اثر افزودن سطوح مختلف جو بر فراسنجه‌های تولید گاز، جمعیت پروتوزوآ و کیفیت سیلاژ تفاله نعناع و سیلاژ تفاله ‌کاسنی

Introduction: Production of animal’s food is constrained by the climate changes.  Severe drought periods cause low availability of feed from natural pastures. Consequently, sheep and goats fed low quality forages. The unavailability of feed was worsened by the continuously increase of imported feed prices. The scarce availability of forage and fluctuant of concentrate prices encouraged the researchers to find new alternatives that have high energy and low cost (Yagoubi et al 2018). During the last decades, to overcome this problem in many countries, many nonconventional feeds such as shrubs and agro-industrial by-products were used. However, the distillation by-products of medicinal plants are used in animal nutrition. Optimum use of agro-industrial co-products in animal nutrition needs some special processing. Silage is an important way for preserving the nutrient of forage, which is a lactic fermentation process driven by epiphytic lactic acid bacteria. Once lactic acid bacteria ferments water-soluble carbohydrates into sufficient lactic acid in an anaerobic silo, low pH is achieved, the activity of undesired microbes is restrained, and the nutrients are well preserved (McDonald et al 1991). Cichorium intybus commonly known as chicory, is fairly woody perennial herb, around 1 m in height with a fleshy taproot of up to 75 cm in length and large basal leaves. Chicory is cultivated for numerous applications such as “forage” chicory, to intensify herbage obtainability in perennial pastures for livestock (Street et al 2013). Mint, (genus Mentha), genus of 25 species of fragrant herbs of the mint family (Lamiaceae) and are widely distributed throughout the temperate areas of the world and have naturalized in many places. Some species are commonly used in herbal medicine. Both of chicory and mint are used for distillation and their residues (pulp) could be used as animal feed. Mint pulp and chicory pulp have high moisture and low non fibrous carbohydrates contents, hence they are not suitable for ensiling. Therefore, it is better to use appropriate additives for ensiling these agro-industrial co-products. This experiment was aimed to study the effect of adding different levels of barley powder to mint pulp silage and chicory pulp silage on chemical compositions, silage quality traits, in vitro gas production parameters, N-ammonia concentration, and protozoa population.
Material and methods: Fresh mint pulp and chicory pulp were collected from an agro industry processing factory. Chemical compositions of mint pulp and chicory pulp were measured. Before ensiling, each pulp was chopped to particles with 3-4 cm length. Powdered barley grain was added to chicory pulp at three levels (10, 20, and 30 % (w/w)) and it was added to mint pulp at two levels (10 and 20 % (w/w)) and ensiled for 30 days. Chemical compositions (dry matter, neutral detergent fiber, acid detergent fiber, crude protein, and ash), gas production parameters, total protozoa population and N-ammonia concentration of experimental silages were measured. Silage quality traits including pH and buffering capacity (Jasaitis et al, 1987) were measured and fleig point of each silage was calculated (Kilic 1986). For in vitro gas production tests, the rumen fluid was taken from two rumen fistulated Kordish rams. For measuring kinetic parameters of gas production, 200 mg of samples were incubated with 40 ml buffered-rumen fluid for 120 hours. The cumulative produced gas was recorded at different times of incubation and gas production parameters were fitted to an exponential equation (France et al 1993). For estimating metabolizable energy, organic matter digestibility and total volatile fatty acids, 40 ml buffered rumen fluid was added to 200 mg of silage samples and incubated at 39 °C for 24 hours. After 24 hours of incubation, gas production recorded and metabolizable energy, organic matter digestibility (Menke and Steingass 1988) and total volatile fatty acids (Makkar 2010) were estimated. N-ammonia concentration was measured based on Broderick and Kang (1980). Rumen protozoa were identified according to the method of Dehority (2003).  After 24 h incubation, 5 ml of buffered rumen fluid was pipetted into a screw-capped test tube containing 5 ml of formalin. Thereafter, two drops of brilliant green dye (2 g brilliant green and 2 ml glacial acetic diluted to 100 ml with distilled water) were added to the test tube, mixed thoroughly, and allowed to stand overnight at room temperature. Total and differential counts of protozoa were made with five replications.  All in vitro gas production trials were carried out in three runs. Data were analyzed based on a completely randomized design using Proc GLM of SAS software. The differences among treatments were evaluated using Tukey adjustment, when the overall F-test was ≤ 0.05. Trends were declared when 0.05 < P≤ 0.10. In addition, independent comparisons were done for mint pulp silage vs. chicory pulp silages.
Results and discussion: The results showed that with increasing the barely level, dry matter increased and acid detergent fiber decreased in experimental silages and chicory pulp containing 10% of barley grain had the lowest acid detergent fiber content. Similar to the current results, adding different levels of wasted date to Mentha pulegium pulp silage increased dry matter and decreased neutral detergent fiber (Eshaghi Maskoni and Dayani 2016). Average pH, buffering capacity, and fleig point of mint pulp silages and chicory pulp silages were 4.15, 41.62 Meq.1^-1, 87.5 and 5.26, 46.52 Meq.1^-1 and 59, respectively. Gas production, constant rate of gas production when half the potential of gas is produced, lag time, and N-ammonia concentration did not differ among all experimental silages. Mint pulp silage with 20% of barley grain had the greatest gas production rate, estimated metabolizable energy content, total volatile fatty acids concentrations, and organic matter digestibility (P < 0.05) and total protozoa population (P = 0.06). Similar to the present experiment, adding wheat bran to citrus pulp silage increased gas production rate and organic matter digestibility (Kordi et al 2014).
Conclusion: Considering the obtained data regarding the chemical compositions and in vitro gas production parameters, it is concluded that among all experimental silages, mint pulp silage containing 20% of barley grain could be used as a good silage in ruminant nutrition. Furthermore, these co-product silages could be used as a part of forage portion in ruminant diets. More experiments are needed to study the inclusion of mint pulp silage and chicory pulp silage in diets of productive ruminants.