چكيده لاتين :
Introduction: Generally, most feeds used in livestock nutrition are deficient in some nutrients, and require nutritional supplements. Among the supplements, micro and macro minerals are particular importance. Selenium (Se) plays an important role in the reproductive function and immune system and is known as an antioxidant and catalyst for the production of thyroid hormone. It is believed that low selenium absorption in ruminants is due to the deficiency of selenium in ration and its conversion into insoluble form (Peterson and Spedding 1963; Surai 2006). Nano-particles are smaller and more active than larger particles. The importance of Selenium for rumen microorganisms are not entirely clear. The present experiment was conducted to evaluate the effect of nano-selenium on activity of whole population of microorganisms, bacteria and fungi, which isolated from the rumen liquid of sheep and goats.
Material and methods: The experimental sample in the present experiment was a basal diet including: 29% barley grain, 25% wheat bran, 20% wheat straw, 25% corn silage, 1% selenium-free mineral-vitamin supplement. In the present experiment 0, 0.2, 0.4 and 0.6 ppm nano-Se was added to the basal standard diet of sheep and goats, then digestibility and fermentation parameters of diets were measured by the rumen fluid of sheep and goats in vitro. The rumen fluid was taken through the stomach tube from four Najdi goat and Arabi sheep before the morning meal, mixed separately, filtered using four layers of cheesecloth, and potted in a flask content warm water. These animals were fed with a diet, approximately similar to basal ration, but without selenium, about three weeks. Gas production of the basal diet containing different levels of nano-Se was determined using the Menke and Steingass (1988) in six replications. The rumen fluid was mixed with artificial saliva (1:2 ratio, respectively) in lab, and then nano-Se levels added to it. The gas production was recorded at zero, 2, 4, 6, 8, 12, 24, 48, 72 and 96 hours after the start of incubation in water bath. The gas production data were analyzed using the exponential model and the gas production parameters were calculated (Ørskov and McDonald, 1979). Two steps digestion (Tilley and Terry 1963) method in six replications was used to measure digestibility of experimental diets. The rumen fluid and buffer was prepared as mentioned for gas production experiment. Isolation and purification of bacteria and fungi, and studying the effect of nano selenium on their digestibile activity conducted by preparing the specific medium cultures of ruminal anaerobic bacteria or fungi according to recommended method (Zhang et al., 2007; Mohammadabadi et al. 2012).
Results and discussion: The highest digestibility of dry matter (DM) and neutral detergent fiber (NDF) of experimental diets in sheep and goats were for the level of 0.6 ppm nano-Se that was higher than control diet (P<0.05). Regardless the nano-Se level, the DM and NDF digestibility by rumen microorganisms of sheep was more than goat. Regardless the type of animal, digestibility of DM and NDF increased with increasing the amount of nano-Se (P<0.05). It has been reported that cell wall digestibility in sheep was not affected by treatments containing 0.2 and 0.4 mg/kg selenium as sodium selenite (Alimohamady and Aliarabi, 2013). The use of 0.2, 0.4 and 0.6 mg/kg of nano-selenium in buffalo reduced the digestibility of dry matter and NDF (Chaji et al. 2015). In contrast, using 0.15, 0.20 and 0.45 mg/kg nano-Se in diet resulted to increase the digestibility of NDF (Wang et al. 2009). Differences in results can be derived from the unknown or different properties of nano compounds relative to the conventional form, such as surface activity, catalytic efficiency, high absorption ability and low toxicity; because it has been reported that selenium nanoparticle uptake efficiency is higher than non-nano sized particles (Wang et al. 2007). Potential of gas production was maximum in diets containing 0.6 ppm nano-Se by microorganisms of sheep and was more than goat for all levels (P<0.05). The researchers reported that using nano selenium in the diet and incubating it with rumen fluid of cow resulted to reduce the potential of gas production (Chaji et al., 2014), which was in contrast with the results of the present experiment. While in another experiment, the rate of gas production in the diet containing 0.2 mg of nano-Se was the highest (Chaji et al., 2014), which was consistent with the results of the present experiment. The digestibility of DM and NDF by rumen bacteria of sheep was significantly higher than the goat, reversely; digestibility of these nutrients by fungi isolated from goat was more than sheep. The exact reason for higher digestible activity of isolated bacteria from rumen of sheep than goats, affected by nano-Se, was not ascertained. The various studies were shown that sheep and goat, along with similarities, has many different properties, such as resistance to nitrate, tannin, the populations of bacterial, protozoa and fungi (Kamra 2005); also, type of food, nutritional behavior (grazer or browser), rumen ammonia nitrogen, salivation (in goats more than sheep), and rumen passage rate and so on (Agrawal et al. 2014). Therefore, the differences in the effect of nano-Se in these two species may be related to each of these differences, especially the differences in their microbial population.
Conclusion: Therefore, the use of nano-Se resulted to increase digestibility and fermentation of nutrients by whole rumen microorganisms and bacteria of both species.
