Investigation the effect of diets containing different levels of oak kernel on ruminal digestion and fermentation and degradability of cow and buffalo in Khuzestan

Oak kernel contains high starch, so it can be used as an energy source in the concentrate of ruminant diet. Also, oak kernel containing active biological compounds, such as tannin, gallic acid, galloyl or hexahydroxy decanol derivatives (Saffarzadeh et al. 1999). Tannins form complexes with a large number of nutrients and bacterial cell membranes, enzymes, and decrease digestion in the rumen (Rajablo 2009). The aim of this study was to investigate the effect experimental diets including 0, 15.80, 31.58, and 47.37% oak kernel on degradability parameters, fermentative and in vitro digestibility in Holstein cow and river Khuzestani buffalo. Oak kernel used by 15.8, 31.58 and 47.37 % in diet (balanced on the base of NRC, 2001) of cow and buffalo. Gas production and fermentation parameters of experimental diets were determined by Menke and Steingass (1988). Rumen fluid was collected from animals before the morning feeding. About 200 mg sample (1.0 mm screen) incubated in 100 ml vials with 35 ml buffered rumen fluid under continuous CO2 reflux for 2, 4, 6, 8, 10, 12, 16, 24, 48, 72 and 96 h, in a water bath maintained at 39°C. Cumulative gas production data were fitted to the exponential equation Y=b (1−e−ct), where b is the gas production (mL) from the fermentable fraction, c is the rate constant of gas production (mL/h), t is the incubation time (h) and Y is the volume of gas produced at time t. Partitioning factor, microbial biomass and truly digested organic matter was calculated by Makkar and Becker (1997). For determination of partitioning factor 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. Digestibility of dry matter and NDF of experimental diets were determined using Tilly and Terry method (Tilly and Terry 1963). Rumen fluid was collected from animals and was mixed with McDougall buffer in a ratio 1:4. After gasifying with CO2, tubes were incubated at 39 ˚C. After 48 h of fermentation, 6 mL of 20% HCl solution and 5 mL pepsin solution were added and the incubated for 48 h simulating post-ruminal degradation. After incubation, the residual substrates of each tube were filtered and used to determine digestibility of DM and NDF.
Dry matter degradability was measured by in situ technique using cow and buffalo fitted with rumen fistula (400±12 Kg, BW). Five g of each milled sample (2.0 mm screen) were transferred into a polyester bag (10×20 cm, 52 μm pore size) and incubated in the rumen for 2, 4, 6, 8, 16, 24, 4 8, 72 and 96 hours (n= 4). The degradability of DM were calculated using the equation P = a + b (1- e -ct). The obtained data were analyzed in a split plot design using the General Linear Model (GLM) procedure of SAS software, version 9.2. The Duncan multiple range test was used to compare means at P< 0.05. Dry matter digestibility and NDF were the highest in treatment including 31.58% oak kernel in cow and buffalo (P<0.05). Regardless of the type of treatment, dry matter digestibility was not significant in cow and buffalo (P>0.05), but NDF digestibility in buffalo was more than cows (P<0.05). The highest potential of gas production was for diets containing oak kernel (P<0.05). The value of PF, microbial biomass, microbial biomass efficiency and organic matter digested was not significant between diets containing different amounts of oak kernel (P>0.05). Slowly degradable fraction (b), potential of degradability (PD) and effective degradability (ED) were the highest in the diet containing 31.58% oak kernel (P<0.05). Fraction of rapidly degradable (a), slowly degradable fraction (b), constant degradable rate (c), potential of degradability (PD) and effective degradability (ED) was not different in cow and buffalo (P>0.05). Researchers reported that tannins cause inhibition of microbial enzymes and decrease in fermentation (Danesh Mesgaran 2009). Tannins can reduce microorganism adhesion to nutrients; inhibit microbial activity which has negative effects on fermentation and methane production (Frutos 2004). According to the result, it can be concluded, 31.58% oak kernel by improving in vitro fermentative condition of rumen can be used in diet of cow and Khuzestan buffalo, but it requires more studies.