The effect of oak nut on the activity of rumen bacteria and fungi and the protozoa population of Najdi goat and Arabi sheep

Introduction: Oak nut is containing 55% starch and can be used as an energy source in the ruminant nutrition. In addition to nutritional compounds, oak nut contains high amounts of active biological compounds, such as tannin, gallic acid, galloyl or hexahydroxy decanol derivatives. Tannins form complexes with a large number of nutrients such as carbohydrates, proteins, polysaccharides, bacterial cell membranes, digestive enzymes, and minerals, but decrease microbial digestion in the rumen. This experiment was conducted to determine the effect of oak nut on the population and digestive activity of bacteria, fungi, and protozoa counts in the rumen of Najdi goat and Arabi sheep.
Material and methods: For this purpose, six Najdi goats and six Arabi sheep (average weight 35 ± 2 kg) were fed with a diet containing oak nut (63 %) and a diet without oak nut for 28 days. Iso-energetic and iso-nitrogenous diets were formulated according to NRC, in diet 30:70 forage to concentrate (3 animals per treatment). Samples of rumen fluid were collected before the morning feeding. Then, digestive activity of rumen bacteria and fungi, fermentation parameters, and protozoa counts of animals which fed with experimental diets were determined. Growth and digestive activity of rumen bacteria and fungi were determined by measuring DM, NDF and ADF disappearance in specific culture for each incubation time (9 replicates for each treatment). Gas production and fermentation parameters by fungi and bacteria were determined. The protozoa count, genus, and species were identified on the basis of Yanez Ruiz et al (2004).
Cumulative gas production data were fitted into the exponential equation: Y = b (1 ₋ e^−ct), where b = gas production from the fermentable fraction (mL), c= the gas production rate constant (mL/h), t = the incubation time (h), and Y = gas produced in time t. Partitioning factor (PF), microbial biomass, and truly digested organic matter were calculated by Olivera (1998). For determination of partitioning factor (PF) at the end of each incubation period, the content of vials was transferred into an Erlenmeyer flask, mixed with 20 mL neutral detergent fiber solution, boiled for 1 hour, filtered, dried (in oven at 60 °C for 48 h), and ashed.
 The data were subjected to analysis as a split plot design using the General Linear Model (GLM) procedure of SAS (version 9.1). The Duncan’s multiple range test was used to compare the mean differences at p < 0.05.
Results and discussion:The disappearance of DM, NDF, and ADF by goat rumen bacteria at 24, 48 and 72 h were significantly higher in the control group than oak nut treatment (p < 0.05). According to the results, there were no significant differences for the disappearance of DM, NDF, and ADF by the sheep and goat rumen fungi between the control group and oak nut treatment at 1, 3, and 6 days of incubation (P>0.05). The disappearance of DM, NDF, and ADF by the rumen fungi was not different between treatments at all times of incubation (p < 0.05). The gas production potential of wheat straw, PF, microbial biomass production, the efficiency of microbial biomass, and truly digested organic matter by the rumen bacteria and fungi of sheep and goats did not have any significant differences in control treatment compared with oak nut treatment (P>0.05). Truly digested organic matter in the control treatment were higher than oak nut treatment (p < 0.05). The PF by rumen fungi of sheep in diets containing oak nut was higher than goats, while the truly digested organic matter by the rumen fungi of goats was higher than the control diet in sheep (p < 0.05). The total population of protozoa and Holotriches species was deceased in oak nut treatment (p < 0.05). The population of goat rumen bacteria and fungi in control group was higher than that in control sheep group.
The phenolic compounds (tannins) in diets containing oak nut decreased fibrolytic enzyme activity, inhibited carbohydrates fermentation, and consequently decreased fiber digestibility by rumen microorganism (Tavendale et al. 2005). Tannins can reduce microorganism adhesion to nutrients; inhibit microbial activity which has negative effects on fermentation and methane production. But, the increase of gas production rate by oak nut is due to higher soluble carbohydrate and lower NDF and ADF in diets containing oak nut, which increases the digestibility (Hadi et al. 2003). Phenols may disrupt protozoal membranes, inactivate protozoal enzymes, and deprive protozoa of substrates and metal ions, which are essential for protozoa cell metabolism (Calsamiglia et al. 2007).
Conclusion: Based on the results, using 63% oak nut caused a decrease in microbial population, a decrease in the disappearance of nutrients and fermentation parameters of bacteria and fungi and a decline in the rumen protozoa population of Arabi sheep and Najdi goat. Also, the results showed higher tolerance of goats to the diet's tannin.