Introduction: Zagros forests that are classified as semi-arid forests, approximately includes around 40 percent of the Iran forests. Dominant tree species of Zagros forests is Oak trees. Oak leaves are an inexpensive and available feed source for ruminant, in particular in low forage seasons. The main problem for the use of Oak leaves and fruit are their phenolic compounds and its negative effects on animal performance at high concentration. The negative effects of high concentration of tannin and phenolic compounds on ruminant performance dependent on the kind and concentration of phenolic compounds, diet composition, and animal species. There are evidence that supplementation of polyethylene glycol (PEG) at high concentration of phenolic compounds resulted in a decrease of the negative effect of phenolic compounds. In contrast, low concentration of phenolic compounds resulted in an improvement in daily gain, milk production, ovulation rate and a decrease in methane and ammonia production. The objective of this study was to investigate the effect of different drying methods of oak leaves (Q. persica) on the concentration of phenolic components of dried leaves and PEG supplementation on in vitro protozoa population and total gas and methane production.
Materials and Methods: This experiment was conducted in a completely randomized design with a 4× 2 factorial arrangement of treatments to investigate the effects of dryings methods (sunshine, shadow, oven and freeze drying ) on the concentration of phenolic compounds of Oak leaves and effects of PEG supplementation on in vitro ruminal microbial fermentation of dried Oak leaves. An in vitro gas production technique was used to measure the effects of drying methods and PEG supplementation on total gas and methane production and protozoa abundance with fermentation of Oak leaves. Rumen content was obtained from two fistulated sheep (39±4.5 kg body weight) before morning feeding. The ruminal content was immediately strained through four layers of cheesecloth. Animals were fed twice daily with a 50:50 alfalfa hay: concentrate diet that formulated for maintenance requirements. In the laboratory, under anaerobic conditions, 37.5 mL of buffered rumen fluid (ratio of rumen fluid to buffer was 1:2) was added into 120 mL bottles containing 0.375 g of ground Oak leaves with (0.75g) or without PEG (12 replicates for each treatment in two runs). The buffer was prepared as proposed by McDougall. Bottles were sealed and placed in shaking water bath for 96 h at 38.6°C. Headspace gas pressure was recorded using a pressure transducer at 2, 4, 6, 9, 12, 24, 48, 72 and 96 h of the incubation. Methane production and protozoa population were determined at 24 h of incubation. The concentration of phenolic compounds, condensed and hydrolysable tannins were determined.
Results and Discussion: Results of the present study showed that concentration of phenolic compounds, condensed and hydrolysable tannins affected by drying methods (P<0.01), but total tannins was not affected (P>0.01). In all experimental treatments, the protozoa population was increased by PEG supplementation (P<0.01). The highest and the lowest protozoa population were observed in freeze and oven drying methods, respectively (P<0.05). In all treatment (except for sunshine and oven drying) adding PEG resulted in a significantly increased (P<0.01) in the methane production after 24 h of incubation. It is notable that the highest and the lowest percentage of methane production were observed in freeze and oven dryings methods, respectively (P<0. 01). The effect of drying method on the gas production was not significant (P<0.05) and the addition of PEG resulted to numerically increase in gas (P>0.05). Although, gas production at 24h of incubation not affected by treatments, but results of this experiment demonstrated an increase in 96h gas production with PEG supplementation.
Conclusion: The results of the present study demonstrated that the oven drying of oak leaves resulted in a further reduction in total phenolic compounds and hydrolysable tannins concentration and the most decrease in methane production due to microbial fermentation of oak leaves, relative to the control. In addition, it appears that PEG supplementation not recommendable method for decrease negative effects of tannins, because resulted in an increase in the methane production.
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