onu and Oboke (2010) report that live yeast administration also improved dry matter digestibility, in addition to a considerable positive effect on ADF. Positive effects of S. cerevisiae on fungal zoospore germination and cellulose degradation have been reported by Chaucheyras et al. (1995), who recently confirmed that yeasts can enhance fungal colonization of plant cell walls (Chaucheyras-Durand et al., 2016). A stable cecal pH provides a suitable environment for microbial growth, as fungi and bacteria degrade cellulose. Consequently, these microbial species facilitate fiber digestion. In contrast, Tripathi and Karim, (2010) reported no effect of yeast supplementation on nutrient digestibility. These variations in nutrient digestibility may be related to the quality and nature of the diet fed to animals, as described by Elghandour et al. (2019). 

Our results show that administration of the probiotic Saccharomyces cerevisiae (Biosaf® Sc47 and Procreatin ®7), at doses of 6.4 ×109 CFU and 12.8 ×109 CFU/kg, added to the basal diets of fattening rabbits, improves OM, DM and NDF digestibility as well as growth performance characteristics (TWG, ADG, CW and FCR).